Diphtheria

Diphtheria, a respiratory tract infection, is caused by Corynebacterium diphtheriae, a non-spore-forming, gram-positive bacterium.

It is characterized by sore throat, fever, coughing, nasal discharge, and progressive difficulty breathing in severe cases.

In the environment, some strains of Corynebacterium diphtheriae are infected by a bacteriophage carrying the tox gene. The phage genome integrates into the bacterial chromosome, enabling exotoxin production.

Diphtheria is transmitted through respiratory droplets or by contact with contaminated surfaces.

Upon host entry, the bacteria adhere to epithelial cells in the upper respiratory tract, where they multiply and remain localized, releasing exotoxin.

Diphtheria exotoxin has two subunits, A and B. Subunit B attaches to host cell receptors, triggering uptake of toxin by endocytosis.

The A subunit blocks the elongation factor on ribosomes, halting protein synthesis.

This causes rapid cell death, forming a thick pseudomembrane in the throat that blocks the airways.