Usmle Step 1 Review Bacteriology

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Bacteria producing an AB exotoxin that prevents acetylcholine release.

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Clostridium Botulinum - causes flaccid paralysis.

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Mechanism of action of shiga toxin.

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An AB exotoxin that cleaves 28S rRNA in 60S ribosomal subunit - disrupts protein synthesis. Damages intestinal epithelium and glomerular endothelial cells.

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Cause of secretory diarrhea in cholera infection.

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AB exotoxin activates adenylate cyclase by ADP ribosylation of G protein - increases cAMP.

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Exotoxin that binds gangliosides.

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Tetanus toxin - blocks inhibitory neurotransmitter release and causes spastic paralysis.

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Mechanism of pseudomembrane formation in corynebacterium diphtheria infection.

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AB exotoxin inactivates EF-2 and inhibits protein synthesis - causes cell death.

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Type of toxin produced by S. aureus or S. pyogenes and mechanism of action.

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Superantigens - bind to T-cell receptor and MHC II of another cell simultaneously and cause massive non-specific release of interleukins.

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effects of endotoxin.

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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.

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Portion of LPS responsible for activity.

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Lipid A.

Front 9

Organism causing double zone of hemolysis on blood agar.

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Clostridium perfringens. Alpha toxin is a lecithinase that causes gas gangrene.

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Mechanism of B. Pertussis toxin.

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Stimulates adenylate cyclase by ADP ribosylation.

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Gram negative aerobic organism producing a heat-labile toxin that activates adenylate cyclase to cause watery diarrhea.

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E. coli.

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Gram negative facultative anaerobe producing a toxin that activates adenylate cyclase to cause a watery diarrhea.

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V. cholerae.

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Protein that allows certain species of bacteria to colonize mucosal surfaces.

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IgA protease.

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Catalase

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An enzyme that catabolizes hydrogen peroxide into water and oxygen gas.

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Catalase positive organisms

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Staphylococci.

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Catalase negative organisms.

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Streptococci, enterococci.

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The only human bacterial species that produces coagulase.

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Staph aureus.

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Coagulase action.

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Binds a serum factor - converts fibrinogen to fibrin to form clot. Produced by S. aureus.

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Function of protein A.

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Binds Fc receptor of IgG and prevents Ab-mediated immune clearance. Extracellular protein A can produce immune complexes. Produced by S. aureus.

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Lancet-shaped gram positive diplococci.

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Pneumococcus.

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Quellung reaction.

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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.

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Use of optochin.

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Differentiation of S. pneumoniae from viridans strep. Viridans and enterococci are optochin resistant.

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Differentiation of S. pneumoniae from other alpha-hemolytic strep.

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Bile solubility - S. pneumoniae lyse in bile, while others do not. Also: pneumococci are sensitive to optochin, where others are not.

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Differentiation of Group A beta-hemolytic strep from Group B.

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Group A is bacitracin sensitive, Group B is resisitant.

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Gamma hemolytic (no hemolysis) strep species.

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Enterococcus and peptostreptococcus.

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Gram positive rods.

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Clostridium, Corynebacterium, Listeria, Bacillus.

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Coagulase negative staph.

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S. epidermidis, S. saprophyticus (nobobiocin resistant).

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Gram negative cocci.

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N. meningitidis (Maltose fermenter), N. gonorrhea.

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Gram negative coccobacilli.

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H. influenzae, Pasteurella, Brucella, Bordetella.

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Gram negative, lactose-fermenting rods.

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E. coli, Klebsiella.

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Gram negative Non-lactose fermenting, oxidase negative rods.

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Shigella, Salmonella, Proteus.

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Gram negative, Non-lactose fermenting, oxidase positive rods.

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Pseudomonas.

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Obligate intracellular organisms.

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Rickettsia and Chlamydia can't make their own ATP.

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Facultative intracellular organisms.

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Mycobacteria, Listeria, Yersinia, Legionella, Salmonella.

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Organism requiring chocolate agar with factors V (NAD) and X (hematin).

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H. influenzae.

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Organism requiring Thayer-Martin (VCN) medium.

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N. gonorrheae.

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Organism requiring Bordet-Gengou (potato) agar.

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B. pertussis.

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Organism requiring Lowenstein-Jensen agar.

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M. tuberculosis.

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Organism requiring charcoal yeast extract agar with increased iron and cysteine.

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Legionella pneumophila.

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Organisms producing pink colonies on MacConkey's agar.

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Lactose-fermenting enterics - Escherichia, Klebsiella, Enterobacter.

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Organisms requiring Tellurite plate, Loffler's medium, blood agar.

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C. diphtheriae.

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Organisms requiring Sabouraud's agar.

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Fungi.

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Obligate aerobes.

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Nocardia, Pseudomonas aeruginosa, Mycobacterium TB, Bacillus.

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Organisms stained with Giemsa.

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Stains blood parasites, viral and chlamydial inclusion bodies, intracellular organisms. Borrelia, Plasmodium, trypansosomes, Chlamydia, yeast.

