Thesis (M.Sc.) - Cairo University - Faculty of Agriculture - Department of Microbiology

Dairy products are a healthy important and used as a source for vitamins and minerals for body healthy. But, it is also rapid to spoilage. Also, some food products are used as fermented foods. Therefore, the present study aims to focus on the general considerations of lactic acid bacteria and what is known of their direct effect on shelf life for some fermented foods. Twenty five of dairy products were collected from local markets of Giza governorate, from which, 132 pure isolates were obtained. Selected isolates were transferred to MRS medium until morphological characters were examined. Long rods gram positive gave the highest number of isolates reach the 56 isolates followed by cocci form (28 isolates). While, the other forms of isolates were ranged between 13 to 19 isolates. The bacteriocins obtained showed antimicrobial activity against escherichia. coli, S. aureus and B. cereus. For escherichia. coli, there was 100% of inhibition activity of the bacteriocins, while for B. cereus there was less bacteriocin activity (98%) using the bacteriocin from lactobacillus spp. For Staphylococcus species, there was 100% inhibition activity. Also, the isolates were checked for their antimicrobial activity against B. cereus, L. monocytogenes and E. coli which are common food borne pathogens that infect the gastro-intestinal tract and other seven bacterial species. The results showed that two of the isolates gave positive results against 8 and 6 of tested bacteria on Lac1 and Lca2. Total microbial count in salami at zero time reached to 2.1{u00D7}10⁸ cfu/g, while, after 15 days of storage period at 0 {u00B0}C decreased to 10⁵. By increasing the storage period to 30 and 60 days, the counts decreased and reached to 52 to 72 cfu/g depending on the isolate type tested

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