Corynebacterium ulcerans are small irregular rods with club forms that may stain irregularly and metachromatic granules are seen, similar to C. diphtheriae var. gravis. This organism will grow well on blood agar as yellowish to white in color and a dry to waxy appearance with a small zone of beta-hemolysis around the colony. Also, like C. diphtheriae, isolates are blackish on tellurite agar and can produce the diphtheria toxin and a similar toxin to C. pseudotuberculosis.
C. ulcerans can cause disease that is not easily distinguished from C. diphtheriae including the growth of a pharyngeal membrane. C. ulcerans may also cause less severe nasopharyngeal disease. Strains that lack the diphtheria toxin are associated with pulmonary nodules and necrotic granulomas. This organism has been known to cause acute mastitis in cows and has also been recovered in horses.
