Listeria monocytogenes (L. monocytogenes) is a significant foodborne pathogen, posing a threat to public health. This study investigated the prevalence and genomic diversity of L. monocytogenes in 466 wild animals sampled across Central and Southern Italy (2017-2023), including species such as wild boar, red fox, and wolf, to assess their role as reservoirs and potential links to the food chain. Overall, 22.5% of the animals tested positive, and 118 L. monocytogenes strains were isolated, predominantly from wild boar (n=46), red fox (n=20), and Italian wolf (n=15). Whole Genome Sequencing (WGS) analysis revealed high genomic diversity, classifying the strains into 27 Clonal Complexes (CCs) and 31 Sequence Types (STs). Both hypervirulent clones (e.g., CC1, CC6, CC207) and hypovirulent clones (e.g., CC9, CC19), known for their persistence, were identified, with wild boars harboring a majority of the hypervirulent isolates. All strains carried key virulence genes, and accessory virulence factors, particularly LIPI-3, were detected in hypervirulent strains. Persistence factors, such as the Stress Survival Islet 1 (SSI-1) and genes for metal/disinfectant resistance (cadA, qacA), were also detected, particularly in wild boar isolates. Crucially, core-genome MLST (cgMLST) analysis demonstrated direct genomic links between the wildlife isolates and the Italian National Reference Laboratory database. Multiple clusters were identified, connecting strains from wild animals (wild boars, foxes, wolves) with those from meat products, fresh salads, and food processing environments. A persistent CC9 cluster, circulating in the meat chain for seven years, was strongly correlated with wild boar isolates, underscoring the role of wildlife as a reservoir that continuously introduces both high-virulence and highly persistent strains into the food production system. These findings emphasize the necessity of integrating wildlife surveillance into public health strategies to mitigate the risk of zoonotic transmission, particularly through game meat consumption and handling.
Chiaverini et al. (Tue,) studied this question.