Prevalence of Listeria monocytogenes in traditional cheeses obtained from food sale centers of Tehran, Iran

The bacteria Listeria monocytogenes can contaminate food and cause disease, not just in underdeveloped, but also in developed countries. Cheese is one of the dairy products that can cause listeriosis if it is consumed with contaminated milk. Sixty samples of traditional unpasteurized white cheese weighing approximately 100 g were obtained from sales centers in Tehran for three consecutive weeks. Then, 25 g of each weighed sample was added to 225 ml of initial enrichment medium and incubated at 30°C for 24 h. In the next step, they were cultured in Polymyxin Acriflavin Lithium-chloride Ceftazidime Esculin Mannitol medium and incubated at 35°C for 24 h. The growth and non-growth of Listeria monocytogenes bacterial colonies were examined, and additional tests were performed. The results of this study showed that out of 60 traditional cheese samples that were examined, based on the results of culture and supplementary tests, one cheese sample (1.6%) was infected with Listeria monocytogenes. In general, our study showed a lower level of contamination by Listeria monocytogenes compared to other studies. Iranian cheeses can be found in many varieties and there are differences in processing traditional cheese in different regions. Thereby, continuous monitoring is required.