The 500-base-pair fragment of the putative gene RvD1-Rv2031c is also present in the genome of Mycobacterium tuberculosis.

Background: It has been proposed that differentiation between M. bovis and M. tuberculosis is possible by using a PCR assay for the 500bp fragment present only in the M. bovis genome.

Materials And Methods: Forty clinical samples and 16 clinical isolates from the Department of Microbiology, as well as 4 clinical isolates obtained from another laboratory, were tested for the purpose of this study. As controls we tested 2 M. bovis (M. bovis BCG Pasteur TMC1011 and M. bovis BCG Copenhagen), 1 H37Rv M. tuberculosis strain, 2 M. avium (ATCC15765 and ATCC1975, respectively) and 1 M. paratuberculosis (ATCC19698) strains.

Results: None of the mtp40- negative clinical isolates amplified the 500bp fragment, whereas 4 out of 17 mtp40-positive clinical isolates scored positive for the 500bp fragment. All clinical isolates scored positive for IS6110, mtp40, the pncA and oxyR PCR's. All but one of the clinical isolates amplified the 500bp fragment. Sequence analysis of the pncA and oxyR PCR products revealed the presence of nucleotide C at position 169 and G at position 285 respectively, suggesting M. tuberculosis as the causative agent.

Conclusion: Our data suggest that the 500bp PCR fragment is present not only in M. bovis but also in M. tuberculosis.