Micro exam 3

what is a descriptive study?

Descriptive study: data collected (time, place, individuals affected) during an outbreak to determine possible risk factors for disease spread.

describe the structure of A B toxins

*A-B toxins* have two parts. A (active) subunit is toxic, usually an enzyme. B subunit binds to cell, determines cell type to be infected. Many AB toxins have multiple B subunits (i.e. A1B5: cholera toxin; shiga toxin). Structure allows novel approaches for vaccines and therapies; can use B subunit to deliver medically useful compounds to specific cell type.

when establishing an infection, what is the first step to take place?

*Adherence*. *adhesions* attach to host cell *receptor*. Often located at tips of short pili called fibriae. Can be component of capsules or various cell wall proteins. Binding highly specific; dictates type of cell to which bacterium can attach, as well as species specificity.

what occurrs after a pathogen adheres to a cell?

*Colonization and Establishment of Disease*. After attachment, the microbe must multiply. Must deal with host defenses. Microbe may produce *siderophores* to bind iron. Siderophores strip Fe from lactoferrin and transferrin to use for pathogen. Bacteria need large amount of Fe to grow. Microbe must avoid secretory IgA. This is present on mucous surfaces. Rapid pili turnover, antigenic variation, and *IgA proteases* help with this. IgA proteases cleave IgA, letting the pathogen survive. Microbe must compete with normal microbiota; tolerate toxic products of other microbes.

describe how T cells become activated.

*Dendritic cells* play a crucial role in activation of T cells. Reside in peripheral tissues (skin, mucosa). Gather materials via phagocytosis, pinocytosis. Can send extensions between epithelial cells of mucosal barriers and sample material in respiratory tract and lumen of intestine. Toll like receptors (TLRs) and others recognize pathogens. If pathogens detected, cell takes up more material. Travels to secondary lymphoid organs; matures. Produces *co stimulatory molecules* signaling danger. Presents antigens on both MHC class I and class II. T cell is activated by dendritic cell with co stimulatory molecules. T cell becomes anergic or develops into Treg cells if no co stimulatory molecules. Mechanisms of tolerance.

what is an endotoxin?

*Endotoxin*, other bacterial cell wall components. Endotoxin is lipopolysaccharide (LPS) found in outer membrane of gram negative cell wall; contains lipid A. Lipid A triggers inflammatory response. When localized, response helps clear infection. When systemic, causes widespread response: septic shock or endotoxic shock. Lipid A released following cell lysis. Toll like receptors induce cytokine production. T independent antigen may activate a variety of B cells. Heat stable; autoclaving does not destroy. Limulus amoebocyte lysate (LAL) assay detects endotoxin. This is helpful because many biologics are produced by gram negative bacteria. Have to make sure they are endotoxin free before administering to patient. Peptidoglycans, other components also trigger sepsis and septic shock.

Compare and contrast Endotoxins and Exotoxins

*Exotoxins*: from gram positives and negatives. Protein, potent, usually heat inactivated. distinct toxic mechanism for each. synthesized in the cytoplasm, may or may not be secreted. *Endotoxins*: from gram negatives only. Lipid A component of LPS; small localized amounts yield appropriate response, but systemic distribution can be deadly. Heat stable. Component of the outer membrane of the gram negative cell wall. Innate immune response; a systemic response can lead to fever, a dramatic drop in blood pressure, and disseminated intravascular coagulation.

what determines diversity in MHC genes?

*Human leukocyte antigens (HLAs)* that determine tissue compatibility are coded for by MHC genes. MHC sites are polygenic and polymorphic, ensuring tremendous variety.

describe the properties of membrane damaging toxins

*Membrane damaging toxins*: cytotoxins that disrupt eukaryotic cytoplasmic membranes, lyse cells. Hemolysins lyse red blood cells. *Pore forming toxins* insert into membranes, form pores. ex. Streptolysin O from Streptococcus pyogenes. *Phospholipases* hydrolyze phospholipids of membrane. ex. alpha toxin of Clostridium perfringens (gas gangrene)

what are the differences between the different types of lymphocytes?

*Naive lymphocyte:* has never encountered antigen that it has recognition for; cannot react until it receives confirming signals. *Activated lymphocyte*: has received confirming signals, proliferates, differentiates. *Effector lymphocytes*: short lived, primary response *Memory lymphocytes*: long lived, activated more quickly to provide secondary response

what is the difference between natural passive and artificial passive immunity?

*Natural passive immunity*: during pregnancy, mother's IgG antibodies cross placenta. Breast milk contains secretory IgA. *Artificial passive immunity*: Injection of antiserum containing antibodies. Can prevent disease before or after likely exposure. Limit duration of certain diseases. Block action of microbial toxins. antitoxin is antiserum that protects against a toxin ex. tetanus. *hyperimmune globulin*: antibodies to specific disease. *immune globulin*: IgG fraction from many donors; variety of antibodies.

what are the different types of immunity?

*Naturally acquired immunity* is gained through normal events, such as illness. ex. immunity gained from breastmilk. *Artificially acquired immunity* is gained through immunization. *Active immunity* results from exposure to antigen. Lymphocytes are activated; memory cells provide long lasting protection. Natural by infection; passive through vaccination. *Passive immunity* results from addition of another's antibodies. Temporary protection; no memory cells formed.

what is pathogenicity?

*Pathogenicity*: ability of a pathogen to cause disease. *Primary pathogen* is a microbe or virus that causes disease in otherwise healthy individual. Diseases such as plague, malaria, measles, influenza, diphtheria, tetanus, tuberculosis. *opportunistic pathogen* (opportunist) causes disease only when body's immune defenses are compromised or when introduced into unusual location. Can be members of normal microbiota or common in environment ex. pseudomonas. *virulence* refers to degree of pathogenicity. *virulence factors* substnces that allow microorganism to cause disease (capsules, toxins, immune avoidance mechanisms, etc.)

how do pathogens avoid being killed by host defenses by complement system proteins?

*Serum resistant bacteria*. Neisseria gonorrhoeae (and N. menigitidis) hijacks mechanism that host uses to prevent their surfaces from activating complement. Complement deficient individuals are 1,000-10,000 times more likely to come down with a N. meningitidis infection. Organism binds complement regulatory proteins to avoid membrane attack complex (MAC)

describe the properties of superantigens

*Superantigens*: stimulate high number of TH cells, causing cytokine storm. Simultaneously bind MHC class II and T cell receptor. In an antigen non restricted manner (i.e. every class II TcR pair). T cell interprets this as antigen recognition. Toxic effect is from massive cytokine release. T cells undergo apoptosis; suppresses immune response

describe one way in which pathogens avoid destruction by phagocytes

*Surviving within phagocytes allows pathogens to avoid antibodies, control some immune responses, and move throughout the body*. 1. Escape from phagosome: prior to lysis with lysosomes. Listeria monocytogenes produces molecule that forms pores in membrane; Shigella species lyse phagosome. 2. Prevent phagosome lysosome fusion: avoid destruction. Salmonella sense ingestion by macrophage, produce protein that blocks fusion process. 3. Survive within phagolysosome: few can survive destructive environment. Coxiella burnetii (Q fever) can withstand; delays fusion, allows time to equip itself for growth

what is the difference between acute, chronic, and latent infections?

*acute infections*: symptoms develop quickly, last a short time (strep). *Chronic infections*: develop slowly, last months or years (TB). *Latent infections*: never completely eliminated; microbe exists in host tissues without causing symptoms. Decrease in immunity may allow reactivation. ex. stress.

what are anti human IgG antibodies?

*anti human IgG antibodies* produced by animals immunized with IgG from human serum. ex. mouse, rabit, goat. These and other anti human antibodies available commercially

what are the differences between attenuated vaccines and inactivated vaccines?

*attenuated vaccine*: agent can replicate. Stronger immune response, but may cause disease. live pathogen. usually viruses. injected, oral, or nasal. No need for adjuvant (substance that stimulates immune system). Antibody memory response is IgG, secretory IgA if administered orally or nasally. good cell mediated immune response. longer relative duration of protection. usually one or two doses. very low risk of mutation to virulence. can have significant risk to immunocompromised recipient. poor stability in warm temperatures. ex. measles, mumps, rubella, chickenpox, yellow fever, rotavirus. *inactivated vaccine*: agent cannot replicate. Weaker immune response, but cannot cause infections. Inactivated whole agents, toxoids, subunits, VLPs (virus like particles), polysaccharides, conjugates. must be injected. Adjuvant needed (substance that stimulates immune system). Antibody memory response is IgG. poor cell mediated immune response. Shorter relative duration of protection. multiple doses needed. no risk of mutation to virulence. no risk to immunocompromised recipient. good stability in warm temperatures.

describe exotoxins

*exotoxins*: proteins with specific damaging effects. Secreted or leak into tissue following bacterial lysis. Foodborne intoxication results from consumption. Most destroyed by heating. Can act locally or systemically. Immune system can usually generate antibodies. Many diseases due to toxin producing bacteria were fatal before adequate immune response; vaccines important. *toxoids* are inactivated toxins. ex. tetanus, diphtheria. *Antitoxin* is a suspension of neutralizing antibodies.

what characteristics do antibiotics that inhibit protein synthesis have in common?

*generally bacteriostatic, but aminoglycosides bactericidal*. Can exploit differences between prokaryotic and eukaryotic ribosomes. Prokaryotes have 70S eukaryotes have 80S ribosomes. Mitochondria also have 70S ribosomes, which may account for toxicity of some of these antibiotics.

how do lymphocytes change as they encounter antigens?

*immature lymphocytes* lack fully developed antigen specific receptors. *naive lymphocytes* have receptors; have not yet encountered appropriate antigen. *activated lymphocytes* have bound antigen and received confirmation, are able to proliferate. *effector lymphocytes* are descendants of activated lymphocytes: plasma cells, TC cells, TH cells. *memory lymphocytes* are long lived descendants of activated lymphocytes; responsible for rapid secondary response if antigen encountered again.

describe the progression of infectious diseases.

*incubation period*: time between infection (first exposure) and onset. Varies considerably; depends on growth rate, host's condition, infectious dose. *Illness*: signs and symptoms of disease are prevalent. May be preceded by prodromal phase (vague symptoms). *Convalescence*: recuperation, recovery from disease. After recovery (or vaccination) memory cells usually protect from reinfection with the same microbe.

what is the difference between innate immunity and adaptive immunity

*innate immunity*: our rapid, non-specific immunity, general protection plan that is present at birth and serves as our first line of defense our entire life *Adaptive immunity*: is our specific immunity that develops throughout life and is tailor made to defend against the microbes or foreign material that we are exposed to

what is the minimum bactericidal concentration (MBC)?

*minimum bactericidal concentration (MBC) is lowest concentration that kills 99% of cells in vitro*. Determined from plate count prepared from tubes with no growth in MIC test. Techniques precise but labor-intense, expensive.

What is the minimum inhibitory concentration (MIC)?

*minimum inhibitory concentration (MIC) is lowest concentration that prevents growth in vitro*. Serial dilutions of chemical in suitable growth medium used; cultures added, incubated, examined for turbidity. Inhibition does not necessarily mean successful treatment; level may not be achieved in person's blood. Microbes with MIC between susceptible (treatable) and resistant (untreatable) are intermediate.

what is the difference between positive and negative selection of T cells

*positive selection*: T cells must recognize MHC. Eliminated if unable to recognize. *negative selection*: T cells also eliminated if recognize "self" peptides presented on MHC molecules. Process is so stringent that over 95% of developing T cells undergo apoptosis in thymus.

How do vaccines protect individuals against disease? how do vaccines relate to herd immunity?

*vaccine* is preparation of pathogen or its products used to induce active immunity. Protect individual; prevent spread in population. *herd immunity* develops when critical portion of population is immune to disease; infectious agent unable to spread due to insufficient susceptible hosts. Responsible for dramatic declines in childhood disease. ex. pertussis, diphtheria. Diseases sometimes reappear and spread as result of failure to vaccinate children. Effective vaccines should be safe, have few side effects. Give long lasting protection. Ideally low in cost, stable, easy to administer.

what is the difference between direct ELISA and indirect ELISA

Direct ELISA: sandwich method. Antigen captured by antibodies attached to surface. Enzyme labeled antibody added to detect antigens. Commercial modifications available, including rapid group A strep tests, home pregnancy kits. Indirect ELISA: Detects antibodies in human blood and serum. Blood routinely screened for antibodies to HIV. May yield false positives; more reliable test (western blooding) used to confirm.

what characteristics of the host influence epidemiology of disease?

