Bacterial Pathogens

Question 1

Describe Staph aureus

Answer 1

Gram + cocci; Clusters, catalase and coagulase positive, facultative anaerobe

Question 2

Virulence factors of staph aureus

Answer 2

Capsule: anti-phagocytic, anti-chemotactic

 Slime layer: facilitates adherence/biofilms, leukocyte chemoattractant

 Protein A: binds F c of IgG to prevent opsonization, leukocyte chemoattractant

 Peptidoglycan: activates alternate complement, leukocyte chemoattractant

 Teichoic acid: binds fibronectin, activates complement

Question 3

Toxins produced by S. aureus

Answer 3

α-hemolysin: pore-forming

 β-toxin: sphingomyelinase C hydrolyzes membrane phospholipids

 δ-toxin: dermonecrotic toxin, acts as surfactant

 P-V leucocidin/g-toxin: pore-forming, phage-encoded, necrotizing lung infections

Question 4

Describe streptococci

Answer 4

Gram +, catalase -, LANCET shaped, strictly fermentative, alpha hemolytic

Question 5

What are the clues of Streptococci?

Answer 5

Splenectomy

Question 6

How is a streptococci infection diagnosed?

Answer 6

urine assay for C polysaccharide, gram stain (purple), quelling test for capsular Ag Abs, α-hemolytic

Question 7

Which organism is a gram positive rod?

Answer 7

Corynebacterium diptheriae

Question 8

What are the virulence factors of pseudomonas?

Answer 8

1. Exotoxin A

2. Exoenzyme S (acts on G proteins via type 3 secretion system)

Question 9

How is a pseudomonas infection diagnosed?

Answer 9

1. Fruity odor
2. Coagulative necrosis
3. Blue-green pigment on culture
4. Thick green secretions w/ thin G- rods

Question 10

How is legionella diagnosed?

Answer 10

Clues: immunosuppressed (non-AIDS; chemotherapy or on steroids), culture on selective media, artificial water supply

 Dx: urine Ag or urine culture

Legionnaire’s disease or Pontiac fever

Question 11

Describe E.coli

Answer 11

(glucose fermenters, oxidase (-), can respire but do NOT make cytochrome C oxidase)

Facultative anaerobe

Question 12

Discuss Klebsiella pneumoniae

Answer 12

1. Normal GI flora
2. Most common cause of G- pneumonia
3. large, capsulated G- bacilli, unilateral infiltrate, currant jelly-like sputum,
4. Common in alcoholics

Question 13

Discuss H. influenzae

Answer 13

1. grow on chocolate agar (need hematin & NAD), NO growth on MacConkey agar
2. No exotoxins
3. Most common cause of COPD exacerbation
4. Can cause epiglottidis

Question 14

How would pneumonia via Mycoplasma pneumoniae present?

Answer 14

non-productive cough, normal WBCs, no bacteria on gram stain, NO cell wall

Question 15

Discuss a Tuberculosis infection

Answer 15

1. Proliferates inside the macrophage
2. Effects lower segments of UL and upper segments of LL
3. Gohn lesions and complexes: focal caesous necrosis
4. Likes apices of lungs