الفهرس 
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Abstract
One hundred and twenty samples, 40 each of raw milk, Kareish cheese and Damietta cheese were collected from supermarkets, dairy shops and street vendors in El- Gharbia governorate for microbiological analysis. Microbiological examination of the examined samples revealed that S. aureus could be detected in 60, 52.5 and 20% of examined raw milk, Kareish cheese and Damietta cheese samples, respectively. The mean count values were 1.6x104±2.915x103, 8.38x103±1.88x103 and 6.63x103±1.7x103, respectively. E. coli could be detected in 25, 37.5 and 15% of examined raw milk, Kareish cheese and Damietta cheese samples, respectively. Serological typing of fourteen strains of E. coli proved that they belong to ten serotypes: O159, O142, O18, O15, O125, O111, O55, O119, O26 and O128. Salmonella Typhimurium could be isolated from one sample Kareish cheese (2.5%) with serological typing proved that the strain has antigenic structure of O: 1, 4, 5, 12, H: i: 1, 2. B. cereus could be detected in 12.5, 15 and 7.5% of examined raw milk, Kareish cheese and Damietta cheese samples, respectively. Concerning the antimicrobial activities of some probiotics bacteria lactobacillus planterum (p1), lactobacillus acidophilus (p7), lactobacillus brevii (p102) and lactobacillus casii (l.c) using an agar well diffusion as in vitro assay against selected isolates of E. coli, B. cereus, S. aureus and Salmonella Typhimurium, indicated that probiotics bacteria appeared to have antimicrobial effect against E. coli and B. cereus. Probiotics bacteria; lactobacillus planterum (p1), lactobacillus acidophilus (p7), lactobacillus brevii (p102) and lactobacillus casii (l.c) that injected with E. coli in sterilized skim milk as in vitro experiment, proved to reduce significally the count of E. coli during the periods of incubation.