1. *Gender:* women more likely to develop UTI; urethra is shorter; microbes more likely to ascend. 2. *Behavioral practices*: Breastfeeding provides protective antibodies to infant. consumers of raw fish are more likely to acquire tapeworm Diphyllobothrium lactum, which is killed by cooking 3. *Genetic background*: natural immunity varies widely. Specific receptors may differ. Lack of receptor on red blood cell confers immunity to Plasmodium vivax. Lack of receptor on white blood cell reduces susceptibility to HIV.

describe the source and effect of various interleukins (ILs)

1. *IL-1*: source: macrophages, epithelial cells. effect: T-cell activation; macrophage activation; induces fever 2. *IL-2*: source: T-cells. effect: T-cell proliferation 3. *IL-4*: source: T-cells, mast cells. effect: Promotes antibody responses 4. *IL-6*: T lymphocytes, macrophages. effect: T and B cell growth; inflammatory response; fever

what are some protective outcomes of antibody antigen binding?

1. *Neutralization*: prevents toxins, viruses from binding. 2. *Opsonization*: enhancement of phagocytosis 3. *complement system activation*: classical pathway 4. *Immobilization and prevention of adherence*: binding to bacterial flagella or pilli interferes. 5. *Cross linking*: two arms of antigen bind separate antigens 6. *Antibody dependent cellular cytotoxicity (ADCC)*: targets cell for destruction by natural killer (NK) cells.

describe the three major outcomes of the activation of the complement system

1. *Opsonization*: C3b binds to bacterial cells and foreign particles, promotes engulfment by phagocytes that attach to opsonins (like C3b). 2. *Inflammatory Response*: C5a attracts phagocytes to area; C3a and C5a increase permeability of blood vessels, induces mast and other cells to release histamine and other cytokines, resulting in diapedesis. 3. *Lysis of foreign cells*: membrane attack complexes (MACs) formed by proteins C5b, C6, C7, C8, and C9 molecules assembling on the surface of gram negative bacteria resulting in cell lysis and death

What are the two other ways in which pathogens can breach anatomical barriers?

1. *Penetrating the skin*. Difficult barrier to penetrate; bacteria rely on injuries. Staphylococcus aureus enters via cut or would; Yersinia pestis is injected by fleas (all pathogens that employ insect or arthropod vectors). 2. *Penetrating mucous membranes*. Entry point for most pathogens. Directed uptake by cells. Exploiting antigen sampling processes.

describe one way in which pathogens avoid destruction by phagocytes

1. *Preventing encounters with phagocytes*. C5a peptidase: degrades chemoattractant C5a. ex. Streptococcus pyogenes. Membrane damaging toxins: kill phagocytes, other cells. ex. S. pyogenes makes streptolysin O.

what are the three key mechanisms of action in antiviral medications?

1. *prevent viral entry.*: some HIV medications prevent viral entry. Enfuvirtide (ENF) is a fusion inhibitor; binds to a HIV protein that promotes fusion of viral envelope with cell membrane. Maraviroc (MCV) blocks HIV co-receptor CCR5. 2. *Interfere with viral uncoating*: Nucleic acid must separate from protein coat. two chemicals target this step in influenza, but they are no longer used due to widespread resistance. 3. *Interfere with nucleic acid synthesis*: most effective target virally encoded enzymes used during replication of viral nucleic acid. Mostly limited to treating herpesviruses, HBV, HCV, HIV. Nucleoside and nucleotide analogs. Structure similar to building blocks of DNA, RNA. When incorporated into growing nucleotide chain, many analogs act as chain terminators. Selective toxicity since virally encoded enzymes more likely than host cell polymerases to incorporate. More damage done to rapidly replicating viral genome.

what are the three epidemiological factors to focus on for the future?

1. *threat of pandemic respiratory pathogen*: easily transmitted. We are living this today with SARS-CoV2 pandemic. H1N1 influenza world-wide death toll over 500,000 2. *Pathogens jumping the species barrer*: (zoonotic diseases that now have ability to infect humans). Balanced pathogenicity has not taken place. Morbidity and mortality can be high. ex. SARS, MERS, SARS-CoV2, Canine Parvoviruses, H3N2 and H1N1 influenzas 3. *Threat of bioterrorism*: Class A bioterror agents: Bacillus anthracis (anthrax), Clostridium botulinum toxin (botulism), Yersinia pestis (plague), smallpox virus, Francisella tularensis (tularemia), viruses that cause hemorrhagic fevers

describe the three pathways of complement system activation

1. Alternative pathway: triggered when C3b binds to foreign cell surfaces (C3 unstable, so some C3b always present) 2. Lectin pathway: pattern recognition molecules (mannose-binding lectins, or MBLs) bind to mannose of microbial cells, interact with complement system components 3. Classical pathway: activated by antibodies bound to antigen, which interact with complement system

describe examples of direct transmission and indirect transmission in healthcare settings.

1. Direct transmission: healthcare personnel. Must be vigilant with handwashing, disinfecting, gloves. 2. Indirect transmission: medical devices. often breach first-line barrers of defense: catheters, IV lines, mechanical ventilators, inadequately sterilized invasive instruments 3. indirect transmission: airborne. reduce with air pressure, careful mopping, HEPA filters

what are the two arms (or facets) of the adaptive immune system?

1. Humoral immunity: antibody mediated, eliminates extracellular antigens. Bacteria, toxins, viruses in bloodstream, tissue fluids. Involves B cells (B lymphocytes) 2. Cell mediated immunity (CMI): or cellular immunity deals with antigens residing within a host cell. ex. invading virus infecting cell. Also attacks cancer cells. Involves T cells (T lymphocytes)

describe the mechanism Shigella uses to exploit the antigen sampling process

1. Macrophages in the peyer's patches engulf material that passes through M cells. Shigella cells survive and replicate, causing the phagocytes to undergo apoptosis. 2. Shigella cells attach to the base of the epithelial cells and induce these cells to engulf them. 3. Within an epithelial cell, Shigella cells cause the host actin to polymerize. This probels the bacterial cell, sometimes with enough force to push it into the next cell

how do immune cells communicate with one another?

1. Surface receptors serve as eyes and ears of cell. Usually span membrane, connect outside to inside. Binding to specific ligand induces response. 2. Cytokines are voices of the cell. Produces by cells, diffuse to others, bind to appropriate receptors to induce changes: growth, differentiation, movement, cell death. Act at low concentration; effects local, regional, systemic. 3. Adhesion molecules allow cells to adhere to other cells. For example, phagocytic cells can adhere to endothelial cells, allowing them to exit bloodstream.

what are the different ways in which indirect transmission can occur?

1. airborne 2. vehicle-borne 3. vector borne

describe the mechanisms of acquired resistance.

1. antibiotic inactivating enzymes. Bacteria produce enzymes that interfere with drug. Penicillinase, extended spectrum beta lactamases, chloramphenicol, acetyltransferase. 2. alteration in target molecule. Minor structural changes in bacteria can prevent binding of antibiotic. PBPs (beta lactam antibiotics) ribosomal RNA (macrolides, lincosamides, streptogramins) 3. decreased uptake of medication. Changes in porin proteins of outer membrane of gram negatives. 4. increased elimination of medication. *efflux pumps* remove compounds from the cell. increased production or structural changes of pumps allows faster removal. Resistance to range of antimicrobials.

what bacterial processes and structures do antibacterial medications target?

1. cell wall synthesis 2. Protein synthesis 3. Nucleic acid synthesis 4. Metabolic pathways 5. cell membranes

what are some factors that contribute to emergence or reemergence of disease?

1. microbial evolution: ex. vibrio cholerae gained ability to produce capsule; antibiotic resistance can contribute to reemergence of disease 2. complacency and public health efforts: success can divert attention: ex. tuberculosis 3. changes in human society: ex, day-care centers relatively new in US allow easy transfer of pathogens such as those that cause colds or diarrhea 4. advances in technology: ex. contact lenses 5. Population expansion: increased contact with reservoirs of disease; ex. lyme disease; deforestation in amazon basin; close contact with wild animals 6. development: ex, dams extend range of schistosomiasis by increasing habitat for host snail 7. mass production, widespread distribution, and importation of food: foodborne illnesses easily spread. 8. war and civil unrest: disruption of infrastructure and eradication efforts, refugee camps with poor conditions 9. climate changes: warm temperatures favor reproduction of some arthropods that serve as vectors; heavy flooding from el nino may have increased cholera cases in africa

what are the characteristics of adaptive immunity?

1. molecular specificity: targets specific antigens on foreign invaders 2. memory: stronger response to re-exposure. Vaccination relies on this ability. 3. Tolerance: must distinguish between "healthy self" and "dangerous"

what are some reservoirs of infectious agents in healthcare settings?

1. other patients: pathogens discharged via skin cells, respiratory droplets, other bodily secretions and excretions 2. healthcare environment: some gram-negative rods can thrive in sinks, ventilators, toilets. Pseudomonas aeruginosa resistant to many disinfectants, antimicrobials; requires few nutrients. 3. Healthcare workers: sick workers, carriers of pathogens ex. staphylococcus aureus 4. visitors: number of visitors may be limited 5. patient microbiota: invasive procedures can transmit normal microbiota to sterile body sites; compromised immune system may allow infection to develop

How does the human microbiome benefit us?

1. significant contribution in protection against pathogens. Covering of binding sites prevents attachment. Consumption of available nutrients. Production of compounds toxic to other bacteria ex. E coli. when microbiome is suppressed (ex. during antibiotic treatment) pathogens may colonize, cause disease. ex. yeast infections, clostridium difficile 2. Stimulation of adaptive immune system. Antibodies against normal microbiota may also bind to pathogens. ex. adult immunity to H. influenzae. 3. Important in development of oral tolerance. Immune system lessens response to many microbes in gut as well as food. Basis of *hygiene hypothesis*, insufficient exposure to microbes leads to allergies. 4. Aid in digestion: break down fiber; increase nutrients 5. Produce important substances, such as vitamin K

IgA monomer, secretory IgA

10 to 13% of serum. half life of 6 days. Most abundant class produced, but the majority of it is secreted into mucus, tears, and saliva, providing mucosal immunity. Protects mucous membranes by neutralizing viruses and toxins, immobilizing motile organisms, and preventing attachment of microbes to cell surfaces. Component of breast milk; protects the intestinal tract of breast fed infants. Most IgA is a dimer: secretory IgA (sIgA). Important in mucosal immunity in gastrointestinal, genitourinary, and respiratory tracts. Protects breast fed infants against intestinal pathogens. Produced by plasma cells of mucosa associated lymphoid tissue (MALT); secretory component (polypeptide) added to attach antibody to mucus. IgA is most abundant immunoglobulin class produced.

describe one way in which pathogens avoid destruction by phagocytes

2. *Avoiding recognition and attachment*. Capsules: interfere with opsonization; some bind host's regulatory proteins that inactivate C3b. ex. Streptococcus pneumoniae. M protien: cell wall of streptococcus pyogenes binds regulatory protein and prevents C3b activation. Fc receptors: bind Fc region of antibodies. ex. Staphylococcus aureus, Streptococcus pyogenes

what is direct transmission? What are the different types?

Direct transmission involves immediate transfer of infectious agent to portal of entry. One example of direct transmission is through direct contact, which includes touch, handshake, kissing, sexual intercourse. This is easiest when infectious dose is low, such as Shigella. Handwashing considered single most important measure for preventing spread of infectious disease. Some pathogens cannot survive in environment, require intimate sexual contact ex. all STIs. Another example of direct transmission is through droplet transmission, which can spread respiratory disease when pathogen laden droplets are inhaled after a sneeze, cough, talking, etc. Droplets generally fall to the ground within a meter. Spread minimized by covering mouth when sneezing.

IgM

5 to 13% of total serum. half life of 10 days. First antibody class produced during the primary response. Principal class produced in response to T independent antigens. Provides direct protection by neutralizing viruses and toxins, immobilizing motile organisms, preventing microbes from adhering to cell surfaces, and cross linking antigens. Binding of IgM to antigen leads to activation of the complement system (classical pathway). Pentamer: five monomeric subunits give 10 antigen binding sites. Aggregates very effectively. Large size prevents crossing from bloodstream to tissues. Primary role in bloodstream infections. Most efficient class in triggering classical pathway of complement system.

