Development of a multiplex PCR for detection of pathogenic Mycobacterium orygis in cattle tissues harboring tuberculous-like lesions.
Mycobacterium orygis, a recently defined member species of Mycobacterium tubercuolsis complex (MTBC), is emerging as a major threat to zoonotic tuberculosis control, especially in the Asian Subcontinent. The dearth of low-cost diagnostic assay to differentiate M. orygis from other members of the MTBC leads to unavailability of information about the actual burden of this species in human and animal population. In this study, we developed a multiplex PCR for distinguishing M. orygis from other MTBC based on two M. orygis-specific nonsynonymous point mutations in mbtG and fadD23 genes identified by comparative genome analysis. The specificity of the assay shows that a 434 bp IS1081 fragment was amplified from common MTBC species including M. orygis while 240 bp and 181 bp mbtG and fadD23 gene fragments were amplified only from M. orygis. No amplification was observed for nontuberculous Mycobacterium (NTM) and non-Mycobacterial pathogens. The multiplex PCR assay showed a detection limit of 32 pg of M. orygis DNA. Furthermore, a total of 85 tuberculous-like lesions in the different tissues of slaughtered cattle were tested for identification of the M. orygis, and the results showed IS1081, mbtG and fadD23 amplicons in three tissue DNA extracts confirming they contain M. orygis DNA. Also, a single IS1081 amplicon was amplified from one tissue sample signifying presence of DNA of any MTBC species other than M. orygis. An established TaqMan real time PCR assay targeting region of differences (RD) in M. orygis genome was carried out to validate the result of the assay. This showed 100 % accuracy of the in-house developed multiplex PCR.