Corynebacterium diphtheriae, the causative agent of the nasopharyngeal and skin infection known as diphtheria, is a club-shaped, gram-positive, unencapsulated, nonmotile, nonsporulating rod.

• The bacteria often form clusters of parallel arrays (palisades) in culture, referred to as Chinese characters.
• Some strains produce diphtheria toxin, which can cause myocarditis, polyneuropathy, and other systemic toxicities and is associated with the formation of pseudomembranes in the pharynx during respiratory infection.