chapter 15
exotoxin work by
destroying particular parts of the host cells or inhibiting certain metabolic functions -most lethal substances known
saxitoxin
dinoflagellates such as, Alexandrium, medically important because they produce _________________ mollusk feed on dinoflagellates, show no symptoms of disease, people who eat mollusks develop paralytic shellfish poisoning
exotoxins are
disease specific example; botulismis usually due to ingestion of _______________ not to bacterial infection disease caused by bacteria that produce exotoxins are often caused by minute amounts of exotoxins, not by bacteria themsleves
fungi
do not have well defined set of virulence factors -toxic metabolic products -provoke allergic response -some toxins inhibit protein synthesis proteases= modify host cell membranes, allow attachment of fungus to host cell -capsules prevent phagocytosis example; Trichothecenes fungal toxins inhibit protein synthesis Trichophyton = secrete proteases
mycotoxins
few mushrooms produce toxin called _____________ -produced by fungi example; phalloidin and amanitin ingestion of amanitin mushroom can cause death
gastrointestinal tract
gain access in food and water, via contaminated fingers -most microbes that enter the body this way are destroyed by hydrochloric acid (HCI) and enzymes in the stomach -those that survive cause disease, such as hepatitis A, thyphoid fever
toxins
poisonous substances that are produced by certain microorganisms -produce fever, cardiovascular problems, diarrhea, and shock -transported by blood or lymph can cause serious, sometimes fatal effects 2 types: endotoxin and exotoxin
genitourinary tract
portal of entry for pathogens contracted sexually -sexually transmitted infections (STIs) -may penetrate unbroken mucous membrane -cut or abrasion example; HIV, genital warts, herpes
intoxication
presence of toxin without microbial growth
toxemia
presence of toxins in host blood
exotoxin
produced inside some bacteria as part of their growth and metabolism, secreted by bacterium into the surrounding medium or released following lysis -proteins -many are enzymes that catalyze certain biochemical reactions -small amounts are harmful -carried on bacterial plasmids or phages can be gram + or -
Opa
protein allows attachment to host cells outermembrane protein example; Neisseria gonorrhoeae grows inside himan epithelial cells and leukocytes bacteria use fimbriae and _________ to attach to host cell
viral mechanisms (of evading host defenses)
-viruses can penetrate and grow inside host cell (where components of immune system cannot reach) -attachment sites, use receptors on host cells to attach -attachment site can mimic substances useful to host cells (example; attachment sites of rabies virus can mimic neurotransmitter acetylcholine) HIV = hides attachment sites from immune response, attacks components of immune system directly variation in attachment sites makes them unrecognizable by immune system -destroy immune cells
cytopathic variation (of effects)
1. macromolecular synthesis within host cell to stop 2. cells lysosome to release enzyme, results in destruction of intracellular contents and host cell death 3. creating inclusion bodies in cell cytoplasm 4.fusing cells to create syncytium 5.changing host cell function or inducing chromosomal changes with no visible changes 6. produce interferons to protect uninfected cells 7. induce antigenic changes on surface of infected cell 8. loss of contact inhibition in cell, leading to cancer
endotoxins and the pyrogenic response
1. macrophage ingest gram negative bacterium 2. bacterium is degraded in vacuole, releasing endotoxins that induce the macrophage to produce cytokines, IL-1 and TNF-a 3. cytokines are released into blood stream by macrophages, travel to hypothalamus of brain 4. cytokines induce hypothalamus to release lipids called prostaglandins, which reset the thermostat in hypothalamus at higher temperature, results in fever
exotoxins are divided into
3 principal types based on structure and function 1. A-B toxins 2. membrane disrupting toxins 3. superantigens
D. toxin (diphtheria toxin)
C. diphtheriae produces ___________________ when infected by lysogenic phage carrying tox gene -cytotoxin inhibits protein synthesis in eukaryotic cells does this using A-B toxin mechanism
toxigenicity
ability of microorganism to produce toxin
another consequence of endotoxins
activation of blood clotting proteins causing formation of small blood clots -blood clots obstruct capillaries and resulting decreased blood supply induces death of tissues (condition referred to as DIC
syncytium
adjacent infected cells fuse to form large multinucleate cell common cold, measles, mumps
toxoids
altered exotoxins inactivated exotoxins used in vaccines they simulate antitoxin production so immunity is produced
adhesins (or ligands)
attachment between pathogen and host accomplished by means of surface molecules on pathogen called ___________ bind specifically to complementary surface receptors on cells of certain host tissues -are glycoproteins or lipoproteins found on... -glycocalyx -fimbriae, pili, flagella
kinases
bacterial enzyme that break down fibrin and digest clots formed by the body to isolate infection -better known is fibrinolysin produced by streptococci
