Abstract:

Objective To clarify the evolutionary pathway of Beijing genotype of Mycobacterium tuberculosis (MTB) and to elucidate the sublineages of Beijing strains.Methods The Beijing genotype isolates were identified from the 567 MTB isolates, which collected from the patients with pulmonary tuberculosis from Jan. 2014 to Apr. 2016 in Tianjin, China, by analyzing the deletion of regions of difference 207 (RD207). Large sequence polymorphism (LSP) of the Beijing strains were determined based on the presence or absence of RD105, RD181, RD150 and RD142. The insertion sequence 6110 (IS6110) insertion in noise transfer function (NTF) region was also analyzed.Results Of the 567 clinical isolates, 517 (91.2%) were identified as Beijing genotype. Among these Beijing strains, 447 (86.5%) belonged to modern Beijing strains that possessed IS6110 insertion in NTF region, whereas 70 (13.5%) belonged to ancient Beijing strains that had no IS6110 insertion in NTF region. Based on the LSP analy-sis, all 517 Beijing strains were further divided into five sublineages. 22 (4.3%) were RD181(+), and all these RD181(+) strains belonged to ancient Beijing genotype. 41 (7.9%) and 7 (1.4%) were RD181(-)/RD150(+) and RD181(-)/RD150(-) ancient Beijing strain, respectively. Of the 447 modern Beijing strains, there were 404 RD181(-)/RD150(+) and 43 RD181(-)/RD150(-) strains, accounting for 78.1% and 8.3% of the Beijing isolates, respectively.Conclusion Modern Beijing strains are the most predominant in Tianjin, China. Based on the LSP analysis, the Beijing genotype strains have evolved five sublineages and the majority of isolates is the RD181(-)/RD150(+) modern sublineage.

Key words: Mycobacterium tuberculosis, Genotype, Gene deletion, Amplified fragment length polymorphism analysis, Biological evolution