Variable number tandem repeats diversity of Mycobacterium tuberculosis isolates

Objective To investigate the genetic diversity of variable number tandem repeats (VNTR) of Mycobacterium tuberculosis (M.tb) isolates and their impact factors on transmission. Methods A total of 1 310 patients with smear-positive pulmonary tuberculosis registered during 2013 from 30 counties of drug-resistance monitoring sites in Guangxi were enrolled. The VNTR genotyping technique was used to identify and analyze M. tb genotypes. Count data was analyzed by Chi-square test using descriptive statistical method, unconditioned Logistic regression was used to analyze the characteristics of gene clusters. Results A total of 1 310 strains of M. tb were classified into 964 genotypes, of which 779 strains were classified into a single gene cluster, 531 strains were classified into 185 clusters. Each cluster contained 2 to 40 strains (mean 6.6). Patients aged between 41 and 60 years old had a highest gene cluster proportion (45.5%). Seven hundred and forty-six strains were Beijing genotype, while 564 were non-Beijing genotype, among which 7.4% was original Beijing genotype. The estimated recent infection (cluster rate) was 26.41%. The cluster rate was higher in sensitive strains (24.40%) than in drug-resistant strains (9.55%, χ2=23.621, P=0.000) and multi-drug resistant (MDR) strains (8.97%, χ2=9.675, P=0.002), and that was higher in Beijing genotype (28.69%) than Non-Beijing genotype (23.40%, χ2=4.610, P=0.032). The clusters proportion in sensitive strain (37.43%) was higher than drug-resistant strains (14.09%) and MDR strains (15.38%), and that was higher in Beijing genotype (40.88%) than Non-Beijing genotype (37.77%). Conclusions M. tb genetic polymorphisms display highly diversity in Guangxi region. Sensitive strains and Beijing genotype strains are the main epidemic strains. Key words: Mycobacterium tuberculosis; Variable number tandem repeats; Beijing family; Cluster