coagulases
bacterial enzymes that coagulate (clot) by fibrinogen in blood -fibrin clot may protect the bacterium from phagocytosis and isolate it from other defenses of the host some members of genus Staphyloccus
TNF
binds to many tissues of the body and alters metabolism in number of ways
antitoxins
body produces antibodies called ______________ provide immunity to exotoxins -antibodies against specific exotoxins
superantigens
cause intense immune response -bacterial proteins T cells are simulated to release enormous amounts of chemicals called cytokines cause symptoms of fever, nausea, vomiting, diarrhea, shock, and death include staphylococcal toxins
membrane disrupting toxin
cause lysis of host cell by disrupting plasma membrane -some do this by forming protein channels in plasma membrane -others disrupt phospholipid portion of membrane example; S. aureus = cell lysing exotoxon, forms protein channels C. perfringens = exotoxin that disrupts phospholipids
lysogenic conversion
change in characteristics of microbe due to prophage -as a result bacterial cell is immune to infection by same type of phage example; Virbrio cholerae, pathogenic strains carry lysogenic phages these phages can transmit cholera toxin gene to nonpathogenic V. cholerae strains, increasing number of pathogenic bacteria
A-B toxins
consist of 2 parts designated A and B both are polypeptides A part = active (enzyme) component B part = binding component example; diphtheria toxin
respiratory tract
easiest and most frequently traveled portal of entry for infectious microorganisms -inhaled into the nose or mouth in drops of moisture and dust particles example; common cold, pneumonia, influenza,
collagenase
enzyme produced by several species of clostridium -facilitates the spread of gas gangrene colagenase breaks down protein collagen, which forms connective tissue of muscles and other body organs and tissues
hyaluronidase
enzyme secreted by certain bacteria such as streptococci -digest polysaccharides that hold cells together spreading infection -hydrolyzes hyaluronic acid, type of polysaccharide that holds together certain cells of the body, particularly cells in connective tissue, helps microorganism spread from its initial site
the parenteral route
gain access to body when deposited directly into the tissues beneath the skin or into mucous membrane when barriers are penetrated or injured -punctures, injections, bites, cuts, wounds, surgery, and splitting of skin or mucous membrane example; HIV, hepatitis virus
portals of entry
gain entrance to the human body and other hosts through several avenues -mucous membrane gastrointestinal respiratory conjuctiva genitourinary -skin -parenteral route (direct deposition, beneath skin or membrane)
inclusion bodies
granules found in cytoplasm or nucleus of some infected cells sometimes viral parts nucleic acids or proteins in process of being assembled into virions characterized by ability to stain with acidic (acidophilic) or basic (basophilic)
sclerotia
highly resistant portions of mycelia of fungus that can detach toxin is contained in ______________
ID50
infectious dose for 50% of sample population -compare relative virulence under experimental conditions (measures virulence of a microbe) ______ through skin (cutaneous anthrax) is 10 to 50 endospores inhalation of anthrax is 10,000 to 20,000 endospores gastrointestinal anthrax is 250,000 to 1,000,000 endospores data shows that cutaneous anthrax is significantly easier to acquire than the gas. or inhalation
skin
largest organ of body in terms of surface area -some microbes gain access to body through openings in the skin, such as hair follicles and sweat glands example; some fungi grow on keratin in skin or infect the skin itself
LD50
lethal dose for 50% of sample population potency of toxin expressed (measures potency of a toxin) ____ for botulinum toxin in mice 0.03 ng/kg for shiga toxin, 250 ng/kg staphylococcal enterotoxin 1350 ng/kg compared to other two toxins a smaller dose of butulinum toxin is needed to cause symptoms
shock
life threatening decrease in blood pressure
mucous membrane
many bacteria and viruses gain access to body by penetrating ___________, lining of respiratory tract, gastrointestinal tract, genitourinary tract and conjunctiva (delicate membrane that covers eyeballs and lines eyelids)
preferred portal of entry
many pathogens have a preferred portal of entry that is required for them to be able to cause disease example; Salmonella typhi = produces all symptoms of disease when swallowed (preferred route) , although if rubbed on skin there would be no reaction streptococci that are inhaled caused pneumonia
plasmid
may carry genes for... toxins = neurotoxin resistance to antibiotics (R factors)= B-lactamase enzymes = dextransucrase small circular DNA molecules capable of independent multiplication
biofilm
microbes form ____________ (communities that share nutrients) -communities that constitute masses of microbes and extracellular products that can attach to living and nonliving surfaces -adheres to surface, typically moist and contains organic matter -dental plaque, stents, catheters, heart valves, hip replacements