IgG

80 to 85% of total serum. half life of 21 days. Most abundant class in the blood and tissue fluids. Exits bloodstream to enter tissues. Provides longest term protection because of its long half life. Provides direct protection by neutralizing viruses and toxins, immobilizing motile organisms, preventing microbes from adhering to cell surfaces, and cross linking antigens. Binding of IgG to antigen facilitates phagocytosis, leads to activation of the complement system (classical pathway), and allows antibody dependent cellular cytotoxicity. Transported across the placenta, providing protection to a developing fetus; long half life extends the protection though the first several months after birth. Maternal IgG protects fetus and newborn, degrades gradually over 6 month period. Infant begins producing its own antibodies. IgG found in colostrum, absorbed by newborn's intestinal tract. Generally first and most abundant circulating class produced during secondary response.

what is the difference between direct and indirect effects on the host from a pathogen

Direct= toxins produced. Indirect= immune response. Damage may help pathogen to exit and spread. Vibrio cholerae induces watery diarrhea, up to 20L/day, which contaminates water supplies. Bordetella pertussis triggers severe coughing, pathogens released into air.

what is directed uptake? How does it work and what is its goal?

Directed uptake by cells is one way in which pathogens breach anatomical barriers. Pathogen induces non phagocytic cells to engulf them via endocytosis. Salmonella uses type III secretion system. Actin molecules in host cells rearrange, causing *membrane ruffling*. Ruffles enclose bacteria, bringing them into the cell

what is a portal of entry? what are the different types?

A portal of entry is a body surface or orifice that serves as an entry route for a pathogen. *Respiratory route*: respiratory pathogens generally cause disease only when inhaled (nose). *Alimentary route*: Pathogens entering by this routhe (oral) generally cause disease only when of the intestinal tract. Fecal oral transmission: fecal organisms transported to mouth and ingested. *Parenteral route*: penetration of the skin. Pathogen usually ends up in lymphatic system and/ or blood stream. Can be very serious.

How does Humoral immunity work?

Activated B cells differentiate into plasma cells (which make antibodies) in response to extracellular antigens. Produce Y shaped proteins called antibodies. Arms of the antibody molecules bind to antigens with a high degree of specificity. Many different antibodies needed for wide array of antigens. Stem of antibody molecule is red flag marking bound antigen for elimination; serves as a receptor for phagocyte. *B cell receptor (BCR)* recognizes antigen by membrane bound antibody; must receive T cell signal to proliferate. Some B cells form long lived memory B Cells. Respond quickly if antigen encountered again.

describe the differences in progression in acute, chronic, and latent diseases.

Acute: incubation period --> illness --> convalescence. ex. flu Chronic: incubation period--> illness (long lasting). ex. TB, lyme disease Latent: incubation period --> illness --> convalescence --> latency --> recurrence. ex. herpes

give some examples of nucleoside and nucleotide analogs and describe how they work

Acyclovir and others; little harm to uninfected cells since converted by virally encoded enzymes in infected cells. Herpesviruses (chickenpox, cold sores). Sofosbuvir interferes specifically with hepatitis C (HCV)'s replicase. Highly effective against hep C when used with another anti-HCV medication. Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) used to treat Hepatitis B virus (HBV) and HIV. Often used in combination with other anti-retroviral medications to minimize development of resistance. Include zidovudine (anti-HIV), tenofovir (anti-HBV). Some reserved for severe infections; significant side effects. Ganciclovir used to treat life or sight threatening cytomegalovirus (CMV) infections in immunocompromised.

when does adaptive immunity develop? How does it develop?

Adaptive Immunity develops throughout life. It develops most effective means to eliminate an invader. Lymphocytes recognize foreign material and proliferate, leading to adaptive immunity. Takes a week or more to build following first exposure.

what are agglutination reactions?

Agglutination reactions cross link relatively large particles such as cells. Direct agglutination test (DAT): antibody mixed with antigen (cells, microorganisms); binding yields clumping. Hemagglutination used for blood typing. Passive agglutination used when antigens are small. antibodies or antigens attached to particles (latex beads) to form larger aggreates. Beads mixed with drop of body fluid or microbial culture.

How do beta lactam antibiotics work?

All have beta lactam ring and high therapeutic index. ex. penicillin, cephalosporins, cerbapenems, monobactams. Competitively inhibit Penicillin binding proteins (PBPs) that catalyze formation of peptide bridges between adjacent glycan strands; disrupt cell wall synthesis. In other words, B lactam antibiotics bind to PBPs so they cannot form the cell wall. *Only effective against growing cells*

what are the effector functions of TC (CD8) cells?

All nucleated cells present portions of the proteins they produce on MHC class I. Binding of the protein by TC indicates recognition of pathogen or cancer. TC can release perforin that forms pores in the target cell, allowing proteases to enter. TC can induce apoptosis. Minimizes release of intracellular microbes. TC can release cytokines to strengthen responses.

how did ancient people view diseases? How did that change?

Ancients thought diseases were divine punishment. Leeuwenhoek's discovery of microorganisms in 17th century led people to suspect they might cause disease. Robert Koch (1876) offered evidence of what is now known as germ theory of disease. Showed Bacillus anthracis causes anthrax; later work on tuberculosis. Formalized criteria for establishing cause of disease, now known as Koch's postulates.

what is bacitracin?

Antibiotic that inhibits cell wall synthesis. Its toxicity limits it to topical applications. Interferes with transport of peptidoglycan precursors across membrane. Common in first aid skin ointments.

describe the structure and properties of antibodies/

Antibodies also called immunoglobulins. Y shaped proteins with two general parts. Two identical arms (Fab regions) bind antigen. Stem (Fc region). Named from early studies that yielded two types of fragments: antigen binding (Fab) fragments and those that could be crystalized (Fc). Antibodies have basic Y shape: antibody monomer. Two copies each of *heavy chains and light chains*. Amino acids fold into characteristic domains. Light chains have two; heavy chains usually have four. Fork of Y is flexible hinge region. Disulfide bond join heavy, light chains and two halves. *Variable region* at ends of Fab regions; accounts for specificity. Antigen binding site attaches to specific epitope. Fit precise but reversible: numerous non-covalent bonds. *Constant region* includes Fc and part of two Fab regions. Allows immune system components to recognize otherwise diverse antibody molecules.

what is an Enzyme linked immunosorbent assay (ELISA)?

Antibodies labeled with enzyme (such as peroxidase). Enzyme converts colorless substrate to colored product; detected using colorimetric assay. Relatively easy; bases of many rapid tests, blood screening. Often in microtiter plate to test many samples at once. ex. pregnancy test. A colorimetric assay is used to locate enzyme labeled antibodies bound to antigens. When done in microtiter plates, large numbers of specimens can be screened all at once, but in some cases false positives can be a problem. Commercially available options are easy to perform and widely used. Used in over the counter *pregnancy tests*, in physicians offices to diagnose *strep throat*, in clinical labs as part of the diagnosis of a wide range of diseases, including *Lyme disease, west nile fever, hepatitis B and C, and HIV disease.* Also used to screen donated blood for antibodies that suggest that the blood may contain HIV, hepatitis B virus, or Hepatitis C virus.

Ouchterlony technique

Antigen and antibody solutions are placed into separate wells cut in the gel contained in the dish. If the antibody molecules recognize the antigen, a line of precipitation will form at the zone of optimal proportions. Can detect autoantibodies

what is an antigen? What do they do?

Antigen comes from antibody generator. Describes a molecule that reacts specifically with antibody, a B cell receptor, or a T cell receptor. Two general categories. Most are *T dependent antigens*: B cells requires confirmation from TH cell to be activated; protein component. *T independent antigens*: can activate B cells without TH cell help; include lipopolysaccharide (LPS) and molecules with repeating subunits. Antigen that elicits immune response is *immunogenic*. Proteins are more immunogenic than nucleic acids or lipids. Small molecules are usually not immunogenic. Antigens are generally large molecules, but adaptive immune system recognizes distinct regions of the molecule called *epitopes*, or antigenic determinants. Epitopes of macromolecules may be stretches of 10 or so amino acids or distinct 3D shapes. Bacterial cells possess an enormous number of different epitopes.

what are some adverse effects to antimicrobial medications?

Antimicrobials have saved countless lives when properly prescribed and used, however, toxicity and intolerance can be significant issues. 1. *allergic reactions*: may be life threatening, may wear bracelet alert ex. sulfa drugs 2. *toxic effects*: montor those taking low therapeutic index drugs. Some side effects are life threatening (ex. chloramphenicol may cause aplastic anemia) 3. *dysbiosis*: imbalance in the microbiome. For example, broad spectrum antimicrobials may allow growth of Clostridium difficile without competition, resulting in diarrhea or colitis.

how is the B cell activated by T dependent antigens?

B cell receptor binds to antigen; antigen is internalized via endocytosis and degraded into peptide fragments. Fragments delivered to MHC class II molecules for inspection by TH cells: *antigen presentation*. If T cell receptor binds a fragment, T cell activates B cell with Cytokines, initiates clonal expansion. If no TH cells recognize peptides, B cell may become anergic (unresponsive to future exposure of antigen). Results in tolerance to antigen.

what is the significance of lymphocyte receptors in the context of adaptive immunity?

B cells and T cells have membrane bound receptors. Function is to recognize specific antigens. BCR is specific antibody the B cell is programmed to make. TCR does not recognize free antigen; must be presented by body's own cells

how do glycopeptide antibiotics work?

Bind to amino acid side chain of NAM molecules; block peptidoglycan synthesis in cell wall. *effective only against gram positives; does not cross outer membrane of gram negatives. Side effects give low therapeutic index. Vancomycin is most widely used glycopeptide*. Poorly absorbed from intestinal tract, usually administered via IV except for intestinal infections. Often antibiotic of last resort to treat gram positives resistant to beta lactam antibiotics. Fairly toxic, can cause liver and kidney failure.

what is the difference between broad spectrum antimicrobials and narrow spectrum antimicrobials? How are they used?

Broad spectrum antimicrobials affect a wide range. Important for treating acute life-threatening diseases, especially when no time to culture for identification and susceptibility testing. Negative side effect: can disrupt microbiome that helps keep out other pathogens (dysbiosis). Narrow spectrum antibiotics affect limited range. Requires identification and susceptibility of pathogen. Less disruptive to microbiome. Patients may be started on broad spectrum antimicrobial and later switched to narrow spectrum once more is known about the pathogen.

what are beta lactam antibiotics used for?

Broad spectrum penicillins act against gram positives and many gram negatives (ampicillin, amoxicillin). Inactivated by many B-lactamases. Extended spectrum penicillins have greater activity against Enterobacteriaceae, pseudomonas species. Reduced activity against gram positives; destroyed by many beta lactamases. *Augmentin: Penicillin + beta lactamase inhibitor (clavulanic acid) added to protect penicillin from being degraded by bacterial beta lactamase.

what are dendritic cells? What do they do?

Dendritic cells are sentinel cells, function as scouts. Engulf material in tissues, bring it to cells of adaptive immune system for inspection. Usually develop from monocytes.

are all T helper cells the same? explain

Dendritic cells can guide development of TH cells based on the MAMPs they detect (Microbe Associated molecular patterns). TH1 cells promote response effective against intracellular invaders. TH2 cells effective against parasitic worms. TH17 cells effective against extracellular invaders. Macrophages and B cells also present exogenous antigen on MHC class II molecules and can produce co-stimulatory signals. Possibly encounter memory T cells for help in secondary response, but do not encounter naive T cells

what is the difference between the CDC's work in controlling healthcare associated infections (HAIs) and the National healthcare safety network (NHSN)?

CDC has established healthcare infection control practices advisory committee (HICPAC). Advises hospitals and issues recommendations. Responds to emerging threats (zika virus in 2016, covid 19 in 2020). National healthcare safety network (NHSN) tracks data, identifies problem areas, assessing progress in prevention of HAIs, and publishes updates. In 2014, data from over 17,000 hospitals showed decreases in almost every type of HAI

what is the CDC? What do they do?

