Microbiology Final

A "chunk" of DNA that can move from one double-stranded DNA molecule to another

Transposon

What are the three kinds of exotoxin?

Type I cell surface-active: Type I toxins bind to a receptor on the cell surface and stimulate intracellular signaling pathways Type II: membrane damaging: Membrane-damaging toxins exhibit hemolysin or cytolysin activity in vitro. However, induction of cell lysis may not be the primary function of the toxins during infection. At low concentrations of toxin, more subtle effects such as modulation of host cell signal transduction may be observed in the absence of cell lysis. Membrane-damaging toxins can be divided into two categories, the channel-forming toxins and toxins that function as enzymes that act on the membrane. Type III: intracellular: Type III exotoxins can be classified by their mode of entry into the cell, or by their mechanism once inside.

A needle like assemblage of proteins that enables pathogens to inject proteins into host cells

Type III Secretion

Imagine you are a health care provider counseling a new mother about vaccinations. What will you tell her to convince her of the importance of vaccinating her child against diseases that now seem rare?

Vaccinating your child protects him/her from diseases that others may carry due to non-vaccination. It also protects others by herd immunity and prevents death by dangerous diseases that may come back later in child's life.

List three things that microbes can use to evade destruction be the human immune system:

a) capsule b) o-antigen c) phagosome (myobacterium)

List three things that make people more susceptible to infection:

a) fatigue b) chemotherapy c) age

A molecule that is bound by an antibody and can elicit an immune response

antigen

alternatives to antibiotic therapy

bacteriophage and probiotics

Provide one alternative to antibiotic therapy:

bacteriophage therapy

Composed of phospholipid bi-Iayer, separates "in" from "out" enables the production of ATP by harnessing chemical gradients

cell membrane

Why doesn't your immune system attack your own body? (usually)

central tolerance of T-cells and B-cells

Describe one way antibodies are used in diagnostic Microbiology (to detect the presence of microbes)?

fluorescently labeled antibodies are used to specifically detect microbes

What factors lead to the spread of nosocomial infection?

high prevalence of pathogens high prevalence of compromised hosts efficient mechanisms of transmission from patient to patient*

What are the physical methods used to kill all bacteria, endospores and viruses

high temp, pasteurization, cold, filtration, irradiation

What are the major components of bacterial cells that are targeted by antibiotics?

inhibit RNA polymerase, inhibit metabolic pathways, gyrase, cell wall biosynthesis, ribosome inhibitors,

Contains reactive oxygen molecules, low pH, and enzymes that destroy bacterial cells after phagocytosis

lysosome

A symbiotic relationship in which both partners benefit

mutualist

What are some things that Humans do that promote antibiotic resistance?

not taking entire prescription and taking other people's prescriptions

Define the following terms: Opsonization and enterotoxin

opsonization: "marked for death" antibodies signal to macrophage to eat what they are bound to enterotoxin: any toxin affecting the small intestine

A symbiotic relationship in which one partner is harmed and the other is benefited

parasitic

Antibiotic containing a beta-Iactam ring that prevents cell wall synthesis

penicillin

Give an example of a disease (or disease causing organism) that is transmitted by each of the following mechanisms: Person-to-person, Zoonotic, vectorborne, waterborne, foodborne

person-to-person: HIV Zoonotic: rabies vectorborne: Lymes disease waterborne: typhoid foodborne: salmonella enterica

What are the two cell types that B-cells differentiate into?

plasma B-cells and memory B-cells

What is the difference between a Prokaryote and a Eukaryote?

prokaryote = no nucleus eukaryote= nucleus

Protein and RNA complex used to manufacture proteins

ribosome

Small molecules used to scavenge iron within the human body enabling bacterial pathogens to gain access to this essential nutrient

siderophore

What are the innate host defenses?

skin, mucous membranes, GALT, defensins,

An exotoxin that causes systematic inflammatory response, overwhelming the immune system and damaging organs in the human body

super antigen

How do Microbes influence the cycling of nutrients in nature?

-"fix" nutrients -convert inorganic to organic forms usable by other organisms -Cycle nutrients between various forms used by other organisms

"eating together" - occurs when organisms rely on each other's presence in an ecosystem for their own survival

syntrophy

What is the difference between Natural Killer cells and T-cytotoxic cells?

-Natural killer cells (or NK cells) are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses. They kill cells by releasing small cytoplasmic granules of proteins called perforin and granzyme that cause the target cell to die by apoptosis (programmed cell death). NK cells are defined as large granular lymphocytes (LGL) and constitute the third kind of cells differentiated from the common lymphoid progenitor generating B and T lymphocytes.[1] They do not express T-cell antigen receptors (TCR) or Pan T marker CD3 or surface immunoglobulins (Ig) B cell receptors but they usually express the surface markers CD16 (FcγRIII) and CD56 in humans, NK1.1 or NK1.2 in C57BL/6 mice. Up to 80% of human NK cells also express CD8. They were named "natural killers" because of the initial notion that they do not require activation in order to kill cells that are missing "self" markers of major histocompatibility complex (MHC) class I. They are distinct from Natural Killer T cells. -A cytotoxic T cell (also known as TC, Cytotoxic T Lymphocyte, CTL, T-Killer cell, cytolytic T cell, CD8+ T-cells or killer T cell) belongs to a sub-group of T lymphocytes (a type of white blood cell) that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses (or other pathogens), or are otherwise damaged or dysfunctional. Most cytotoxic T cells express T-cell receptors (TCRs) that can recognize a specific antigenic peptide bound to Class I MHC molecules, present on all nucleated cells, and a glycoprotein called CD8, which is attracted to non-variable portions of the Class I MHC molecule. The affinity between CD8 and the MHC molecule keeps the TC cell and the target cell bound closely together during antigen-specific activation. CD8+ T cells are recognized as TC cells once they become activated and are generally classified as having a pre-defined cytotoxic role within the immune system. However, CD8+ T cells also have the ability to make some cytokines.

defensins

-Small, antimicrobial, cationic peptides -Destroy invader's cell membrane -Produced by many human cells -Two classes of vertebrate defensins: -alpha defensins: Stored in cytoplasmicgranules -beta defensins: Not stored in granules

How do bacteria evade the immune system?

...

How do some microbes take advantage of macrophages to infect the host?

...

What are cytokines and what role do they play in immune response?

...

What cells do bone marrow stem cells differentiate into?

...

What does complement do to bacteria?

...

Name two differences between a gram (+) and gram (-) bacteria

1. Gram (+) stains purple, Gram (-) stains pink 2. Gram (+) thick peptidoglycan, Gram (-) thin

Provide two major mechanisms that lead bacteria to become antibiotic resistant?

1. Mutation of antibiotic target. 2. Destruction of antibiotic

What factors affect microbial growth?

