microbiology USMLE

Question 1

Actinomyces israeli

Answer 1

G+ branching rod
Anaerobic
Yellow “sulfur granules”
normal in mouth and vagina

Question 2

B. anthracis

Answer 2

Bacillus
G+ rod
Spore-forming
Aerobic
Non-motile

Woolsorter’s Dz –> animal hinds
Polypeptide capsule!! (D-glut capsule)

Question 3

B. cereus

Answer 3

Bacillus
G+ rod
Spore-forming
Aerobic
Motile

Food poisoning –> Reheated rice

Question 4

C. botulinium

Answer 4

Clostridium
G+ rod
Anaerobic
Spore-forming
Motile
Honey in infant or canned food
Blocks ACh release at NMJ (peripheral NS) --> flaccid paralysis

Question 5

C. difficile

Answer 5

Clostridium
G+ rod
Anaerobic
Spore-forming
Motile
Normal gut flora –> superinfxn following clindamycin
Psuedomembranous colitis –> toxic megacolon –> perforation –> death

Tx. metronidazole & oral vancomycin

Question 6

C. diphtheriae

Answer 6

Corynebacterium
G+ rod
Non-spore forming
Aerobic
Non-motile

Grows on K. Tellurite agar (Teletubbies!)
Unimmunized child w/ psuedomembrane

Question 7

C. perfringens

Answer 7

Clostridium
G+ rod
Anaerobic
Spore-forming
Non-motile
a-toxin (lecithinase) –>disrupts lecithin found in our cell membranes
Gas gangrene –> crepitus, bubbles, crackles

Question 8

C. tetani

Answer 8

Clostridium
G+ rod
Anaerobic
Spore-forming
Motile
Penetrating wound (found in soil, low O2)
Tetanospasmin (inhibits motor neurons) --> spastic paralysis
Stops Gly & GABA

Question 9

Enterococcus

Answer 9

G+ cocci in chains
Catalase - (Strep)
a or y hemolysis
Grows in 6.5% NaCl

Question 10

Listeria monocytogenes

Answer 10

G+ rod –> only one with LPS
Non-spore forming
Aerobic
Motile (tumbling motility)

Deli meats, Unpastuerized milk
Intracellular –> cell mediated (cytotoxic T)

Question 11

Nocardia asteroidies

Answer 11

G+ branching rod
slightly acid fast
aerobic
–> pulmonary infxn

Question 12

Non-enterococcus

Answer 12

G+ cocci in chains
Catalase - (Strep)
y hemolysis
anaerobis
Does not grow in 6.5% NaCl
Grows in bile

Question 13

S. agalactiae

Answer 13

GROUP B Strep
G+ cocci in chains
Catalase - (Strep)
b hemolysis
Bacitracin resistant --> colonizes vaginal tract

Question 14

S. aureus

Answer 14

G+ cocci in clusters
Catalase + (Staph)
Coagulase +
Gold color

Question 15

S. epidermidis

Answer 15

G+ cocci in clusters 
Catalase + (Staph)
Coagulase -
White color
Novobiocin sensitive --> Causes infxns in catheters and central lines

Question 16

S. pneumoniae

Answer 16

G+ cocci in chains
Catalase - (Strep)
a hemolysis
CAPSULE (+ quelling reaction)
bile soluble (doesn't grow)
Optochin sensitive --> MCC of pneumonia >60

Question 18

S. pyogenes

Answer 18

GROUP A Strep
G+ cocci in chains
Catalase - (Strep)
b hemolysis
Bacitracin sensitive --> M protein cleaves C3 convertase, Abs can cause rheumatic fever

Question 19

S. saprophyticus

Answer 19

G+ cocci in clusters
Catalase + (Staph)
Coagulase +
Novobiocin resistant –> 2nd MC cause of UTIs

Question 20

Viridans Strep. (S. mutans, S. Sanguis)

Answer 20

G+ cocci in chains
Catalase - (Strep)
a hemolysis
No Capsule (+ quelling reaction)
bile soluble (doesn't grow)
Optochin resistant --> dental caries (mutans), subacute endocarditis (sanguis)