Utility of mycobacterial interspersed repetitive unit typing for differentiating multidrug-resistant Mycobacterium tuberculosis isolates of the Beijing family

Mycobacterial interspersed repetitive unit (MIRU) typing has been found to allow rapid, reliable, high-throughput genotyping of Mycobacterium tuberculosis and may represent a feasible approach to study global M. tuberculosis molecular epidemiology. To evaluate the use of MIRU typing in discriminating drug-resistant M. tuberculosis strains of the Beijing genotype family, 102 multidrug-resistant (MDR) clinical isolates and 253 randomly selected non-MDR isolates collected from 2000 to 2003 in Hong Kong were subjected to 12-locus MIRU typing, spoligotyping, and IS6110 restriction fragment length polymorphism (RFLP) typing. Spoligo-typing showed that 243 (68.5%) of 355 isolates belonged to Beijing family genotype. MIRU typing showed lower discrimination in differentiating between the Beijing family strains (Hunter-Gaston discriminative index [HGI] of 0.8827) compared with the IS6110 RFLP method (HGI = 0.9979). For non-Beijing strains, MIRU typing provided discrimination (HGI = 0.9929) comparable to that of the RFLP method (HGI = 0.9961). There was no remarkable difference in discrimination power between the two methods in differentiating both within and between MDR and non-MDR strains of M. tuberculosis. Dendrograms constructed with the MIRU typing data showed a clear segregation between the Beijing and non-Beijing genotype. Addition of RFLP to MIRU typing offered a higher discrimination ability (92.6%) than did addition of MIRU typing to RFLP (40.0%). This supported the potential use of this method to analyze the global genetic diversity of MDR M. tuberculosis strains that may be at different levels of evolutionary divergence.