Corynebacterium And Listeria (Non-Spore-Forming Rods) Flashcards Preview

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Flashcards in Corynebacterium And Listeria (Non-Spore-Forming Rods) Deck (19):

What is the morphology of Corynebacterium diphtheriae?

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


How is C.diphtheriae transmitted?

Respiratory droplets from a carrier.


What is the metabolism of C.diphtheriae?

1. Facultative anaerobe
2. Catalase-positive


What is the virulence of C.diphtheriae?

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


Describe briefly the exotoxin of C.diphtheriae.

A subunit: blocks protein synthesis by inactivating EF2.
B subunit: provides entry into cardiac and neural tissue.


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

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


What can C.diphtheriae cause?

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


What is the neurologic problems caused by C.diphtheriae?

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


How do we identify C.diphtheriae?

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.


How does C.diphtheriae acquire its exotoxin?

From a temperate bacteriophage by lysogenic conversion.


What is the Schick test?

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


What is the morphology of L.monocytogenes?

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


How is L.monocytogenes transmitted?

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


What is the metabolism of L.monocytogenes?

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


What is the virulence of L.monocytogenes?

1. Motile (via flagella) so has H-antigen.
2. Hemolysin: (like streptolysin O) heat labile and antigenic.


What are the toxins of L.monocytogenes?

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


What can L.monocytogenes cause?

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


How do we identify L.monocytogenes?

Gram stain --> Gram (+) rods.
Culture --> Can grow at temperatures as low as 0 C. So use cold enrichment technique to isolate from mixed flora.


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

1. It is facultative intracellular parasite.
2. Cell-mediated immunity is protective against it.