1. Physical requirements a. Temperature Bacteria have a minimum, optimum, and maximum temperature for growth and can be divided into 3 groups based on their optimum growth temperature: 1. Psychrophiles (def) are cold-loving bacteria. Their optimum growth temperature is between -5C and 15C. They are usually found in the Arctic and Antarctic regions and in streams fed by glaciers. 2. Mesophiles (def) are bacteria that grow best at moderate temperatures. Their optimum growth temperature is between 25C and 45C. Most bacteria are mesophilic and include common soil bacteria and bacteria that live in and on the body. 3. Thermophiles (def) are heat-loving bacteria. Their optimum growth temperature is between 45C and 70C and are comonly found in hot springs and in compost heaps. 4. Hyperthermophiles (def) are bacteria that grow at very high temperatures. Their optimum growth temperature is between 70C and 110C. They are usually members of the Archae and are found growing near hydrothermal vents at great depths in the ocean. b. Oxygen requirements Microorganisms show a great deal of variation in their requirements for gaseous oxygen. Most can be placed in one of the following groups: 1. Obligate aerobes (def) are organisms that grow only in the presence of oxygen. They obtain their energy through aerobic respiration (def). 2. Microaerophiles (def) are organisms that require a low concentration of oxygen (2% to 10%) for growth, but higher concentrations are inhibitory. They obtain their energy through aerobic respiration (def). 3. Obligate anaerobes (def) are organisms that grow only in the absense of oxygen and, in fact, are often inhibited or killed by its presense. They obtain their energy through anaerobic respiration (def) or fermentation (def). 4. Aerotolerant anaerobes (def), like obligate anaerobes, cannot use oxygen to transform energy but can grow in its presence. They obtain energy only by fermentation (def) and are known as obligate fermenters. 5. Facultative anaerobes (def) are organisms that grow with or without oxygen, but generally better with oxygen. They obtain their energy through aerobic respiration (def) if oxygen is present, but use fermentation (def) or anaerobic respiration (def) if it is absent. Most bacteria are facultative anaerobes. c. pH Microorganisms can be placed in one of the following groups based on their optimum pH (def) requirements: 1. Neutrophiles (def) grow best at a pH range of 5 to 8. 2. Acidophiles (def) grow best at a pH below 5.5. 3. Allaliphiles (def) grow best at a pH above 8.5. d. Osmosis Osmosis (def) is the diffusion of water across a membrane from an area of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration). Osmosis is powered by the potential energy of a concentration gradient and does not require the expenditure of metabolic energy. While water molecules are small enough to pass between the phospholipids in the cytoplasmic membrane, their transport can be enhanced by water transporting transport proteins known as aquaporins (def). The aquaporins form channels that span the cytoplasmic membrane and transport water in and out of the cytoplasm (see channel proteins below). To understand osmosis, one must understand what is meant by a solution (def). A solution consists of a solute (def) dissolved in a solvent (def). In terms of osmosis, solute refers to all the molecules or ions dissolved in the water (the solvent). When a solute such as sugar dissolves in water, it forms weak hydrogen bonds with water molecules. While free, unbound water molecules are small enough to pass through membrane pores, water molecules bound to solute are not (see Fig. 4C and Fig. 4D).Therefore, the higher the solute concentration, the lower the concentration of free water molecules capable of passing through the membrane. A cell can find itself in one of three environments: isotonic (def), hypertonic (def), or hypotonic (def). (The prefixes iso-, hyper-, and hypo- refer to the solute concentration). In an isotonic environment (see Fig. 5A), both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. Flash animation showing osmosis in an isotonic environment. If the environment is hypertonic (see Fig. 5B), the water concentration is greater inside the cell while the solute concentration is higher outside (the interior of the cell is hypotonic to the surrounding hypertonic environment). Water goes out of the cell. Flash animation showing osmosis in a hypertonic environment. In an environment that is hypotonic (see Fig. 5C), the water concentration is greater outside the cell and the solute concentration is higher inside (the interior of the cell is hypertonic to the hypotonic surroundings). Water goes into the cell. Flash animation showing osmosis in a hypotonic environment. Most bacteria require an isotonic environment (def) or a hypotonic environment (def) for optimum growth. Organisms that can grow at relatively high salt concentration (up tp 10%) are said to be osmotolerant (def). Those that require relatively high salt concentrations for growth, like some of the Archea that require sodium chloride concentrations of 20 % or higher halophiles (def). 2. Nutritional requirements In addition to a proper physical environment, microorgaisms also depend on an available source of chemical nutrients. Microorganisms are often grouped according to their energy source and their source of carbon. a. Energy source 1. Phototrophs (def) use radiant energy (light) as their primary energy source. 2. Chemotrophs (def) use the oxidation (def) and reduction (def) of chemical compounds as their primary energy source. b. Carbon source Carbon is the structural backbone of the organic compounds that make up a living cell. Based on their source of carbon bacteria can be classified as autotrophs or heterotrophs. 1. Autotrophs (def): require only carbon dioxide as a carbon source. An autotroph can synthesize organic molecules from inorganic nutrients. 2. Heterotrophs (def): require organic forms of carbon. A Heterotroph cannot synthesize organic molecules from inorganic nutrients. Combining their nutritional patterns, all organisms in nature can be placed into one of four separate groups: photoautotrophs, photoheterotrophs, chemoautotrophs, and chemoheterotrophs. 1. Photoautotrophs (def) use light as an energy source and carbon dioxide as their main carbon source. They include photosynthetic bacteria (green sulfur bacteria, purple sulfur bacteria, and cyanobacteria), algae, and green plants. Photoautotrophs transform carbon dioxide and water into carbohydrates and oxygen gas through photosynthesis (def). Cyanobacteria, as well as algae and green plants, use hydrogen atoms from water to reduce carbon dioxide to form carbohydrates, and during this process oxygen gas is given off (an oxygenic process). Other photosynthetic bacteria (the green sulfur bacteria and purple sulfur bacteria) carry out an anoxygenic process, using sulfur, sulfur compounds or hydrogen gas to reduce carbon dioxide and form organic compounds. 2. Photoheterotrophs (def) use light as an energy source but cannot convert carbon dioxide into energy. Instead they use organic compounds (def) as a carbon source. They include the green nonsulfur bacteria and the purple nonsulfur bacteria. 3. Chemolithoautotrophs (def) use inorganic compounds such as hydrogen sulfide, sulfur, ammonia, nitrites, hydrogen gas, or iron as an energy source and carbon dioxide as their main carbon source. 4. Chemooganoheterotrophs (def) use organic compounds (def) as both an energy source and a carbon source. Saprophytes (def) live on dead organic matter while parasites (def) get their nutrients from a living host. Most bacteria, and all protozoans, fungi, and animals are chemoorganoheterotrophs. c. Nitrogen source Nitrogen is needed for the synthesis of such molecules as amino acids, DNA, RNA and ATP (def). Depending on the organism, nitrogen, nitrates, ammonia, or organic nitrogen compounds may be used as a nitrogen source. d. Minerals 1. sulfur Sulfur is needed to synthesisize sulfur-containing amino acids and certain vitamins. Depending on the organism, sulfates, hydrogen sulfide, or sulfur-containing amino acids may be used as a sulfur sorce. 2. phosphorus Phosphorus is needed to synthesize phospholipids (def), DNA, RNA, and ATP (def). Phosphate ions are the primary source of phosphorus. 3. potassium, magnesium, and calcium These are required for certain enzymes to function as well as additional functions. 4. iron Iron is a part of certain enzymes. 5. trace elements Trace elements are elements required in very minute amounts, and like potassium, magnesium, calcium, and iron, they usually function as cofactors (def) in enzyme reactions. They include sodium, zinc, copper,molybdenum, manganese, and cobalt ions. Cofactors usually function as electron donors or electron acceptors during enzyme reactions. e. Water f. Growth factors Growth factors are organic compounds such as amino acids (def), purines (def), pyrimidines (def), and vitamins (def) that a cell must have for growth but cannot synthesize itself. Organisms having complex nutritional requirements and needing many growth factors are said to be fastidious (def).

