Genome-Informed Identification of Species-Specific Diagnostic Markers for Listeria Using Pangenome Analysis

The genus Listeria comprises diverse bacteria with significant public health relevance, particularly Listeria monocytogenes. A comparative genomic analysis of ten representative Listeria species was conducted using 33 high-quality genome assemblies to investigate core and accessory genome dynamics and identify candidate diagnostic loci. Pangenome reconstruction was performed using the Roary Integer Linear Programming Bacterial Annotation Pipeline (RIBAP) to classify core, soft-core, and accessory genes, while average nucleotide identity (ANI) analysis assessed genomic relatedness across thresholds of 60-95%. Functional annotation of core and species-specific genes was conducted using Genome Annotation and Information Analysis (GAIA). Core genes were highly conserved and associated with essential cellular functions, whereas the accessory genome contributed to species-level diversification and ecological adaptation. Candidate molecular markers were derived from accessory genes and evaluated based on presence/absence across genomes, retaining loci present in ≥80% of target strains and absent in non-target strains. Experimental validation of selected primers was performed using two L. monocytogenes reference strains (ATCC 19117 and ATCC BAA-679) with conventional PCR and gel electrophoresis to confirm expected amplicon sizes and specificity. These findings establish a genome-informed, specificity-driven framework for marker development and highlight the accessory genome as a valuable source of diagnostic loci, supporting accurate detection, epidemiological surveillance, and food safety monitoring.