Competition between substrates of the efflux pump system of Salmonella enteritidis

AIM To determine whether tetracycline competes with ethidium bromide (EB), used as substrate of efflux pumps, for extrusion by the efflux pump system of Salmonella enteritidis NCTC 13349 reference strain. MATERIALS AND METHODS Evaluation of efflux of EB in competition with tetracycline was conducted with the aid of an automated EB method and by EB agar method. RESULTS The EB agar method demonstrated that the accumulation of EB by S. enteritidis NCTC 13349 reference strain is reduced by high concentrations of tetracycline and that tetracycline accumulates within the cells. The use of the automated EB method confirmed the EB agar results and demonstrated that accumulation of EB is not affected by tetracycline unless the concentration of the antibiotic exceeds 100 mg/l. CONCLUSION These results suggest that tetracycline is preferentially retained and that EB is preferentially extruded by the efflux pump of Sientintidis NCTC 13349.