Centers for disease control and prevention (CDC) provides support for labs in the US and abroad; collects data on diseases that impact public health. Publishes Morbidity and Mortality Weekly Report (MMWR). Collects data on over 50 notifiable diseases (with state health departments). Disease trends, significant cases published in MMWR. Conducts research on infectous disease. Can send teams worldwide to assist with identifying and controlling epidemics. ex. 2014 Ebola epidemic, 2020 Covid 19 pandemic

what is the difference between bacteria's intrinsic (innate) resistance and bacteria's acquired resistance?

Certain bacteria have intrinsic (innate) resistance. For example, Mycoplasma lack cell wall, resistant to penicillin that interferes with peptidoglycan synthesis. Outer membrane of gram negatives block many medications. Pseudomonas species have very narrow porin diameter (channel through outer membrane). Bacteria may develop acquired resistance through spontaneous mutations or horizontal gene transfer (drug resistance plasmids, transposons, etc.)

what is class switching

Class switching: plasma cells normally secrete IgM. TH cells can induce some activated B cells to become plasma cells that secrete other antibody classes. B cells in lymph nodes usually switch to IgG. B cells in MALT often switch to IgA. After class switching, memory cells are formed.

How does the microbiome develop or change over time?

Colonization begins at birth because fetus is sterile. Microbiome different after vaginal birth than after caesarian birth. Breastfeeding affects composition of microbiome. Composition different among individuals over time. Changes with physiological state and life style of host. ex. more Firmicutes in obese people, more bacteroidetes in thin people; microbiota change with weight loss. *Dysbiosis*: imbalance in the microbiome. Related to some disease states. Often caused by over treatment with antibiotics.

what is the difference between colonization and infection? How does one know if they have an infection?

Colonization refers o microbe establishing itself and multiplying; Infection used for colonization of pathogen. Can be *subclinical*: no symptoms or mild symptoms. *Infectious disease*: prevents normal function. Initial infection is *primary infection*. Damage can predispose individual to developing a secondary infection (respiratory illness impairing mucociliary escalator) ex. influenza --> bacterial pneumonia.

what conditions are common causes of healthcare associated infections (HAIs)?

Colostridium difficile Enerococcus species UTIs Bloodstream infections surgical site infections pneumonia GI infections

what are some other ways in which susceptibility rates can be tested?

Commercial modifications of susceptibility testing. Less labor-intensive, often faster results. One automated system determines growth rate via turbidity in cards, interprets results to determine MICs in 6 to 15 hours. E test is modification of disc diffusion test, uses strip with gradient of antibiotic; intersection of zone of inhibition indicates MIC. *New systems detect genes encoding antibiotic resistance*

what is the difference between communicable and non-communicable diseases

Communicable diseases are contagious. Transmitted from one host to another. ex. measles, colds, influenza. Transmission may be direct ex. kiss or indirect ex. drinking from a glass used by someone else Non-communicable diseases do not spread from host to host. Microorganisms most often arise from individual's normal microbiota or environment (for example, legionella pneumonphila in water systems of buildings)

what is the difference between communicable and contagious

Communicable or contagious diseases easily spread from one host to another. Not all infectious diseases are communicable ex. tetanus.

How does normal microbiota (flora) play a role in first line defenses?

Competitive exclusion of pathogens. Cover binding sites, consume available nutrients. Production of toxic compounds. Cutibacterium species degrade lipids, produce fatty acids. E. coli synthesizes colicins in intestinal tract. Lactobacillus in vagina produces low pH. Disruption of normal microbiota (ex. antibiotic use), can predispose person to infections. For example, clostridium difficile in intestine and candida albicans in vagina. Essential to development of the immune system.

how do the different types of T cells relate to the different MHC classes?

Cytotoxic T cells recognize antigen presented on MHC class I molecules (endogenous antigens). Helper T cells recognize antigen presented on MHC class II molecules (exogenous antigens). *Cluster of differentiation (CD) markers*: TC cells have CD8 on surface. TH cells have CD4 on surface. CD4 is receptor for HIV, which infects TH cells.

What is an emerging infectious disease?

Emerging infectious diseases: novel or have recently increased in incidence. New or newly recognized diseases include Severe acute respiratory syndrome (SARS), middle east respiratory syndrome (MERS), Ebola virus disease, and zika virus disease. Diseases increasing in incidence include malaria and tuberculosis. many factors contribute to emergence or reemergence of disease.

what is epidemiology?

Epidemiology is study of distribution and causes of disease in populations. Epidemiologists collect, compile data about sources of disease and risk factors. Design strategies to prevent/predict spread of disease. Expertise in many disciplines including ecology, microbiology, sociology, statistics, and psychology. Many daily habits (handwashing, waste disposal) are based on epidemiology

what is the difference between a primary and secondary response?

First response to antigen is a primary response. This is slower than secondary. Adaptive immune system remembers mechanism that proved effective against that specific antigen. Stronger secondary response results with later exposure.

describe first line defenses

First-line defenses are barriers blocking entry ex. skin

describe the immunoglobulin classes.

Five major classes: IgM, IgG, IgA, IgD, IgE. Have same basic monomeric structure. Each class has different constant region of heavy chain. Some form multimers of basic monomeric structure. Each class has distinct functions and properties.

what is hematopoiesis? what are the three categories of blood cells?

Formation and development of blood cells termed hematopoiesis. Blood cells originate from hematopoietic stem cells. Found in bone marrow. Induced to develop by colony stimulating factors (CSFs). Always found in normal blood. Numbers increase during infections. Some reside in various tissues. Three general categories. Red blood cells (erythrocytes) carry oxygen. Platelets (from megakaryocytes) involved in clotting. White blood cells (leukocytes) important in host defenses. Granulocytes, mononuclear phagocytes, lymphocytes.

how does gene rearrangement relate to lymphocyte development?

Gene rearrangement generates diversity. Process similar for B cells and T cells. Each B cell responds to only 1 epitope, but population in body responds to more than 100 million epitopes. But not 100 million antibody genes! V (variable), D (diversity), and J (joining) regions joined by deleting sections of DNA. *Imprecise joining*: nucleotides often added, deleted; changes reading frame, adds further diversity. Light, heavy chains formed separately; combination of two chains creates diversity of antigen binding site.

what role does gene transfer have in acquisition of microbial resistance?

Genes encoding resistance can spread to different strains, species, even genera. Most commonly through conjugative transfer of R plasmids, which often carry several different resistance genes. Resistance genes on R plasmids originate from spontaneous mutations and microbes that naturally produce the antibiotic. Gene coding for enzyme that modifies aminoglycoside likely originated from the streptomyces species that produces the antibiotic.

describe the discoveries of Paul Ehrlich (1854-1915)

German physician and bacteriologist. Observed some dyes stain bacterial but not animal cells. Indicated fundamental difference between cell types. Searched for "magic bullet" (selective toxicity) that would kill microbial pathogens without harming human host. Tested arsenic compounds to treat syphilis, caused by spirochete Treponema pallidum. The 606th tested compound proved effective in laboratory animals. Arsphenamine, named Salvarsan. Potentially lethal for patients but did cure infections previously considered hopeless. Proved some chemicals could selectively kill microbes.

what are granulocytes? describe the different types?

Granulocytes contain cytoplasmic granules; named based on staining properties. granulocytes make up the vast majority of white blood cells. 1. Neutrophils circulate in the blood, engulf and destroy bacteria; granules contain enzymes, antimicrobials; also called PMNs, increase in number during infection, primary microbial killers in blood. Most abundant killing machines. 2. Basophils involved in allergic reactions, inflammation; granules contain histamine. Mast cells are similar, found in tissues. 3. Eosinophils fight parasitic worms; involved in allergic reactions; granules contain antimicrobials and histamine. In order of abundance: Never Let Monkeys Eat Bananas

describe the different types of cytokines

Groups of cytokines often act together or in sequence to generate a response. For example, pro-inflammatory cytokines ex. TNF, IL1, IL6, others 1. Chemokines: chemotaxis of immune cells 2. Colony stimulating factors (CSFs): multiplication and differentiation of leukocytes 3. Interferons (IFNs): control of viral infections, regulation of immune responses 4. Interleukins (ILs): produced by leukocytes; important in innate and adaptive immunity 5. Tumor necrosis factor (TNF): inflammation, apoptosis

why are Hospital acquired infections (HAIs) bad? How do we prevent them?

HAIs pose risk to patients, increase time in hospital, increase price of healthcare. Most are preventable; important to detect, establish policies to prevent them. Hospitals have infection control committee; implement policies based on standard precautions and the transmission-based precautions. includes guidelines on hand hygiene, personal protective equipment, respiratory hygiene/cough etiquette, patient placement, patient-care equipment and instruments/devices, care of the environment, textiles and laundry, safe injection practices, infection control practices for special lumbar puncture procedures, and worker safety.

what are healthcare associated infections (HAIs)? Why are they significant?

Healthcare-assoicated infections (HAIs) are acquired while receiving treatment in a healthcare setting such as a hospital, therapy center, urgent care facility, or long-term care residence. One of top ten causes of death in united states. Occur in dense populations of unusually susceptible people, where the most resistant and virulent pathogens may circulate. Hospital acquired nosocomial infections affect up to 5% of patients.

what are the advantages for a pathogen to hide within a host cell

Hiding within a host cell allows avoidance of complement proteins, phagocytes, and antibodies. Shigella directs transfer from intestinal epithelial cell to adjacent cells by causing host cell actin polymerization. Listeria monocyogenes does the same.

what happens if a pathogen breaches the first line defenses?

If invaders brach the barriers, sensor systems detect. *Sentinel cells* use *pattern recognition receptors (PRRs)* to identify unique microbial components. *complement system* found in blood and tissue fluid (second line defense).

How do pathogens avoid recognition by antibodies?

IgA protease cleaves IgA, found in mucus, secretions. Produced by Neisseria gonorrhoeae, Heamophilus influenzae, and others. Antigenic variation: alter structure of surface antigens, stay ahead of antibody production. Neisseria gonorrhoeae varies antigenic structure of pili. Mimicking host molecules: cover surface with molecules similar to those found in host cell, appear to be "self". Streptococcus pyogenes form capsule from hyaluronic acid, a polysaccharide found in human tissues.

what is immunization? Why is it significant?

Immunization is process of inducing immunity. Has probably had greatest impact on human health of any other medical procedure. Example of how knowledge is power with respect to fighting disease. Useful applications of immunological reactions in diagnostic tests.

what is an immunoassay?

Immunoassay: in vitro test that uses antibody antigen interactions to detect or quantify given antigens or antibodies in a sample. Binding of known antibodies identifies unknown pathogen. Binding of patient's antibodies to known pathogen demonstrates current or previous infection.

what are the different types of immunoassays?

Immunoassays that use labeled antibodies. Markers are enzymes, fluorescent dye or radioactive isotopes. Sensitive. Immunoassays that involve visible antigen antibody aggregates. Simple, cheaper. Largely replaced by labeled antibody tests.

what is incubation period?

Incubation period is time between invasion by a pathogen and the onset of symptoms. Influences extent of spread. Long incubation period (anything over 10 days) can allow extensive spread before first symptoms appear

what is the purpose of the inflammatory response? What triggers it?

Infection or tissue damage results in inflammation. *Purpose is to contain site of damage, localize response, eliminate invader, and restore tissue function. Results in swelling, redness, heat, pain, sometimes loss of function.* Pattern recognition receptors (PRRs) trigger. Detect MAMPs and DAMPs (microbe associated molecular patterns). Host cells release inflammatory mediators (cytokines, histamine). Inducers include microbes, tissue damage. MAMPs cause release of tumor necrosis factor (TNF) that induces liver to produce acute phase proteins that activate complement. Blood vessel damage starts two enzymatic cascades; lead to coagulation and increased vessel permeability.

what is an infectious dose?

Infectious dose: number of microbes necessary to establish infection. Shigellosis results from approximately 10 to 100 ingested Shigella. Salmonellosis results from as many as 10^6 ingested Salmonella cells. Difference partially reflects ability to survive stomach acid. ID50 is number of cells required to infect 50% of the population of test animals (can be considered a measure of virulence). Shigella and Salmonella have same pathogenicity (same ability to cause disease), different virulence (more contagious). higher infectious dose= shorter incubation period

what are the sequence of events that take place in the inflammatory response?

Inflammatory process involves sequence of events. 1. Dilation of small blood vessels. Greater blood flow (heat, redness); slower flow rate. Leakage of fluids (swelling, pain). Fluids contain transferrin, complement, antibodies. 2. Migration of leukocytes from bloodstream to tissues. Endothelial cells grab phagocytes, slow them down (margination). Phagocytes squeeze between cells of vessel (diapedesis). 3. Clotting factors wall off site of infection. Prevents bleeding, stops spread of microbes 4. Dead neutrophils, tissue debris accumulates as pus.

