Responses of some Escherichia coli clinical isolate strains with multiple drug resistance and overexpressed efux pumps against efux pump inhibitors

Antibiotics are compounds, which inhibit the growth of or destroy microorganisms, thus are used to treat and prevent infections. But for some reason, microorganisms in time develop resistance to antibiotics. One of the reasons for resistance to antibiotics is efflux pumps. By means of these pumps, microorganisms export antibiotics entered into the bacterial cell; therefore, they cannot inhibit the growth of or destroy bacteria. This situation decreases the activity spectrum of the antibiotic and increases the antibiotic resistance. Thus, microorganisms could develop multiple drug resistance against not only the antibiotic used, but also for many other antibiotics and rapidly spread to the environment. For this reason, antibiotic resistance has become a major problem all over the world, and new antibiotics and efflux pump inhibitor studies are continuing rapidly. The aim of this study is to observe the response of some Escherichia coli clinical isolate strains with multiple drug resistance and overexpressed efflux pumps against efflux pump inhibitors, in order to use these strains for further studies. Ethidium bromide (EtBr)-agar cartwheel method was firstly used to identify E. coli strains with overexpressed efflux pumps by transferring inoculum of all strains to EtBr containing agars, and overexpressed efflux pumps were determined by exposing agar plates to UV light. Verapamil, phenyl arginine beta naphthylamide (PAβN) and thioridazine hydrochloride were used as efflux pump inhibitors (EPIs), and the lowest concentration of EPIs those inhibit the growth of E. coli strains were determined by minimal inhibition concentration (MIC) test. Lastly, the responses of microorganisms against efflux pump inhibitors were determined with a microplate based assay, by using EPIs below their MIC values. According to the results of this study; effect of verapamil and thioridazine was observed to be more effective than PAβN. As a result 98.41% of the E. coli strains used in the study was found to be affected by verapamil, where 96.82% by thioridazine and only 38.09% was affected by PAβN inhibitor.