Purpose: To better understand the prevalence and antimicrobial resistance of Salmonella in retail foods in China, 1,503 Salmonella isolates collected in five years (2007, 2008, 2010, 2011, and 2012) were characterized by serotyping and antimicrobial susceptibility.
Methods: Isolates recovered from retail chicken, beef, fish, pork, dumplings, cold dishes, and salmonellosis were isolated based on the method of Microbial Food Safety Laboratory at NWAFU. Serotypes and antimicrobial susceptibility were determined by slide agglutination and the agar dilution method according to the White-Kauffmann classification scheme and CLSI standards, respectively.
Results: Among the 1,503 isolates, a total of 129 serotypes were diagnosed. Salmonella Enteritidis (21.5%), Salmonella Typhimurium (11.0%), Salmonella Indiana (10.8%), Salmonella Thompson (5.4%), and Salmonella Derby (5.1%) were most prevalent ones. Multi-drug resistance could be commonly detected among Salmonella isolates. A total of 1,344 (89.4%) isolates resisted to three or more antimicrobial agents. Resistance was most frequently detected among sulfisoxazole (78.1%), followed by tetracycline (70.6%), trimethoprim/sulfamethoxazole (68.0%), and nalidixic acid (63.4%). Lower resistance rates were found among gatifloxacin (17.9%), ceftriaxone (17.7%), and cefoxitin (13.2%). Different from Salmonella Enteritidis and Salmonella Typhimurium isolates, those of Salmonella Indiana, Salmonella Thompson, and Salmonella Shubra were more resistant to antimicrobial agents. Resistance to fluoroquinolones was most frequently found among Salmonella Shubra and Salmonella Indiana isolates, while to cephalosporins was predominantly detected among Salmonella Thompson isolates.
Significance: Our results highlighted the diversity of the serotype and phenotype of multi-drug resistant (MDR) Salmonella isolates, and indicated the complexity and importance for acquiring those serovars of the highest epidemiological data.