Prevalence and characteristics of Salmonella isolates recovered from retail raw chickens in Shaanxi Province, China

In this study, we evaluated the prevalence of Salmonella in retail raw chickens in Shaanxi Province, China, on a monthly basis. In addition, we studied the antibiotic susceptibility, serotype, and genotype of Salmonella isolates and explored their relationships with sampling time, location, market type, and chicken type. The results showed that Salmonella was more prevalent in chickens sampled during the spring and summer than during the autumn and winter. Thirty-nine serotypes were identified from 406 Salmonella isolates, of which Salmonella typhimurium (16.7%) was the most prevalent. Other prevalent serotypes included S. thompson (12.8%), S. essen (9.1%), S. infantis (6.9%), S. rissen (5.7%), and S. enteritidis (5.4%). Approximately 71.4% of the 406 isolates were resistant to 3 or more antibiotics, 11.8% to 12 or more, and 1.7% to all 14 antibiotics tested. The most frequently detected resistance was to trimethoprim/sulfamethoxazole (82.0%), followed by nalidixic acid (71.9%) and tetracycline (59.4%). The frequencies of resistance to ampicillin, chloramphenicol, and amoxicillin/clavulanic acid were moderately high (similar to 50% each). Resistance to kanamycin, ceftiofur, streptomycin, gentamicin, and ciprofloxacin was less common (<40% each). Serotype distribution and antibiotic susceptibility of Salmonella isolates were related to sampling time, location, chicken type, and market type. Isolates recovered from the same sampling time, market type, location, and chicken type commonly exhibited identical or similar genotypes and antibiotic resistance profiles. However, DNA profiles and antibiotic resistance phenotypes of isolates within some serotypes were diverse. Our results revealed that multiple Salmonella subtypes with antibiotic resistance were prevalent in retail raw chickens in Shaanxi Province. Our study findings provide information for developing preventive measures against contamination of retail foods with Salmonella.