Genomic diversity and distribution of Listeria monocytogenes strains isolated from imported and national fresh produce in Mexico from 2014 to 2018.

Listeria monocytogenes is a major foodborne pathogen associated with fresh produce contamination, posing a significant public health risk due to its adaptability and virulence. This study investigates the genomic diversity and distribution of L. monocytogenes strains isolated from imported and domestic fresh produce in Mexico between 2014 and 2018. A total of 113 L. monocytogenes strains were isolated from produce commodities and subjected to whole-genome sequencing. The analysis focused on identifying lineages, serogroups, clonal complexes (CCs), antimicrobial resistance genes, virulence factors, prophage-associated regions, and SNP clusters, while the pangenome was characterized to assess both core and accessory gene diversity. Two main lineages (I and II) were identified, with lineage I predominantly associated with imported produce. Thirty-two CCs were detected, with CC4, CC11, and CC20 being the most prevalent. The pangenome analysis revealed 2188 core genes and 3739 accessory genes. Antimicrobial resistance genes, including fosX, lin, norB, and sul, were present in all strains. Virulence analysis identified 78 virulence genes, with notable differences among serogroups. Prophage analysis revealed 189 prophage-associated regions, with common phages such as A118 and LP-101 detected predominantly in serogroup IIa. The SNP cluster analysis grouped the strains into 33 clusters, with 48 % of the strains from imported produce concentrated in only three major clusters, indicating potential common sources or similar environmental exposures. The significant genomic diversity and SNP clustering of L. monocytogenes strains underscore the pathogen's adaptability and widespread dissemination potential in the global food supply chain. The presence of virulent CCs and antimicrobial resistance genes highlights an ongoing public health risk, emphasizing the need for enhanced surveillance and targeted interventions to prevent listeriosis outbreaks.