Molecular genotyping of Mycobacterium tuberculosis in Xi'an, China, using MIRU-VNTR typing

The molecular genotyping of Mycobacterium tuberculosis is expected to lead to a better understanding of M. tuberculosis transmission in Xi'an, one of the largest cities in Western China.

To characterize the population of M. tuberculosis strains circulating in Xi'an and to evaluate the feasibility of the mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR) typing method.

A total of 195 M. tuberculosis clinical isolates from Xi'an were genotyped using spoligotyping and MIRU-VNTR.

Thirty-two different genotypes were identified by spoligotyping, with the Beijing family identified as the largest lineage (84.6%), followed by the T1 (3.08%), T2 (1.54%), H3 (1.03%) and U (1.03%) families. The Hunter-Gaston discriminatory index (HGDI) of spoligotyping is low (HGDI = 0.392). In contrast, 15-locus MIRU-VNTR shows a higher discriminatory power (HGDI = 0.998) than 12-locus MIRU-VNTR (HGDI = 0.948). By replacing the ETR C locus with the MIRU39 locus, the discriminatory power of 15-locus MIRU-VNTR is increased to 0.999.

The Beijing family accounts for the vast majority of M. tuberculosis isolates in Xi'an, China. The modified 15-locus MIRU-VNTR showed high HGDI and can be used as a first-line genotyping method in combination with spoligotyping in routine epidemiological investigations in Xi'an, China.