Northeastern U.S. Salmonella Strains from Retail Meat Are More Prevalent and More Resistant to Antimicrobials

Between 2002 and 2017, the National Antimicrobial Resistance Monitoring System (NARMS) recovered 5,803 Salmonella isolates from retail meat samples of chicken parts, ground turkey, pork chops, and ground beef collected in 21 states. NARMS tested these isolates for susceptibility to amoxicillin-clavulanic acid, ampicillin, azithromycin, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, gentamicin, nalidixic acid, streptomycin, tetracycline, trimethoprim-sulfamethoxazole (cotrimoxazole), sulfisoxazole, and ciprofloxacin. To evaluate possible geographic differences in the prevalence and distribution of antimicrobial-resistant Salmonella, we used a chi-square test of association. We used the U.S. Department of Agriculture Office of Investigation, Enforcement and Audit map for the regional subdivisions. A significant association was found between region, Salmonella prevalence, and Salmonella resistance to all tested antimicrobials except cotrimoxazole, streptomycin, ciprofloxacin, and azithromycin. The Northeast region was the most influential contributor to overall prevalence and resistance to most of the antimicrobials tested, and Salmonella Typhimurium was the serotype driving these associations. Although this work did not elucidate the reasons for differences in prevalence and antimicrobial resistance for Salmonella Typhimurium strains in the Northeast, lack of certain resistance mechanisms in Salmonella strains from other regions was ruled out by analysis of 484 sequences from the 485 isolates resistant to ampicillin, sulfonamides, and tetracycline.