Prevalence, plasmid transmission, and chromosomal integration of blaCTX-M genes in Salmonella isolated from retail chicken and pork meats in China
- Food Res Int. 2026 Aug 31:238:119421. doi: 10.1016/j.foodres.2026.119421.
- 1. College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China; National Key Laboratory of Veterinary Public Health and Safety, Department of Basic Veterinary Medicine, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
- 2. College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China; Changji Vocational and Technical College, Changji, Xinjiang 831199, China.
- 3. College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China.
- 4. National Key Laboratory of Veterinary Public Health and Safety, Department of Basic Veterinary Medicine, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
- 5. National Key Laboratory of Veterinary Public Health and Safety, Department of Basic Veterinary Medicine, College of Veterinary Medicine, China Agricultural University, Beijing 100193, China. Electronic address: [email protected].
- 6. Hebei Food Inspection and Research Institute, Hebei Food Safety Key Laboratory, Shijiazhuang 050000, China. Electronic address: [email protected].
- 7. College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China. Electronic address: [email protected].
Extended-spectrum β-lactamase (ESBL)-producing Salmonella poses a growing threat to food safety, yet the transmission of blaCTX-M genes in foodborne Salmonella remains incompletely understood. This study investigated the prevalence, antimicrobial resistance profiles, horizontal transferability, and genetic characteristics of blaCTX-Ms in 950 Salmonella isolates recovered from retail chicken and pork in China. A total of 103 (10.8%) blaCTX-M-positive isolates were identified, with a significantly higher prevalence in chicken (20.7%, 96/464) than in pork (1.4%, 7/486). Geographically, blaCTX-M-positive isolates were more prevalent in the 3 northern provinces (19.93%, 59/296) than in the 5 southern provinces (6.73%, 44/654). These isolates represented 11 "sequence type (ST)-serotype" combinations, predominantly ST26 Salmonella enterica serovar Thompson (S. Thompson) (36.9%, 38/103), ST198 S. Kentucky (31.1%, 32/103), and ST17 S.Indiana (13.8%, 18/103). Nine blaCTX-M subtypes were identified, dominated by blaCTX-M-55 (33.0%, 34/103) and blaCTX-M-65 (33.0%, 34/103). Overall, 78.6% (81/103) of blaCTX-M-positive isolates failed to yield detectable transconjugants in Escherichia coli C600, with no transconjugants detected in ST198 S. Kentucky or ST17 S.Indiana. The blaCTX-Ms were mainly carried by IncHI2-HI2A plasmids, which exhibited significantly lower conjugation frequencies than blaCTX-M-positive IncN and IncFII-X1 plasmids. Chromosomal integration of blaCTX-Ms was detected in ST198 S. Kentucky, ST26 S. Thompson, ST17 S.Indiana, and ST13 S. Agona, characterized by signature direct repeats and mediated by ISEcp1, IS15, and IS26. Consistent with these findings, further analysis of 418 blaCTX-M-positive complete Salmonella genomes from the NCBI database showed that 310 plasmids carried blaCTX-Ms, mainly on IncHI2-HI2A plasmids (33.9%, 105/310), whereas 117 isolates carried chromosomal blaCTX-Ms, dominated by blaCTX-M-55 (76.1%, 89/117) and most frequently occurring in ST413 S. Mbandaka, ST198 S. Kentucky, and ST13 S. Agona. Our findings highlight that blaCTX-Ms disseminate in Salmonella through plasmid-mediated transfer and chromosomal integration, providing a mechanistic basis for the long-term persistence of ESBL-producing Salmonella and associated food safety risk.