Corynebacterium And Listeria (Non-Spore-Forming Rods)

Question 0

How is C.diphtheriae transmitted?

Answer 0

Respiratory droplets from a carrier.

Question 1

What is the morphology of Corynebacterium diphtheriae?

Answer 1

1. Gram(+) - very pleomorphic and club-shaped.
2. Non-spore-forming.
3. Non-motile.

Question 2

What is the metabolism of C.diphtheriae?

Answer 2

1. Facultative anaerobe

2. Catalase-positive

Question 3

What is the virulence of C.diphtheriae?

Answer 3

Pseudomembrane forms in the pharynx, which serves as a base from where it secretes its toxin.

Question 4

Describe briefly the exotoxin of C.diphtheriae.

Answer 4

A subunit: blocks protein synthesis by inactivating EF2.

B subunit: provides entry into cardiac and neural tissue.

Question 5

What is important to keep in mind about the exotoxin of C.diphtheriae?

Answer 5

It is like an anti-human antibiotic, as it inhibits eucaryotic protein synthesis, just as tetracycline inhibits protein synthesis in bacteria.

Question 6

What can C.diphtheriae cause?

Answer 6

1. Mild sore throat with fever initially.
2. Pseudomembrane forms on pharynx.
3. Myocarditis causing A-V block and dysrhythmia.
4. Neural involvement.

Question 7

What is the neurologic problems caused by C.diphtheriae?

Answer 7

1. Peripheral nerve palsies
2. Guillain-Barre-like syndrome
3. Palatal paralysis and cranial neuropathies

Question 8

How do we identify C.diphtheriae?

Answer 8

Gram stain –> Gram(+) pleomorphic rods - “Chinese letters”.
Culture –>
1. Potassium tellurite: get dark black colonies.
2. Loeffler’s medium: after 12 hours of growth, stain with methylene blue. Reddish granules can be seen.

Question 9

How does C.diphtheriae acquire its exotoxin?

Answer 9

From a temperate bacteriophage by lysogenic conversion.

Question 10

What is the Schick test?

Answer 10

Injection of diphtheria exotoxin into the skin, to determine whether a person is susceptible to infection by C.diphtheriae.

Question 11

What is the morphology of L.monocytogenes?

Answer 11

1. Gram(+) rods.
2. Non-spore-forming
3. Motile: tumbling motility is seen when grown at 25C.

Question 12

How is L.monocytogenes transmitted?

Answer 12

1. Ingestion of contaminated raw milk or cheese from infected cows.
2. Vaginally (during birth).
3. Transplacental infection of fetus from bacteremic mother.

Question 13

What is the metabolism of L.monocytogenes?

Answer 13

1. Facultative anaerobe
2. Catalase (+)
3. Beta-hemolytic on blood agar

Question 14

What is the virulence of L.monocytogenes?

Answer 14

1. Motile (via flagella) so has H-antigen.

2. Hemolysin: (like streptolysin O) heat labile and antigenic.

Question 15

What are the toxins of L.monocytogenes?

Answer 15

Listeriolysin O and phospholipases –> allows escape from the phagolysosomes of macrophages.

Question 16

What can L.monocytogenes cause?

Answer 16

1. Neonatal meningitis
2. Meningitis in immunosuppressed patients and the elderly (>50)
3. Septicemia in pregnant women

Question 17

How do we identify L.monocytogenes?

Answer 17

Gram stain –> Gram (+) rods.

Culture –> Can grow at temperatures as low as 0 C. So use cold enrichment technique to isolate from mixed flora.

Question 18

What is important to keep in mind about L.monocytogenes?

Answer 18

1. It is facultative intracellular parasite.

2. Cell-mediated immunity is protective against it.