Identification and evolution of novel-carrying plasmids in XDRstrains from a chicken farm.

Abstract

Thegene is typically located on plasmids, playing a crucial role in both intra-species and inter-species transmission among bacteria. This study focused on two-positivestrains, J21CTR26 and J21CTR30, isolated from environmental samples of a chicken farm. Antimicrobial susceptibility testing showed that these strains exhibited an extensively drug-resistant (XDR) phenotype, including resistance to 16 antibiotics across nine classes, notably tigecycline and colistin. Sequence analysis identified both strains as belonging to K10-ST6262, harboring 32 resistance genes and 5 virulence genes. Despite their genetic similarity, hybridization and whole-genome sequencing revealed distinct plasmid profiles. Strain J21CTR26 harbored a 5,404,868 bp chromosome and three plasmids: pCTR26-1 (485,030 bp), pCTR26-2 (141,660 bp) carrying, and pCTR26-3 (106,823 bp). In contrast, J21CTR30 possessed a 5,405,166 bp chromosome and three plasmids: pCTR30-1 (394,261 bp) carrying, pCTR30-2 (234,624 bp), and pCTR30-3 (106,770 bp). Conjugation experiments demonstrated the transferability of the-positive plasmid pCTR26-2 from J21CTR26 toJ53, with a conjugation frequency of 4.2 × 10. Reverse PCR indicated the formation of a circular intermediate, IS, in both-positive strains. Sequence analysis suggested that pCTR30-1 likely originated from a recombination event between pCTR26-1 and pCTR26-2 facilitated by Tn-mediated homologous recombination. Identification of a fusion plasmid and its daughter plasmids in different XDRstrains underscored the dynamic recombination and spread of resistance plasmids in agricultural environments. In conclusion, this study provided insights into the dissemination and evolution of-positive plasmids in husbandry, shedding light on their critical role in antibiotic resistance persistence.IMPORTANCEThis study highlights the alarming role ofin the spread of antibiotic resistance within agricultural environments. Two strains isolated from a chicken farm were found to carry thegene, conferring resistance to multiple critical antibiotics, including tigecycline and colistin. Despite their genetic similarity, the strains exhibited distinct plasmid structures, emphasizing the complexity of plasmid evolution. The identification of a fusion plasmid and its derived plasmids underscores the dynamic nature of resistance gene transfer facilitated by recombination events. Importantly, the transferability of the-positive plasmid todemonstrates the potential for cross-species dissemination. This work sheds light on how agricultural practices contribute to the persistence and evolution of resistance genes, with significant implications for public health and the global fight against antimicrobial resistance.