Fig. 2

Assessment of EtBr efflux for the strains in study. Efflux capacity was evaluated at the beginning (orange) and at the end of the exposure process to ethidium bromide (EtBr, red), ciprofloxacin (CIP, green) and cetrimide (CET, blue) at half MIC (dashed lines) and at the MIC (full lines). All assays were conducted in the presence of 0.4 % glucose. EtBr-loaded cells were obtained by incubation with 200 mg/L of VER plus the following EtBr concentrations: 0.125 mg/L (ATCC25923: P0, CIP(½MIC)_P20, CIP(MIC)_P20, CET(½MIC)_ P20; SM2: P0, CET(½MIC)_P20; SM50_CET(½MIC)_P20); 0.25 mg/L (ATCC25923: EtBr(½MIC)_P20, CET(MIC)_P20; SM2: CET(½MIC)_P20, CET(MIC)_P20; SM50: P0, EtBr(½MIC)_P20, EtBr(MIC)_P20, CIP(MIC)_P20); 0.5 mg/L (ATCC25923_EtBr(MIC)_P20; SM2: EtBr(½MIC)_P20, EtBr(MIC)_P20, CIP(MIC)_P20; SM50_CIP(½MIC)_P20). The data presented was normalized against the data obtained in conditions of no efflux (dotted line, cells incubated without glucose in the presence of 200 mg/L of VER). The slope (m) of the EtBr efflux curves was calculated by a linear regression of the values obtained in the first minutes of the assay and it relates to the rate of EtBr efflux in each condition tested. The Relative Index of Efflux activity (RIE) values were calculated as described in Methods and allow the direct comparison of the EtBr efflux activity of the strain after exposure (P20) to their initial efflux activity (P0)