The Contribution of Efflux Pumps in Complex Resistance to Clarithromycin.

The basis of drug resistance in is still poorly understood. Nevertheless, as seen in other microorganisms, the efflux of antimicrobials may also play a role in drug resistance. Here, we investigated the role of efflux pumps in clarithromycin resistance using nine clinical isolates of complex belonging to the T28 (41) sequevar responsible for the inducible resistance to clarithromycin. The strains were characterized by drug susceptibility testing in the presence/absence of the efflux inhibitor verapamil and by genetic analysis of drug-resistance-associated genes. Efflux activity was quantified by real-time fluorometry. Efflux pump gene expression was studied by RT-qPCR upon exposure to clarithromycin. Verapamil increased the susceptibility to clarithromycin from 4- to ≥64-fold. The efflux pump genes and were found consistently overexpressed. The results obtained demonstrate that the T28 (41) polymorphism is not the sole cause of the inducible clarithromycin resistance in subsp. or with efflux activity providing a strong contribution to clarithromycin resistance. These data highlight the need for further studies on efflux response to antimicrobial stress in order to implement more effective therapeutic regimens and guidance in the development of new drugs against these bacteria.