Frequency of Listeria species from raw milk, traditional cheese and ice-cream in Shahrekord and Shiraz

Listeria bacteria are widespread and commonly found in soil, sewage, dust and water. Listeria monocytogenes and the other Listeria species have been isolated from a variety of raw and processed foods as well. The objective of this study was to determine the prevalence of Listeria spp. in retail stores located retail raw milk, traditional cheese and ice-cream in Shahrekord and Shiraz. A total of 178 samples of raw cow milk (n=45), raw goat milk (n=32), traditional cheese (n=41) and traditional ice-cream (n=60) collected randomly. All the samples were evaluated for the presence of Listeria spp. by using standard cultural methods, then confirmed with Polymerase Chain Reaction (PCR). Based on conventional bacteriologic tests, 24 of 178 samples (13.5%) were positive for Listeria spp. The prevalence of Listeria in raw cow milk, raw goat milk, traditional cheese and traditional ice-cream were 11.1%, 3.1%, 24.4% and 13.3%, respectively. The most species isolated was L. innocua (62.5%) and the others were L. monocytogenes (37.5%). Our results indicate the potential risk of infection with Listeria among people who consume raw and unpasteurized dairy products. Further intensive studies is suggested to evaluate of the prevalence of Listeria spp. in the other food products especially ready to eat foods.