Microbiology

Question 1

diphtheria toxin

Answer 1

produced by Corynebacterium diphtheriae; AB toxin; ADP-ribosylates and inactivates EF2

Question 2

exotoxin A

Answer 2

produced by Pseudomonas aeruginosa; AB toxin; ADP-ribosylates and inactivates EF2; leads to host cell death

Question 3

shiga toxin

Answer 3

produced by Shigella spp.; AB toxin; ADP-ribosylates and inactivates 60S ribosome by removing adenine from rRNA; leads to dysentery, cytokine release, and HUS

Question 4

shiga-like toxin

Answer 4

produced by EHEC; AB toxin; ADP-ribosylates and inactivates 60S ribosome by removing adenine from rRNA; leads to cytokine release and HUS

Question 5

heat-labile toxin

Answer 5

produced by ETEC; AB toxin; ADP-ribosylates and activates adenylate cyclase; leads to increased Cl secretion into gut and water efflux (watery diarrhea)

Question 6

heat-stabile toxin

Answer 6

produced by ETEC; overactivates guanylate cyclase; leads to decreased NaCl and water resorption from gut (watery diarrhea)

Question 7

edema toxin

Answer 7

produced by Bacillus anthracis; ADP-ribosylating AB toxin; mimics activity of adenylate cyclase; leads to edematous borders of characteristic black eschar in cutaneous anthrax

Question 8

cholera toxin

Answer 8

produced by Vibrio cholerae; AB toxin; overactivates adenylate cyclase by ADP-ribosylating/permanently activating Gs; leads to rice-water diarrhea

Question 9

pertussis toxin

Answer 9

produced by Bordatella pertussis; AB toxin; ADP-ribosylates and disables Gi, leading to overactivation of adenylate cyclase; also impairs phagocytosis

Question 10

tetanospasmin

Answer 10

produced by Clostridium tetani; ADP ribosylating AB toxin; protease that cleaves SNARE, prevents release of inhibitory neurotransmitters (GABA and glycine) from Renshaw cells in spinal cord; leads to spastic paralysis

Question 11

botulinum toxin

Answer 11

produced by Clostridium botulinum; ADP ribosylating AB toxin; protease that cleaves SNARE, prevents release of stimulatory neurotransmitters (ACh) at neuromuscular junction; leads to flaccid paralysis

Question 12

alpha toxin

Answer 12

produced by Clostridium perfringens; phospholipase (lecithinase) that degrades tissue and cell membranes; leads to gas gangrene and “double zone” of hemolysis

Question 13

streptolysin O

Answer 13

produced by Streptococcus pyogenes; degrades cell membranes, lyses RBCs; leads to beta hemolysis; host antibodies are diagnostic for acute rheumatic fever

Question 14

toxic shock syndrome toxin

Answer 14

produced by Staphylococcus aureus; cross-links MHC II and TCR outside of antigen binding site, causing overwhelming cytokine release (IL-1, IL-2, IFN-y, TNF-a) and shock

Question 15

exotoxin A

Answer 15

produced by Streptococcus pyogenes; cross-links MHC II and TCR outside of antigen binding site, causing overwhelming cytokine release (IL-1, IL-2, IFN-y, TNF-a) and shock

Question 16

Staphylococcus aureus

Answer 16

gram (+) cocci in clusters, catalase (+), coagulase (+)
virulence factors: Protein A (binds Fc-IgG, inhibits complement activation/phagocytosis), TSST-1, forms fibrin clot (abscess formation)
diseases: skin infection, abscesses, pneumonia, endocarditis, septic arthritis, osteomyelitis, toxic shock syndrome (associated with tampons/nasal packing), scalded skin syndrome, rapid-onset food poisoning (heat-stabile toxin)
MRSA: altered PBP, resistent to methicillin and nafcillin

Question 17

Staphylococcus epidermidis

Answer 17

gram (+) cocci, catalase (+), coagulase (-), urease (+), novobiocin sensitive
virulence factors: biofilm formation
diseases: prosthetic and catheter infection

Question 18

Staphylococcus saprophyticus

Answer 18

gram (+) cocci, catalase (+), coagulase (-), urease (+), novobiocin resistant
diseases: second-most common cause of uncomplicated UTI in young women

Question 19

Streptococcus pneumoniae

Answer 19

gram (+) lancet-shaped diplococci, catalse (-), optichin sensitive, alpha-hemolytic
virulence factors: capsule, IgA protease
diseases: meningitis, otitis media, pneumonia, sinusitis

Question 20

Streptococcus mutans

Answer 20

gram (+) cocci, catalase (-), optichin resistant, alpha-hemolytic
diseases: dental caries

Question 21

Streptococcus sanguinis

Answer 21

gram (+) cocci, catalase (-), optichin resistant, alpha-hemolytic
diseases: subacute bacterial endocarditis at damaged heart valves (binds fibrin-platelet aggregates)

Question 22

Streptococcus pyogenes

Answer 22

gram (+) cocci in chains, catalase (-), PYR (+), bacitracin sensitive, beta-hemolytic (group A)
virulence factors: streptolysin O (degrades cell membranes), exotoxin A (similar to TSST)
diseases: phyringitis, cellulitis, impetigo, erysipelas, scarlet fever, toxic shock syndrome (associated with skin infection), rheumatic fever, glomerulonephritis

Question 23

Streptococcus agalactiae

Answer 23

gram (+) coccin in chains, catalase (-), hippourate (+), bacitracin resistant, beta-hemolytic (group B)
virulence factors: CAMP factor (enlarges area of hemolysis formed by S. aureus)
diseases: colonizes vagina, infantile pneumonia/meningitis/sepsis (intrapartum penicillin prophylaxis)

Question 24

Enterococci (E. faecalis and E. faecium)

Answer 24

gram (+), group D Strep, penicillin G resistant, variable hemolysis, can grow in 6.5% NaCl and bile
diseases: normal colonic flora, UTI, biliary tract infections, subacute endocarditis (following GI/GU procedures), nosocomial infections (VRE)

Question 25

Streptococcus bovis

Answer 25

gram (+)

diseases: colonic flora, subacute endocarditis associated with colon cancer

Question 26

Corynebacterium diphtheriae

Answer 26

gram (+) club-shaped, metachromatic granules, black colonies on cystine-tellurite agar
virulence factors: diphtheria toxin, encoded by beta-prophage, ADP-ribosylates EF2
diseases: pseudomembranous pharyngitis w/ lymphadenopathy, myocarditis, and arrhythmias
ABCDEFG: ADP-ribosylation, beta-prophage, Corynebacterium diphtheriae, EF2, granules

Question 27

Clostridium difficile

Answer 27

gram (+), dx by detection of toxins in stool via PCR
virulence factors: toxin A (binds brush border of gut) and toxin B (cytotoxin, causes actin depolymerization)
diseases: pseudomembranous colitis, often secondary to antibiotic use (esp. ampicillin or clindamycin)
tx: metronidazole, oral vancomycin, fidaxomicin