Mycobacterial subpopulations with differential tolerance to anti-TB drugs in in vitro cultures and TB patients' sputum

We had earlier reported that mid-log phase cultures of Mycobacterium tuberculosis (Mtb), Mycobacterium smegmatis (Msm), Mycobacterium xenopi (Mxe) and pulmonary tuberculosis patients' sputum harbor a minor subpopulation (~10-20% of the population) of low buoyant density, short-sized cells (short-sized cells; SCs) and a major subpopulation (~80-90% of the population) of high buoyant density, normal-sized/long (normal-sized cells; NCs). We discovered that the presence of SCs and the NCs in the sputum of pulmonary tuberculosis patients as well (see the Figure given in the next page). Further, Msm NCs were found to be significantly more tolerant to rifampicin and isoniazid, and hydrogen peroxide and acidified nitrite, than the SCs. Similarly, Mtb NCs were more tolerant to H2O2 than the SCs. These observations alluded to the existence of molecular differences between NCs and SCs that might have contributed to their differential susceptibility to the stress agents. The antibiotics-exposed NCs showed very low oxidative status while the equivalent number of antibiotics-exposed SCs showed significantly higher oxidative status.

Presently, we are determining the molecular differences between the SCs and the NCs that are responsible for the generation of differential levels of oxidative stress between them that confer differential antibiotic tolerance.