The genus Corynebacterium consists of a diverse group of bacteria including animal and plant pathogens, as well as saprophytes. Some corynebacteria are found as part of the normal flora of humans in the skin, upper respiratory tract, and urogenital tract. Corynebacteria (from the Greek words koryne, meaning club, and bacterion, meaning little rod) areGram-positive, aerobic or facultative anaerobic, nonmotile, and catalase-positive rod-shaped bacteria. They have a cell wall with arabinose, galactose, meso-diaminopimelic acid, and short-chain mycolic acids. They do not form spores or branch as do the actinomycetes, but they have the characteristic of forming irregular-shaped, club-shaped, or V-shaped arrange-ments in normal growth. Gram staining shows bacteria in short chains or clumps resembling characteristic Chinese letters.
The genus Corynebacterium consists of 46 species, of which at least 30 species are known to be associated with human diseases.Corynebacterium species that can cause infections in humans are summarized in Table 27-1. Corynebacteriumdiphtheriae, the causal agent of the disease diphtheria is themost widely studied species. Nondiphtherial corynebacteria— collectively referred to as diphtheroids—originally were believed to be mainly contaminants. These diphtheroids have recently been recognized as pathogenic, especially in immunocompro-mised hosts.