Emergence of the Coexistence of mcr-1, bla(NDM-5), and bla(CTX-M-55) in Klebsiella pneumoniae ST485 Clinical Isolates in China

INTRODUCTION: Polymyxin resistance caused by the plasmid-mediated mcr-1 gene in gram-negative bacilli poses a huge threat to our health. In recent years, many regions have reported that mcr-1 and β-lactamase genes can coexist in a single strain. METHODS: In this study, 107 nonduplicate Klebsiella pneumoniae (K. pneumoniae) isolates were collected from a tertiary hospital in Jiangxi, China. Antimicrobial susceptibility testing of isolates was performed using gram-negative susceptibility cards on the VITEK system. The minimum inhibitory concentrations (MICs) of polymyxin B was detected using the microdilution broth method. The presence of resistance genes was assessed using polymerase chain reaction (PCR). We subjected isolates to genotyping using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) and analyzed the transferability of plasmids with filter mating and electroporation. Subsequently, whole-genome sequencing was performed for plasmids. RESULTS: Of the 107 K. pneumoniae isolates, 15 (14.0%) were resistant to polymyxin B. All polymyxin B-resistant isolates harbored at least one of the extended-spectrum β-lactamase genes tested. Only one isolate simultaneously harbored mcr-1, bla(NDM−5), bla(CTX-M-55), and bla(SHV-27) genes. MLST results showed that 15 carbapenem-resistant K. pneumoniae isolates belonged to five sequence types (STs). PFGE results displayed nine different PFGE clusters. Conjugation and transformation experiments and sequencing analysis showed that the strain had three plasmids, and mcr-1, bla(NDM−5), and bla(CTX-M-55) were located on different plasmids. CONCLUSION: The present study demonstrated for the first time the coexistence of mcr-1, bla(NDM−5), and bla(CTX-M-55) in a K. pneumoniae ST485 isolate. The three plasmids carrying the mcr-1, bla(NDM−5), and bla(CTX-M-55) genes can be transmitted in Enterobacteriaceae strains, which may lead to more severe bacterial resistance.