26- Corynebacterium

Question 1

What is the mechanism of action of the diptheria toxin?

Answer 1

Has AB toxin, B binds to the receptor and allows the A (active) portion to enter the cell. Once there, it transfers ADP-ribosyl transferase to Elongation Factor 2 (Translation, on ribosome), EF2 can’t work so it can’t do protein synthesis. (inactivation of EF2)


Question 2

Corynebacterium diphtheriae- transmission

Answer 2

Diphtheria may result in asymptomatic colonization in fully immune people, mild respiratory disease in partially immune patients, or a fulminant, sometimes fatal disease in nonimmune patients.
Respiratory droplets or skin contact transmit this organism from person to person.

Question 3

C. diptheriae- clinical features

Answer 3

The onset is sudden with malaise, sorethroat, exudative pharyngitis, and a low-grade fever.
The exudate evolves into a thick pseudomembrane composed of bacteria, lymphocytes, plasma cells, fibrin, and dead cells that can cover the tonsils, uvula, and palate and can extend up into the nasopharynx or down into the larynx firmly adheres to the underlying tissue making the tissue bleed (unique to diphtheria).
One week course of the disease, the membrane dislodges and expectorates.
Systemic complications in patient with severe disease primarily involve the heart and nervous system.
Neurotoxicity is proportional to severity of disease usually developing locally in soft palate and pharynx in the beginning and later involving oculomotor and ciliary paralysis with progression to peripheral neuritis.

Question 4

C. diptheriae- media

Answer 4

Colistin-nalidixic agar (CNA) is the most commonly used in the clinical lab.

Question 5

Which test can you use to detect the exotoxin production?

Answer 5

This is done through the usage of in vitro immunodeiffusion assay (Elek test), a tissue culture neutralization assay using specific antitoxin. Detection of exotoxin can be done through PCR-based nucleic acid amplification method which can detect the tox gene in clinical isolates and directly in clinical specimens. Although the test is rapid and specific, strains with the tox gene not expressed, most likely due to the diphtheria toxin repressor, can give a positive signal.