List three structures or chemicals that aid bacteria in infection of human hosts:

1. capsule 2. fimbriae 3. Type III secretion system

Give three examples of how humans manipulate the conditions that influence microbial growth to prevent microbial growth or kill them

1. cooking (high temp) 2. pickling (low pH, salty) 3. cleaning (remove nutrients)

list five physical or chemical factors that influence microbial growth

1. pH 2. concentration of O2 3. temp 4. salinity 5. nutrient availability

Name three cellular systems that are essential for bacterial survival that are targeted by antibiotics

1. replication 2. transcription 3. cell wall

Provide three things that bacteria living in or on our body provide for humans:

1. vitamins 2. protection from pathogens 3. educate immune system

Give an example of one thing that Humans do that promotes antibiotic resistance?

70% of ALC antibiotics used in USA go to healthy livestock to promote growth

what is an enterotoxin.

A toxin produced in or affecting the intestines, such as those causing food poisoning or cholera

What is an endotoxin?

A toxin that is present inside a bacterial cell and is released when the cell disintegrates. It is sometimes responsible for the characteristic symptoms of a disease, e.g., in botulism

What does a Natural Killer cell do if it finds a cell with no MHCI complex?

Alternatively, class I MHC itself can serve as an inhibitory ligand for natural killer cells (NKs). Reduction in the normal levels of surface class I MHC, a mechanism employed by some viruses during immune evasion or in certain tumors, will activate NK cell killing.

Why are mitochondria and chloroplasts considered "endosymbionts"?

An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis. Many instances of endosymbiosis are obligate- that is, either the endosymbiont or the host cannot survive without the other. The most common examples of obligate endosymbiosis are mitochondria and chloroplasts. The endosymbiosis theory attempts to explain the origins of organelles such as mitochondria and chloroplasts in eukaryotic cells. The theory proposes that chloroplasts and mitochondria evolved from certain types of bacteria that eukaryotic cells engulfed through endophagocytosis. These cells and the bacteria trapped inside them entered a symbiotic relationship, a close association between different types of organisms over an extended time. However, more specifically, the relationship was endosymbiotic, meaning that one of the organisms (the bacteria) lived within the other (the eukaryotic cells).

Describe how B-cells are selected and become memory B-cells and Plasma cells.

Antibodies on the surface of B-cells bind antigens, resulting in activation of that B-cell , causing proliferation of that cell and differentiation to memory B-cells and plasma cells. Memory B-cells (many of them) circulate in blood and immediately activate (see above) when antigen is again encountered.

How do antibodies help defend the body?

Antibodies or immunoglobulins (def) are specific glycoprotein configurations produced by B-lymphocytes and plasma cells in response to a specific antigen and capable of reacting with that antigen. The antibodies produced during humoral immunity ultimately defend the body through a variety of different means. These include: 1. Opsonization 2. MAC Cytolysis 3. Antibody-dependent Cellular Cytotoxicity (ADCC) by NK Cells 4. Neutralization of Exotoxins 5. Neutralization of Viruses 6. Preventing Bacterial Adherence to Host Cells 7. Agglutination of Microorganisms 8. Immobilization of Bacteria and Protozoans.

How is diversity generated in Antibodies?

Antibody diversity is accounted for by three main theories: 1) the germ line theory, which holds that each antibody-producing cell has genes coding for all possible antibody specificities, but expresses only the one stimulated by antigen; 2) the somatic mutation theory, which holds that antibody-producing cells contain only a few genes, which produce antibody diversity by mutation; and 3) the gene rearrangement theory, which holds that antibody diversity is generated by the rearrangement of variable region gene segments during the differentiation of the antibody-producing cells.

What is the difference between a bacterium and a virus?

Bacteria are free-living cellular organisms Viruses are not considered living and require a host for replication

Viruses in Bacteria

Bacteriophages are a common and diverse group of viruses and are the most abundant form of biological entity in aquatic environments - there are up to ten times more of these viruses in the oceans than there are bacteria,[201] reaching levels of 250,000,000 bacteriophages per millilitre of seawater.[202] These viruses infect specific bacteria by binding to surface receptor molecules and then entering the cell. Within a short amount of time, in some cases just minutes, bacterial polymerase starts translating viral mRNA into protein. These proteins go on to become either new virions within the cell, helper proteins, which help assembly of new virions, or proteins involved in cell lysis. Viral enzymes aid in the breakdown of the cell membrane, and, in the case of the T4 phage, in just over twenty minutes after injection over three hundred phages could be released.[203] The major way bacteria defend themselves from bacteriophages is by producing enzymes that destroy foreign DNA. These enzymes, called restriction endonucleases, cut up the viral DNA that bacteriophages inject into bacterial cells.[204] Bacteria also contain a system that uses CRISPR sequences to retain fragments of the genomes of viruses that the bacteria have come into contact with in the past, which allows them to block the virus's replication through a form of RNA interference.[205][206] This genetic system provides bacteria with acquired immunity to infection.

EXPLAIN the concept of herd immunity

By vaccinating >70% of the population, vaccinated individuals protect unvaccinated individuals by preventing spread of disease

pros and cons associated with culture based assays

Can be dangerous... Take a long time...

How can bacteria become antibiotic resistant?

Change the target: mutation, circumvent blocked pathway Change the drug: chew it up, modify the chemical structure, pump it out

What does a T-cytotoxic cell do if it finds an MHCI complex with viral antigen in it

Class I MHC molecules bind peptides generated mainly from degradation of cytosolic proteins by the proteasome. The MHC I:peptide complex is then inserted into the plasma membrane of the cell. The peptide is bound to the extracellular part of the class I MHC molecule. Thus, the function of the class I MHC is to display intracellular proteins to cytotoxic T cells (CTLs). However, class I MHC can also present peptides generated from exogenous proteins, in a process known as cross-presentation. A normal cell will display peptides from normal cellular protein turnover on its class I MHC, and CTLs will not be activated in response to them due to central and peripheral tolerance mechanisms. When a cell expresses foreign proteins, such as after viral infection, a fraction of the class I MHC will display these peptides on the cell surface. Consequently, CTLs specific for the MHC:peptide complex will recognize and kill the presenting cell.

What is a pathogenicity island and how does it affect whether a microbe is a pathogen or commensal organisms?

Collection of genes of foreign origin within genome of bacterium resulting in production of pathogenicity factors that allow that organism to become pathogenic

What is complement?

