rpoB Gene Sequencing for Identification of Rapidly Growing Mycobacteria

Background: Rapidly growing mycobacteria (RGM) are increasingly recognized as a cause of human infections. Rapid and reliable identification of RGM at species level should be carried out as a means of effective patient managements. Methods: Twenty clinical samples of RGM isolated from suspected tuberculosis (TB) patients were included. Different phenotypic tests and a hsp65-PCR restriction analysis (PRA) method were used to identify the isolated organisms to species level. Sequence analysis of the rpoB gene was also used for molecular identification of clinical isolates. Results: Phenotypic evaluation of clinical isolates assigned 19 (95%) isolates of RGM to M. fortuitum complex. Using hsp65-PRA, 13 isolates of M. fortuitum complex were identified as M. fortuitum, 4 isolates as M. abscessus and 1 isolates as M. chelonae. However, two isolates had identical hsp65-PRA patterns; one was indistinguishable from M. conceptionense and M. senegalense and another was indistinguishable from M. peregrinum and M. porcinum. By the rpoB gene sequence analysis, all species studied were readily discriminated from each other. Conclusions: rpoB gene sequencing has a high discriminatory power, which easily permits the identification of clinical isolates of RGM to the species level. It unambiguously differentiates between closely related species with restricted biochemical and PRA differences. This procedure is suggested as a first-line identification method for RGM.