Plasmid-Encoded bla(NDM-5) Gene That Confers High-Level Carbapenem Resistance in Salmonella Typhimurium of Pork Origin

PURPOSE: Carbapenem resistance is rarely reported in Salmonella Typhimurium, especially from a food origin. Here, we report a plasmid-mediated mobile carbapenem-resistant bla(NDM-5) gene in Salmonella Typhimurium isolated from pork in Shanghai, China in 2016. PATIENTS AND METHODS: In July 2016, the S. Typhimurium SH160 strain was recovered from minced pork meat purchased from a supermarket in Yangpu District, Shanghai, China. Antimicrobial susceptibility testing, multi-locus sequence typing, conjugation, S1-PFGE, southern hybridization, whole-genome sequencing and data analysis were performed. RESULTS: This isolate was found to be a ST34 strain and resistant to carbapenems, cephalosporins, and most other commonly used antibiotics. The bla(NDM-5) gene was harbored by a 46161-bp IncX3 plasmid which was found to be transferable. The IncX3 plasmid contains a composite cassette, consisting of ISSwil-IS3000-ΔISAba125-IS5-bla(NDM-5)-bleMBL-trpF-dsbC-IS26-ctuA1-ΔumuD. In addition, this strain was found to harbor an additional 161706-bp IncHI2 plasmid which carries nine resistant genes, such as aadA1, aadA3, aph(3ʹ)-la, sul1, sul2, sul3, floR, cmlA and dfrA12. CONCLUSION: We reported the S. Typhimurium with transferable IncX3 plasmid harboring bla(NDM-5) gene from minced pork. We characterized the complete genetic features of the plasmid, which demonstrated the potential for spreading in different bacterial pathogens. Therefore, extensive surveillance and monitoring for carbapenem-resistant bacterium in the food chain and public health are urgently required.