Predominance of L. monocytogenes Lineage I Clones in Wastewater, Ruminants, and Natural Environments

Listeria monocytogenes is a saprophytic bacterium and a foodborne pathogen of humans and animals. Little is known about its distribution and genetic diversity across different environments within the same geographical region. We conducted a large-scale longitudinal study in southeastern Spain monitoring Listeria spp. in untreated wastewater, ruminant farms, and natural environments over four seasons (N = 1490 samples, N = 545 isolates) and in food and food-processing environments (N = 7395 samples, N = 255 isolates). Listeria spp. were more abundant in host-associated than natural environments, and non-pathogenic Listeria were more prevalent than L. monocytogenes in both niches. L. monocytogenes was detected in 42.7%, 11.4%, 4.2%, and 3.4% of wastewater, ruminant farms, natural environments, and food-related samples, respectively. Hypervirulent lineage I accounted for 82.9% of L. monocytogenes isolates from wastewater, ruminant farms, and natural environments, while lineage II represented 74.1% in food-related samples. Among 255 L. monocytogenes cgMLST types, 5% were shared across environments, demonstrating circulation between different environments. Persistent L. monocytogenes clones were detected in food processing environments and ruminant farms. Our data suggest anthropogenic activities and livestock drive Listeria spp. dissemination. These results provide insights into the interactions of Listeria spp. in the environment, improving surveillance strategies to reduce pathogen transmission, food contamination, and clinical cases.