High-resolution MIRU-VNTRs typing reveals the unique nature of Mycobacterium tuberculosis Beijing genotype in Okinawa, Japan.

Mycobacterium tuberculosis Beijing lineage is highly prevalent in Japan. The aim of the present study was to describe the population structure of the Beijing lineage in this country based on 12-, 15-, and 21-loci MIRU-VNTR genotyping schemes. The MIRU-VNTR patterns of Beijing strains from Okinawa, Ryukyu Islands were compared to those recently published from the Osaka-Kobe megalopolis of the main island of Japan, Honshu (Wada et al., 2009). We also compared proportions of "modern/typical" vs. "ancient/atypical" Beijing strains as defined by structure of the NTF locus. Contrarily to the 12-loci Minimum Spanning Tree (MST), the 15- and 21-loci trees allowed the distinction of two groups of strains in Okinawa. A 12-loci MIRU-VNTR pattern (223325173533) corresponding to MIRU international type MIT17 was identified as the most prevalent Beijing genotype in Japan. In the SITVIT2 database, this pattern was found to be disseminated worldwide and corresponded to the most widely distributed Beijing profile in East Asia and former USSR countries. A comparison of 15- and 21-loci MIRU-VNTR patterns showed that two loci (QUB-4156 and Mtub21) were most polymorphic in our study, and could be potential candidates to distinguish between NTF locus based subclassification of Beijing strains. High-resolution VNTR typing using 15- and 21-loci underlined an evolutionarily distinct "ancient/atypical" subpopulation of the Beijing genotype in Okinawa as well as a subgroup of strains closely related to "modern/typical" Beijing strains observed in Osaka/Kobe.