Prevalence and Genomic Characterization of Multidrug-Resistant Serovar Kentucky Sequence Type 198 Circulating - Beijing Municipality, China, 2016-2023.

Introduction: Highly fluoroquinolone-resistant serovar Kentucky ( Kentucky) of sequence type (ST) 198 has emerged as a global multidrug-resistant (MDR) clone, posing a threat to public health.

Methods: Whole genome sequencing and antibiotic susceptibility testing was used to characterize the population structure and evolutionary history of 54 Kentucky isolates recovered from food and human clinical cases in Beijing from 2016 to 2023.

Results: All 54 Kentucky ST198 isolates exhibited resistance to quinolones, carrying point mutations in the quinolone resistance-determining regions (_S83F and _S80I). Resistance to other antibiotics (folate pathway inhibitors, cephems, aminoglycosides, phenicols, rifamycin, fosfomycin, macrolides, and tetracyclines), mediated by the , , , , , , , , , , , , , , , and genes, was also observed in different combinations. The Beijing Kentucky ST198 evolutionary tree was divided into clades 198.2-1 and 198.2-2, which were further differentiated into three subclades: 198.2-2A, 198.2-2B, and 198.2-2C. Compared with the extended-spectrum β-lactamase-encoding gene in 198.2-1, the co-existence of and , as well as chromosomally located , was detected in most 198.2-2 isolates, which showed more complex MDR phenotypes. Kentucky ST198 outbreak isolates derived from two predominant clonal sources: 198.2-1 with cgST236434 and 198.2-2A with cgST296405.

Conclusions: The Kentucky population in Beijing is genetically diverse, consisting of multiple co-circulating lineages that have persisted since 2016. Strengthening surveillance of food and humans will aid in implementing measures to prevent and control the spread of AMR.