Emergence of extensively drug-resistant Salmonella Kentucky ST198 in Southwest China

The study aimed to investigate the prevalence, antimicrobial resistance profiles, and virulence characteristics of Salmonella isolates from clinical cases in Sichuan, China, collected from 2019 to 2021.

A total of 153 Salmonella isolates from 19 regions in Sichuan Province were analysed. Sequence types (STs) were identified using multi-locus sequence typing. Antimicrobial susceptibility testing was conducted to assess resistance profiles, while whole-genome sequencing was used to detect antimicrobial resistance genes (ARGs) and virulence genes.

Among the 153 Salmonella isolates, 49 STs were identified. ST11 (S. Enteritidis) was the most prevalent, while S. Kentucky comprised 3.27% (5/153) of isolates, significantly higher than the national average (0.33%, P < 0.05). All S. Kentucky ST198 isolates were extensively drug-resistant, exhibiting resistance to at least seven antimicrobial classes, including fluoroquinolones and extended-spectrum cephalosporins. S. Kentucky ST198 harboured significantly more ARGs (P < 0.001) and virulence genes (P < 0.001) than other strains. ARGs such as CTX-M-55, TEM-216, TEM-90, and TEM-150 were significantly more prevalent (P < 0.05), conferring resistance to extended-spectrum cephalosporins and β-lactams. Additionally, the absence of sifA (16.7% vs. 91.8%, P < 0.001) and shdA (0.0% vs. 68.7%, P = 0.001), suggesting that these genes may influence the reduced risk of human infection by ST198.

These findings highlight the emergence of extensively drug-resistant Salmonella Kentucky ST198 in Southwest China and underscore the urgent need for ongoing surveillance in this region due to its significant public health impact.