Consists of about 20 proteins -Activate each other via proteolytic cleavage •The alternative complement pathway begins with complement factor C3. •C3 normally made and degraded quickly. -Stabilized by Gram-negative LPS -Inserts into bacterial outer membrane -Reacts with other components -Factor B, Factor D, properdin -Cleaves C5 to C5b •Complement C5b protein binds C6, C7. -Form preporecomplex in target cell membrane -C8, C9 proteins attach. -Form membrane attack complex -Lyses target membrane •C3b is also a potent opsonin. -Promotes phagocytosisof an organism •C3a and C5a are anaphylatoxins. -Trigger degranulationand chemotaxis The complement system helps or "complements" the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the immune system called the innate immune system that is not adaptable and does not change over the course of an individual's lifetime. However, it can be recruited and brought into action by the adaptive immune system. The complement system consists of a number of small proteins found in the blood, generally synthesized by the liver, and normally circulating as inactive precursors (pro-proteins). When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cleavages. The end-result of this activation cascade is massive amplification of the response and activation of the cell-killing membrane attack complex. Over 25 proteins and protein fragments make up the complement system, including serum proteins, serosal proteins, and cell membrane receptors. They account for about 5% of the globulin fraction of blood serum. Three biochemical pathways activate the complement system: the classical complement pathway, the alternative complement pathway, and the mannose-binding lectin pathway.

What are cytokines and what role do they play in immune response?

Cytokines (Greek cyto-, cell; and -kinos, movement) are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication. Cytokines can be classified as proteins, peptides, or glycoproteins; the term "cytokine" encompasses a large and diverse family of regulators produced throughout the body by cells of diverse embryological origin.[1]

Information storage molecule

DNA

How do phagocytes identify foreign invaders?

During an infection, chemical signals attract phagocytes to places where the pathogen has invaded the body. These chemicals may come from bacteria or from other phagocytes already present. The phagocytes move by a method called chemotaxis. When phagocytes come into contact with bacteria, the receptors on the phagocyte's surface will bind to them. This binding will lead to the engulfing of the bacteria by the phagocyte.[13] Some phagocytes kill the ingested pathogen with oxidants and nitric oxide.[14] After phagocytosis, macrophages and dendritic cells can also participate in antigen presentation, a process in which a phagocyte moves parts of the ingested material back to its surface. This material is then displayed to other cells of the immune system. Some phagocytes then travel to the body's lymph nodes and display the material to white blood cells called lymphocytes. This process is important in building immunity.[15] However, many pathogens have evolved methods to evade attacks by phagocytes.[2]

Extracellular polymeric substance

EPS

What features of bacteria aid in infection?

EVASION OF HOST DEFENSES Some pathogenic bacteria are inherently able to resist the bactericidal components of host tissues. For example, the poly-D-glutamate capsule of Bacillus anthracis protects the organisms against cell lysis by cationic proteins in sera or in phagocytes. The outer membrane of Gram-negative bacteria is a formidable permeability barrier that is not easily penetrated by hydrophobic compounds such as bile salts which are harmful to the bacteria. Pathogenic mycobacteria have a waxy cell wall that resists attack or digestion by most tissue bactericides. And intact lipopolysaccharides (LPS) of Gram-negative pathogens may protect the cells from complement-mediated lysis or the action of lysozyme. Most successful pathogens, however, possess additional structural or biochemical features which allow them to resist the main lines of host internal defense against them, i.e., the phagocytic and immune responses of the host. Overcoming Host Phagocytic Defenses Microorganisms invading tissues are first and foremost exposed to phagocytes. Bacteria that readily attract phagocytes, and that are easily ingested and killed, are generally unsuccessful as parasites. In contrast, most bacteria that are successful as parasites interfere to some extent with the activities of phagocytes or in some way avoid their attention. Microbial strategies to avoid phagocytic killing are numerous and diverse, but are usually aimed at blocking one or of more steps in the phagocytic process. Recall the steps in phagocytosis: 1. Contact between phagocyte and microbial cell 2. Engulfment 3. Phagosome formation 4. Phagosome-lysosome fusion 5. Killing and digestion Avoiding Contact with Phagocytes Bacteria can avoid the attention of phagocytes in a number of ways. 1. Invade or remain confined in regions inaccessible to phagocytes. Certain internal tissues (e.g. the lumen of glands) and surface tissues (e.g. the skin) are not patrolled by phagocytes. 2. Avoid provoking an overwhelming inflammatory response. Some pathogens induce minimal or no inflammation required to focus the phagocytic defenses. 3. Inhibit phagocyte chemotaxis. e.g. Streptococcal streptolysin (which also kills phagocytes) suppresses neutrophil chemotaxis, even in very low concentrations. Fractions of Mycobacterium tuberculosis are known to inhibit leukocyte migration. Clostridium ø toxin inhibits neutrophil chemotaxis. 4. Hide the antigenic surface of the bacterial cell. Some pathogens can cover the surface of the bacterial cell with a component which is seen as "self" by the host phagocytes and immune system. Phagocytes cannot recognize bacteria upon contact and the possibility of opsonization by antibodies to enhance phagocytosis is minimized. For example, pathogenic Staphylococcus aureus produces cell-bound coagulase which clots fibrin on the bacterial surface. Treponema pallidum binds fibronectin to its surface. Group A streptococci are able to synthesize a capsule composed of hyaluronic acid. Inhibition of Phagocytic Engulfment Some bacteria employ strategies to avoid engulfment (ingestion) if phagocytes do make contact with them. Many important pathogenic bacteria bear on their surfaces substances that inhibit phagocytic adsorption or engulfment. Clearly it is the bacterial surface that matters. Resistance to phagocytic ingestion is usually due to a component of the bacterial cell wall, or fimbriae, or a capsule enclosing the bacterial wall. Classical examples of antiphagocytic substances on the bacterial surface include: Polysaccharide capsules of S. pneumoniae, Haemophilus influenzae, Treponema pallidum and Klebsiella pneumoniae M protein and fimbriae of Group A streptococci Surface slime (polysaccharide) produced by Pseudomonas aeruginosa O antigen associated with LPS of E. coli K antigen of E. coli or the analogous Vi antigen of Salmonella typhi Cell-bound or soluble Protein A produced by Staphylococcus aureus

Why do we need to treat infections caused by Eukaryotes with drugs that are different than we use for Prokaryotic (bacterial) infections?

Eukaryotes use proteins and other systems more similar to our own.

pros and cons of molecular diagnostic tools

Expensive... Take special equipment Specialized knowledge to perform

Hair-like protrusions used to attach to surfaces

Fimbriae

plasmids in bacteria

In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA.[1] They are double-stranded and, in many cases, circular. Plasmids usually occur naturally in bacteria, but are sometimes found in eukaryotic organisms (e.g., the 2-micrometre ring in Saccharomyces cerevisiae). Plasmid sizes vary from 1 to over 1,000 kbp. The number of identical plasmids in a single cell can range anywhere from one to even thousands under some circumstances. Plasmids can be considered part of the mobilome because they are often associated with conjugation, a mechanism of horizontal gene transfer. The term plasmid was first introduced by the American molecular biologist Joshua Lederberg in 1952.[2] Plasmids are considered "replicons", capable of autonomous replication within a suitable host. Plasmids can be found in all three major domains: Archaea, Bacteria, and Eukarya.[1] Similar to viruses, plasmids are not considered by some to be a form of "life".[3] Unlike viruses, plasmids are "naked" DNA and do not encode genes necessary to encase the genetic material for transfer to a new host, though some classes of plasmids encode the sex pilus necessary for their own transfer. Plasmid host-to-host transfer requires direct, mechanical transfer by conjugation or changes in host gene expression allowing the intentional uptake of the genetic element by transformation.[1] Microbial transformation with plasmid DNA is neither parasitic nor symbiotic in nature, because each implies the presence of an independent species living in a commensal or detrimental state with the host organism. Rather, plasmids provide a mechanism for horizontal gene transfer within a population of microbes and typically provide a selective advantage under a given environmental state. Plasmids may carry genes that provide resistance to naturally occurring antibiotics in a competitive environmental niche, or the proteins produced may act as toxins under similar circumstances. Plasmids can also provide bacteria with the ability to fix elemental nitrogen or to degrade recalcitrant organic compounds that provide an advantage when nutrients are scarce.[1]

What makes an antigen a good immunogen?

