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Phenotypic TB drug resistance, also known as drug tolerance, has been previously attributed to slowed bacterial growth in vivo. The increased activity and expression of efflux systems can lower the intracellular concentration of many antibiotics thus reducing their efficacy. We hypothesized that efflux pump activation and expression could be a risk factor for TB drug tolerance in patients initiated on treatment. Analyses of gene expression levels of six select efflux pumps associated with drug tolerance in Mycobacterium tuberculosis and its correlation with the cell’s ability to efflux ethidium bromide (a common efflux substrate) were assayed. Efflux pump gene expression differed significantly between the strains from treatment failures and treatment successes. Efflux of ethidium bromide by M. tuberculosis isolates revealed that isolates from treatment failures rapidly efflux ethidium bromide more than isolates from treatment successes or the H37Rv control strains. The efflux pumps efpA, jefA (Rv2459c), Rv1258c, p55 and mmpL7 may have a role in TB drug tolerance. Quantifying the expression levels of M. tuberculosis efflux pump genes may be a new method to diagnose clinically persistent tuberculosis. High efflux pump activity and expression at baseline can be associated with tuberculosis treatment failure even when the Mycobacterium tuberculosis does not have established resistance mutations.
Journal of Medical and Biomedical Sciences (2017) 6(1), 8-17
Keywords: drug resistance, Efflux, Mycobacterium tuberculosis, expression, treatment outcome