The relative fold change of MICs of OtrC-expressing cells with different drugs compared to OtrC-nonexpressing cells. A: The relative change in the MIC of OtrC-expressing E. coli/pETC02 cells (gray) to ampicillin (A), rifampicin (R), oxytetracycline (O), doxorubicin (D), ethidium bromide (E), vancomycin (V), ofloxacin (Of), erythromycin (Er) and streptomycin (S), using the OtrC-nonexpressing E.coli/pET28a cells (light gray) as the controls. The relative change in MIC to the drug that could completely inhibit the cell growth of E.coli/pET28a was set as “0”, while the MIC of drug which could not inhibit the cell growth was set as “1”. Cells were grown in LB liquid medium supplemented with kanamycin, IPTG and different concentrations of test drugs at 37°C, and spun at 170 rpm for 12 h. Cells were then resuspended in fresh LB and spread immediately on the LB plates with kanamycin, IPTG and different concentration of the test drugs. The MICs to drugs were determined after the plates were cultured at 37°C for 12 h. B: The relative fold of MICs of OtrC-expressing S. rimosus mutants, M4018/pSET152 (light gray) and M4018/pSEC (gray), to the above-mentioned drugs, using the OtrC-nonexpressing mutant M4018/pKCΔotrC (dark gray) as the control. The relative change in the MIC to drugs that could completely inhibit the cell growth of M4018/pKCΔotrC was set as “0”, while the MIC of drug which could not inhibit the cell growth was set as “1”. Cells were grown in TSB liquid medium supplemented with different concentrations of drugs at 28°C, and the centrifuged at 220 rpm for 30 h, resuspended in fresh TSB and spread immediately on TSB plates with different concentrations of test drugs. The MICs of drugs were determined after the plates were cultured at 28°C for 3 d. ** indicate significantly higher MIC values than the control cells; * indicate higher MIC values than the control cells.