In summary, a good immunogen has three chemical features: - It must have an epitope that can be recognized by the cell-surface antibody found on B cells. - It must have at least one site that can be recognized simultaneously by a class II protein and by a T-cell receptor. - Usually, it must be degradable. These three properties are the only intrinsic chemical features needed for a molecule to elicit a strong antibody response.

lipopolysaccharide

LPS

How do vaccines work?

Live vaccines are made up of a weakened version of the bacteria or virus responsible for the disease. In some, vaccines are made from dead forms of the organism. These dead organisms were killed in a way to preserve their ability to provide immunity or protection. In other cases, an inactivated toxin that is made by the bacteria or a piece of the bacteria or virus is used. When the vaccine is given, the body's immune system detects this weakened or dead germ or germ part and reacts just as it would when a new full blown infection occurs. It begins making antibodies against the vaccine material. These antibodies remain in the body and are ready to react if an actual infectious organism attacks. In a sense, the vaccine tricks the body into thinking it is under assault, and the immune system makes weapons that will provide a defense when a real infection becomes a threat.

What types of things are used as vaccines?

Live, Attenuated Vaccines Live, attenuated vaccines contain a version of the living microbe that has been weakened in the lab so it can't cause disease. Because a live, attenuated vaccine is the closest thing to a natural infection, these vaccines are good "teachers" of the immune system: They elicit strong cellular and antibody responses and often confer lifelong immunity with only one or two doses. Despite the advantages of live, attenuated vaccines, there are some downsides. It is the nature of living things to change, or mutate, and the organisms used in live, attenuated vaccines are no different. The remote possibility exists that an attenuated microbe in the vaccine could revert to a virulent form and cause disease. Also, not everyone can safely receive live, attenuated vaccines. For their own protection, people who have damaged or weakened immune systems— because they've undergone chemotherapy or have HIV, for example—cannot be given live vaccines. Another limitation is that live, attenuated vaccines usually need to be refrigerated to stay potent. If the vaccine needs to be shipped overseas and stored by health care workers in developing countries that lack widespread refrigeration, a live vaccine may not be the best choice. Live, attenuated vaccines are relatively easy to create for certain viruses. Vaccines against measles, mumps, and chickenpox, for example, are made by this method. Viruses are simple microbes containing a small number of genes, and scientists can therefore more readily control their characteristics. Viruses often are attenuated through a method of growing generations of them in cells in which they do not reproduce very well. This hostile environment takes the fight out of viruses: As they evolve to adapt to the new environment, they become weaker with respect to their natural host, human beings. Live, attenuated vaccines are more difficult to create for bacteria. Bacteria have thousands of genes and thus are much harder to control. Scientists working on a live vaccine for a bacterium, however, might be able to use recombinant DNA technology to remove several key genes. This approach has been used to create a vaccine against the bacterium that causes cholera, Vibrio cholerae, although the live cholera vaccine has not been licensed in the United States. Inactivated Vaccines Scientists produce inactivated vaccines by killing the disease-causing microbe with chemicals, heat, or radiation. Such vaccines are more stable and safer than live vaccines: The dead microbes can't mutate back to their disease-causing state. Inactivated vaccines usually don't require refrigeration, and they can be easily stored and transported in a freeze-dried form, which makes them accessible to people in developing countries. Most inactivated vaccines, however, stimulate a weaker immune system response than do live vaccines. So it would likely take several additional doses, or booster shots, to maintain a person's immunity. This could be a drawback in areas where people don't have regular access to health care and can't get booster shots on time. Subunit Vaccines Instead of the entire microbe, subunit vaccines include only the antigens that best stimulate the immune system. In some cases, these vaccines use epitopes—the very specific parts of the antigen that antibodies or T cells recognize and bind to. Because subunit vaccines contain only the essential antigens and not all the other molecules that make up the microbe, the chances of adverse reactions to the vaccine are lower. Subunit vaccines can contain anywhere from 1 to 20 or more antigens. Of course, identifying which antigens best stimulate the immune system is a tricky, time-consuming process. Once scientists do that, however, they can make subunit vaccines in one of two ways: They can grow the microbe in the laboratory and then use chemicals to break it apart and gather the important antigens. They can manufacture the antigen molecules from the microbe using recombinant DNA technology. Vaccines produced this way are called "recombinant subunit vaccines." A recombinant subunit vaccine has been made for the hepatitis B virus. Scientists inserted hepatitis B genes that code for important antigens into common baker's yeast. The yeast then produced the antigens, which the scientists collected and purified for use in the vaccine. Research is continuing on a recombinant subunit vaccine against hepatitis C virus. Toxoid Vaccines For bacteria that secrete toxins, or harmful chemicals, a toxoid vaccine might be the answer. These vaccines are used when a bacterial toxin is the main cause of illness. Scientists have found that they can inactivate toxins by treating them with formalin, a solution of formaldehyde and sterilized water. Such "detoxified" toxins, called toxoids, are safe for use in vaccines. When the immune system receives a vaccine containing a harmless toxoid, it learns how to fight off the natural toxin. The immune system produces antibodies that lock onto and block the toxin. Vaccines against diphtheria and tetanus are examples of toxoid vaccines. Conjugate Vaccines If a bacterium possesses an outer coating of sugar molecules called polysaccharides, as many harmful bacteria do, researchers may try making a conjugate vaccine for it. Polysaccharide coatings disguise a bacterium's antigens so that the immature immune systems of infants and younger children can't recognize or respond to them. Conjugate vaccines, a special type of subunit vaccine, get around this problem. When making a conjugate vaccine, scientists link antigens or toxoids from a microbe that an infant's immune system can recognize to the polysaccharides. The linkage helps the immature immune system react to polysaccharide coatings and defend against the disease-causing bacterium. The vaccine that protects against Haemophilus influenzae type B (Hib) is a conjugate vaccine. DNA Vaccines Thumbnail of The Making of a DNA Vaccine Against West Nile Virus The Making of a DNA Vaccine Against West Nile Virus. View the illustration. Credit: NIAID Once the genes from a microbe have been analyzed, scientists could attempt to create a DNA vaccine against it. Still in the experimental stages, these vaccines show great promise, and several types are being tested in humans. DNA vaccines take immunization to a new technological level. These vaccines dispense with both the whole organism and its parts and get right down to the essentials: the microbe's genetic material. In particular, DNA vaccines use the genes that code for those all-important antigens. Researchers have found that when the genes for a microbe's antigens are introduced into the body, some cells will take up that DNA. The DNA then instructs those cells to make the antigen molecules. The cells secrete the antigens and display them on their surfaces. In other words, the body's own cells become vaccine-making factories, creating the antigens necessary to stimulate the immune system. A DNA vaccine against a microbe would evoke a strong antibody response to the free-floating antigen secreted by cells, and the vaccine also would stimulate a strong cellular response against the microbial antigens displayed on cell surfaces. The DNA vaccine couldn't cause the disease because it wouldn't contain the microbe, just copies of a few of its genes. In addition, DNA vaccines are relatively easy and inexpensive to design and produce. So-called naked DNA vaccines consist of DNA that is administered directly into the body. These vaccines can be administered with a needle and syringe or with a needle-less device that uses high-pressure gas to shoot microscopic gold particles coated with DNA directly into cells. Sometimes, the DNA is mixed with molecules that facilitate its uptake by the body's cells. Naked DNA vaccines being tested in humans include those against the viruses that cause influenza and herpes. Recombinant Vector Vaccines Recombinant vector vaccines are experimental vaccines similar to DNA vaccines, but they use an attenuated virus or bacterium to introduce microbial DNA to cells of the body. "Vector" refers to the virus or bacterium used as the carrier. In nature, viruses latch on to cells and inject their genetic material into them. In the lab, scientists have taken advantage of this process. They have figured out how to take the roomy genomes of certain harmless or attenuated viruses and insert portions of the genetic material from other microbes into them. The carrier viruses then ferry that microbial DNA to cells. Recombinant vector vaccines closely mimic a natural infection and therefore do a good job of stimulating the immune system. Attenuated bacteria also can be used as vectors. In this case, the inserted genetic material causes the bacteria to display the antigens of other microbes on its surface. In effect, the harmless bacterium mimics a harmful microbe, provoking an immune response. Researchers are working on both bacterial and viral-based recombinant vector vaccines for HIV, rabies, and measles.

