[Non-tuberculous mycobacterium strains that show positive test for identification kits of M. tuberculosis complex]

Saito et al. isolated novel mycobacterium strains from the sputum of 12 patients with pulmonary disease. They reported, that the strains were clearly different from Mycobacterium tuberculosis (TB) in cultural, biochemical and immunological properties, despite the high homology (99.1%) of the 16S rRNA gene sequence between the two. Recently, we isolated four strains having similar properties as the above strains among mycobacterial strains that were sent to the Research Institute of Tuberculosis for identification. We examined these isolates using commercial systems for identification of mycobacteria.

Four strains of the unidentified mycobacteria were used in this study.

Tests used in the study included cultural on solid media, biochemical characteristics, DNA sequence analyses of 16S rRNA and rpoB genes, TRC, COBAS AMPLICOR, COBAS TaqMan, MTD, DDH, Accu-Probe, Capilia TB, and a drug susceptibility tests.

After three weeks of culture, smooth and non-photochromogenic colonies were formed. The niacin accumulation test was negative. The homologies of DNA sequence between the new strains and M. tuberculosis for 16S rRNA and rpoB genes were 97.8% and 90.2%, respectively. The tests with TRC and MTD kits were positive, whereas the tests with AMPLICOR, TaqMan, Accu-Probe and Capilia TB kits were negative. The organism was not identified with the DDH system.