What are innate effector actions?

Innate effector actions destroy invaders. *interferon (IFN)* secreted with viral infection. *Phagocytes* engulf microbes or cell debris by *phagocytosis*. *Inflammatory response* limits the infection and signals for help. *fever* interferes with pathogen growth and enhances other immune responses.

what are Koch's postulates?

Koch's postulates provide foundation for establishing that a given microbe causes a specific infections disease. Microorganism must be present in every case of disease. Organism must be grown in pure culture from diseased host. Same disease must be produced when pure culture is introduced into susceptible hosts. Organisms must be recovered from experimentally infected hosts.

what are the different types of labeled antibody immunoassays?

Labeled antibodies can detect a given antigen, or can detect antibodies that bind to a given antigen. *Direct immunoassays*: identify unknown antigen. Antigen attached to solid surface. Labeled antibodies of known specificity added. Washing removes unbound; binding identifies antigen. *indirect immunoassays*: detect specific antibodies in patient's serum. Known antigen attached to surface; serum added. Washing removes unbound primary antibodies. Secondary antibodies (labeled anti human IgG) added. Washing removes unbound; binding identifies primary antibody bound to antigen.

why is the lymphatic system important to adaptive immunity?

Lymphatic system is a collection of tissues and organs. Brings populations of lymphocytes into contact with antigens. Important because each lymphocyte is specific to only one or a few antigens. Lymphocyte must encounter appropriate antigen. Everything in bloodstream will be recognized by lymphatic system.

what are the functions of lymphatic vessels

Lymphatic vessels (lymphatics) carry lymph. Some fluid from blood flowing though capillaries is pushed out to join tissue fluid; some re-enters capillaries, but some enters lymphatic vessels. Lymph contains antigens from tissues. Lymph flows through lymph nodes before emptying back into circulatory system. Inflammatory response causes more fluid to enter tissues; increases antigen containing fluids entering lymphatic system.

What are lymphocytes? What do they do?

Lymphocytes are responsible for adaptive immunity. B cells, T cells highly specific in recognition of antigen. Generally reside in lymph nodes, lymphatic tissues. Innate lymphoid cells (ILCs) lack specificity. Can promote inflammatory response. Natural Killer (NK) cells destroy certain types of cells.

what are macrolides? how do they work?

Macrolides: *Erythromycin and azithromycin*. Reversible bind to 50S ribosomal subunit, prevent continuation of translation, therefore bacteriostatic. Often antibiotic of choice for patients allergic to penicillin. bacteriostatic against many gram positives and most common causes of atypical pneumonia. Outer membrane of Enterobacteriaceae blocks. Resistance occurs from modification of ribosomal RNA target, enzyme that modifies chemical, and decreased uptake.

Describe the function of macrophages

Macrophages are everyday beat cops. Phagocytize dead cells, debris, destroy invaders. Live weeks or months; regenerate lysosomes. Always present in tissues; replaced by monocytes. *activated macrophages*- response to cytokines. M1 macrophages have greater killing power. M2 macrophages lessen inflammation. If insufficient, can fuse to form giant cells. Macrophages, giant cells, T cells form granulomas. Wall of organisms or material resistant to destruction. Prevent escape but interfere with normal tissue function. Tuberculosis and other diseases. Macrophages are important sentinel cells; alerts other immune cells

how are diseases reduced or eradicated?

Many diseases reduced through improved sanitation, reservoir and vector control, vaccination, and antibiotic treatment. In US, many formerly common diseases are rare. Smallpox has been eradicated globally; work underway to eradicate measles, polio, dracuncaliasis (GWD).

How can exotoxins be subdivided?

Many exotoxins can be grouped according to the tissues they affect. *Neurotoxins* damage nervous system. *Enterotoxins* cause intestinal disturbance. *Cytotoxins* damage variety of cell types. Most exotoxins can be categorized by their structure and mechanism of action. A-B toxins, Membrane damaging toxins, and superantigens

what are the molecular koch's postulates?

Molecular Koch's postulates rely on molecular techniques to study a microbe's virulence factors. Virulence factor gene or its product found in pathogenic strains of organism. Mutating gene to disrupt function should reduce virulence. Reversion or replacement of gene should restore virulence. ex. Diphtheria toxin produced by pathogen causes disease. If we could introduce a mutation into the pathogen that inhibits production of the toxin, we could stop the disease

what are monoclonal antibodies?

Monoclonal antibodies (MAbs, Mabs, mAbs) recognize a single epitope. Difficult and expensive to produce. Made in mice. Complex process requires fusing animal B cells and cells that divide continuously in culture. Produces clones of a single cell and antibody to one epitope. Mabs can be used in immunoassays or in therapy. Medications end in mab. Obiltoxaximab neutralizes anthrax toxin. Mabs can be tagged with drug or toxin and delivered to specific cells in vivo. Antibody drug conjugates (ADCs) being developed against certain types of cancers. Immuno toxin therapeutics. Monoclonal antibodies can be humanized. Most of the animal derived antibody molecule is replaced with human equivalents using recombinant DNA techniques. Called a rhuMab: recombinant humanized monoclonal antibody. Longer half life than standard monoclonal antibodies. Human immune system less likely to destroy antibodies. Medications have names ending in zumab. Some used to treat certain cancers.

what are mononuclear phagocytes?

Mononuclear phagocytes comprise mononuclear phagocyte system (MPS). Includes monocytes (circulate in blood) and cell types that develop as they leave bloodstream. Macrophages differentiate from monocytes. Sentinel cells found in nearly all tissues. Can leave bloodstream, go to lymph, differentiate into macrophages = more effective killer. Killing machine, but not to extent of neutrophil.

how do pathogens exploit the antigen sampling process

Mucosal associated lymphoid tissue (MALT) samples material. Some pathogens use M cells to cross intestinal barrier. Shigella survives phagocytosis by macrophages; induces apoptosis; binds to base of mucosal epithelial cells and induces uptake. Some invade by alveolar macrophages (Mycobacterium tuberculosis produces surface proteins, directs uptake, avoids macrophage activation)

why are mucous membranes important for the innate immune system?

Mucous membranes includes the digestive, respiratory, and genitourinary tracts. Constantly bathed in secretions (ex. mucus). Peristalsis of intestines, mucociliary escalator of respiratory tract to remove microbes.

what is the purpose of the receptors on the T cells?

Multiple copies of T cell receptor (TCR). Two polypeptide chains: alpha plus beta or gamma plus delta; each has a variable and constant region. Structurally comparable to one "arm" of B cell receptor. T cell receptor does not interact with free antigen. Antigen must be presented by another cell. Held in *major histocompatibility complex molecules (MHC)* on surface of cell

Shiga toxin - producing E. Coli (STEC)

Name of disease: Bloody diarrhea, hemolytic uremic syndrome Name of toxin: shiga toxin Characteristics of disease: diarrhea that may be bloody; kidney damage. Mechanism: Inactivates the 60S subunit of eukaryotic ribosomes, stopping protein synthesis.

Corynebacterium diphtheria

Name of disease: Diphtheria Name of toxin: diphtheria toxin Characteristics of disease: pseudomembrane in the throat; heart, nervous system, kidney damage. Mechanism: Inhibits protein synthesis by inactivating an elongation factor of eukaryotic cells. Kills local cells (in the throat) and is carried in the bloodstream to various organs

Shigella dysenteriae

Name of disease: Dysentery, hemolytic uremic syndrome. Name of toxin: Shiga toxin Characteristics of disease: Diarrhea that contains blood, pus, and mucus; kidney damage. Mechanism: Inactivates the 60S subunit of eukaryotic ribosomes, stopping protein synthesis.

Streptococcus pyogenes

Name of disease: Pharyngitis and other infections Name of toxin: Streptolysin O Characteristics of disease: accumulation of pus. Mechanism: Inserts into membranes, forming pores that allow fluids to enter the cells. Lysing host cells: RBCs, leukocytes and others.

Staphylococcus aureus

Name of disease: Scalded skin syndrome Name of toxin: exfoliatin Characteristics of disease: Separation of the outer layer of skin Mechanism: Destroys material that holds the layers of skin together.

Staphylococcus aureus (certain strains)

Name of disease: Staphylococcal toxic shock Name of toxin: toxic shock syndrome toxin (TSST). Characteristics of disease: Fever, vomiting, diarrhea, muscle aches, rash, low blood pressure. Mechanism: Systemic toxic effects due to the resulting massive release of cytokines.

Clostridium botulinum

Name of disease: botulism Name of toxin: botulinum toxin Characteristics of disease: flaccid paralysis Mechanism: Blocks transmission of nerve signals to the muscles by preventing the release of acetylcholine.

vibrio cholerae

Name of disease: cholera Name of toxin: cholera toxin Characteristics of disease: severe watery diarrhea Mechanism: Modifies a regulatory protein in intestinal cells, causing those cells to continuously secrete electrolytes and water

Clostridium tetani

Name of disease: tetanus Name of toxin: tetanospasmin Characteristics of disease: Spastic paralysis Mechanism: Blocks the action of inhibitory neurons by preventing the release of neurotransmitters.

what is the function of Natural Killer cells? (NK)

Natural killer (NK) cells induce apoptosis in abtibody bound self cells. Antibody dependent cellular cytotoxicity (ADCC). Antibodies bound to foreign proteins in host membrane. NK cells have FC receptors for IgG molecules. NK cells bind, deliver perforin and protease containing granules to cell, initiating apoptosis. Also recognize host cells lacking MHC class I and kill those as well.

What is negative selection of self reactive B cells

Negative selection of self reactive B cells. B cells are exposed to "self" in bone marrow; if bind, induced to undergo apoptosis. This *negative selection* removes most B cells; critical for preventing immune system from attacking body.

describe the significance and function of neutrophils

Neutrophils act as SWAT team. Rapid response; move into area and eliminate invaders. Critical role in early stages of inflammation. First to be recruited from bloodstream to site of damage. More powerful than macrophages, but short life span of 1 to 2 days in tissues. Die once an assault on a microbe is made. Kill microbes via phagocytosis and release of granule content. Granular contents include: lysozyme, defensins (and other antibacterial peptides), myeloperoxidase (makes compound similar to bleach), lactoferrin, proteases, glucosidases, lipases, etc. Neutrophils can release DNA to form neutrophil extracellular traps (NETs) catching microbes, allowing enzymes and peptides from granules to destroy them.

describe the interferon response

PRRs detect viral RNA; cell produces interferon (IFN). Interferon causes neighboring cells to express inactive antiviral proteins (iAVPs). iAVPs activated by viral dsRNA. Degrade mRNA, stop protein synthesis, infected cells undergo apoptosis.

what is balanced pathogenicity

Pathogens and hosts generally evolve towards *balanced pathogenicity*. ex. influenza. Pathogen becomes less virulent while host becomes less susceptible.

how do pattern recognition receptors (PRRs) work?

Pattern recognition receptors (PRRs) see signs of microbial invasion; lead to cytokine secretion. *Microbe associated molecular patterns (MAMPs)* detected by PRRs. Include cell wall components (peptidoglycan, lipoteichoic acid, lipopolysaccharide, lipoproteins), flagellin subunits, microbial nucleic acid. PAMPs are pathogen associated, but not exclusive to pathogens. *Damage associated molecular patterns (DAMPs)* indicate cell damage.

where are Pattern recognition receptors (PRRs) found?

Pattern recognition receptors are located: 1. *on cell surface*: detect microbial components present in the cell's surroundings. 2. *in endosomes and phagosomes*: detect components of microbes ingested by the cell 3. *Free in cytoplasm*: Detect cell damage as well as microbial components in the cell's cytoplasm.

what is the difference between a localized and systemic infection?

Portal of entry has large impact on whether a disease is localized or systemic. *Localized infection*: microbe limited to small area (boil caused by staphylococcus aureus). *systemic infection*: agent spread throughout body (lyme disease). Suffix emia means in the blood. Bacteremia: bacteria circulating in blood. May lead to systemic inflammation called sepsis. Toxemia: toxins circulating in bloodstream. Viremia: viruses circulating in bloodstream.

what is a portal of exit? what are the different types?

