Occurrence, Species Distribution, and Antimicrobial Resistance of Listeria spp. in Foods from Retail and Farm Outlets in North Carolina, USA.

Contamination of retail foods by Listeria species, compounded by emerging antimicrobial resistance (AMR), presents a critical public health challenge that demands continuous surveillance. This study evaluated prevalence, species distribution, and AMR profiles of Listeria spp. isolated from 861 retail food samples in North Carolina, USA, (2018 and 2020). Isolation and molecular characterization were achieved through selective culturing, multiplex PCR, and antimicrobial susceptibility profiling via disk diffusion. Listeria was detected in 8.48% (73/861) samples, with 68 isolates identified to species level. Non-pathogenic strains predominated, led by L. welshimeri (24.66% of isolates) and L. innocua (21.92%). Pathogenic species (L. monocytogenes; L. ivanovii) represented 17.81% of isolates and were recovered exclusively from raw commodities. Vegetables yielded the most positive samples overall, but raw milk showed the highest individual category prevalence. Processed foods remained largely uncontaminated. Unprocessed foods were 27 times more likely to harbor Listeria than processed alternatives (RR = 27.19; 95% CI: 3.84-192.51. p < 0.0001). Phenotypic resistance was most frequent to Penicillin G (33.82%). Multidrug resistance (MDR) was identified in 64.71% of isolates, encompassing 84.62% of pathogenic and 60.00% of non-pathogenic species. Raw agricultural commodities serve as critical reservoirs for resistant Listeria, emphasizing the need for integrated surveillance frameworks.