Major histocompatability complex

MHC

Methicillin Resistant Staphylococcus aureus

MRSA

How are microbes killed by macrophages?

Macrophages are voracious eaters that "swallow" cellular debris and invading organisms. They kill microbes with ROS. All aerobic cells inadvertently produce ROS that can, if left unchecked, damage DNA and other cellular components and cause cell death. Bacteria and animal cells contain special enzymes, called superoxide dismutases, which neutralize an important ROS, called superoxide. Macrophages have harnessed these lethal compounds, dumping large quantities of superoxide onto engulfed bacteria to kill them.

Ways to prevent nosocomial infection:

Methods of prevention of nosocomial infection (and breaking the chain of transmission ) include: 1. observance of aseptic technique 2. frequent hand washing especially between patients 3. careful handling, cleaning, and disinfection of fomites 4. where possible use of single-use disposable items 5. patient isolation 6. avoidance where possible of medical procedures that can lead with high probability to nosocomial infection 7. various institutional methods such as air filtration within the hospital 8. general awareness that prevention of nosocomial infection requires constant personal surveillance 9. active oversight within the hospital

In what ways to all multi-cellular organisms rely on microorganisms for their survival?

Microbes play a huge role in converting chemicals into forms that are uasableby humans and other organisms

A hospital acquired infection

Nosocomial

Pathogen Associated Molecular Patterns

PAMP

A technique used to amplify specific DNA sequences enabling the detection of microbes containing those sequences

PCR

Pattern Recognition Molecules

PRM

Deactivated toxin used to immunize against that toxin

toxoid

PAMPs and PRMs (also called toll-like receptors)

Pathogen-Associated Molecular Patterns (PAMPs) Pathogens, especially bacteria, have molecular structures that 1. are not shared with their host; 2. are shared by many related pathogens; 3. are relatively invariant; that is, do not evolve rapidly (in contrast, for example, to such pathogen molecules as the hemaglutinin and neuraminidase of influenza viruses). Examples: the flagellin of bacterial flagella; the peptidoglycan of Gram-positive bacteria; the lipopolysaccharide (LPS, also called endotoxin) of Gram-negative bacteria; double-stranded RNA. (Some viruses of both plants and animals have a genome of dsRNA. And many other viruses of both plants and animals have an RNA genome that in the host cell is briefly converted into dsRNA [link to examples]). unmethylated DNA (eukaryotes have many times more cytosines, in the dinucleotide CpG, with methyl groups attached — Link). Pattern Recognition Receptors (PRRs) There are three groups: 1. secreted molecules that circulate in blood and lymph; 2. surface receptors on phagocytic cells like macrophages that bind the pathogen for engulfment; 3. cell-surface receptors that bind the pathogen initiating a signal leading to the release of effector molecules (cytokines). 1. Secreted PRRs Example: Circulating proteins (e.g., C-reactive protein) that bind to PAMPs on the surface of many pathogens. This interaction triggers the complement cascade leading to the opsonization of the pathogen and its speedy phagocytosis. 2. Phagocytosis Receptors Macrophages have cell-surface receptors that recognize certain PAMPs, e.g., those containing mannose. When a pathogen covered with polysaccharide with mannose at its tips binds to these, it is engulfed into a phagosome. 3. Toll-Like Receptors (TLRs) Macrophages, dendritic cells, and epithelial cells have a set of transmembrane receptors that recognize different types of PAMPs. These are called Toll-like receptors (TLRs) because of their homology to receptors first discovered and named in Drosophila. Mammals have 12 different TLRs each of which specializes — often with the aid of accessory molecules — in a subset of PAMPs. In this way, the TLRs identify the nature of the pathogen and turn on an effector response appropriate for dealing with it. These signaling cascades lead to the expression of various cytokine genes.

pathogenicity islands in bacteria

Pathogenicity islands (PAIs) are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. They are incorporated in the genome of pathogenic organisms but are usually absent from those non-pathogenic organisms of the same or closely related species. These mobile genetic elements may range from 10-200 kb and encode genes which contribute to the virulence of the respective pathogen. Typical examples are adherence factors, toxins, iron uptake systems, invasion factors and secretion systems. Pathogenicity islands are discrete genetic units flanked by direct repeats, insertion sequences or tRNA genes, which act as sites for recombination into the DNA. Cryptic mobility genes may also be present, indicating the provenance as transduction.biosis island.

PRMs and how they work

Phagocytes Recognize foreign contaminants using pattern-recognition molecules (PRMs) •Toll-like receptors are an example •PRMS recognize pathogen-associated molecular paterns(PAMPs) »Lipopolysaccharideis a PAMP »CpG(a DNA pattern) is a PAMP -Interaction with PAMPs triggers production of enhanced lysosomes: »Hydrogen peroxide »Superoxide anions »Hydroxyl radicals »Singlet oxygen »Hypochlorousacid »Nitric oxide -Respiratory burst -use of lots of O2

Composed of amino acids and perform a wide variety of functions for cells

Protein / Enzyme

Temporary information storage molecule that can sometimes catalyze chemical reactions

RNA

Choose one region of the human body. Describe the physical and chemical conditions present at this site and provide an example of one bacterium that might be found there .

