Development and evaluation of a multiplex PCR for rapid detection and differentiation of Mycobacterium tuberculosis complex members from non-tuberculous mycobacteria

Abstract

Most mycobacterial infections are still caused by Mycobacterium tuberculosis complex (MTC) strains; however, infections by non-tuberculous mycobacteria (NTM) are increasing, particularly among immunocompromised patients. Conventional species-specific identification and proper patient management are delayed due to the slow-growing nature of mycobacteria. We have developed a multiplex PCR (mPCR) targeting the oxyR-ahpC intergenic region and rpoB gene for direct detection and differentiation of clinical isolates as MTC or NTM in primary culture. Two amplicons of 473 bp and 235 bp from MTC members and a single amplicon of 136 bp from NTM are expected. The mPCR was developed using several mycobacterial species and was evaluated by testing extracted DNA from liquid cultures, flagged as positive for bacterial growth, of 100 consecutive mycobacterial isolates. The results were validated by DNA sequencing of the species-specific 16S-23S internal transcribed spacer (ITS) region. The mPCR with template DNA from reference Mycobacterium spp. yielded the expected amplicons. When 100 consecutive clinical isolates of Mycobacterium spp. were tested, 92 strains yielded MTC member-specific amplicons, and DNA sequences from 10 randomly selected isolates matched completely with the ITS sequence from M. tuberculosis. Eight isolates were identified as NTM, and DNA sequencing of the ITS region confirmed the NTM status of each of these isolates. The mPCR developed in this study allowed rapid detection and differentiation of primary cultures as MTC or NTM, thus helping in timely institution of specific therapy.