Corynebacterium diphteriae

exotoxin encoded by beta-prophage;

potent exotoxin A subunit inhibits protein synthesis via ADP-ribosylation of EF-2 (similar to Pseudomonas)

(B subunit allows binding and penetration of exotoxin A; the toxoid vaccine activates IgG against circulating toxin B and prevent infection)

Myelin is composed of water, various lipids and proteins (such as myelin basic protein). Inhibition of protein synthesis by diphtheria toxin results in impaired myelin formation and peripheral nerve demyelination.

Neurotoxicity presents with flaccid paralysis and sensory disturbances

It can also causes carditoxicity which may presents with cardiac conduction defects; myocarditis and heart failure.

Dx

gram +ve, club shaped, rods with metachromatic granules (blue and red stains with aniline dyes such as methylene blue) with V or Y formation, or often found in clumps (classically said to resemble Chinese characters)

positive Elek test for toxin

Treatment of an acute C. diphtheriae infection requires administration of (in order of importance):

1. Diphtheria antitoxin (passive immunization)

2. Penicillin or erythromycin

3. DPT vaccine (active immunization)

Diphtheria toxid is basically IgG against circulating protein (exotoxin B subunit)

Px

5-10% mortality rate, esp. in younger patients or those with myocarditis.

Cardiomyopathy is the most common cause of death.