Genomic diversity and environmental factors associated with Listeria monocytogenes presence in surface water

This study aimed to detect and characterize Listeria monocytogenes (L. monocytogenes) in irrigation water to help reduce the risk of foodborne illnesses. Over nearly a year, water samples (n = 1050) were collected monthly from 120 locations across four Chilean watersheds to assess the prevalence and genetic diversity of the pathogen. The average detection of L. monocytogenes across all watersheds ranged from 15 % to 25 %, underscoring the variability in L. monocytogenes contamination at various sites. Water type, collection month, watershed, pH and season were the primary determinants of the likelihood of L. monocytogenes in surface waters. The genetic analysis of the isolates revealed that clonal L. monocytogenes isolates were identified across regions and were collected throughout the study period. Genomic characterization revealed that most of the 221 isolates sequenced were of serogroup IVb. Virulence-related genes in LIPI1 were present in almost all isolates, while LIPI3 and LIPI4 were less common. Moreover, although infrequent, we found three isolates carrying antimicrobial resistance genes mefA and msrD. These results highlight the genetic diversity of L. monocytogenes in Chilean freshwater environments. At the same time, the environmental persistence ability of L. monocytogenes strains or the presence of reservoirs across different areas could explain the dissemination and persistence of some strains. Ultimately, we did not identify an association between the presence of Salmonella and L. monocytogenes in these watersheds. Insights from this study are vital for improving monitoring efforts and developing targeted control strategies to mitigate public health risks.