Microbio

Question 1

What two diseases are caused by BK viruses in the immunocompromised?

Answer 1

1. nephropathy (esp. post-transplant)

2. hemorrhagic cystitis

Question 2

What three antibiotics disrupt peptidoglcan?

Answer 2

Vancomycin, cephalosporins, penicillins

Question 3

What is azithromycin?

Answer 3

a macrolide

Question 4

Which bacteria has a capsule made of polyribosylribitol phosphate (PRP)?

Answer 4

H. flu

Question 5

Match the description with the opportunistic fungi:

1. Psuedohyphae, germ tubes at 37 degrees C
2. Septate hyphae that branch at 45 degree angle
3. Wide capsular halos and unequal budding
4. Irregular, broad, nonseptate hyphae branching at wide angles

Answer 5

1. candida albicans
2. aspergillus fumigatus
3. cryptococcus neoformans
4. mucor

Question 6

Where does S. aureus live on the body?

Answer 6

25-30% of people have it in their nose, especially the anterior nares (this applies to both MRSA and non-MRSA)

Question 7

Explain why anemia accompanies a mycoplasma infection:

Answer 7

shares antigens w/ human erythrocytes → cold agglutinating hemolytic anemia

Question 8

What kind of virus typically generates a polyprotein that must be cleaved into final protein products?

Answer 8

Linear, positive-sense, non-segmented ssRNA (eg. Picornaviruses s.a. echo)

Question 9

What is granulomatous disease? What organisms is a patient with CGD susceptible to?

Answer 9

Defect of NADPH oxidase →  ↓ ROS/absent respiratory burst in neutrophils → susceptibility to catalase + organisms (PLACESS)
- Pseudomonas
- Listeria
- Aspergillus
- Candida
- E. coli
- S. aureus
- Serratia
(- Nocardia)

Question 10

3 organisms which have polysaccharide vaccines available?

Answer 10

1. Streptococcus pneumonia
2. Neisseria meningitidis
3. Haemophilus influenza

Question 11

Describe the resistance mechanisms in MRSA

Answer 11

S. aureus that has penicillinase → not susceptible to most penicillins → if additionally has altered binding proteins → resistant to penicillinase-stable penicillins: methicillin, oxacillin, nafcillin

Question 12

What are the two classes of Group D strep and when would each cause a problem?

Answer 12

1. Growth in bile and 6.5% NaCl:
   Enterococci and E. faecium
   - seen in endocarditis after GU procedures
2. Growth in bile but not 6.5% NaCl:
   Nonenterococci, S. bovis
   - seen in endocarditis assoc. w/ colon cancer

Question 13

What conditions are usually present that –> S. viridans endocarditis?

Answer 13

abnormal heart valve already present + dental extraction

Question 14

What does exotoxin A of diptheria do?

Answer 14

transfers a ribose residue from NAD to histidine on EF2 (i.e. ribosylates EF2) → inactivates EF2 → inhibits protein synth → cell death

Question 15

What toxin is released by C. perfringens?

Answer 15

lecithinase (aka phospholipase C aka C. perfringens alpha toxin) → degrades membrane phospholipids → cell membrane destruction → cell death → gas gangrene

Question 16

What test would you use to confirm Staph epidermidis?

Answer 16

1. Catalase (negative → staph; positive → strep)

2. Coagulase (negative → epidermidis or other; positive → aureus)

Question 17

What causes the cardiomyopathy and neuropathy in diptheria?

Answer 17

diptheriae exotoxin in blood stream deactivates EF-2 → inhibits elongation of protein on ribosome → inhibited protein synthesis

Question 18

What gram positive cocci synthesize dextrans from glucose?

Answer 18

Strep. viridans (the extracellular dextran is thought to help it colonize host surfaces)

Question 19

How long does it take for acute rheumatic fever to develop? Sydenham chorea? Rheumatic heart disease?

Answer 19

10d - 6wk: main symptoms include pancarditis and migratory polyarthritis
2-3 mo: Sydenham chorea
10-20 yr: Rheumatic HD

Question 20

How can you distinguish EHEC (0157:H7) from other forms of E. coli in the lab? What is its toxin and mechanism of action?

Answer 20

does not ferment sorbitol (containing MacConkey agar) or produce glucuronidase; produces Shiga-like toxin which inactivates the 60S ribosomal subunit

Question 21

Is the shiga-toxin or invasion by shigella more important in the disease state caused by shigella infection?

Answer 21

invasion - strains that don’t produce the toxin have been found to cause significant disease

Question 22

Does staph aureus cause GI absesses?

Answer 22

Not typically, it causes skin abscesses

Question 23

What does hep D need from Hep B to become infectious?

Answer 23

coating (of HDAg) by HBsAg

Question 24

Infection whose lab finding is ↓ Na+?

Answer 24

legionella

Question 25

Which cephalosporin is useful for pseudomonas?

Answer 25

Cefepime - 4th generation
Ceftazidime - 3rd generation
Note: ceftriaxone does not cover pseudomonas