Portal of exit is a body surface or orifice that serves as an exit route for a pathogen. 1. Intestinal tract: shed in feces ex. vibrio cholerae, E. coli, Salmonella, Shigella) 2. Respiratory tract: can exit in droplets of saliva, mucus ex. tuberculosis, pertussis, influenza, coronavirus 3. Skin: shed on skin cells ex. staphylococcus aureus 4. genital pathogens: semen, vaginal secretions. ex. neisseria gonorrhoeae, HPV

how do primary lymphoid organs contribute to adaptive immunity?

Primary lymphoid organs include bone marrow, thymus. Hematopoietic stem cells reside in bone marrow; give rise to all blood cells including lymphocytes. B cells mature in bone marrow. T cells migrate to thymus and mature there. Once mature, lymphocytes gather in secondary lymphoid organs and wait to encounter antigen.

how do antivirals that prevent assembly and release of viral particles work?

Protease inhibitors. During replication of some viruses, several proteins translated as a polyprotein that must be cleaved by a protease. virus specific. Include atazanavir (anti HIV) and grazoprevir (anti HCV). Neuraminidase inhibitors. Enzyme encoded by influenza viruses, needed for release. Several available, ingested, inhaled, or injected.

what are the effector functions of TH (CD4) cells?

Recognize antigen presented on MHC class II from *antigen presenting cells (APCs)*. Activate B cells and macrophages through release of cytokines. B cells likely present a variety of epitopes. TH cell may recognize any epitope and activate B cell. *conjugate vaccine* against T independent antigen (capsule of Haemophilus influenzae) produced by attaching a protein to it. B cell responds to polysaccharide capsule; TH reponds to protein component, activates B cell. *Hapten* is a molecule that binds a B cell receptor, but does not elicit response unless bound to a large carrier compound. Penicillin in body forms penicillin protein conjugate. If IgE antibodies form, allergic reaction. TH cells can recognize peptides presented on MHC class II; activate macrophage to increase power. Increases size, metabolism, number of lysosomes; produces nitric oxide and other toxic compounds. If needed, activated macrophages can fuse to form *giant cells* that participate in granuloma formation to wall of infectious agents and protect other cells.

what antimicrobial substances in the first line defenses help defend against infection?

Salt accumulates on skin from perspiration, kills many microbes. Lysozyme degrades peptidoglycan, killing gram positives. Peroxidases form antimicrobials; consume hydrogen peroxide to create more reactive forms of oxygen, such as superoxide anion. Lactoferrin and transferrin bind iron in blood and secretions. Antimicrobial peptides (AMPs). Defensins form pores in microbial membranes

describe the discovery of antimicrobial medications

Salvarsan (Paul Ehrlich, 1910) first documented case. Red dye Prontosil (Gerhard Domagk, 1932) used to treat streptococcal infections in animals. No effect in test tubes; enzymes in blood split to produce sulfanilamide, the first sulfa drug. Both are *chemotherapeutic agents*: chemicals used to treat disease. Synonyms are antimicrobial medications, antimicrobial drugs, or antimicrobials

what is the significance of secondary lymphoid organs to adaptive immunity?

Secondary lymphoid organs are sites where lymphocytes gather to contact antigens. lymph nodes, spleen, tonsils. Situated throughout body. *Peyer's patches* allow sampling of intestinal contents via specialized M cells, dendritic cells. Part of *mucosa associated lymphoid tissue (MALT*. *Mucosal immunity* prevents microbial invasion via mucous membranes. Lymphoid tissues under the skin are *skin associated lymphoid tissue (SALT)*.

How are effector proteins delivered to host cells?

Secretion systems in some gram negatives. Several types discovered; some can inject molecules other than proteins. *Type III secretion system* (injectisome). Effector proteins induce changes (altering of cell's cytoskeleton structure). Can induce uptake of bacteria cells

how did selman waksman contribute to the discovery of antibiotics?

Selman Waksman purified streptomycin from soil between Streptomyces griseus. Researchers began screening hundreds of thousands of microbes for antibiotics. Pharmaceutical companies today examine soil samples from around the world.

what is the chain of infection? What are its steps?

Spread of infectious disease follows series of steps called the chain of infection. Knowing the chain for a given disease allows determination of where the chain can be broken. Steps: 1. Reservoir of infectious agent 2. portal of exit 3. transmission 4. portal of entry 5. susceptible host

how can a pathogen be successful?

Successful pathogen needs to overcome host defenses only long enough to multiply and exit. Pathogen that overwhelms the host may kill it and lose nutrients and opportunity for transmission. Must survive to exit diseased host and infect new host.

what is the difference between symptomatic and asymptomatic infections?

Symptomatic infections provide a clear source of pathogens. Disease may be spread before symptoms appear or after they go away. Asymptomatic infections are harder to identify, carriers may not notice infection, but can spread it to others may lead to uncontrollable spread ex. Covid 19. This is why testing is very important. In Asymptomatic infections, Immune system may be responding to pathogen, inhibiting expression of symptoms. Up to 50% of women infected with Neisseria gonorrhoeae are asymptomatic, easily transmit it. High percentage of Covid 19 infections are likely asymptomatic. Potential pathogens may be part of normal microbiota. Many people carry staphylococcus aureus.

what is the difference between a sign and a symptom?

Symptoms are subjective effects experienced by patient (Pain, nausea, malaise, headache, queasy feeling). Signs are objective evidence that can be observed or measured (rash, pus formation, fever, swelling, vomiting diarrhea, etc.)

describe the difference between the different types of T cells

T cells play different role than B cells. Never produce antibodies. Effector T cells directly interact with target cells. Cause distinct changes in target cells. *Cytotoxic T cell*: Antigen recognition: peptides presented on MHC class I molecules. Effector Form: TC cell. Potential target cells: all nucleated cells. Effector function: Induces target cell to undergo apoptosis. Source of antigen recognized by effector cell: endogenous (produced within the target cell) *Helper T cell*: antigen recognition: Peptides presented on MHC class II molecules. Effector form: TH cell. Potential Target Cells: B cells, macrophages. Effector function: activates target cell. Source of antigen recognized by effector cell: exogenous (produced outside of the target cell)

Describe the primary response

Takes 10 to 14 days for significant accumulation after first exposure to antigen. Person may experience signs and symptoms of infection, although immune system is actively responding. Naive B cells bind antigen, are activated by TH cells. Some activated B cells continue dividing, others differentiate to form antibody secreting plasma cells. Individual plasma cells undergo apoptosis after a few days. Activated B cells continue proliferating and differentiating in presence of antigen, so antibody titer steadily increases. Proliferating B cells undergo changes that result in production of more effective antibodies. Affinity maturation. Class switching.

how do tetracyclines and glycylcyclines work?

Tetracyclines and glycylclines inhibit protein synthesis. Tetracyclines *reversibly* bind to 30S ribosomal subunit (*thus bacteriostatic*). Block tRNA attachment; prevent translation. Effective against certain gram positives and gram negatives. Some have longer half life meaning less frequent doses. Resistance from decreased uptake or increased excretion. The glycylcylines are related to the tetracyclines. Wider activity. Effective against bacteria resistant to the tetracyclines. Relatively new, so acquired resistance is rare. Tigecycline is only one currently approved.

what is the complement system? What are its functions?

The complement system complements activities of adaptive immune system. Proteins circulating in blood and tissue fluid. Proteins named in order discovered: C1 through C9. Can split into fragments, for example, C3 splits to C3a and C3b. Activated by three different pathways that lead to formation of C3 convertase (C4b2b; or thrombin, or plasmin, all serine proteases), which splits C3. *Three protective functions of Complement: Opsonization (enhancing phagocytosis), Promote inflammation, Lysis of invading cells*.

why are time, place, and individuals affected important to include in a descriptive study?

The person: age, gender, ethnicity, occupation, personal habits, previous illnesses, socioeconomic status, marital status may all yield clues about risk The Place: geographic location helps pinpoint source, yield clues about potential reservoirs, vectors, or boundaries that might affect transmission. Time: the season can affect transmission. vector-borne diseases are more common in warm weather.

what is the reservoir of infection? Why is it significant?

The reservoir of infection is the natural habitat of a pathogen. can be In or an animal, human, or in the environment ex. soil, water, air. Identification of reservoir important in disease control. A pathogen is often easier to control if humans are the only reservoir. ex. smallpox (easier to control b/c of vaccine). But this is not always the case ex. gonorrhea, syphillis, AIDS, others.

How do B cells respond in humoral immunity?

The rsponse to T independent antigens. Can activate B cells without aid of TH cells. Relatively few antigens, but can be important medically. Molecules with numerous identical evenly spaced epitopes (for ex. polysaccharide capsules) are bound by clusters of B cell receptors. Leads to activation. Not very immunogenic in young children. LPS is another T independent antigen.

What are the general mechanisms of Pathogenesis?

There are several general patterns. 1. *Produce toxins that are ingested*. ex. Colostridium botulinum, Staphylococcus aureus. 2. *Colonize mucous membranes, produce toxins. ex. vibrio cholerae, E. coli 0157:H7, Corynebacterium diphtheriae. 3. *Invade host tissues, avoid defenses*. ex. Mycobacterium tuberculosis, yersinia pestis (plague), Salmonella enterica. 4. *Invade host tissues, produce toxins*. ex. Shigella dysenteriae, colostridium tetnai.

what other characteristics of antimicrobial medications are important to take into consideration when prescribing these medications?

Tissue distribution, metabolism, and excretion of the medication. Antimicrobial behaviors differ in body. Only some can access the brain; only some can withstand stomach acid (ex. penicillin G has to be given IM). Half life of medication is time it takes for blood serum concentration to decrease by 50%. Dictates frequency of doses required to maintain effective level in body. ex. Penicillin V is taken 4 times a day, azithromycin is taken no more than once a day. Patients with kidney or liver dysfunction excrete or metabolize medications more slowly; must adjust dosage to avoid toxic levels.

what are toll like receptors (TLRs)?

Toll-like receptors (TLRs) anchored in membranes of sentinel cells. Surface TLRs monitor extracellular environment. TLRs in phagosomal or endosomal membranes of organelles characterize ingested material. Specific for distinct MAMPs. Dendritic cells have both TLRs and CLRs (C type lectin receptors).

What is a therapeutic index? A therapeutic window?

Toxicity is relative and expressed as *therapeutic index*. Therapeutic index is calculated as the lowest dose toxic to patient divided by dose used for therapy. *Penicillin G useful, has high therapeutic index*; interferes with cell wall synthesis, a process not present in humans. Also has high therapeutic window, the range between the therapeutic dose and the toxic dose. Medications too toxic for systemic use may be used topically (applied to body surface)

how does cell mediated immunity work?

Two subsets of T cells help eliminate antigens; differ in surface proteins, called CD markers. *Cytotoxic T cell* destroys corrupted host cells. *Helper T cell* directs and assists adaptive immune responses. Both have multiple surface molecules of *T cell receptor (TCR)*, analogous in function to the B cell receptor (BCR). TCR does not recognize free antigen; antigen must be presented by body's own cells. Helper T cells and cytotoxic T cells must be activated before they can multiply. Dendritic cells are responsible for T cell activation. Dendritic cells have same lineage as macrophages. Once activated, T cell proliferates, differentiates. Forms effector helper T cells (TH cells) or effector cytotoxic T cells (TC cells). Both types can form memory cells (cell lines). TC cells respond to intracellular antigens, induce cell to undergo apoptosis (ex. virally infected cell). TH cells activate B cels, macrophages; produce cytokines to direct and support other cells, including other T cells. *Regulatory T cells (Treg) stop immune system from overreacting and responding to harmless substances. Focus of research.

describe the different types of MHC molecules

Two types of MHC molecules. *MHC class I* present endogenous antigens. Produced by all nucleated cells of the body. *MHC class II* present exogenous antigens. Produced only by *antigen presenting cells (APCs)*, dendritic cells, B cells, macrophages. T cell recognizes peptide: as part of an MHC complex

what is a fluorescent antibody (FA) test?

