الفهرس 
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Abstract
Assessing the microbial quality and safety of the market raw milk, pasteurized milk, UHT milk, and yogurt is the basal objective of this study. Two hundred and forty (240) samples (60 samples of each) were collected randomly from different supermarkets and retailer shops in Dakahlia governorate, Egypt. Samples were analyzed for Total bacterial count (TBC), total Coliforms (TCC), Total Staphylococcus count (TSC), and Total yeast and mould count. All market milk samples, and yogurt were found to be contaminated and judged poor. Listeria spp. were isolated on Oxford agar and then subjected to biochemical and molecular identification. The prevalence of Listeria species isolated from raw milk, results showed that Listeria species were isolated from 17 samples recovered from 60 samples (28.33%) where 8 L. monocytogenes (13.33%), 2 L. innocua (3.33%) and 7 Other Listeria species (11.67%) while in yogurt , results showed that Listeria species were isolated from 3 samples recovered from 60 samples (5%) where 1 L. monocytogenes (1.67%), and 2 Other Listeria species (3.3%), but L. innocua were not detected in yogurt. However Listeria species were not detected in pasteurized milk and UHT milk. Polymerase chain reaction (PCR) was used to detect the virulence genes (16SrRNA, hylA, and prfA) of 9 biochemically identified L. monocytogenes strains recovered from raw market milk and yogurt using specific primers. 16SrRNA, hylA, and prfA genes are considered the best indicator for virulence determination of L. monocytogenes isolated from examined samples. In conclusion, a high microbial load of market milk and yogurt may present a public health hazard to the consumers and emphasizes the need for improved hygienic standards.