Investigating the Biological Characteristics and Pathogenic Potential of Listeria innocua Isolated from Food Through Comparative Genomics

<i>L. monocytogenes</i> is a common foodborne pathogen that typically causes infections through the consumption of food contaminated with this bacterium. This study seeks to elucidate the biodiversity as well as evolutionary characteristics of <i>L. innocua</i> strains from different regions using comparative genomics, exploring the virulence and pathogenic potential of these strains. The findings are expected to deepen our understanding of <i>L. innocua</i> and provide valuable reference for public health risk assessment related to this bacterium. We performed comparative genomics on 108 food-source <i>L. innocua</i> isolates sourced from the USA, England, China, and Egypt to explore their biological traits and assess their pathogenic potential by predicting virulence and antibiotic resistance genes, with subsequent validation of pathogenicity through animal studies. Pan-genomic analysis showed that geographically distinct <i>L. innocua</i> strains possess open genomes, offering a stable genetic basis that facilitates adaptation to diverse environments. Through virulence gene prediction, we found that <i>L. innocua</i> strains from different regions harbor virulence genes identical to those found in pathogenic <i>L. monocytogenes</i>, such as <i>inlA</i> and <i>inlB</i>, as well as internal genes that may enhance the pathogenic potential of the strains. This finding demonstrates that <i>L. innocua</i> strains exhibit pathogenic potential. To validate their virulence, we subsequently conducted virulence assays utilizing the Galleria mellonella larval model. Following infection with <i>L. innocua</i>, 100% mortality was observed in a subset of Galleria mellonella larvae, albeit with a delayed time to death compared to <i>L. monocytogenes</i> infection. This indicates that while <i>L. innocua</i> exhibits attenuated virulence relative to <i>L. monocytogenes</i>, it retains pathogenicity. Consequently, the potential contribution of <i>L. innocua</i> to listeriosis cannot be overlooked in public health risk assessments. <i>L. innocua</i> strains isolated from food can carry virulence and resistance genes identical to those found in pathogenic <i>L. monocytogenes</i> strains, indicating that these <i>L. innocua</i> strains possess certain virulence and pathogenic potential, which was further validated through subsequent animal experimentation. This study enhances our genomic understanding of <i>L. innocua</i> and underscores that detecting its key virulence genes is critical for public health safety, thereby providing valuable insights into its pathogenic potential.