RESUMO
OBJECTIVE To study the antibiotic sensitivities and characterization of ?-lacamase activity and the antibiotic resistance mechanisms.METHODS The extended-spectrum ?-lactamases were detected.Agar dilution method was used to determine the minimum inhibitory concentration(MIC)of severel antibiotics.The plasmids of clinical isolates were cloned into competent cells(K-12).RESULTS Isoelectric focusing(IEF):The last 5 clinical isolates have all got an activity at a high pH 9 which could be presumptively identified as AmpC.The last two clinical isolates had a weak activity with pH of about 8.0,which belonged to SHV type ?-lactamases.All the isolates had a group of activities at the lower pH range of the gel(pH5).These could be presumptively identified as TEM ?-lactamases.CONCLUSIONS The data suggest that each isolate clearly originate from the same population but possess mutations that leads to antibiotic resistance.The combinations of mutations in same isolates suggest that an earlier strain have infected other compartments and become the founder for later antibiotic resistant variants.