Molecular epidemiology of Mycobacterium tuberculosis isolates from Kerala, India using IS6110-RFLP, spoligotyping and MIRU-VNTRs.

Abstract

Tuberculosis (TB) continues to be a major health problem in India, and there is very little information about the prevalent genotypes of tubercle bacilli that cause TB in India, especially in Kerala. Our aim was to study the different circulating strains of Mycobacterium tuberculosis (MTB) that are prevalent in Kerala, India. We analyzed 168 MTB isolates from as many pulmonary TB patients using IS6110-RFLP, spoligotyping and MIRU-VNTRs. The results of IS6110-RFLP revealed that majority of isolates had null copy (10.89%) or single copy (44.87%) of IS6110 insertion. Low copy (<6) isolates accounted for 71.5% in the isolates studied. Genotypic clade designations were done by comparing with the SITVIT2 database which showed 68 patterns; of which 51 corresponded to different shared types whereas 17 patterns were orphans. Among the 51 SITs recorded, 42 SITs matched a preexisting SIT in the SITVIT2 database, whereas 9 SITs were newly-created. Majority of the isolates (64.28%) belonged to the ancestral East-African Indian (EAI) lineage. MIRU-40 and 31 (HGDI=0.6555 and 0.6524) showed highest discrimination, while MIRU-2 and 20 (HGDI=0.0354 and 0.0696) had the least discriminatory power. ETR-A and B (HGDI 0.7382 and 0.6743) discriminated better as compared to other MIRU loci. The overall HGDI for MIRU-VNTRs at 0.9735 (calculated for 166 isolates) showed a better discriminatory power than spoligotyping used alone. This study of MTB genotypic diversity was useful by providing a first snapshot of circulating MTB genotypic clones in Kerala.