Mechanisms of antibiotic resistance and strategies to counter them

To identify mechanisms of resistance, our first model system is a nonpathogenic soil bacteria, Streptomyces coelicolor. Streptomyces species account for more than two-thirds of all antibiotics. These bacteria are resistant to both endogenously produced antibiotics and that encountered in the soil environment. Our first study explored the multiple mechanisms of resistance exhibited by Streptomyces coelicolor against ciprofloxacin, a fluoroquinolone drug. Transcriptomic analysis using whole-genome microarrays suggests that in addition to the up-regulation of target genes, the bacteria counters stress due to antibiotics through up-regulation of efflux pumps and high expression of anti-oxidant genes. Further, growth conditions such as the growth media can modulate gene expression and thus increase the minimum inhibitory concentration of the drug by many folds. Similarly, we have shown that efflux plays an important role in resistance to multiple antibiotics in Mycobacterium smegmatis.

We are also working at ways to counter antibiotic resistance using nano-particles in collaboration with the colloids and nanomaterials group in the department. We have recently demonstrated that a combination of coated iron-oxide (Fe3 O4 ) nanoparticles and anti-TB drugs (for example, rifampicin or isoniazid) can lower the minimum inhibitory concentration required to kill M. smegmatis, and thus overcome intrinsic resistance. While the nanoparticles themselves are not toxic, a synergistic effect is observed, when used in combination with the drug. We have demonstrated, for the first time, through accumulation and efflux kinetics, that nanoparticles inhibit active efflux of molecules from M. smegmatis cells. Further, to mimic clinically resistant strains, we demonstrated that the nanoparticles are effective against laboratory-derived highly drug resistant strains.