Which bacterium causes diphtheria, a disease marked by a thick throat membrane?

Corynebacterium diphtheriae is the bacterium that causes diphtheria, a disease marked by a thick membrane in the throat.

This Gram-positive, rod-shaped bacterium causes illness mainly when it carries a gene for diphtheria toxin. The toxin can damage tissues at the infection site and may enter the bloodstream, where it can affect organs such as the heart and nervous system.

A characteristic gray or white pseudomembrane may form across the throat, tonsils, or nose. Removing it can cause bleeding, so suspected diphtheria requires urgent medical care. The infection can spread through respiratory droplets and close contact.

Diphtheria vaccination uses a purified, inactivated form of the toxin called a toxoid. Widespread immunization has greatly reduced disease in many countries, although outbreaks can still occur where vaccination coverage is low. Corynebacterium diphtheriae is different from Bordetella pertussis, the bacterium responsible for whooping cough.