Genotype analysis of human Mycobacterium avium isolates from India

Mycobacterium avium has emerged as a major opportunistic pathogen, infecting nearly 50 per cent of HIV/AIDS patients in the western world. There is no report from India regarding the typing profile of M. avium, a potential pathogen, the present study was undertaken to assess the genotypic diversity of Indian M. avium isolates of human origin.

A total of 65 biochemically identified M. avium isolates from sputum samples of patients with chronic pulmonary illness were subjected to IS1245 based restriction fragment length polymorphism (RFLP) and polymerase chain reaction (PCR) typing.

IS1245 insertion sequence based RFLP demonstrated polymorphism in 84.6 per cent isolates, while 15.4 per cent isolates did not hybridize on Southern blot and therefore were RFLP negative. Among the 55 RFLP positive isolates, 8 showed 1-3 bands, 19 had bands ranging between 4-9, and 28 isolates had >10 bands each. Although the isolates could be clubbed on the basis of number of bands, the banding profile was highly polymorphic. Among the 55 isolates typeable by RFLP, four clusters and 40 unique types of polymorphism were observed. Application of IS1245 based PCR typing on the same isolates showed that 87.7 per cent isolates were typeable. Interestingly the 10 isolates that were not typeable by IS1245 RFLP were typeable by IS1245 based PCR typing. Among the 57 PCR typed isolates a cluster of 14 isolates with identical 3-banded pattern was observed. Notably, 5 of the ten IS1245 RFLP negative isolates were within this cluster.

Our results demonstrated that M. avium isolates from India were highly polymorphic with remarkable genetic diversity and heterogeneous RFLP profile. We observed that 47 per cent (n=27) isolates had RFLP profile suggestive of bird and animal origin indicating a strong association with the environment. By applying two typing methods based on IS1245 on the isolates 100 per cent typeability could be achieved.