First report of two foodborne Salmonella enterica subsp. enterica serovar Bovismorbificans isolates carrying a novel mega-plasmid harboring blaDHA-1 and qnrB4 genes.

Salmonella enterica displaying resistance to extended-spectrum cephalosporins and fluoroquinolone (FQs) has been deemed a high-priority pathogen by the World Health Organization (WHO). While CTX-M type acquired β-lactamases have been detected in S. enterica serovar Bovismorbificans, DHA enzymes have been rarely reported in S. Bovismorbificans. In this study, we here report for the first time the isolation of two multi-drug resistant (MDR) S. Bovismorbificans strains co-harboring plasmid-encoded AmpC (pAmpC) β-lactamase gene (bla DHA-1) and qnrB gene, 16Sal017 isolated from a chicken meat sample and 16Sal018 from a grass carp fish sample, collected from retail markets in Guangzhou, China. The bla DHA-1 and qnrB genes in these two strains were both located on the same novel 217,773 bp IncHI2 plasmid belonged to ST2. The plasmid contained 16 additional acquired antimicrobial resistance genes encoding resistance to eight antibiotic classes and quaternary ammonium compound. Besides, 16Sal017 contained an additional 10,124 bp Col (pHAD28)-like plasmid harboring qnrS1. The bla DHA-1 and qnrB4 genes were located in an 18,198 bp region, sul1 - qacEΔ1 - ampR - bla DHA-1 - pspABCDF - qnrB4 - sapABC -IS 91 - sul1 - qacEΔ1 , which has been identified in various bacteria species, indicating the high transfer ability of bla DHA-1 and qnrB4 genes within this gene cluster. The IncHI2 plasmid was found to be transferable to Escherichia coli J53 by conjugation and resulted in the acquiring of multiple resistance in the transconjugants. Genome sequence comparisons by cgMLST and MAUVE alignment indicated 16Sal017 and 16Sal018 are highly similar and are not epidemiologically linked with strains from other sources and countries. Our findings suggest S. Bovismorbificans as a new host for conjugative mega-plasmid harboring bla DHA-1 and qnrB4 genes, and highlight the potential transmission opportunity of these S. Bovismorbificans clones through the food chain, which need continuous investigation. • Two foodborne S. Bovismorbificans isolates of different origins were isolated in China. • The two isolates were highly similar and co-resistant to CIP and CTX. • The two isolates harbored a same novel IncHI2-ST2 type conjugative plasmid. • bla DHA-1 and qnrB located gene cluster was firstly reported in S. Bovismorbificans. • One isolate contained one more Col (pHAD28)-like plasmid harboring qnrS1. [ABSTRACT FROM AUTHOR]