Skin - dry, salty, low pH, high oxygen, nutrient rich (staphylococcus aureous)

Transposons in bacteria

Some transposons in bacteria carry — in addition to the gene for transposase — genes for one or more (usually more) proteins imparting resistance to antibiotics. When such a transposon is incorporated in a plasmid, it can leave the host cell and move to another. This is the way that the alarming phenomenon of multidrug antibiotic resistance spreads so rapidly. Transposition in these cases occurs by a "copy and paste" (command/control-C -> command/control-V) mechanism. This requires an additional enzyme — a resolvase — that is also encoded in the transposon itself. The original transposon remains at the original site while its copy is inserted at a new site.

How do bacteria evade the immune system?

Survival Inside of Phagocytes Some bacteria survive inside of phagocytic cells, in either neutrophils or macrophages. Bacteria that can resist killing and survive or multiply inside of phagocytes are considered intracellular parasites. The environment of the phagocyte may be a protective one, protecting the bacteria during the early stages of infection or until they develop a full complement of virulence factors. The intracellular environment guards the bacteria against the activities of extracellular bactericides, antibodies, drugs, etc. Most intracellular parasites have special (genetically-encoded) mechanisms to get themselves into their host cell as well as special mechanisms to survive once they are inside. Intracellular parasites usually survive by virtue of mechanisms which interfere with the bactericidal activities of the host cell. Some of these bacterial mechanisms include: 1. Inhibition of phagosome-lysosome fusion. The bacteria survive inside of phagosomes because they prevent the discharge of lysosomal contents into the phagosome environment. Specifically phagolysosome formation is inhibited in the phagocyte. This is the strategy employed by Salmonella, M. tuberculosis, Legionella and the Chlamydiae. 2. Survival inside the phagolysosome. With some intracellular parasites, phagosome-lysosome fusion occurs but the bacteria are resistant to inhibition and killing by the lysosomal constituents. Also, some extracellular pathogens can resist killing in phagocytes utilizing similar resistance mechanisms. Little is known of how bacteria can resist phagocytic killing within the phagocytic vacuole, but it may be due to the surface components of the bacteria or due to extracellular substances that they produce which interfere with the mechanisms of phagocytic killing. Bacillus anthracis, Mycobacterium tuberculosis and Staphylococcus aureus all possess mechanisms to survive intracellular killing in macrophages. 3. Escape from the phagosome. Early escape from the phagosome vacuole is essential for growth and virulence of some intracellular pathogens. This is a very clever strategy employed by the Rickettsias which produce a phospholipase enzyme that lyses the phagosome membrane within thirty seconds of after ingestion. Products of Bacteria that Kill or Damage Phagocytes One obvious strategy in defense against phagocytosis is direct attack by the bacteria upon the professional phagocytes. Any of the substances that pathogens produce that cause damage to phagocytes have been referred to as "aggressins". Most of these are actually extracellular enzymes or toxins that kill phagocytes. Phagocytes may be killed by a pathogen before or after ingestion. Killing phagocytes before ingestion. Many Gram-positive pathogens, particularly the pyogenic cocci, secrete extracellular enzymes which kill phagocytes. Many of these enzymes are called "hemolysins" because their activity in the presence of red blood cells results in the lysis of the rbcs. Pathogenic streptococci produce streptolysin. Streptolysin O binds to cholesterol in membranes. The effect on neutrophils is to cause lysosomal granules to explode, releasing their contents into the cell cytoplasm. Pathogenic staphylococci produce leukocidin, which also acts on the neutrophil membrane and causes discharge of lysosomal granules. Other examples of bacterial extracellular proteins that inhibit phagocytosis include the Exotoxin A of Pseudomonas aeruginosa which kills macrophages, and the bacterial exotoxins that are adenylate cyclases (e.g. anthrax toxin EF and pertussis AC) which decrease phagocytic activity. Killing phagocytes after ingestion. Some bacteria exert their toxic action on the phagocyte after ingestion has taken place. They may grow in the phagosome and release substances which can pass through the phagosome membrane and cause discharge of lysosomal granules, or they may grow in the phagolysosome and release toxic substances which pass through the phagolysosome membrane to other target sites in the cell. Many bacteria which are the intracellular parasites of macrophages (e.g. Mycobacteria, Brucella, Listeria) usually destroy macrophages in the end, but the mechanisms are not understood. Evading Complement Antibodies that are bound to bacterial surfaces will activate complement by the classical pathway and bacterial polysaccharides activate complement by the alternative pathway. Bacteria in serum and other tissues, especially Gram-negative bacteria, need protection from the antimicrobial effects of complement before and during an immunological response. One role of capsules in bacterial virulence is to protect the bacteria from complement activation and the ensuing inflammatory response. Polysaccharide capsules can hide bacterial components such as LPS or peptidoglycan which can induce the alternate complement pathway. Some bacterial capsules are able to inhibit formation of the C3b complex on their surfaces, thus avoiding C3b opsonization and subsequent formation of C5b and the membrane attack complex (MAC) on the bacterial cell surface. Capsules that contain sialic acid (a common component of host cell glycoproteins), such as found in Neisseria meningitidis, have this effect. One of the principal targets of complement on Gram-negative bacteria is LPS. It serves as the attachment site for C3b and triggers the alternative pathway of activation. It also binds C5b. LPS can be modified by pathogens in two ways that affects its interaction with complement. First, by attachment of sialic acid residues to the LPS O antigen, a bacterium can prevent the formation of C3 convertase just as capsules that contain sialic acid can do so. Both Neisseria meningitidis and Haemophilus influenzae, which cause bacterial meningitis, are able to covalently attach sialic acid residues to their O antigens resulting in resistance to MAC. Second, LPS with long, intact O antigen side-chains can prevent effective MAC killing. Apparently the MAC complex is held too far from the vulnerable outer membrane to be effective. Bacteria that are not killed and lysed in serum by the complement MAC are said to be serum resistant. As might be expected many of the Gram-negative bacteria that cause systemic infections, (bacteremia or septicemia) are serum resistant. Gram-positive bacteria are naturally serum-resistant since their cells are not enclosed in an outer membrane. Other ways that pathogens are able to inhibit the activity of complement is to destroy one or more of the components of complement. Pseudomonas aeruginosa produces an extracellular elastase enzyme that inactivates components of complement. Avoiding Host Immunological Responses On epithelial surfaces the main antibacterial immune defense of the host is the protection afforded by secretory antibody (IgA). Once the epithelial surfaces have been penetrated, however, the major host defenses of inflammation, complement, phagocytosis, Antibody-mediated Immunity (AMI), and Cell-mediated Immunity (CMI) are encountered. If there is a way for a pathogen to successfully bypass or overcome these host defenses, then some bacterial pathogen has probably discovered it. Bacteria evolve very rapidly in relation to their host, so that most of the feasible anti-host strategies are likely to have been tried out and exploited. Ability to defeat the immune defenses may play a major role in the virulence of a bacterium and in the pathology of disease. Several strategic bacterial defenses are described below.

What are helper T-cells and what do they do?

