Detection of extended spectrum β lactamases and ampC β lactamases from Escherichia coli and Klebsiella pneumoniae

Objective: To know the distribution and ant-i microbial susceptibility of extended spectrum βLactamase- and AmpCβLactamase-producing Escherichia coli and Klebsiella pneumoniae which are resistant to cephalosporins. Methods: AmpC βLactamase and extended spectrumβLactamases were detected by three-dimensional test,double disk synergy test and disk confirmatory test recommended by National Committee for Clinical Laboratory Standards. Disk diffusion test was used for ant-i microbial susceptibility test,the MIC values of AmpC βLactamase-producing strains were examined by micro-dilution test. Results: From Escherichia coli and Klebsiella pneumoniae resistant to cefotaxime,extended spectrum βLactamase-producers were 91. 4% and 96. 7%,AmpC βLactamase producers accounted for 17. 1% and 10%, extended spectrum βLactamase plus AmpCβLactamase producers were 8. 6% and 6. 7%,respectively. These strains were highly resistant to the third-general cephalosporins,but susceptible to imipenem. Their resistance ratio to ciprofloxacin,gentamicin amd trimethoprim/sulfamethoxazole were higher than that of nonproducers. AmpC βLactamase producers possessed high resistanceto antibiotics combined with inhibitors. Conclusion: Extended spectrum βLactamases and AmpCβLactamases are the most important resistance mechanisms of Escherichia coli and Klebsiella pneumoniae to cephalosporins, much attention should be paid to the ir detection and surveillance,their resistance to ant-i microbial agents should be known by clinicians.