Identification and genetic characterization of two conjugative plasmids that confer azithromycin resistance in .

With the development of multidrug resistance in spp. in recent years, ciprofloxacin, ceftriaxone, and azithromycin have become the principal antimicrobial agents used for the treatment of infections. The underlying mechanisms of plasmid-mediated ciprofloxacin and ceftriaxone resistance have attracted extensive research interest, but not much is focused on azithromycin resistance in . In this study, we investigated the genetic features of two conjugative plasmids and a non-transferable virulence plasmid that encode azithromycin resistance in food-borne strains. We showed that the azithromycin resistance phenotype of these strains was conferred by gene and/or the complete genetic structure ISIS Comparative genetic analysis showed that these conjugative plasmids might originate from and play a role in the rapid dissemination of azithromycin resistance in . These conjugative plasmids may also serve as a reservoir of antimicrobial resistance (AMR) genes in in which these AMR genes may be acquired by the virulence plasmids of via genetic transposition events. Importantly, the formation of a novel macrolide-resistance and virulence-encoding plasmid, namely pS1380-118 kb, was observed in this study. This plasmid was found to exhibit transmission potential and pose a serious health threat as the extensive transmission of azithromycin resistant and virulent strains would further compromise the effectiveness of treatment for salmonellosis. Further surveillance and research on the dissemination and evolution routes of pS1380-118kb-like plasmids in potential human pathogens of the family of are necessary.