Among the six genus of Listeria ( L . monocytogenes , L.inoccua , L.seeligeri , L.ivanovi , L.grayi , L.murrayi ), L . monocytogenes is a major pathogenic microorganism. It causes abortions, stillbirth, meningitis, sepsis and/or bacteraemia, while diarrhoea and fever are milder clinical symptoms in healthy adults. Immunocompromised people, such as infants, elderly, pregnant women and individual s s ubjected to immunosuppressive therapy (e.g., patients with cancer, AIDS and other chronic diseases), are the most sensitive groups. Incidence of serious disease caused by Listeria , economical losses due to recalling of contaminated foods, and expenses to remedy listeriosis, Lack of accurate recovery method for isolation of this microorganism, and long induction period of listeriosi s s how the importance of study of Listeria in foods . Soft cheese is the one of the main foods that witch is considered to be susceptible source to contaminating by Listeria . This microorganism is transfered to milk via ill cows and ewes therefore it can cause contamination of milk product s s uch as cheese. The aim of thi s s tudy was determining the presence of Listeria in domestic and industrial cheeses,raw milk and farm environment in Isfahan and use some methods to prevention of Listeria in foods. In thi s s tudy incidence of listeria specially L.monocytogenes investigated in a period of 9 month in 74 type of samples of traditional cheese , 2 samples of industrial cheese (each in 5 repetition) , in milk and environment of contaminated samples of Isfahan,.Chemical properties of cheese samples (pH, acidity, salt and moisture) were determined. For determination of colonies Catalase, Gram, Spore, motility, hemolysis, MR/VP and sugar tests were performed. One positive indicator ( L. monocytogenes RITCC1293, 4a serotype) was used with each of test for assurance of accuracy of experiments. Among traditional samples L. murrayi , L. grayi and L.ivanovi were isolated 6.66%,4% and 2.66% from samples respectively. L. monocyogenes could not be isolated from cheese, milk and environment. It could be because of acting of
