Detection of Listeria Species in Farm Milk and White Soft Cheese

Abstract

Background : Listeria is one of the food-borne pathogens common contaminant in dairy products. Consumption of milk and dairy products, in particular soft cheese often implicated as the source of infection in severe outbreaks of listeriosis. Objective : This work aimed to investigate the prevalence of Listeria monocytogenes and other Listeria spp. in raw milk and white soft cheese by conventional methods and polymerase chain reaction. Methodology : Two hundreds samples (50 of each market raw milk, individual farm milk and Kariesh cheese plus 25 of each Damietta cheese and Talaga cheese) where randomly collected from dairy farms, different shops and supermarkets in Mansoura City, Dakahlia governorate. Direct isolation of Listeria on Oxford media was performed and compared with indirect (enrichment) method followed by biochemical identification. Polymerase chain reaction was done for accurate detection of Listeria monocytogenes. Results : The prevalence of Listeria monocytogenes by direct method was 10%, 8%, 8% and 4% in market raw milk, Kariesh cheese, Talaga cheese and Damietta cheese, respectively. On the other hand, indirect (enrichment) isolation of Listeria monocytogenes showed prevalence of 8% and 4% in market raw milk and Talaga cheese, respectively. Listeria ivanovii and Listeria Seeligeri were also detected as 24% and 12% in market raw milk, 24% and 30% in individual farm milk, 16% and 32% in Kariesh cheese, 48% and 36% in Talaga cheese and 24% and 36% in Damietta cheese by direct method. On the other hand, by indirect (enrichment) method the prevalence of Listeria ivanovii and Listeria seeligeri was 14% and 2% in market raw milk, 6% and 14% in individual farm milk, 12% and 12% in Talaga cheese and 12% and 16% in Damietta cheese, but Kariesh cheese was free form Listeria ivanovii and Listeria seeligeri was 4%. Conclusions : The general principles of food hygiene should still be enforced in order to minimize count of Listeria monocytogenes in milk and dairy products during the handling, storage and manufacturing in traditional dairies. Control of the feeding cattle and milk pasteurization can also limit the contamination with Listeria monocytogenes.