Occurrence and Genomic Characterization of Listeria monocytogenes ST121 in Animal-Derived Food Samples from Bejaïa, Algeria

Listeria monocytogenesis an important foodborne pathogen that can cause severe invasive disease in vulnerable populations. This study assessed the occurrence of L. monocytogenes in animal-derived foods collected in Bejaïa, Algeria, and characterized recovered isolates using whole-genome sequencing (WGS). A total of 553 samples (red meat, minced meat, sausage, chicken carcasses, raw milk, and artisanal butter) were analyzed using ISO 11290-based culture, with species confirmation by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Twenty-two isolates were recovered (overall prevalence 4% ± 1.6), with the highest positivity in chicken carcasses (10.9% ± 5.8, 12/110) and artisanal butter (12.5% ± 16.2, 2/16). All isolates belonged to sequence type ST121 and carried the same plasmid replicon rep26. No acquired antimicrobial resistance genes were identified in any isolate. Screening of virulence-associated loci indicated genomic carriage of all conserved set of loci. A truncation in inlA gene was present, which has been associated with decreased virulence pattern. These findings highlight the occurrence of L. monocytogenes in multiple animal-derived products in Bejaïa and support the integration of WGS into routine food-chain surveillance.