Comparative analysis of Mycobacterium tuberculosis Beijing strains isolated in three remote areas of Japan

•Quantitative differences of Mycobacterium tuberculosis Beijing strains were analyzed.•Qualitative differences of these strains were also compared by population genetics.•No significant differences were observed in strains isolated in three remote areas of Japan.•M. tuberculosis Beijing subgroups diverged prior to introduction into Japan.

A quantitative and qualitative comparison was carried out of Mycobacterium tuberculosis Beijing strains isolated in three remote areas of Japan. A total of 452 strains from Chiba Prefecture, 75 from Yamagata Prefecture, and 315 from Kobe City were analyzed for 24 loci by variable number of tandem repeats typing (24Beijing-VNTR). All strains were classified in six Beijing subgroups (BSUB), B1 to B5 and T, based on a minimum spanning tree reconstructed using data of a standard set of 15 VNTR loci. No significant difference was found in the distribution of strains in the BSUB in the three areas, with one exception due to a B5 outbreak in Yamagata, indicating no significant quantitative difference in the BSUB in the three areas (P < 0.01, Chi-square test). In addition, when strains in each BSUB isolated in the three areas were mixed and standardized index of association (IAs) and variance (ΦPT) values were calculated, no significant qualitative difference in the BSUB in the three areas was found. These results suggested that the BSUB diverged prior to the introduction of M. tuberculosis Beijing strains into Japan. Differences in the distribution of strains in each BSUB between Japan and continental Asian countries suggested there had been genetic drift in the continental Asian countries in which B4 had been dominant.