Species identification of Mycobacterium avium complex isolates by a variety of molecular techniques

Organisms in the Mycobacterium avium complex (MAC; M. avium, M. intracellul are, and "nonspecific or X" MAC) are emerging pathogens among individual or ganisms of which significant genetic variability is displayed, The objectiv e of the present study was to evaluate various molecular methods for the ra pid and definitive identification of MAC species. Isolates were obtained fr om both human immunodeficiency virus (HIV)-positive patients and HIV-negati ve patients with and without known predisposiug conditions. The isolates we re initially hybridized with nucleic acid probes complementary to the rRNA of the respective mycobacterial species (AccuProbe Culture Confirmation kit s for M. avium, M. intracellulare, and MAC species; Gen-Probe). Isolates we re also examined by PCR and in some cases by Southern blot hybridization fo r the insertion element IS1245. Two other techniques included a PCR assay t hat amplifies the mig gene, a putative virulence factor for MAC, and hsp65 gene amplification and sequencing, This study led to the following observat ions. Eighty-five percent of the isolates from HIV-positive patients were M . avium and 86% of the isolates from HIV-negative patients were M. intracel lulare. Fifteen of the M, avium isolates did not contain IS1245 and 7% of t he M. intracellulare isolates were found to carry IS1245. All of the M. avi um strains were mig positive, and all of the M. intracellulare strains were mig negative.