Antimicrobial resistance, class 1 integrons, and horizontal transfer in Salmonella isolated from retail food in Henan, China

Introduction: Salmonellosis remains one of the most frequently occurring foodborne diseases worldwide, especially in developing countries. The increasing prevalence of multidrug resistance among Salmonella isolates from food has been an emerging problem in China. Methodology: In this study, a total of 638 food samples including raw meat, seafood, vegetables, and cooked meat were collected in Henan province of China between July 2007 and August 2008 to determine the prevalence of Salmonella. These isolates were subjected to serotyping, antimicrobial susceptibility, presence of class 1 integrons, and horizontal transfer of integrons. Results: The overall percentage of Salmonella prevalence was 9.7% (n = 62). Among these isolates, S. Anatum and S. Senftenberg were most common, and high rates of antimicrobial resistance were observed to sulfamethoxazole (90.3%), trimethoprim/sulfamethoxazole (87.1%), streptomycin (29.0%), and ciprofloxacin (25.8%). Class 1 integrons were detected in 16.1% of these isolates, and contained gene cassettes dfrA12-aadA2, dfrA1-aadA1, and dfrA1. Three Salmonella isolates could transfer their integrons and resistance genes to Escherichia coli by conjugation. Conclusions: Our findings indicate that the mobile DNA elements could play an important role in the dissemination of resistance determinants among those Salmonella isolates.