Corynebacterium diphtheriae is a Gram-positive, rod-shaped bacterium in the genus Corynebacterium that produces diphtheria toxin and causes diphtheria.
Explanation
Corynebacterium diphtheriae is a facultative anaerobe belonging to the Actinobacteria phylum. It exhibits pleomorphic, club-shaped cells that often form palisades or “Chinese letter” arrangements. The bacterium was first described by Friedrich Löffler in 1884 when he isolated it from diphtheritic membranes and established it as the causative agent of diphtheria. Pathogenicity is linked to a prophage-encoded exotoxin that inhibits protein synthesis by ADP‑ribosylating elongation factor 2, leading to cell death and formation of necrotic pseudomembranes in the oropharynx. There are four biovars—gravis, mitis, intermedius and belfanti—that differ in colony morphology and virulence but are all considered C. diphtheriae.
The organism spreads via respiratory droplets or contact with skin lesions and primarily colonizes the nasopharynx. Toxigenic strains cause classic respiratory diphtheria characterized by fever, sore throat and a thick pseudomembrane that can obstruct the airway, while non‑toxigenic strains may cause systemic infections such as endocarditis and septicemia. Effective diphtheria toxoid vaccination has markedly reduced incidence, yet outbreaks still occur in under‑immunized populations, making C. diphtheriae a re‑emerging pathogen. Diagnosis relies on culture, toxin detection and PCR, and treatment includes administration of antitoxin and antibiotics such as erythromycin or penicillin to eradicate carriage.
Notable Facts and Examples
- Friedrich Löffler’s isolation of C. diphtheriae in 1884 proved the bacterium causes diphtheria.
- Lysogenic conversion by a β‑phage carrying the tox gene converts non‑toxic strains into toxin producers.
- The four biovars gravis, mitis, intermedius and belfanti differ in colony morphology, metabolic traits and virulence.
- Routine vaccination with diphtheria toxoid provides long‑term protection; booster doses are needed to maintain immunity.
- Treatment of diphtheria involves immediate administration of diphtheria antitoxin plus antibiotics to prevent transmission.
Corynebacterium diphtheriae remains relevant despite vaccination programs because under‑immunized communities permit resurgence. Understanding the bacterium’s toxin, biovars and transmission dynamics supports clinical management and public health control measures.
Related Terms: Diphtheria, Corynebacterium, Toxoid Vaccine, Lysogenic Conversion, Exotoxin