Purpose: The objective of this study was to characterize the antimicrobial resistance determinants of the Salmonella enterica isolates.
Methods: Salmonella enterica isolated from food samples were characterized for antimicrobial resistance phenotypes, genotypes, PCR detection of antimicrobial resistance genes, sequencing of integrons, plasmid analysis and transferability of antibiotic resistance by conjugation.
Results: Twenty four (20.2%) out of 119 S. enterica isolates were resistant to various antibiotic classes including ß-lactam, aminoglycoside, phenicol, glycopeptide, sulfonamide, or trimethoprim antimicrobials. Fourteen of the isolates were resistant to multi-antimicrobials. Four Salmonella isolates (PSS_903, PSS_913, PSS_984 and PSS_988) were resistant to at least 4 different classes of antibiotics used in the study. The antimicrobial resistant genes, including blaTEM-1, blaCTX-M-9, blaOXA-1, tet(A), tet(B), tet(D), dfrA1, dfrV, dhfrXII, drf17, aadA1, aadA2, aadA5, and/or orfC, were detected. Conjugation data showed that the antimicrobial resistant genes can be transferred to E. coli J53. The transconjugants E. coli were also resistant to antibiotics like parent S. enterica strains. Plasmid profiles showed that 18 isolates (75.0%) of the 24 antibiotic resistant Salmonella strains harbored plasmids having incompatibility group IncFIB, IncHI1, IncI1, IncN, IncW, and IncX.
Significance: The results of this study showed that various imported food products were contaminated with S. enterica strains and some of them were multidrug-resistant. We report that emergence of multidrug resistance mediated by conjugative plasmids in S. enterica food isolates may become a global threat. Therefore, our monitoring data combined with molecular characterization of antimicrobial resistance determinants in Salmonella isolated from imported food products provides information that can contribute significantly to enhance food safety and public health.