yellowish-white in Loeffler's medium. In TSA, they can form grey colonies with black centers and dentated borders that either resemble flowers (C. gravis), continuous borders (C. mitis), or a mix between the two forms (C. intermedium). Habitat Corynebacterium species occur commonly in nature in soil, water, plants, and food products. The nondiphtheiroid Corynebacterium species can even be found in the mucosa and normal skin flora of humans and animals. Unusual habitats, such as the preen gland of birds, have been recently reported for Corynebacterium uropygiale. Some species are known for their pathogenic effects in humans and other animals. Perhaps the most notable one is C. diphtheriae, which acquires the capacity to produce diphtheria toxin only after interacting with a bacteriophage. Other pathogenic species in humans include: C. amycolatum, C. striatum, C. jeikeium, C. urealyticum, and C. xerosis; all of these are important as pathogens in immunosuppressed patients. Pathogenic species in other animals include C. bovis and C. renale. This genus has been found to be part of the human salivary microbiome. Role in disease The most notable human infection is diphtheria, caused by C. diphtheriae. It is an acute, contagious infection characterized by pseudomembranes of dead epithelial cells, white blood cells, red blood cells, and fibrin that form around the tonsils and back of the throat. In developed countries, it is an uncommon illness that tends to occur in unvaccinated individuals, especially school-aged children, elderly, neutropenic or immunocompromised patients, and those with prosthetic devices such as prosthetic heart valves, shunts, or catheters. It is more common in developing countries It can occasionally infect wounds, the vulva, the conjunctiva, and the middle ear. It can be spread within a hospital. The virulent and toxigenic strains produce an exotoxin formed by two polypeptide chains, which is itself produced when a bacterium is transformed by a gene from the β prophage. Several species cause disease in animals, most notably C. pseudotuberculosis, which causes the disease caseous lymphadenitis, and some are also pathogenic in humans. Some attack healthy hosts, while others tend to attack the immunocompromised. Effects of infection include granulomatous lymphadenopathy, pneumonitis, pharyngitis, skin infections, and endocarditis. Corynebacterial endocarditis is seen most frequently in patients with intravascular devices. Several species of Corynebacterium can cause trichomycosis axillaris. C. striatum may cause axillary odor. C. minutissimum causes erythrasma. Industrial uses Nonpathogenic species of Corynebacterium are used for important industrial applications, such as the production of