Corynebacterium diphtheriae

Corynebacterium diphtheriae is a Gram-positive pathogenic bacterium that causes diphtheria. It is also known as the Klebs–Löffler bacillus because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834–1913) and Friedrich Löffler (1852–1915). While nontoxigenic C. diphtheriae may rarely produce systemic disease by invading tissues, virulence is enhanced when the bacteria are infected by a bacteriophage carrying a gene which gives rise to a toxin. This toxin causes the disease.

Diphtheria is caused by the adhesion and infiltration of the bacteria into the mucosal layers of the body, primarily affecting the respiratory tract and causing the subsequent release of an exotoxin. The toxin has a localized effect on skin lesions, as well as a metastatic, proteolytic effects on other organ systems in severe infections. Originally a major cause of childhood mortality, respiratory diphtheria has become rare in the United States by the vigorous administration of diphtheria vaccines starting in 1914.

The incidence of diphtheria has decreased since the development of a toxoid vaccine in 1923. Although diphtheria outbreaks continue to occur, this is often in developing countries where the majority of the population is not vaccinated. Cutaneous diphtheria, skin lesions infected by toxigenic C. diphtheriae, are prevalent in tropical climates and may contribute to diphtheria outbreaks.