RAPID DIFFERENTIATION OF BOVINE AND HUMAN TUBERCLE-BACILLI BASED ON ACHARACTERISTIC MUTATION IN THE BOVINE PYRAZINAMIDASE GENE

Bovine tuberculosis (TB) caused by Mycobacterium bovis is an important veterinary disease that can also afflict humans. Although M. bovis sh ares an almost identical genome with M. tuberculosis, subtle differenc es in host specificity and several biochemical parameters can be used to distinguish the two closely related species. The current method for distinguishing M. bovis from M. tuberculosis relies on tedious testin g of biochemical parameters, including natural resistance to pyrazinam ide and defective pyrazinamidase (PZase) activity of M. bovis strains. In this study, we report the development of a rapid PCR-single-strand conformation polymorphism (SSCP) assay to differentiate M. bovis from M. tuberculosis strains, based on the detection of a single character istic point mutation in the PZase gene (pncA) of M. bovis. Eighty-seve n of 89 M. bovis strains could be distinguished from M. tuberculosis s trains. Surprisingly, two animal isolates which were initially identif ied as M. bovis were shown to be M. africanum because they had a wild- type pncA sequence with positive PZase. These two M. africanum strains contain multiple (three and six) copies of insertion sequence IS6110, a feature they have in common with M. tuberculosis. The implication o f this finding for the taxonomy of M. tuberculosis complex is discusse d in relation to host preference and epidemiology. The development of a rapid PCR-SSCP test for distinguishing M. bovis from M. tuberculosis will be useful for monitoring the spread of bovine TB to humans in ar eas where bovine TB is endemic and for directing the treatment of huma n TB caused by M. bovis.