Drug Resistance Analysis of ESBLs and AmpC Beta-lactamases in Clinical Isolates of Escherichia Coli

Objective To study the mechanisms of drug resistance in clinical isolates of Escherichia coli against 15 antibacterial agents. Methods A total of 468 strains of Escherichia coli isolated from January 2004 to December 2004 were collected from Tongji Hospital Affiliated to Tongji Medical College, Huazhong University of Science and Technology. The MIC of 15 antibacterial agents against the clinical isolates was detected by the double agar dilution method. ESBLs and AmpC-producing E. coli isolates were examined by standard disk diffusion susceptibility test and improved new three-dimensional test. Results Altogether 153 ESBLs-producing strains were detected in the 468 Escherichia coli isolates, and the detection rate was 32.7% (153/468). Additional 7 AmpC-producing strains were detected and the detection rate was 1.5% (7/468). Resistant rates of second-generation cephlosporin in ESBLs-producing were more than 90%. In the third-generation cephlosporin, the resistant rates to cefatazidime and cefotaxime were 30.4% and 55.4%, respectively. In the forth-generation cephlosporin, the resistant rate to cefepime was 58.9%. Among the beta-lactamase inhibitor combination regimens, the resistant rates to amoxicillin/clavulanate and cefoperazone/sulbactam were 92.9% and 80.4%, respectively. The resistant rate to ciprofloxacin was 83%. For gentamicin and tetracycline,the rates of resistance were 73.3% and 88%, respectively. The AmpC-producing strains revealed a higher drug resistance comparing with ESBLs-producers. The AmpC-producers were all resistant to the second and third-generation cephlosporins, tetracycline, ciprofloxacin and gentamicin. The resistant rates of non-ESBLs and non-AmpC-producers were less than that of the beta-lactamase producers. For imipenem, no resistant strain was found in all these E. coli strains, which showed a significant antibiotic activity and the MIC_ 50 was only 0.5 microgram per liter. Conclusions The mechanisms of cephlosporin-resistant in Escherichia coli were mainly producing ESBLs. AmpC-producing strains in Escherichia coli revealed a critical drug resistance. Imipenem is the most active antibiotic for treatment of the infections caused by these resistant strains. The choices of antibiotics for clinical therapy must be recommended to the results of susceptibility test in vitro.