Abstract
A survey was conducted to determine the prevalence, population structure, and antimicrobial resistance (AMR) dynamics of Salmonella spp. (Salmonella) from retail ground beef (n=395) in 32 cities across Mexico. Individual municipal data were aggregated into three geographic macro-regions (north, center, and south). The global prevalence of Salmonella was 30% (184 unique isolates collected) and displayed a regional gradient (χ2=9, P=0.0102). Central and southern cities exhibited higher odds of contamination (OR~2.0, prevalence=32.9% and 35.6%, respectively) than northern cities (prevalence=20%). The top 10 serovars included epidemiologically relevant lineages (e.g., Newport, Infantis, and Typhimurium), most of which exhibited intraregional clonal expansion and interregional genetic proximity. The most common AMR phenotypes (30-46%) affected older antibiotics (e.g., tetracycline, streptomycin, and phenicols) and azithromycin (24%). Individual AMR phenotypes and multidrug-resistance (MDR) displayed moderate to strong agreement with AMR genotypes (Cohen’s k=0.6-0.9) and were rather uniform across regions, except for the higher frequency of azithromycin resistance observed in the north relative to the center (P=0.0442) and southern regions (P=0.0143). The AMR burden was concentrated in serovars Newport, Typhimurium, and Senftenberg, which exhibited 5-17 times higher odds of MDR status than their Anatum counterparts. This study showed that ground beef Salmonella contamination is a pervasive food safety challenge across Mexico, underscoring significant deficiencies in Salmonella controls along the beef production continuum. Therefore, coordinated national actions are required to implement genomics-based tracking of priority lineages, identify transmission hotspots, and design more effective control strategies, particularly in the preharvest phase, where the carrier state and selective pressures are established.