[Study on the population-genetics of Mycobacterium tuberculosis from Sichuan Basin in China]

To explore the population-genetics characteristics of Mycobacterium tuberculosis (MTB) prevailing at the Sichuan basin of China.

A total of 413 MTB strains collected from Sichuan basin were genotyped by large sequence polymorphism (LSP) and 15 loci variable number tandem repeat (VNTR). Difference between the distribution of lineage population was analyzed by χ(2)-test and the discriminatory ability of each VNTR locus was evaluated under the Hunter-Gaston Discriminatory Index (HGI). Both phylogeny on population level and genetic structure were demonstrated through N-J tree and the Minimal Spanning Tree (MST). Genetic differentiation of different lineage strains was analyzed by Analysis of Molecular Variance (AMOVA). Time of the Most Recent Common Ancestor (TMRCA) was calculated based on the Bayesian model.

Four hundred and thirteen MTBs were divided into two major lineages, in which the Beijing lineage accounted for 56.2% (232/413) and the Euro-American lineage for 43.8% (181/413). There was no significant difference of population distribution between the two lineages (P > 0.05). The N-J tree of Beijing lineage MTB presented distinctly "star-like" and 72.4% strains were grouped to one clonal complex in MST. The Euro-American lineages MTB presented "branch-like" in N-J tree and were grouped into multiple clonal complexes in MST. There was significant genetic differentiation in Beijing lineage MTBs between Chongqing and Sichuan (FST = 0.018 91, P < 0.05), but not in the Euro-American lineage MTB (FST = 0.005 19, P > 0.05). TMRCA of the largest clonal complex in Euro-American lineage MTB appeared to be 723 (95% CI: 517-946) years.

Both Beijing lineage and Euro-American lineage MTBs were competitively prevalent in the Sichuan basin. There was some difference noticed between the two lineages referring to genetic differentiation. The invasion of Euro-American lineages MTB to the basin area might be associated with a war occurred in this area about 720 years ago.