Characterization of Antimicrobial Resistance Determinants and Class 1 and Class 2 Integrons in Salmonella enterica spp., Multidrug-Resistant Isolates from Pigs.

Antimicrobial resistance (AMR) and Salmonella spp., are primary concerns in public health. The present study characterizes the AMR determinants of 62 multi-drug resistant (MDR) Salmonella enterica spp., isolates from swine, which were obtained between 2004⁻2006, a major source of human salmonellosis. The AMR determinants were investigated by PCR, checking the presence of class 1 and class 2 integrons and 29 resistance genes. Genes sul1 , blaTEM1 -like, aadA2 , tet (A), and dfrA12 were more prevalent ( p < 0.05) within the determinants that were checked for each of these antimicrobials. Co-existence of different genes conferring resistance to the same antimicrobial was common. No differences in AMR determinants prevalence were observed between Salmonella Typhimurium and other serovars from the study. Class 1 integrons were detected in 48 of 62 isolates, again with no differences being linked to any serovar. Nine different variable regions were observed, 1000 bp/ aadA2 -1200 bp/ blaPSE-1 (13 isolates) and bla OXA -like/ aadA1 (eight isolates) were the most common. Four isolates, including S. Typhimurium (2), Salmonella Bredeney (1), and Salmonella Kapemba (1) harboured a class 2 integron 2300 bp estX- sat2-aadA1 . Results from the study highlight the importance of class 1 integrons and certain genes in MDR swine Salmonella isolates. The information is of relevance for monitoring in the forthcoming scope of reduction of antibiotic usage in swine production.