Purpose: The objective of this study was to determine antimicrobial resistance in 115 NTS isolates from food products imported into the US during last four years.
Methods: One hundred fifteen NTS were isolated from a variety of imported food products (n= 3,840). Disk diffusion agar and microdilution assays were performed for antimicrobial susceptibility testing using 10 antimicrobials. A combination of PCR, DNA sequencing, and plasmid analyses were performed to characterize antimicrobial resistance determinants.
Results: Twenty-four out of 115 Salmonella enterica isolates were resistant to various antimicrobial classes including beta-lactam, aminoglycoside, phenicol, sulfonamide, glycopeptide, trimethoprim, and/or fluoroquinolone antimicrobials. Twelve of the isolates were multi-drug resistant strains. Antimicrobial resistance determinants, including blaTEM-1, blaCTX-M-9, blaOXA-1, tetA, tetB, tetD, dfrA1, dfrV, dhfrI, dhfrXII, drf17, aadA1, aadA2, aadA5, orfC, qnrS, and mutations of gyrA and parC, were detected in one or more antimicrobial resistant NTS isolates. Plasmid profiles showed that several antimicrobial resistant strains harbored plasmids having incompatibility groups IncFIB, IncHI1, IncI1, IncN, IncW, and IncX.
Significance: Our study indicates that imported foods contaminated with multidrug resistant NTS may contribute to the spread of antimicrobial resistance genes and potentially compromise the therapeutic activity of antimicrobials. In addition, the data generated from the integrated research approaches reported in this study could be useful for investigations of foodborne illness outbreaks linked to domestic and international food facilities.