Emergence of the Coexistence of , and in ST485 Clinical Isolates in China.

INTRODUCTION

Polymyxin resistance caused by the plasmid-mediated gene in gram-negative bacilli poses a huge threat to our health. In recent years, many regions have reported that and β-lactamase genes can coexist in a single strain.

METHODS

In this study, 107 nonduplicate () 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 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 , and genes. MLST results showed that 15 carbapenem-resistant 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 , and were located on different plasmids.

CONCLUSION

The present study demonstrated for the first time the coexistence of , and in a ST485 isolate. The three plasmids carrying the , and genes can be transmitted in , which may lead to more severe bacterial resistance.