The Genotypes Of Extended Spectrum β-lactamases And The Relations With Antibacterial Resistance

Objective:To investigate the prevalence of Extended spectrumβ-lactamases in clinical isolates of Escherichia coli and Klebsiella pneumonia from Janurary 2003 to September 2003,the genotypical characteristics and the relations with antibacterial resistance of ESBLs,then established the foundation of analyse the drug resistance mechanism, supplied the basis of antimicrobial therapy in clinical.Methods: Escherichia coli and Klebsiella pneumonia were isolated from clinical specimens,and identified by API system.The ESBLs producing strains were detected by K-B disc diffusion method phenotypic confirmatory test which was recommended by NCCLS(National Committee for Clinical Laborary Standards).PCR were performed using primers specific for blaCTX-M-1,blaCTX-M-9, blaSHV, blaTEM. MIC (minimal inhibitory concentration) of 12 kinds of antibacterial drugs were detected with double agar dilution method,and statisticed the MIC range, MIC50, MIC90, resistance rate,susceptibility rate.The SPSS 10.0 was used to analyse the results.Results:In this experiment,31 of the 70 strains (44.29%) of Klebsiella pneumonia and 30 of the 84 strains (35.71%) of Escherichia coli produced ESBLs.The 61 ESBLs producing strains were amplificated by four groups of primers,and 51 strains were positive at least one group of primers.24 of the 51 strains were blaCTX-M-1 positive, 25 of the 51 strains were blaCTX-M-9 positive,2 strains of Klebsiella pneumonia and 2 strains of Escherichia coli were both blaCTX-M-1 and blaCTX-M-9 positive.37 of the 51 strains were blaTEM positive, 8 of the 51 strains were blaSHV positive,38 of the 51 strains produced two or more kinds of genotypes,usually combinded with CTX-M genotype.MIC results showed the highest sensitivity of ESBLs producing strains to imipenem,the susceptibility rate was 100%,and the susceptibility rate to piperacillin/tazobactam was higher than to cefoperazo/subactam and ticarcillin/ claviculanic acid,the resistance rate to cefotaxime was much higher than to ceftazidime, also there were higher resistance rate to cefepime.The resistance rate of ESBLs producing strains to amkacine was higher than non-ESBLs producing strains.The resistance rate of Escherichia coli to quinolones was higher than Klebsiella pneumonia,and had no relations with ESBLs.For every genotype,CTX-M positive strains had obviously higher resistance rate to cefotaxime than to ceftazidime,and had lower resistance rate to piperacillin/ tazobactam than to cefoperazo/subactam and ticarcillin/claviculanic acid.Conclusions:In this experiment,the ESBLs producing rate in Escherichia coli and Klebsiella pneumonia was 39.6%.CTX-M was the prevalent genotype of ESBLs,SHV and TEM genotypes often combinded with CTX-M. ESBLs producing strains had higher resistance rate to cefotaxime than to ceftazidime, also had higher resistance rate to cefepime.This maybe related to the main CTX-M genotype of ESBLs. There had obviously inhibition of piperacillin/tazobactam to CTX-M genotype ESBLs than to cefoperazo/subactam and ticarcillin/claviculanic acid. Imipenem was the most effective antibiotics to infections caused by ESBLs producing strains.