Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/1996
Publication Date: N/A
Interpretive Summary: Most cases of tuberculosis in animals are caused by Mycobacterium bovis while most cases of tuberculosis in humans are caused by M. tuberculosis. Mycobacterium bovis also can infect and cause tuberculosis in humans. These two organisms are nearly identical and are difficult to distinguish. When tuberculosis in humans is diagnosed, it is important to identify which horganism is causing the disease so that proper treatment can be given and the possible source of infection be determined. In this study, we developed a rapid test that can be used to distinguish most strains of M. bovis from M. tuberculosis. The test is based on detection of a single base difference in a gene that is present in both organisms. The gene encodes for an enzyme that makes most strains of M. tuberculosis susceptible to a drug called pyrazinamide. The change in the gene makes most strains of M. bovis resistant to the drug. Results of the new test are available in two to three days compared to three to six weeks required for previous tests. The new test can be used to identify the organism involved in a case of tuberculosis so that appropriate drug treatment can be initiated more rapidly than was previously possible. In addition, test results can be used to aid in investigations to determine the source of infection.
Technical Abstract: Mycobacterium bovis is the etiologic agent of most cases of tuberculosis in animals and of some cases of tuberculosis in humans. Although M. bovis and M. tuberculosis have almost identical genomes, subtle differences in host specificity and several biochemical parameters can be used to distinguish them. The current method for distinguishing M. bovis and M. tuberculosis relies on tedious testing of biochemical parameters including susceptibility to pyrazinamide (PZA) and pyrazinamidase (PZase) activity. Most strains of M. bovis are resistant to PZA and lack PZase activity. In this study, we report the development of a rapid PCR-SSCP assay to differentiate M. bovis from M. tuberculosis strains, based on detection of a single characteristic point mutation in the PZase gene (pncA) of M. bovis strains. Seventy-seven of eighty-two M. bovis strains could be distinguished from M. tuberculosis strains. The five M. bovis strains that tcould not be differentiated had multiple copies (2-11 copies) of insertion sequence IS6110, a feature common to M. tuberculosis. The implication of this finding for taxonomy of M. bovis is discussed in relation to host preference and epidemiology. Furthermore, the development of a rapid PCR-SSCP test for distinguishing M. bovis from M. tuberculosis will be useful for monitoring the spread of bovine tuberculosis to humans and for directing treatment of human tuberculosis caused by M. bovis.