The role of the Mycobacterium tuberculosis P 55 efflux pump in 1 intrinsic drug resistance , oxidative stress responses and growth 2 3 Santiago

21 Bacterial efflux pumps have been traditionally studied as low-level drug 22 resistance determinants. Recent insights have suggested that efflux systems are 23 often involved with fundamental cellular physiological processes, suggesting that 24 drug extrusion may be a secondary function. In Mycobacterium tuberculosis little 25 is known about the physiological or drug resistance roles of efflux pumps. Using 26 Mycobacterium bovis BCG as a model system, we showed that deletion of the 27 Rv1410c gene encoding the P55 efflux pump made the strain more susceptible 28 to a range of toxic compounds including rifampicin and clofazimine, firstand 29 second-line anti-tuberculosis drugs. Efflux pump inhibitors CCCP and 30 valinomycin inhibited P55-determined drug resistance suggesting active export of 31 the compounds using the transmembrane proton and electrochemical gradients 32 as sources of energy. In addition, the P55 efflux pump mutant was more 33 susceptible to redox compounds, and displayed increased intracellular redox 34 potential, suggesting an essential role in detoxification processes coupled to 35 oxidative balance within the cell. Finally, cells that lack the p55 gene displayed 36 smaller colony size and had a growth defect in liquid culture. This, together with 37 an increased susceptibility to the cell-wall targeting compounds bacitracin and 38 vancomycin, suggested that P55 is needed for proper cell wall assembly and 39 normal growth in vitro. Thus, P55 plays a fundamental role in oxidative stress 40 responses and in vitro cell growth, in addition to contributing to intrinsic antibiotic 41 resistance. Inhibitors of P55 efflux pump could help to improve current TB 42 treatment. 43 on N ovem er 3, 2017 by gest httpaac.asm .rg/ D ow nladed fom