Comparative study of class 1 integron, ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline (ACSSuT) and fluoroquinolone resistance in various Salmonella serovars from humans and animals

A total of 499 Salmonella isolates including 9 serovars from humans and various animal hosts were collected to compare prevalence of integron and antimicrobial resistance. The integron and gene cassette were detected by PCR, and then the gene cassette type was further determined by sequencing and restriction fragment length polymorphism (RFLP) analysis. The antimicrobial susceptibility test was conducted by disk diffusion method. The positivity percentage of class 1 integron and the diversity of gene cassettes carried by integron were quite different in various Salmonella serovars, especially comparing those from animals to humans. After sequencing and RFLP analysis, it was identified eight gene cassette types. The gene cassette type D carrying ampicillin/streptomycin resistance genes was the most common one (42.2%) in the integron-positive isolates. More diversity of gene cassette types was identified in humans comparing to that in animals. Several gene cassette types were identified for the first time in some Salmonella serovars. In this study, 31.5% (157/499) of the isolates were multi-resistant to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline (ACSSuT). S. Choleraesuis isolates with the cassette type A1, but S. Typhimurium isolates with the cassette type E1, were frequently associated with ACSSuT-resistant (80.6% and 72.7%, respectively). There was a significant association between the presence of class 1 integron and quinolone resistance in S. Choleraesuis isolates, but not in S. Typhimurium. Our findings imply that transmission efficiency of various gene cassettes through the integron could be different in various Salmonella serovars.