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USMLE step 1 review bacteriology


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Bacteria producing an AB exotoxin that prevents acetylcholine release.
Clostridium Botulinum - causes flaccid paralysis.
Mechanism of action of shiga toxin.
An AB exotoxin that cleaves 28S rRNA in 60S ribosomal subunit - disrupts protein synthesis. Damages intestinal epithelium and glomerular endothelial cells.
Cause of secretory diarrhea in cholera infection.
AB exotoxin activates adenylate cyclase by ADP ribosylation of G protein - increases cAMP.
Exotoxin that binds gangliosides.
Tetanus toxin - blocks inhibitory neurotransmitter release and causes spastic paralysis.
Mechanism of pseudomembrane formation in corynebacterium diphtheria infection.
AB exotoxin inactivates EF-2 and inhibits protein synthesis - causes cell death.
Type of toxin produced by S. aureus or S. pyogenes and mechanism of action.
Superantigens - bind to T-cell receptor and MHC II of another cell simultaneously and cause massive non-specific release of interleukins.
effects of endotoxin.
1. Binds to CD14 (TLR4) on macrophages, B cells and others to stimulate acute phase cytokine release (IL1, TNFa, IL6, PGs).
2. activates alternative complement pathway - fever, hypotension, shock.
3. Activation of blood coagulation pathways - DIC.
Portion of LPS responsible for activity.
Lipid A.
Organism causing double zone of hemolysis on blood agar.
Clostridium perfringens. Alpha toxin is a lecithinase that causes gas gangrene.
Mechanism of B. Pertussis toxin.
Stimulates adenylate cyclase by ADP ribosylation.
Gram negative aerobic organism producing a heat-labile toxin that activates adenylate cyclase to cause watery diarrhea.
E. coli.
Gram negative facultative anaerobe producing a toxin that activates adenylate cyclase to cause a watery diarrhea.
V. cholerae.
Protein that allows certain species of bacteria to colonize mucosal surfaces.
IgA protease.
An enzyme that catabolizes hydrogen peroxide into water and oxygen gas.
Catalase positive organisms
Catalase negative organisms.
Streptococci, enterococci.
The only human bacterial species that produces coagulase.
Staph aureus.
Coagulase action.
Binds a serum factor - converts fibrinogen to fibrin to form clot. Produced by S. aureus.
Function of protein A.
Binds Fc receptor of IgG and prevents Ab-mediated immune clearance. Extracellular protein A can produce immune complexes. Produced by S. aureus.
Lancet-shaped gram positive diplococci.
Quellung reaction.
Used for detection of pneumococcus. Polyvalent anticapsular antibodies are mixed with the bacteria, and then the mixture is examined microscopically. A greater refractiveness around the bacteria is a positive reaction for S. pneumoniae.
Use of optochin.
Differentiation of S. pneumoniae from viridans strep. Viridans and enterococci are optochin resistant.
Differentiation of S. pneumoniae from other alpha-hemolytic strep.
Bile solubility - S. pneumoniae lyse in bile, while others do not. Also: pneumococci are sensitive to optochin, where others are not.
Differentiation of Group A beta-hemolytic strep from Group B.
Group A is bacitracin sensitive, Group B is resisitant.
Gamma hemolytic (no hemolysis) strep species.
Enterococcus and peptostreptococcus.
Gram positive rods.
Clostridium, Corynebacterium, Listeria, Bacillus.
Coagulase negative staph.
S. epidermidis, S. saprophyticus (nobobiocin resistant).
Gram negative cocci.
N. meningitidis (Maltose fermenter), N. gonorrhea.
Gram negative coccobacilli.
H. influenzae, Pasteurella, Brucella, Bordetella.
Gram negative, lactose-fermenting rods.
E. coli, Klebsiella.
Gram negative Non-lactose fermenting, oxidase negative rods.
Shigella, Salmonella, Proteus.
Gram negative, Non-lactose fermenting, oxidase positive rods.
Obligate intracellular organisms.
Rickettsia and Chlamydia can't make their own ATP.
Facultative intracellular organisms.
Mycobacteria, Listeria, Yersinia, Legionella, Salmonella.
Organism requiring chocolate agar with factors V (NAD) and X (hematin).
H. influenzae.
Organism requiring Thayer-Martin (VCN) medium.
N. gonorrheae.
Organism requiring Bordet-Gengou (potato) agar.
B. pertussis.
Organism requiring Lowenstein-Jensen agar.
M. tuberculosis.
Organism requiring charcoal yeast extract agar with increased iron and cysteine.
Legionella pneumophila.
Organisms producing pink colonies on MacConkey's agar.
Lactose-fermenting enterics - Escherichia, Klebsiella, Enterobacter.
Organisms requiring Tellurite plate, Loffler's medium, blood agar.
C. diphtheriae.
Organisms requiring Sabouraud's agar.
