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

Articles in Press

Document Type : Original Articles

Authors

1 Veterinary Sciences Institute, Blida1 University, 09000 Blida, Algeria ; Laboratory of Food Hygiene and Quality Insurance System, High National Veterinary School, 16000 Algiers

2 Veterinary Sciences Institute, Blida1 University, 09000 Blida, Algeria

3 University of Blida 1

4 Laboratory of Food Hygiene and Quality Insurance System, High National Veterinary School, 16000 Algiers, Algeria

5 Laboratory of Food Hygiene and Quality Insurance System, High National Veterinary School, 16000 Algiers, Algeria Veterinary Sciences Institute, Blida1 University, 09000 Blida, Algeria

Abstract

Abstract
Raw milk and its derived cheeses are frequently implicated in foodborne outbreaks worldwide. This study initially aims 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 their production in three units located in the Algiers region. This work provides a rigorous and comprehensive 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 related to the control of this pathogenic bacterium within the dairy sector. Samples were analyzed using the standard procedure EN ISO 11290. Out of a total of 385 samples analyzed, 52 (13.5%) tested positive for a Listeria species. Contamination was higher in the processing unit, with a prevalence of 18%, compared to 11.9% in the production units. Four Listeria species were identified. Listeria monocytogenes, the major pathogenic species, had an overall prevalence of 5.2%, with higher contamination in processed products (12%) compared to locally produced cheeses (2.8%). Listeria innocua was the most frequently encountered species, with an overall prevalence of 6.5% (6.7% in local products and 6% in processed ones). Listeria grayi (1.3%) and Listeria welshimeri (0.5%) were isolated exclusively from locally produced cheeses. These results demonstrate the diversity of Listeria species in the studied cheeses and reveal a higher presence of L. monocytogenes in processed products.
Keywords: Algeria, Listeria spp., Listeria monocytogenes, Prevalence, Raw milk cheeses

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Articles in Press, Accepted Manuscript
Available Online from 15 December 2025

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