Diphtheria

University of Oklahoma Study Abroad Microbiology in Arezzo, Italy[1]

File:Cdiphtheriametachromatic.jpg

C. diphtheriae bacteria, in green, showing metachromatic granules on the ends of the cell. From: http://textbookofbacteriology.net/diphtheria.html

Etiology/Bacteriology

Taxonomy

| Domain = Bacteria | Phylum = Actinobacteria | Class = Actinobacteria | Order = Actinomycetales | Family = Corynebacteriaceae | Genus = Corynebacterium | Species = Diphtheriae

Description

C. diphtheriae infections are the causal agent of diphtheria. Four subspecies are recognized: C. d. mitis, C. d. intermedius, C. d. gravis, and C. d. belfanti. C. diphtheria is known to produce diphtheria toxins. C. diphtheria are Gram-positive, rod-shaped (and highly pleomorphic), aerobic, and nonmotile.

Pathogenesis

Virulence factors

Diphtheria toxin

Diphtheria toxin is an exotoxin that prevents protein synthesis through inactivation of eEF2 (eukaryotic elongation factor 2). This is done by ADP-ribosylating the amino acid diphthamide, inhibiting RNA translation.

Clinical features

Diphtheria is characterized by sore throat, fever, and an adherent membrane (called a pseudomembrane) on the tonsils, pharynx, and/or nasal cavity. Diphtheria toxin produced by C. diphtheriae can cause myocarditis, polyneuritis, and other systemic toxic effects. A milder form of diphtheria can be restricted to the skin.