Twenty-seven isolates of Escherichia coli from cattle with clinical mastitis were subjected to sensitivity tests regarding main antimicrobials used in the treatment of this disease. We also evaluated in vitro effectiveness of two inhibitors of multidrug efflux systems, fenilalanina arginyl ß naftilamida (PAβN) and 1-(1-Naphthylmethyl)-piperazine (NMP), using the minimum inhibitory concentration (MIC) as a reference. MIC and multidrug efflux systems were detected in the growth curves, using optical density (D.O550) at different drug concentrations and the presence and absence of inhibitors. Only four isolates of E. coli were resistant to ampicillin and trimethoprim/sulfamethoxazole, simultaneously. However, all isolates were sensitive to the other antimicrobials. Were observed values ranging from 6mg to 250mg ampicillin/mL, and 12mg to 1500mg/mL trimethoprim/sulfamethoxazole. There was a reduction of the MIC of antimicrobials for all isolates in the presence of inhibitors, except for trimethoprim/sulfamethoxazole in the presence of NMP. In conclusion, these isolates have a narrow resistance profile and PAßN showed better inhibitory effect against ampicillin and trimethoprim/sulfamethoxazole, and is a candidate for the adjuvant treatment of mastitis.
multirresistance; bacteria; milk; resistance mechanism
