Oxy-Imino-Cephalosporin Induces Expression of Secondary Resistance Genes repB and mtgA in Escherichia coli Harboring blaCTX-M ESBL.

Escherichia coli is considered a major extended-spectrum β-lactamases producer, of which CTX-M is the most common member. However, the different variants of this primary resistance-determinant make it challenging to detect by conventional PCR-based techniques. Therefore, in this study, we investigated the transcriptional response of 2 secondary resistance genes, repB and mtgA, under sub-inhibitory concentrations of oxy-imino cephalosporins in resistant isolates of E. coli harboring blaCTX-M. The STRING database and Cytoscape software were used to identify the secondary resistance genes by gene network analysis. The cephalosporin-resistant isolate of E. coli co-harboring repB and mtgA, along with blaCTX-M, was employed for the current study. The blaCTX-M-carrying plasmid was successfully eliminated from the native-type isolate using 6% and 8% SDS treatment for 7 days. The plasmid was also transformed into a recipient strain, E. coli DH5α, by the heat-shock method. All three models were grown under sub-inhibitory stress of cephalosporins, and the transcriptional response of repB and mtgA was determined by quantitative real-time PCR. The study revealed that the transcriptional responses of both repB and mtgA were antibiotic-specific, which potentially can serve as a secondary resistance reporter for cephalosporin resistance in E. coli.