Molecular characterization of listeria monocytogenes isolated from raw milk and some dairy products at local markets in Damanhour city, Egypt

Several outbreaks of L. monocytogenes have been involved with milk and dairy productsconsumption. The present study was conducted to investigate the prevalence listeria monocytogenes in raw milk and some dairy products. A total of 225 samples of raw milk (75), pasteurized milk (50), ice cream (50) and Ras cheese (50) were collected randomly from different supermarkets, retail outlets and other markets outlets in Damanhour city, El-Behira governorate, Egypt. Out of 225 samples, 29 (12.88%) were positive for Listeria species. The occurrence of Listeria spp. in raw milk, pasteurized milk, ice cream and Ras cheese samples were 10 (13.33%), 6 (12%), 7 (14%) and 6 (12%), respectively. The most prevalent listeria species isolated from raw milk and dairy products in this study was L. innocua and L. monocytogenes. The biochemically identified isolates of L. monocytogenes (16) were molecularly characterized by multiplex PCR for detection of three virulence genes (iap , hylA and actA ); the results showed that iap gene was demonstrated in all isolates (100%); hylA and actA were detected in 83.3 and 66.7% of isolates from raw milk; 66.7 and 66.7% of isolates from pasteurized milk; 80 and 80% of isolates from ice cream; 100 and 50% of isolated from Ras cheese  samples. Concerning to antibiotic resistance, 16 isolates of L. monocytogenes were tested against 14 antibiotics disc and showed that all the isolates  were resistant to Kanamycin (100%) and Nalidixic acid (93.75%), meanwhile, most of the isolates showed sensitivity against Ciprofloxacin (87.50%) and Ampicillin (68.75%). In conclusion, the results of this study emphasize the need for applying more strict hygienic control measures especially during processing, storage and marketing of dairy products.