Drug resistance among different genotypes of Mycobacterium tuberculosis isolated from patients from Tiruvallur, South India.

India continues to have the highest tuberculosis incidence, accounting for one fifth of the global incidence and 2/3rd of the cases in south East Asia. The TB burden is also augmented by multi drug resistance and HIV. Although inadequate and inappropriate treatment is responsible for drug resistance, pathogen's genetic background may also play a role. The aim of this study was to understand the distribution of different genotypes of Mycobacterium tuberculosis in the Tiruvallur, rural area in South India and its association with drug resistance. A total of 1649 M. tuberculosis isolates were genotyped by IS6110 RFLP and spoligotyping. Drug susceptibility testing was done by minimum inhibitory concentration method (MIC) on all the samples. As reported earlier, the isolates with single and low copy IS6110 accounted for 66% among the 1649 M. tuberculosis strains genotyped. The majority (84%) of our strains belonged to the East African Indian (EAI) lineage, 28.6% to EAI3 sublineage and 19.5% to EAI5 sublineage. Rifampicin and streptomycin mono resistance followed by MDR (Multi-Drug Resistance, resistance to at least rifampicin and isoniazid) [(OR 0.2 [95%CI 0.11-0.46], P < 0.05)] were more common between Central Asian (CAS), T and Beijing compared to EAI lineage. In spite of the predominance of EAI lineage, its association with drug resistance was lower compared to the other genotypes prevalent in Tiruvallur, South India.