Dissemination of blaNDM-5 in Escherichia coli through the IncX3 Plasmid from Different Regions in China

The spread of NDM-5-producing Escherichia coli has become a severe challenge in clinical therapy, which necessitates reliable detection and surveillance methods. However, limited information is available regarding the prevalence and dissemination of the bla(NDM-5) gene in E. coli in China. Therefore, we investigated the dissemination of the bla(NDM-5) gene in carbapenem-resistant E. coli isolates from different regions. A total of 1,180 carbapenem-resistant enterobacteriaceae strains were obtained from patients admitted to the 20 sentinel hospitals in 8 cities. Strains positive for bla(NDM-5) were detected using the Vitek 2 compact system, 16S ribosomal RNA (rRNA) gene sequencing, polymerase chain reaction, the S1 pulsed-field gel electrophoresis assay, and Southern blot hybridization. The horizontal-transfer capability of the bla(NDM) gene was assessed by filter mating with a standard E. coli J53 azide-resistant strain as the recipient. Genotyping, susceptibility testing, and whole genome sequencing were performed. Seven strains of bla(NDM-5)-positive E. coli were detected in 1,180 clinical strains from different regions in China. The bla(NDM-5)-carrying strains showed resistance to multiple tested antibiotics and belonged to two widespread sequence types, sequence type (ST)167 and ST405. Antimicrobial resistance genes, including bla(CTX-M), bla(OXA), bla(CMY), and two novel bla(TEM) variants (bla(TEM-230) and bla(TEM-231)) were also identified. Southern blotting located the bla(NDM-5) gene on 46 kb IncX3 plasmids in all isolates, which showed only two single nucleotide differences between EJN003 and the other strains. This study further confirms the increasing occurrence of bla(NDM-5)-carrying IncX3 plasmids and the dissemination of carbapenem resistance in E. coli isolates using the plasmid from different parts in China, which warrants stringent surveillance and control measures.