Comparative growth pattern of multi drug resistance versus susceptible isolates of Mycobacterium tuberculosis in mice lungs.

BACKGROUND & OBJECTIVE Rise in prevalence of multi-drug resistance (MDR) in tubercle bacilli is a serious cause of concern. As mutations with two house keeping genes rpoB and katG are associated with resistance to two important anti-tubercular drugs rifampicin and isoniazid respectively, there is a need to understand the growth kinetics of organisms with such mutated genes in experimental animals. This study was undertaken to study the growth kinetics of susceptible as well multi-drug resistance Mycobacterium tuberculosis isolates in mice. METHODS Two MDR (having mutations in rpoB and catG) and two drug susceptible isolates of M. tuberculosis along with H37Rv were grown in mice after aerogenic infection. RESULTS The MDR isolates grew slowly up to 3 wk though the growth was significantly different from sensitive strains. However, after 3 wk, the growth in sensitive as well MDR strains was similar, suggesting that even the mutations in the MDR strains did not have any impact on the growth kinetics. INTERPRETATION & CONCLUSION The effect of mutations in other parts of these genes need to be studied. Retention of property of MDR strains to establish infection after aerogenic infection has epidemiological significance in terms of the transmission of MDR tuberculosis.