Use fluorescence microscopy to locate labeled antibodies bound to antigens fixed to microscope slide. Size and shape of antigens seen, but procedure is time consuming. Using different colored labels can detect more than one antigen. Detect rabies virus in brain tissue, antibodies, to agent that causes syphilis. Fluorescence microscopy is used to locate fluorescently labeled antibodies bound to antigens. The size and shape of the antibody bound antigens can often be determined, but each specimen needs to be examined individually. Used in clinical labs to *diagnose certain diseases including syphilis, rabies*, and others.

describe vector-borne indirect transmission

Vector borne: a vector is a living organism that can carry a pathogen. Most often arthropods: mosquitoes, flies, fleas, lice, ticks. Mechanical vector carries microbe on its body from one location to another. Biological vector also participates in life cycle of pathogen. ex. Plasmodium (malaria parasite) multiplies to high numbers of the infectious form of the parasite in the mosquito. Yersina pestis (plague bacillus) causes blockage in the gut of the flea causing it to regurgitate its gut contents (i.e. Y. pestis, into the bite wound). *Vector control important in preventing vector-borne diseases*

what is the difference between vertical and horizontal transmission?

Vertical transmission is pregnant woman to fetus or mother to infant during childbirth or breast feeding. Horizontal transmission is person to person via air, physical contact, ingestion of food or water, or vector

Are all microbes harmful to humans?

We contact numerous microorganisms daily. Breathe in, ingest with food and drink, pick up on skin. Most do not harm us. Some may colonize body surfaces; others shed with dead epithelial cells. Most swallowed microorganisms die in stomach or are eliminated in feces. Relatively few pathogens that cause damage. Distinct characteristics allow avoidance of some body defenses. Most microbes are harmless, many are beneficial. Some can cause disease if there is an opportunity. Weaknesses or defects in immunity leave people vulnerable to invasion; these individuals are *immunocompromised*. Factors include malnutrition, cancer, AIDS or other disease, surgery, wounds, genetic defects, alcohol or drug abuse, and immunosuppressive therapy.

how do antibiotics that interfere with cell membrane integrity work?

a few antimicrobials damage bacterial membranes causing cells to leak, leading to cell death.

what is a pandemic

a pandemic is global ex. AIDS; COVID 19

what are the steps to establishing an infection

adherence --> colonization --> Immune avoidance --> Damage to Host --> Exit and infect new host

describe airborne indirect transmission

airborne: respiratory diseases often transmitted by liquid droplets released while talking, etc. Droplet nuclei (microbes attached to dried material) remain suspended; inhaled, carry pathogens to lungs. Other airborne particles include dead skin cells, dust. Crowds increase number of bacteria in the air. Airborne pathogens are difficult to control. Ventilation systems, negative pressure, and HEPA filters can help prevent spread in healthcare facilities

what is an epidemic

an epidemic is an unusually large number of cases. Can be from introduced or endemic disease.

what is an outbreak

an outbreak is a group of cases at specific time and population. ex. 2019 measles outbreak in USA

what does the term antibiotic mean

antibiotic is a term reserved for compounds produced by microorganisms. In other words, it is a naturally produced antimicrobial

what are precipitation reactions

antibodies bound to soluble antigens can cross link, form precipitate. Certain relative concentrations of antibody and antigen. Proper concentrations determined by placing separate suspensions near each other in gel, allow molecules to diffuse. Precipitate will form in zone of optimal proportions. Although largely replaced, Ouchterlony technique illustrates immunodiffusion test.

how does one quantify antigen antibody reactions using an immunoassay?

antibody concentration determined by serial dilution. Sequential 2 or 10 fold dilutions. Antigen added to each dilution. Titer (concentration) is reciprocal of last dilution that gives a detectable antigen antibody reaction. For example, positive observed in 1: 256 but not 1:512, antibody titer is 256. Usually done in plastic microtiter plates.

what is the difference between bacteriostatic and bactericidal?

antimicrobial agents classified by their toxic action. *Bacteriostatic* chemicals inhibit bacterial growth. Patient's defenses must eliminate pathogen (sulfa drugs). *Bactericidal* chemicals kill bacteria. Sometimes only inhibitory depending upon drug concentration and stage of microbial growth

what is the attack rate

attack rate is a percentage of people who become ill in population after exposure to infectious agent. Reflects infectious dose and immune status of population. Usually determined retrospectively.

surgical site infections

barriers such as skin and mucous membranes are breached, increasing vulnerability to infection; normal microbiota from the skin or GI tract are common causes

how do rifamycins work?

block prokaryotic RNA polymerase; prevents initiation of transcription, which kills the cell. Rifampin is bactericidal against gram positives, some gram negatives, mycobacterium. Resistance develops quickly due to mutation in RNA polymerase gene.

what is case-fatality rate

case fatality rate is the proportion of people who die from a specified disease among all individuals diagnosed with the disease over a certain period fo time. The ebola virus was very feared because of very high case-fatality rate (50%).

what are cephalosporins? How are they similar to other beta lactam antibiotics?

cephalosporins are produced by a different group of organisms than penicillin but have the same beta lactam ring and act on cell wall just as penicillin does. Structure makes it resistant to some beta lactamases. Some have low affinity for PBPs of gram positives. Chemical modifications have led to five generations. Later generations more effective against gram negatives, resist beta lactamases. fifth generation effective against MRSA. Others available with beta lactamase inhibitor.

What is clonal selection

clonal selection applies to B cells and T cells. Populations of B and T cells recognize a functionally limitless variety of antigens. Each cell only recognizes and responds to a single epitope. Cells that bind antigen multiply, generating a population of clones capable fo making the appropriate antibodies. Lymphocytes residing in secondary lymphoid organs wait for dream antigen - antigen with correct epitope. Specificity of antigen receptor governs recognition. Confirmation from another cell type usually needed. Some progeny leave secondary lymphoid organs, migrate to tissues; continue responding as long as antigen is present, then undergo apoptosis.

what is a fluorescence activated cell sorter (FACS)

counts, sorts, cells labeled with fluorescent antibodies. For example, can track progression of HIV by determining serum levels of CD4 T cells. separates and determines the relative concentrations and certain characteristics of fluorescent antibody labeled cells. Widely used to diagnose and monitor the progression of diseases involving white blood cells. Used in clinical labs to track progression of HIV disease, to characterize different types and stages of *lymphomas and leukemias, and to diagnose immunodeficiency diseases.*

what is an endemic disease

endemic disease constantly present in population. ex. common cold, lyme disease, plague

describe challenges of environmental reservoirs of infection

environmental reservoirs are difficult or impossible to eliminate. ex. colostridium, legionella, bacillus anthracis (anthrax)

how do aminoglycosides work?

ex. gentamicin, amikacin, tobramycin, neomycin, and streptomycin. Irreversibly bind to 30S ribosomal subunit, causing it to malfunction, *bacteriocidal*. Blocks initiation of translation, causes misreading of mRNA by ribosomes past initiation. Often toxic; generally used when alternatives unavailable. Generally ineffective against anaerobes, enterococci, and streptococci because they do not enter these cells efficiently. Sometimes used synergistically with. penicillin that allows the aminoglycoside to enter cells. Inhaled form of tobramycin treats pseudomonas lung infections in cystic fibrosis patients. Neomycin too toxic for systemic use; common in first-aid skin ointments.

what antimicrobial medications inhibit cell wall synthesis?

examples of antibiotics that work this way are beta lactam antibiotics, glycopeptide antibiotics, and bacitracin.

how does one defend against mycobacterium tuberculosis?

few antimicrobials effective against mycobacterium. Waxy cell wall prevents entry of many chemicals; slow growth. *First line drugs* are most effective, least toxic. Combination therapy decreases chance of development of resistant mutants. *Second line drugs* given for strains resistant to first-line drugs. Less effective or have a greater toxicity risk. Some target unique cell wall of mycobacteria. Isoniazid inhibits mycolic acid synthesis; ethambutol inhibits enzymes required for synthesis of other cell wall components; pyrazinamide interferes with protein synthesis.

what is affinity maturation

form of natural selection. Spontaneous mutations occur in multiplying B cells resulting in slight changes in B cell receptor. B cells that bind antigen longest are most likely to proliferate.

what are the different types of reactions that can visibly occur to immunoassays?

immunoassays may involve visible antigen antibody aggreagates. Antibodies that cross link antigens create longer mouthfuls for phagocytic cells. Clumped antigen antibody complexes form the basis of: *Agglutination reactions and Precipitation reactions*

describe the discovery of antibiotics

in 1928, fleming identified mold Penicillium secreting compound toxic to Staphylococcus (penicillin). Showed effective in killing many bacterial species. Unable to purify, he later abandoned research. Chain and Florey purified, tested compounds in 1941 on police officer with Staphylococcus aureus infection. Patient improved but supply of purified penicillin ran out and he later died. WWII spurred research and development; penicillin G, the first *antibiotic*

describe the types of inactivated vaccines

inactivated whole agent vaccines: contain killed microorganisms or inactivated viruses. Treated with formalin or other chemical that does not significantly change epitopes. Includes influenza, rabies, hepatitis A. Toxoid vaccines: toxins treated to destroy toxic part, retain antigenic epitopes. Includes diphtheria, tetanus. Subunit vaccines: consist of key protein antigens or antigenic fragments from pathogen. Avoids cell parts that may cause side effects. For example, acellular pertussis (aP) vaccine.

what is incidence

incidence is number of new cases/time/population. Measures risk of an individual contracting a disease. Usually measured over a short time period.

how do human behaviors impact antimicrobial resistance?

increasing use, misuse selects for resistant microorganisms. Only 3% of staphylococcus aureus originally resistant to penicillin G; now more than 90% are resistant. Antimicrobial resistance alarming. Impact on cost, complications, and outcomes of treatment. Dealing with problem requires understanding of mechanisms and spread of resistance

Urinary tract infections (UTIs)

infections of the bladder or kidneys; most hospital-acquired UTIs are associated with catheter use

Bloodstream infections

infectious agents in the blood can lead to sepsis, particularly in sick or immunocompromised individuals; hospital cases are often associated with central lines (catheters placed near the heart) that may allow infectious agents to enter the bloodstream directly.

what is infectious dose?

infectious dose is the number of pathogens introduced; minimum number of pathogens required to produce symptoms. differs with every pathogen. If few cells enter, immune system may eliminate organism before symptoms appear.

how do fluoroquinolones work?

inhibit nucleic acid synthesis. Inhibit topoisomerases, enzymes that maintain supercoiling of DNA; bactericidal against wide variety of bacteria. DNA gyrase breaks, rejoins strands to relieve strain from localized unwinding of DNA; function is essential. Resistance usually due to alteration in DNA gyrase target.

how do non-nucleotide reverse transcriptase inhibitors work (NNRTIs)?

inhibit reverse transcriptase by binding to site other than nucleotide binding site (efavirenz, etavirine)

how do non-nucleotide polymerase inhibitors work?

inhibit viral polymerases by binding to site other than nucleotide-binding site. Dasabuvir is component of fixed-dose combination to treat HCV. Foscarnet used to treat ganciclovir resistant CMV and acyclovir resistant HSV.

how does trimethoprim work?

inhibits enzyme in a later step than sulfa drugs. has little effect on enzyme's counterpart in human cells. Combination of trimethoprim and sulfa drugs (sulfonamide) has synergistic effect; *co-trimoxazole*.

how does chloramphenicol work?

inhibits protein synthesis. Binds to 50S ribosomal subunit, blocks translation. active against a wide range of bacteria. Used as a last resort due to rare, but lethal side effect. May cause aplastic anemia, inability to form white, red blood cells

how do antivirals that prevent genome integration work?

integrase inhibitors interfere with action of HIV encoded enzyme integrase. Prevent virus from inserting DNA copy of genome into host cell.

how do folate inhibitors work

interfere with metabolic pathways. Inhibit steps in synthesis of folate and ultimately synthesis of coenzyme required for nucleotide biosynthesis. Animals lack enzymes to synthesize folate; required in diet. Sulfonamides, trimethoprim inhibit different steps in synthesis: Precursor #1 -PABA-> Precursor #2 -Glutamate-> Dihydrofolate --> Tetrahydrofolate Sulfa drugs between precursor #1 and #2. Trimethoprim between dihydrofolate and tetrahydrofolate.

how do polymyxins work

interferes with cell membrane integrity. Bind to membranes of gram negatives. Generally limits usefulness to topical applications. Also bind to eukaryotic cells, though to a lesser extent.

how does daptomycin work

interferes with cell membrane integrity. inserts into cytoplasmic membrane. Used against gram positives resistant to other antibiotics. Ineffective against gram negatives; cannot penetrate outer membrane.