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Acid fast stains

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Ziehl-Neelsen, Kinyoun, auramine-rhodamine. All stain for mycobacteria and other acid-fast organisms.

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PAS stain

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Stains glycogen, mucopolysaccharides - used to dx whipple's dz.

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India ink.

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Detects cryptococcus neoformans.

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Iron hematoxylin stain.

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Used to detect fecal protozoa.

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Toluidine blue O stain.

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Detects Pneumocystis organisms in sputum.

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Trichrome stain.

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Detects protozoa.

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In order to be a spore-former, an organism must be a:

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Gram positive rod. (examples: bacillus anthracis, clostridium)

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Mechanism of action of Quinolones.

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Prevent supercoiling of DNA.

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Cellular target of aminoglycosides and tetracyclines.

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Ribosomal 30s subunit.

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Portion of LPS giving specificity.

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O-specific chain - repeating sugars. Highly variable, highly antigenic.

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Antibiotics affecting the ribosomal 50s subunit.

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Chloramphenicol, Macrolides (erythromycin, clarithromycin, azithromycin), Lincosamines (Lincomycin, clindamycin).

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Antibiotics affecting bacterial cell wall synthesis.

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Penicillins, cephalosporins, Bacitracin, vancomycin, D-cycloserine.

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Antibiotics that inhibit nucleic acid synthesis.

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Sulfonamides, quinolones.

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Food poisoning from reheated rice.

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Bacillus cereus.

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Food poisoning from meat, mayo, or custard.

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Staph aureus.

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Food poisoning from reheated meat dishes.

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Clostridium perfringens.

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Food poisoning from undercooked beef.

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E. coli.

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Food poisoning from poultry, meat, eggs.

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Salmonella.

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Food poisoning from contaminated seafood.

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Vibrio parahemolyticus.

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Pulmonary infection in immunocompromised patient.

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Nocardia asteroides.

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Dental caries.

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Strep mutans (viridans).

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Acute bacterial endocarditis.

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Staph aureus.

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Food poisoning within a few hours of eating, resolves in 10 hours.

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S. aureus preformed toxin.

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Rheumatic fever.

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Strep pyogenes.

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Diarrhea after Clindamycin use.

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C. difficile.

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Woolsorter's Disease.

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Inhalation anthrax.

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Diarrhea after playing with puppy.

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Y. enterocolitica.

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Diarrhea after eating seafood.

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V. parahemolyticus.

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Diarrhea from comma shaped organism grown at 42 degrees.

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Campylobacter jejuni.

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Diarrhea from tiny amount of non-motile, non-lactose fermenter.

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Shigella.

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Diarrhea from motile non-lactose fermenter.

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Salmonella.

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Diarrhea from lactose fermenter.

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E. coli.

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Gram negative produsing epiglottitis, meningitis, otitis media, pneumonia. Culture on chocolate agar.

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Haemophilus influenzae.

Front 78

Poorly-staining gram negative rod grown on charcoal yeast with iron and cysteine.

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Legionella pneumophila.

Front 79

Gram negative aerobic organism producing otitis externa and burn/wound infections.

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Pseudomonas aeruguinosa.

Front 80

Coccobacillus causing vaginosis.

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Gardernella vaginalis.

Front 81

Gram negative diplococci which ferments maltose and has a capsule.

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N. meningitidis.

Front 82

Fever, night sweats, weight loss, hemoptysis.

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Mycobacterium TB.

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Typical tx for rickettsiae.

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Tetracycline.

Front 84

Q fever (no rash)

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Coxiella burnettii.

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Outward spread of rash.

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R. typhi.

Front 86

Rash starts on palms and soles - inward spread of rash, headache, fever. Endemic to east coast.

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R. rickettsii - rocky mountain spotted fever. (tick spread)

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Weil-Felix reaction.

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Assay for anti-rickettsial Ab. Positive for typhus and spotted fever, negative for Q fever.

Front 88

Insidious onset pneumonia with headache, non-productive cough, diffuse interstitial infiltrate. High titer cold agglutinins.

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Mycoplasma pneumoniae. Only bacterial membrane containing cholesterol.

Front 89

Cytoplasmic inclusions on Giemsa or flourescent ab-stained smear.

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Chlamydiae. Cell wall lacks muramic acid.

Front 90

"Bull's eye" rash, flu-like sx, progessing to neurologic and cardiac manifestations, then to autoimmune migratory polyarthritis.

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Lyme disease.

Front 91

Painless chancre - disseminated dz with maculopapular rash, condylomata lata - aortitis, neurosyphilis, argyll robertson pupil.

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Syphilis (Treponema pallidum)

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FTA-ABS test.

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specific for treponemes - positive earlier in dz, remains positive longer than VDRL.

Front 93

Lung abscess in immunocompromised.

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Nocardia asteroides.

Front 94

alpha-hemolytic strep that lyses in bile.

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S. pneumoniae.

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Coagulase negative staph that is resistant to novobiocin.

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S. sparophyticus.