invasins
microbes produce surface proteins called _______________________ -rearrange nearby actin filaments of the cytoskeleton example; S. tryphimurium makes contact with host cell, _______________ of the microbe cause appearance of host cell plasma membrane to resemble splash of a drop of liquid hitting solid surface this effect is called membrane ruffling, disruption in cytoskeleton of host cell
contact inhibition
most normal cell cease growing in vitro when they come close to another cell leading to cancer
iron is required for
most pathogenic bacteria
adherence (or adhesion)
most pathogens attach to host tissues in process called _______________ necessary step in pathogenicity
waxy lipid
mycolic acid resist digestion by phagocytosis makes up wall of Mycobacterium tuberculosis, also increases virulence by resisting digestion by phagocytes and can multiply inside phagocytes
endotoxin
outer portion of cell wall of gram negative bacteria -lipopolysaccharide -released when gram negative bacteria die, cell wall undergo lysis (also released during bacterial multiplication) -simulate macrophages to release cytokines in very high concentrations (at this level cytokines are toxic) -produce same signs and symptoms regardless of species of microorganism, but not same degree
direct damage
pathogens use host for nutrients and produce waste products -multiply host cells and cause ruptures -disrupt host cell function -penetrate host cell by excreting enzymes and by own motility -done by toxins
IgA proteases
pathogens with the ability to produce enzyme -destroy IgA antibodies example; N. gonorrhoeae has this ability
capsules
resist the host defenses by impairing phagocytosis (process by which certain cells of body engluf and destroy microbes) strains with capsules are virulent, but strains without capsules are avirulent, since they are susceptible to phagocytosis (many nonpathogentic bacteria HAVE capsules and many pathogenic bacteria DO NOT have capsules)
M protein
resists phagocytosis Streptococcus pyogenes, produce heat resistant and acid resistant protein called _________ -mediates attachment of bacterium to epithelial cells of host and helps the bacterium resist phagocytosis by white blood cells (protein increases virulence of microorganism) immunity of S. pyogenes depends on bodys production of antibody specific to _________________
membrane ruffling
result of disruption in cytoskeleton of host cell cell of plasma membrane to resemble drop of liquid
portals of exit
secretions, discharges, excretions or tissue that has been shed ______________________________ are related to part of body that has been infected common are respiratory and gastrointestinal tract example; respiratory tract= coughing and sneezing gastrointestinal tract= feces and saliva genitourinary tract= urine, secretions from penis and vagina (usually sexually transmitted infections) skin
septic shock
shock caused by bacteria gram negative bacteria cause endotoxic shock
antigenic variation
some pathogens can alter their surface antigens by the time body mounts an immune system response against pathogen, pathogen already altered its antigens and is unaffected by the antibodies
algae
some species produces neurotoxins called saxitoxin genera dinoflagellates, such as Alexandrium, medically important because they produce saxitoxin
aflatoxin
toxin that has carcinogenic properties -produced by growth of the mold, Aspergillus flavus -when ingested, toxin might be altered in human body to mutagenic compound
pathogenicity
the ability to cause disease
virulence
the degree of pathogenicity
siderophores
to obtain free iron, some pathogens secrete proteins called _________________ -released into the medium, where they take iron away from iron transport proteins by binding iron even more tightly (pathogens that bind iron more tightly than host proteins -some bacteria bind to iron transport proteins such as hemoglobin and internalize them
ergot
toxin itself alkaloid -can cause hallucinations resembling those produced by LSD -natural source of LSD -constricts capillaries -cause gangrene of limbs by preventing proper blood circulation
protozoa (evade host defenses)
use antigenic variation to stay one step ahead of host immune system example; Trypanosoma = produces and displays specific antigen. In response body produces antibodies against antigen. Within 2 weeks microbe displays different antigen microbe can make up to 1,000 different antigens
helminths
use host tissue for own growth or produce large parasitic masses resulting in cellular damage evokes symptoms
interferons
virus infected cells produce __________________ host DNA actually codes for ______________. This protects neighboring uninfected cells from viral infection
cytopathic effects (CPE)
visible effects of viral infection -cytocidal effects =result in cell death -noncytocidal effects = result in cell damage but not cell death
protozoa
waste products often produces disease symptoms in the host plasmodium= causes rupture toxoplasma= gains entry by phagocytosis, parasite prevents normal acidification and digestion, can grow in phagocytic vacuole Giardia lamblia= attach to host cells by sucking disc, digest cells and tissue fluid