Prevalence of Listeria spp. in Dairy Products With a Focus on Raw Milk Cheeses in Algeria

Introduction: Raw milk and its derived cheeses are frequently implicated in foodborne outbreaks worldwide. This study aimed to assess the contamination by Listeria spp., particularly Listeria monocytogenes, in three types of cheeses made from raw cow’s milk at various stages of production in three units located in the Algiers region. This work provides a synthesis of available data on the prevalence of Listeria spp. in dairy products, especially cheeses, in Algeria and at the international level. It highlights critical contamination points, the influence of production conditions on bacterial proliferation, and the main challenges associated with controlling this pathogenic bacterium within the dairy sector. Materials & Methods: Samples were analyzed according to EN ISO ۱۱۲۹۰-۱ and EN ISO ۱۱۲۹۰-۲, covering both the qualitative detection and quantitative enumeration of L. monocytogenes and other Listeria species.Results: Out of a total of ۳۸۵ samples analyzed, ۵۲(۱۳.۵%) tested positive for a Listeria species. Contamination was higher in the processing unit, with a prevalence of ۱۸%, compared to ۱۱.۹% in the production units. Four Listeria species were identified. L. monocytogenes, the major pathogenic species, had an overall prevalence of ۵.۲%, with higher contamination in processed products (۱۲%) than in locally produced cheeses (۲.۸%). Listeria innocua was the most frequently detected species, with an overall prevalence of ۶.۵% (۶.۷% in local products and ۶% in processed ones). Listeria grayi (۱.۳%) and Listeria welshimeri (۰.۵%) were isolated exclusively from locally produced cheeses. Conclusion: These results demonstrate the diversity of Listeria species present in the studied cheeses and reveal a higher prevalence of L. monocytogenes in processed products.

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Keywords: Algeria ، Listeria spp ، Listeria monocytogenes ، PREVALENCE ، Raw milk cheeses