Antimicrobial resistance and virulence profiling of waterfowl-derived Salmonella in Sichuan from 2021 to 2023

Salmonella is an important zoonotic and foodborne pathogen with a worldwide distribution, posing a significant public health threat through contamination of the food chain. In this study, 144 Salmonella strains were isolated from 594 waterfowl samples collected from eight regions in Sichuan Province between 2021 and 2023. WGS combined with SISTR analysis was used for serotyping, and MLST was performed to determine sequence types. Antimicrobial susceptibility testing, resistance gene profiling and virulence gene screening were also conducted. Serotyping identified seven serovars, with S. Typhimurium (68 isolates, 47.2 %) and S. Indiana (48 isolates, 33.3 %) as the predominant serotypes; other serovars included S. Enteritidis (8 isolates), S. Give (13 isolates), S. Kentucky (3 isolates), S. Potsdam (3 isolates), and S. Senftenberg (1 isolate). MLST revealed nine STs with ST19 and ST17 being dominant. All the isolates exhibited multidrug resistance, with 100 % resistance to streptomycin, gentamicin, sulfamethoxazole, trimethoprim-sulfamethoxazole, erythromycin, and florfenicol, along with high resistance rates to fluoroquinolones, lincosamides, and chloramphenicol. The aminoglycoside resistance gene aac(6')-Iaa was detected in all the isolates; the β-lactamase genes bla_CTX-M-65 and bla_OXA-1 were frequently found in S. Indiana. Notably, this study reports the first isolation of ST516 Salmonella (serovar Give) from waterfowl in China, expanding the ecological host range of this multidrug-resistant clone. Furthermore, the cfr resistance gene was detected in Salmonella from waterfowl for the first time, suggesting its potential dissemination via mobile genetic elements and increasing public health concerns.