Serotype and Commodity Contributions to Quinolone Resistance Trends Among FSIS NARMS Salmonella Isolates, 2013–2023

Food-animal surveillance can identify antimicrobial-resistance patterns that may affect foodborne disease risk, but pooled summaries can obscure commodity and serotype drivers. This study analyzed public FSIS NARMS cecal and HACCP/slaughter-source Salmonella records accessed through FDA NARMS Now to examine quinolone-resistance trends by calendar period, commodity, and serotype. Records were filtered to Salmonella isolates with reported growth collected from 2013 to 2023. Calendar periods were defined descriptively as 2013–2016, 2017–2022, and 2023 to bracket major U.S. antimicrobial-stewardship milestones, including completion of GFI #213 implementation in 2017 and implementation of GFI #263 in 2023; these periods were treated as temporal landmarks rather than causal policy exposures. Outcomes were ciprofloxacin non-susceptibility, ciprofloxacin resistance only, and nalidixic acid resistance. Analyses included commodity-stratified percentages with Wilson 95% confidence intervals, serotype contribution summaries, and binomial models with standard errors clustered by year. The dataset included 42,232 Salmonella isolates; 41,608 were tested for ciprofloxacin and 41,606 for nalidixic acid. Overall, ciprofloxacin non-susceptibility increased from 1.96% in 2013–2016 to 17.84% in 2017–2022 and 25.71% in 2023. Nalidixic acid resistance increased from 1.36% to 17.02% and 24.01%, respectively. These increases were concentrated in chickens, where ciprofloxacin non-susceptibility rose from 1.7% to 28.7% and 42.4%. Salmonella Infantis accounted for 75.0% of all ciprofloxacin non-susceptible isolates, and Infantis plus Enteritidis accounted for 85.6%. After excluding both serotypes, adjusted period odds ratios were substantially attenuated. Findings indicate that quinolone-resistance trends in FSIS NARMS food-animal Salmonella data were strongly shaped by chicken-associated serotype composition, supporting serotype-aware surveillance.