A species of aerobic or facultatively anaerobic, Gram-positive, coryneform, pleomorphic bacilli assigned to the phylum Actinobacteria. This species is nonmotile, non-spore forming, catalase positive, non-lipophilic, produces diphtheria toxin which inhibits elongation factor 2 (EF-2) thus preventing protein synthesis, forms polar granules, and is cultured in Loeffler's serum in a low iron environment or on tellurite agar. C diphtheriae is commensal in the skin and nasopharynx, but toxin producing strains are pathogenic to humans causing diphtheria; both an antitoxin and vaccine are available for disease prevention.

A species of gram-positive, asporogenous bacteria in which three cultural types are recognized. These types (gravis, intermedius, and mitis) were originally given in accordance with the clinical severity of the cases from which the different strains were most frequently isolated. This species is the causative agent of DIPHTHERIA.

Any bacterial organism that can be assigned to the species Corynebacterium diphtheriae.

Species of gram positive, asporogenous bacteria in which three cultural types are recognized; these types (gravis, intermedius, and mitis) were originally given in accordance with the clinical severity of the cases from which the different strains were most frequently isolated; the causative agent of diphtheria.