[Predominant ß-lactamase genotypes of Escherichia coli isolates and induction and inhibition mechanisms of ß-lactamase gene expression].

OBJECTIVE: To understand the predominant ß-lactamase genotypes and their carrying modes of Escherichia coli isolates in Zhejiang province, and the effects of ß-lactam antibiotics on inducing or histidine kinase inhibitor closantel (CLO) on inhibiting the expression of ß-lactamase 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 ß-lactam antibiotics. PCR and sequence analysis of PCR products were conducted to detect the ß-lactamase genotypes and their carrying modes. Real-time fluorescent quantitative RT-PCR and ß-lactamase confirmation test were performed to determine the influence of 1/4 MIC penicillin and cefotaxime, and CLO on the transcription and expression of ß-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 ß-lactamase gene (83.2% or 75.1%) was significantly higher than that of KPC, SHV or OXA ß-lactamase gene (1.4%-10.2%) (P<0.01) and the carrying rate of two or more ß-lactamase genes (68.8%) was also significantly higher than that of single ß-lactamase 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 ß-lactam antibiotics (P<0.01), while the detection rate of ß-lactamases was also decreased from 95.1% to 16.1% (P<0.01). CONCLUSION: TEM and CTX-M are the predominant ß-lactamase genotypes in E. coli isolates in Zhejiang and TEM+CTX-M is the predominant carrying mode of ß-lactamase genes. Low concentrations of ß-lactam antibiotics can up-regulate the expression levels of ß-lactamase genes in E. coli through bacterial two-component signaling systems, but this effect can be inhibited by CLO, a histidine kinase inhibitor.