Characterization of an Extensively Drug-Resistant Kentucky ST198 Co-Harboring , and (A) Variant from Retail Chicken Meat in Shanghai, China.

The emergence of extensively drug-resistant (XDR) foodborne pathogens poses grave threats to food safety. This study characterizes the genome of an XDR Kentucky isolate (Sal23C1) co-harboring , and (A) from Shanghai chicken meat in 2022, which was the only isolate co-harboring these three key resistance genes among 502 screened isolates. Genomic analysis revealed that the multidrug resistance gene , which confers resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins and streptogramin A, was identified within a Tn-IS--IS structure on the transferable plasmid p3Sal23C1 (32,387 bp), showing high similarity to the plasmid pCE32-2 (99% coverage, 99.98% identity). Concurrently, the gene resided in a - structure on the transferable IncI2 plasmid p2Sal23C1 (63,103 bp). Notably, both genes could be co-transferred to recipient bacteria via conjugative plasmids at frequencies of (1.15 ± 0.98) × 10. Furthermore, a novel ~79 kb multidrug resistance region (MRR) chromosomally inserted at the locus was identified, carrying , (A), , and . Additionally, a novel Genomic Island 1 variant (SGI1-KI) harbored , , and the (A) variant. The acquisition of these antibiotic resistance genes in this isolate enhanced bacterial resistance to 21 antimicrobials, including resistance to the critical last-resort antibiotics tigecycline and colistin, which left virtually no treatment options for potential infections. Taken together, this is the first comprehensive genomic report of an XDR poultry-derived Kentucky isolate co-harboring , and the (A) variant. The mobility of these resistance genes, facilitated by IS elements and conjugative plasmids, underscores significant public health risks associated with such isolates in the food chain.