EfpA is required for re-growth of Mycobacterium tuberculosis following isoniazid exposure

Efflux of antibiotics is a survival strategy in bacteria. Mycobacterium tuberculosis has approximately sixty efflux pumps, but little is known about the role of each pump, or which moieties that they efflux. The putative efflux pump, EfpA, is a member of the major facilitator superfamily that has been shown to be essential by saturation transposon mutagenesis studies. It has been implicated in the efflux of the frontline drug isoniazid (INH) in M. tuberculosis. This is supported by evidence from transcriptional profiling that efpA is induced in response to INH exposure. However, its role in physiology and adaptation of M. tuberculosis to antibiotics, have yet to be determined. Here, we describe the repression of efpA using CRISPR interference and the direct effect of this on the ability of M. tuberculosis to survive exposure to INH over a 45-day time-course. We determined that wild-type levels of efpA were required for the recovery of M. tuberculosis cultures following INH exposure and that, after 45-days of INH exposure, no viable colonies were recoverable from efpA-repressed M. tuberculosis cultures. We postulate that EfpA is required for the recovery of M. tuberculosis following INH-exposure and that EfpA may have a role in the development of resistance, during treatment and contributes to relapse in patients.