Predominant β-lactamase genotypes of Escherichia coli isolates and induction and inhibition mechanisms of β-lactamase gene expression / 中华流行病学杂志

ABSTRACT

Objective To understand the predominant β-lactamase genotypes and their carrying modes ofEscherichia coli isolates in Zhejiang province,and the effects of β-1actam antibiotics on inducing or histidine kinase inhibitor closantel (CLO) on inhibiting the expression of β-1actamase genes.Methods Micro-dilution method and E-test were applied to measure the resistant rate and minimal inhibitory concentration (MIC) in E.coli isolates against β-1actam antibiotics.PCR and sequence analysis of PCR products were conducted to detect the β-lactamase genotypes and their carrying modes.Real-time fluorescent quantitative RT-PCR and β-lactamase confirmation test were performed to determine the influence of 1/4 MIC penicillin and cefotaxime,and CLO on the transcription and expression of β-lactamase genes in the resistant E.coli isolates.Results Among the 462 E.coli strains isolated in Zhejiang,285 (61.7％) were resistant to penicillin,ampicillin,cefoxitin,cefotaxim and ceftazidime.In the 285 resistant isolates,the detection rate of TEM or CTX-M β-1actamase gene (83.2％ or 75.1％) was significantly higher than that of KPC,SHV or OXA β-lactamase gene (1.4％-10.2％) (P＜0.01) and the carrying rate of two or more β-1actamase genes (68.8％) was also significantly higher than that of single β-1actamase gene (31.2％) (P＜0.01),and 61.4％ of the resistant isolates carried TEM + CTX-M genes (P＜0.01).Except KPC gene,1/4 MIC of cefotaxim and penicillin induced a rapid increase of TEM-mRNA,CTX-M-mRNA,SHV-mRNA or OXA-mRNA levels (P＜0.01),but 50-500 μg/ml CLO inhibited these levels (P＜0.01).After pre-treatment with 100 μg/ml CLO,82.8％-85.6％ of the resistant isolates became sensitive to β-lactam antibiotics (P＜0.01),while the detection rate of β-lactamases was also decreased from 95.1％ to 16.1％ (P＜0.01).Conclusion TEM and CTX-M are the predominant β-lactamase genotypes in E.coli isolates in Zhejiang and TEM+CTX-M is the predominant carrying mode of β-lactamase genes.Low concentrations of β-lactam antibiotics can up-regulate the expression levels of β-lactamase genes in E.coli through bacterial two-component signaling systems,but this effect can be inhibited by CLO,a histidine kinase inhibitor.