IgE

less than 0.01% of serum. half life of 2 days. Binds via the Fc region to mast cells and basophils. This bound IgE allows those cells to detect parasites and other antigens and respond by releasing their granule contents. Involved in many allergic reactions. Barely detectable in serum; most is tightly bound via Fc region to basophils and mast cells. Allows these cells to detect, respond to antigens. Antigen binds to two adjacent IgE molecules carried by mast cell, cell releases histamine and other inflammatory mediators. Important in eliminating parasitic worms. Basophils and mast cells also release chemicals when IgE binds to normally harmless foods, dusts, pollens, yielding allergic reactions of coughing, sneezing, swelling. Some allergic (hypersensitivity) reactions can be life threatening.

IgD

less than 1% of serum. half life of 3 days. Involved in the development and maturation of the antibody response. Its functions in blood are not well understood.

pneumonia

lung infection; in hospitals, many cases are associated with ventilator use; most common cause of death from nosocomial infection in critically ill patients

what is a normal microbiota or microbiome?

microorganisms routinely growing on a healthy body. Resident microbiota inhabit sites for extended periods. Important to human health. Research underway to study microbiota using *metagenomics*, analysis of DNA.

what is morbidity

morbidity is incidence of disease in a population. Contagious diseases ex. flu often have high morbidity rate: infected individual may transmit to several others. Asymptomatic individuals excluded.

what is mortality

mortality is overall death rate in population

gastrointestinal (GI) infections

most hospital-acquired GI infections are due to clostridium difficile; related to antibiotic use

what impact do spontaneous mutations have on antimicrobial resistance?

mutations happen at low rate during replication, but can have significant effect. Just a single base pair change in gene encoding a ribosomal protein yields resistance to streptomycin. Spontaneous resistance to antibiotics with several different targets or multiple binding sites is less likely. Combination therapy of multiple antibiotics is often used; unlikely cells will simultaneously develop resistance.

describe the challenges of non-human animal reservoirs of infection

non-human animal reservoirs are difficult to control in wild animal populations. ex. Plague (spread by fleas), hantavirus (spread by mice), lyme disease (spread by ticks). Zoonoses (zoonotic disease) are diseases of animals that are transmitted to humans. More severe in humans because there is no co-evolution toward balanced pathogenicity. i.e. attenuation of pathogen and increased resistance of host. Basically, humans have never seen these diseases before, and are therefore at our most vulnerable.

what are some global repercussions of antibiotic resistance?

overuse is a worldwide concern; resistant microbes recognize no political boundaries. Antimicrobial antibiotics available without prescription in many parts of the world, may allow improper use. antimicrobial antibiotics used in animal feeds at low levels to enhance growth; selects for antibiotic resistant microbes. Resistant salmonella strains linked to animals.

Enerococcus species

part of the normal intestinal microbiota; cause a variety of HAIs; have developed multi-drug antimicrobial resistance

describe the steps of phagocytosis

phagocytes engulf and digest material invading microbes (pathogens) 1. *chemotaxis*: phagocytes recruited by chemoattractants (products of microorganisms, phospholipids from injured host cells, chemokines, C5a) 2. *Recognition and attachment:* direct (receptors bind mannose) and indirect (binding to opsonins) 3. *Engulfment*: pseudopods surround, form phagosome 4. *Phagosome maturation and phagolysosome formation*: phagosomes fused with lysosomes containing degradative enzymes and antibacterial substances. 5. *Destruction and digestion*: toxic ROS and nitric oxide produced; pH decreases; enzymes degrade; peptides damage membrane of invader; lactoferrin binds iron. 6. *Exocytosis*: vesicle fuses with cytoplasmic membrane, expels remains

what are polyclonal antibodies?

polyclonal antibodies bind to various epitopes on antigen. Animals immunized with whole or partial agent; resulting antibodies are collected from animal's serum. Multiple B cells respond. produce mix of antibodies to variety of epitopes. More complex antigens will yield more antibodies. Some may bidn closely related organisms (ex. shigella and E. coli outer membrane proteins).

what is prevalence

prevalence is the total number of cases at any time or for a specific period in a given population. Reflects overall impact of disease on society; includes old and new cases, as well as duration of disease. Usually measured over longer period of time, sometimes the entire length of the outbreak

what are the other components of the national disease surveillance network other than the CDC?

public health departments in each state in concert with CDC. Have authority to mandate diseases that must be reported. Washington state health authorities responded rapidly to E coli 0157:H7 outbreak in 1993 and to C. gattii cases in 2007. Other components of the public health network include public schools report absentee rates, hospital laboratories report on isolation of pathogens with epidemiological significance, news media alert public to presence of infectious diseases.

what is puerperual fever? How is it relevant to the history of epidemiology?

puerperual fever is a bacterial infection of the uterus. By mid 19th century, one out of eight women died in vienna hospitals following childbirth. Ignaz Semmelweis observed puerperal fever. Incidence in one section run by medical students was four times second section run by midwives and midwifery students. A fried of Semmelweis sustained a scalpel wound during an autopsy, died of symptoms similar to puerperal fever. Semmelweis reasoned poison that killed his friend was transferred to women in childbirth by medical students. Before Pasteur, Koch: germ theory of disease. Poison was probably streptococcus pyogenes. Washing hands with strong disinfectant: incidence of puerperal fever dropped to one-third previous level.

how do NS5A inhibitors work?

relatively new option for treating HCV. Inhibit NS5A, HCV encoded protein required for replication of viral genome (elbasvir, ombitasvir)

how can we prevent antimicrobial resistance?

responsibilities of patients. carefully follow instructions even if inconvenient. Essential to maintain adequate blood levels of antibiotic; skipping a dose may reduce levels, allowing less sensitive microbes a chance to grow and spread. Failure to complete treatment may not kill least sensitive organisms, allowing subsequent spread. An educated public is important. Antibiotics ineffective against viruses; cannot cure the common cold. Misuse selects for antibiotic resistant bacteria in normal microbiota; they can eventually transfer R plasmids to pathogens

What is the Kirby-bauer disc diffusion test? (Kirby bauer disc diffusion test)

routinely used to determine susceptibility of bacterial strain to antibiotics. Standard sample of strain uniformly spread on agar plate; discs containing different antibiotics placed on surface. Drugs diffuse outward, establish concentration gradients. Resulting *zone of inhibition* compared with specially prepared charts to determine whether strain is susceptible, intermediate, or resistant. Drug characteristics must be taken into account (ex. molecular weight, stability, amount), so not strictly big zone= more effective. other factors at play.

describe the secondary response

secondary response mediated by memory cells. Significantly faster, more effective than primary. Pathogens usually eliminated before causing harm. Vaccination exploits this natural phenomenon. Memory B cells that respond to a specific antigen are present in greater numbers. Receptors already fine tuned through *affinity maturation*. Antibodies coded by these cells bind antigen effectively. When activated, some quickly become plasma cells, producing IgG or IgA due to *class switching*. Proliferating cells again undergo affinity maturation, generating even more effective antibodies. Future exposures elicit an even stronger response.

how do IgG and IgM levels respond to the primary and secondary response

see chart

what is selective toxicity?

selective toxicity: causes greater harm to microbes than to human host. Interferes with essential structures or properties common in microbes but not human cells.

what is serology?

serology is study of in vitro antibody antigen interactions. Serum is fluid portion of blood after blood clots. Plasma is fluid portion of blood treated to prevent clotting. Seronegative: individual not yet exposed to antigen. Has no specific antibodies to that pathogen. Seropositive: individual has been exposed. Has produced specific antibodies to pathogen. Serology is faster than reverse transcripase PCR. Seroconversion, process of producing antibodies; rise in titer is characteristic of active infection. Small, steady antibody level indicates previous exposure. going from negative to positive.

how do sulfa drugs work? (sulonamides)

similar structure to PABA, so mimmic it and prevent pathway of folate synthesis. Inhibit many gram positives and gram negatives. Structurally similar to PABA, so enzyme binds chemical. Example of competitive inhibition. Human cells lack enzyme

what are the three types of symbiosis?

skin, mucous membranes are barriers, but also host complex ecosystem of microorganisms. symbiosis= living together. *Mutualism*: both partners benefit. ex. in large intestine, some bacteria synthesize vitamin K and B vitamins, which host can absorb; bacteria supplied with warmth, energy sources. *Commensalism*: one partner benefits, other is unharmed. Many microbes living on skin neither harmful nor helpful, but obtain food and necessities from host. *Parasitism*: one organism benefits at expense of another. All pathogens are parasites, but medical microbiologists often reserve term for eukaryotic pathogens (ex. protozoa, helminths)

what are some limitations of Koch's postulates?

some organisms cannot be grown in laboratory medium (Causative agent of syphilis - and at the time when Koch developed his postulates, this also applied to viruses). Infected individuals do not always have symptoms. ex. cholera, polio, UTIs, etc. Some diseases are polymicrobial (periodontal disease). Suitable animal hosts not always available for testing. Humans may be only affected host species ex. gonorrhea. Not ethical to test the postulates on humans.

what is a sporadic disease

sporadic diseases have a few cases from time to time

what characteristics of the environment influence epidemiology of disease?

temperature, water and nutrient supply, radiation, availability of light and oxygen, crowding and poor sanitation. endospores allow survival in damaging conditions. exposure to antibiotics allows development of resistant organisms

why is the skin important for the innate immune system?

the skin is difficult for microbes to penetrate. Dermis: tightly woven fibrous connective tissue. Epidermis: many layers of epithelial cells. Outermost are dead, filled with keratin. keratin repels water, maintains dry environment. Continually flake off along with any attached microbes. Some organisms like Syphilis can still penetrate skin.

What is the world health organization (WHO)?

the world health organization (WHO) has four main functions: 1. provide worldwide guidance in field of health 2. set global standards for health 3. cooperatively strengthen national health programs 4. develop and transfer appropriate health technology. WHO also provides education, technical assistance to 193 member states. Distributes information about epidemics, particularly those of global concern. ex. weekly epidemiological record

how does the therapeutic index relate to safety?

therapeutic index is the ratio of doses of the toxic and the desired responses. TI is used as an index of comparative toxicity of two different materials; approximate statement of the relative safety of a drug. The larger the ratio, the greater the relative safety.

colostridium difficile

toxin-producing strains can cause diarrhea and colitis in people taking antibiotics

what factors impact the effectiveness of beta lactam antibiotics?

vary in activity. Peptidoglycan of gram positives exposed; outer membrane of gram negatives blocks. PBPs different in gram positives versus gram negatives; also aerobes versus anaerobes, and in different species. Some bacteria synthesize beta lactamase, which breaks beta lactam ring, destroys activity of antibiotic. Penicillinase inactivates members of the penicillin family. Extended spectrum beta lactamases (ESBLs) inactivate a wide variety of beta lactam medications. Gram negatives produce a more extensive array of beta lactamases than gram positives.

describe vehicle-borne indirect transmission

vehicle borne means transmitted by objects, food, or water. Fomites are inanimate objects that transmit disease such as clothing, keyboards, doorknobs, drinking glasses. Food and water can become contaminated, but they are not considered fomites. Animal products such as meat or eggs frequently carry disease from animal's intestine. Cross-contamination: transfer of microbes between foods. Municipal water systems can distribute to large numbers. ex. Cryptosporidium parvum outbreak in wisconsin in 1993 affected over 400,000 people

what is virulence

virulence is ability to cause disease. Factors that allow pathogen to attach to host cell, avoid immune defenses, damage host, all impact virulence.

why are viruses difficult to target selectively?

viruses rely on host cell's metabolic machinery, lack cell walls, ribosomes, other structures targeted by antibiotics. Many encode polymerases, represent potential targets. Scientists trying to develop antiviral medications that interfere with viral replication. Current options effective only against specific type of virus; none eliminate latent infections. Fixed dose combinations counter development of viral resistance.

what is western blotting?

western blotting first separates proteins of antigen by size using SDS PAGE. (protein electrophoresis). Proteins then transferred to nylon membrane (blotted). Serum added; unbound antibodies washed off. Enzyme or radioactively labeled secondary antibodies added; unbound washed off. Label is detected. Indicates which proteins on the blot were recognized by antibodies in the serum. various methods are used to detect labeled antibodies bound to proteins that have been separated by size. The results are generally more reliable than ELISA tests, such as for HIV and lyme disease. *Used extensively in research laboratories* for identification of natural and recombinant proteins.