Prevalence of Listeria species in some foods and their rapid identification

Abstract

Purpose: To investigate the occurrence of Listeria spp., (particularly L. monocytogenes), in different foods and to compare diagnostic tools for their identification at species level. Methods: Samples of high protein foods such as raw meats and meat products and including beef products, chicken, fish and camel milk were analysed for the presence of Listeria spp. The isolates were characterised by morphological and cultural analyses, and confirmed isolates were identified by protein profiling and verified using API Listeria system. Protein profiling by SDS-PAGE was also used to identify Listeria spp. Results: Out of 40 meat samples, 14 (35%) samples were contaminated with Listeria spp., with the highest incidence (50%) occurring in raw beef products and raw chicken. Protein profiling by SDSPAGE was used to identify Listeria spp. The results were verified with API Listeria system. Approximately 25% of the identified isolates were Listeria seeligeri, Listeria welshimeri, and Listeria grayi (three positive samples), while 16.66% of the isolates were Listeria monocytogenes (two positive samples); 16.6% of the isolates were Listeria innocua (two positive samples), while 8.3% of the isolates were Listeria ivanovii (one positive sample). Conclusion: High protein foods contain different types of Listeria species; whole-cell protein profiles and API Listeria system can help in the identification of Listeria at the species level.