Mycobacteria found in soil and water have been isolated from tissues of animals. Mycobacterium fortuitum, a rapidly growing organism highly resistant to penicillin G, streptomycin, ampicillin, sulfamethoxazole, and chloramphenicol, has been associated with mastitis in cows, pulmonary infections in dogs, lymph node lesions in pigs and certain exotic animals, and cutaneous lesions in cats and dogs. Drug susceptibility tests indicate the organism is inhibited by capreomycin and by ethionamide. M chelonae, another rapidly growing Mycobacterium similar to M fortuitum in biochemical reactions, has been isolated from contaminated wounds and injection abscesses. These organisms must be distinguished from M phlei, M smegmatis, and M vaccae, which are rarely if ever pathogenic.
Fish and other cold-blooded animals may be infected with M marinum, certain serovars of M avium complex, or M intracellulare, which have been recognized as human pathogens. A photochromogenic organism, M kansasii, has been isolated from pigs, cattle, and nonhuman primates. These organisms can be differentiated by biochemical and seroagglutination tests.
M avium paratuberculosis, the cause of Johne’s disease, has been isolated from domestic and wild ruminants (also see Paratuberculosis in Ruminants). It is a slowly progressive diarrheal disease resulting in weight loss and emaciation. Lesions are most often seen in the ileocecal valve and associated lymph nodes. Diagnosis should be based on an organism-based test. No treatment is available.
M scrofulaceum, a scotochromogen, has been isolated from lymph node lesions in pigs, cattle, and certain nonhuman primates. M xenopi, a slowly growing scotochromogen, has been isolated from pigs, seafowl, and amphibians. These organisms should be differentiated from M gordonae and M flavescens and from other slowly growing scotochromogenic mycobacteria that are common contaminants of water.
Numerous nonpathogenic, nonphotochromogenic mycobacteria that closely resemble potential pathogens can be isolated from water and soil; M nonchromogenicum, M gastri, M triviale, and M terrae, which closely resemble strains of the M avium complex, may be differentiated by in vitro laboratory examinations, including molecular techniques.
Although opportunistic mycobacteria usually do not produce progressive disease, they may be important in inducing transient tuberculin skin sensitivity in animals. The application of comparative skin tests, using biologically balanced purified protein derivative tuberculins prepared from culture filtrates of M bovis and M avium, provides useful information on the possible cause of tuberculin skin sensitivity. Tuberculins prepared for veterinary use, containing ~5,000 tuberculin units per test dose, should be used for skin tests in free-ranging, captive, wild, and exotic animals.
M lepraemurium, a nonphotochromogenic, slow-growing, acid-fast bacillus, causes a disease in cats and rats similar in some respects to leprosy in people. It can be grown on media containing cytochrome C and α-ketoglutarate. M leprae, the cause of leprosy in people, has been found in spontaneously occurring disease in armadillos. This organism has not been grown on artificial culture medium; however, M leprae DNA can be identified by molecular techniques.