T helper cells (Th cells) are a sub-group of lymphocytes, a type of white blood cell, that play an important role in the immune system, particularly in the adaptive immune system. These cells have no cytotoxic or phagocytic activity; they cannot kill infected host cells or pathogens. Rather, they help other immune cells -- they activate and direct other immune cells. They are essential in B cell antibody class switching, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages. Mature Th cells express the surface protein CD4 and are referred to as CD4+ T cells. CD4+ T cells are generally treated as having a pre-defined role as helper T cells within the immune system. For example, when an antigen presenting cell expresses an antigen on MHC class II, a CD4+ cell will aid those cells through a combination of cell to cell interactions (e.g. CD40 and CD40L) and through cytokines. Nevertheless, there are rare exceptions; for example, sub-groups of regulatory T cells, natural killer T cells, and cytotoxic T cells express CD4 (although cytotoxic examples have been observed in extremely low numbers in specific disease states, they are usually considered non-existent). All of the latter CD4+ T cell groups are not considered T helper cells. The importance of helper T cells can be seen from HIV, a virus that infects cells that are CD4+ (including helper T cells). Towards the end of an HIV infection the number of functional CD4+ T cells falls, which leads to the symptomatic stage of infection known as the acquired immunodeficiency syndrome (AIDS). There are also some rare disorders that result in the absence or dysfunction of CD4+ T cells. These disorders produce similar symptoms, and many of these are fatal.

chemical methods used to kill all bacteria, endospores, and viruses

•A number of factors influence the efficacy of a given chemical agent, including: -The presence of organic matter -The kinds of organisms present -Corrosiveness -Stability, odor, and surface tension These include: -Ethanol -Iodine (Wescodyneand Betadine) -Chlorine •All of the above damage proteins, lipids, and DNA. -Are used to reduce or eliminate microbial content from objects

Interferons

•Are low-molecular-weight cytokines •Their action is host-specific and notvirus specific. •Are of two general types: -Type I: Have high antiviral potency -Include IFN-a, IFN-b, and IFN-w -Bind to receptors on uninfected host cell, and render them resistant to viral infection -Cleave dsRNAand block viral RNA translation -Type II: IFN-g -Has immunomodulatoryfunction

Natural Killer Cells

•Destroy infected and cancerous host cells •Healthy cells make surface MHC class Iantigens. -Cancerous and infected cells stop making MHC I When an NK cell encounters a cell lacking these markers, it secretes perforinsprotein into the target cell. -Creates membrane pores to lyse cell

Describe the acute inflammatory response:

•Infection releases microbes to tissue. •Resident macrophages phagocytosebacteria. -Release vasoactivefactors •Capillary cells express selectins. -Slows macrophage movement •Additional macrophages extravasate. -Squeeze between capillary cells -Leave capillary -Attack bacteria •Damaged tissue secretes bradykinin. -Promotes extravasation -Stimulates mast cells to degranulate -Release histamine •Histamine stimulates vessels to open further. -Blood plasma, platelets released into area •Prostaglandinis released. -Stimulates nerve endings -Signal itching, pain

How are antibodies selected for mass production and continued immunity?

The B-cell that recognized the foreign antigen clones itself to make many nearly identical copies of itself - with slight variations. Now, there are many B-cells that will recognize this particular foreign antigen. If infected again by an invader with this particular antigen, the immune system is ready and produces many more specific antibodies than before. This kills the invader much more quickly - making the body "immune" to this particular bug. "The B-cells expressing low affinity antibody on their surface become progressively less able to bind and be stimulated by antigen; in the environment of the germinal center, these poorly stimulated B cells are programmed to die by a specific process known as "apoptosis" (Choe et al, J Immunol 157:1006,1996). In contrast, the cells with high affinity antibody continue to bind antigen, and thus continue be stimulated to proliferate and secrete antibody. As the antigen concentration progressively falls while mutation and selection continue, the intensity of the selective pressure for high affinity increases. Repeated cycles of mutation and selection can lead to affinity levels 100-fold higher than that of the original unmutated antibody. The 'competition' for efficient antigen binding has been shown to be the selective force driving the rise in antibody affinity, since if antigen is repeatedly administered to prevent the drop in antigen level and thereby eliminate the selective pressure for efficient antigen binding, antibody affinity does not rise (Eisen and Siskind, Biochemistry 3:996, 1964). Furthermore, when selection pressure has been experimentally removed by engineering mice with impaired capacity for programmed death by apoptosis, many B cells are found that make mutated antibodies with low affinity (Takahashi et al. J Exp Med. 190:39, 1999). Late in the course of an immune response, as antigen becomes completely cleared from the bloodstream the amount of antibody secreted gradually falls and the immune response ends; but a subset of the last group of highly efficient cells persists as a quiescent population known as 'memory cells,' ready to respond with rapid secretion of high affinity antibody should they ever be triggered by another encounter with the same antigen in the future." 3

What are MHCs and how do they interact with the rest of the immune system?

The Major Histocompatibility Complex (MHC) is a set of molecules displayed on cell surfaces that are responsible for lymphocyte recognition and "antigen presentation". The MHC molecules control the immune response through recognition of "self" and "non-self" and, consequently, serve as targets in transplantation rejection. The Class I and Class II MHC molecules belong to a group of molecules known as the Immunoglobulin Supergene Family, which includes immunoglobulins, T-cell receptors, CD4, CD8, and others. This page will describe the MHC molecules and the process of antigen presentation.

Fever

The hypothalamusacts as the body's thermostat. •Pyrogensare substances that cause fever. •Exogenous pyrogensinduce release of endogenous pyrogens(e.g.: IFN, TNF, IL-6). -Stimulate the production of prostaglandins -Cross the blood-brain barrier -Changes the responsiveness of the thermosensitiveneurons that make up the thermoregulatory center -i.e.: It turns up the thermostat.

Why don't vaccines cause illness, but still allow your body to mount an immune response to disease causing pathogens?

The majority of vaccines contain viruses or bacteria that have been weakened or killed. Others contain inactivated toxins. In their altered states, vaccine pathogens are typically safe and unable to cause disease. When a weakened or dead pathogen is introduced into the bloodstream, the body's B-cells go to work. It is these cells that are responsible for fighting disease-causing pathogens. Once the B-cells are stimulated to act, antibodies are formed and the body develops immunity to the particular pathogen.

What is the epidemiological triangle and how is it used to prevent the spread of disease?

The mission of an epidemiologist is to break at least one of the sides of the Triangle, disrupting the connection between the environment, the host, and the agent, and stopping the continuation of disease. (top) host, (r-bottom) environment, (L-bottom) agent

What is PCR and how is it used to identify bacteria

The polymerase chain reaction (PCR) is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence. Using a DNA based assay, one can easily detect bacterial strains directly from clinical samples or from small amounts of cultured bacterial cells, thus improving the sensitivity and decreasing the time required for bacterial identification. PCR has been particularly useful in this regard, which relies on primer sequences designed to facilitate bacterial identification at any level of specificity: strain, species or genus. In recent years, real-time PCR methods have been developed and described for the rapid detection and identification of several bacterial strains. Real-time PCR is a promising tool for distinguishing specific sequences from a complex mixture of DNA and therefore is useful for determining the presence and quantity of pathogen-specific or other unique sequences within a sample. Real-time PCR facilitates a rapid detection of low amounts of bacterial DNA accelerating therapeutic decisions and enabling an earlier adequate antibiotic treatment.

What does opsonization mean?

The process at which opsonins bind to the surface of the antigen so that the antigen will be readily identified and engulfed by phagocytes for destruction. Examples of opsonins are antibody molecules such as the IgM that are capable of activating the complement system to increase the susceptibility of antigens to phagocytosis.