Obligate aerobes.
Nocardia, Pseudomonas aeruginosa, Mycobacterium TB, Bacillus.
Organisms stained with Giemsa.
Stains blood parasites, viral and chlamydial inclusion bodies, intracellular organisms. Borrelia, Plasmodium, trypansosomes, Chlamydia, yeast.
Acid fast stains
Ziehl-Neelsen, Kinyoun, auramine-rhodamine. All stain for mycobacteria and other acid-fast organisms.
PAS stain
Stains glycogen, mucopolysaccharides - used to dx whipple's dz.
India ink.
Detects cryptococcus neoformans.
Iron hematoxylin stain.
Used to detect fecal protozoa.
Toluidine blue O stain.
Detects Pneumocystis organisms in sputum.
Trichrome stain.
Detects protozoa.
In order to be a spore-former, an organism must be a:
Gram positive rod. (examples: bacillus anthracis, clostridium)
Mechanism of action of Quinolones.
Prevent supercoiling of DNA.
Cellular target of aminoglycosides and tetracyclines.
Ribosomal 30s subunit.
Portion of LPS giving specificity.
O-specific chain - repeating sugars. Highly variable, highly antigenic.
Antibiotics affecting the ribosomal 50s subunit.
Chloramphenicol, Macrolides (erythromycin, clarithromycin, azithromycin), Lincosamines (Lincomycin, clindamycin).
Antibiotics affecting bacterial cell wall synthesis.
Penicillins, cephalosporins, Bacitracin, vancomycin, D-cycloserine.
Antibiotics that inhibit nucleic acid synthesis.
Sulfonamides, quinolones.
Food poisoning from reheated rice.
Bacillus cereus.
Food poisoning from meat, mayo, or custard.
Staph aureus.
Food poisoning from reheated meat dishes.
Clostridium perfringens.
Food poisoning from undercooked beef.
E. coli.
Food poisoning from poultry, meat, eggs.
Food poisoning from contaminated seafood.
Vibrio parahemolyticus.
Pulmonary infection in immunocompromised patient.
Nocardia asteroides.
Dental caries.
Strep mutans (viridans).
Acute bacterial endocarditis.
Staph aureus.
Food poisoning within a few hours of eating, resolves in 10 hours.
S. aureus preformed toxin.
Rheumatic fever.
Strep pyogenes.
Diarrhea after Clindamycin use.
C. difficile.
Woolsorter's Disease.
Inhalation anthrax.
Diarrhea after playing with puppy.
Y. enterocolitica.
Diarrhea after eating seafood.
V. parahemolyticus.
Diarrhea from comma shaped organism grown at 42 degrees.
Campylobacter jejuni.
Diarrhea from tiny amount of non-motile, non-lactose fermenter.
Diarrhea from motile non-lactose fermenter.
Diarrhea from lactose fermenter.
E. coli.
Gram negative produsing epiglottitis, meningitis, otitis media, pneumonia. Culture on chocolate agar.
Haemophilus influenzae.
Poorly-staining gram negative rod grown on charcoal yeast with iron and cysteine.
Legionella pneumophila.
Gram negative aerobic organism producing otitis externa and burn/wound infections.
Pseudomonas aeruguinosa.
Coccobacillus causing vaginosis.
Gardernella vaginalis.
Gram negative diplococci which ferments maltose and has a capsule.
N. meningitidis.
Fever, night sweats, weight loss, hemoptysis.
Mycobacterium TB.
Typical tx for rickettsiae.
Q fever (no rash)
Coxiella burnettii.
Outward spread of rash.
R. typhi.
Rash starts on palms and soles - inward spread of rash, headache, fever. Endemic to east coast.
R. rickettsii - rocky mountain spotted fever. (tick spread)
Weil-Felix reaction.
Assay for anti-rickettsial Ab. Positive for typhus and spotted fever, negative for Q fever.
Insidious onset pneumonia with headache, non-productive cough, diffuse interstitial infiltrate. High titer cold agglutinins.
Mycoplasma pneumoniae. Only bacterial membrane containing cholesterol.
Cytoplasmic inclusions on Giemsa or flourescent ab-stained smear.
Chlamydiae. Cell wall lacks muramic acid.
"Bull's eye" rash, flu-like sx, progessing to neurologic and cardiac manifestations, then to autoimmune migratory polyarthritis.
Lyme disease.
Painless chancre - disseminated dz with maculopapular rash, condylomata lata - aortitis, neurosyphilis, argyll robertson pupil.
Syphilis (Treponema pallidum)
FTA-ABS test.
specific for treponemes - positive earlier in dz, remains positive longer than VDRL.
Lung abscess in immunocompromised.
Nocardia asteroides.
alpha-hemolytic strep that lyses in bile.
S. pneumoniae.
Coagulase negative staph that is resistant to novobiocin.
S. sparophyticus.

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