Although M. bovis and M. africanum can cause human tuberculosis, the probability that a M. tuberculosis complex isolated is a species other than M. tuberculosis is extremely small. M. microti is pathogenic in certain animals, but not in humans. This complex consists of two distinct species, M. avium and M. intracellulare , and includes 28 different serovars. Drug Susceptibility Testing Drug susceptibility testing is performed only on M. tuberculosis complex organisms. Each new isolate is automatically tested at the time of identification, and the test is repeated every three months if the organisms is still being isolated.
Results are usually available within seven to ten days after identification of the organisms.
If any of the drugs tests as resistant, the test is repeated, and streptomycin is added to the panel. If the results of the two tests are the same, the isolate is reported as resistant. Currently isolates which are resistant to one or more drugs are sent to the Centers for Disease Control and Prevention for testing with additional drugs. This usually requires approximately four to six weeks. Reports on isolates showing drug resistance for the first time are called to submitters as soon as results are available.