الفهرس 
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Abstract
The aim of the present study was to examine the ability of lactic acid bacteria isolated from Egyptian dairy products to produce antibacterial compounds inhibiting pathogenic and undesirable bacteria in dairy foods. Twentythree samples of traditional Egyptian dairy products were randomly collected from local markets in Mansoura City.Out of the 44 LAB isolates, 11 were found to show variable antibacterial activity. It was found that only one strain of Lactococcus lactis subsp. lactis was able to produce protein agent that had antibacterial activity against the examined organisms. This agent was thus proposed to be a bacteriocinlike substance and termed ?bacteriocinlike Lc?. The Lcproducing strain of Lactococcus lactis subsp. lactis was found to express Lc during the exponential phase of growth. However, the activity of Lc was generally higher in the stationary phase than in the exponential phase. The composition of culture medium in which the Lcproducing strain was propagated was found to affect the activity of Lc. Further studies on Lc showed that it had a destructive effect against the spores of Bacillus subtilis. A safety assessment of Lc as a preservative was carried out using white albino rats. The study recommended, That bacteriocinlike Lc at concentration 5000-20000 Au/ml used in the preservation of dairy products (Domiati cheese (fresh) and icecream). And the addition of Lc at concentrations of 10 000 and 20 000 for the preservation of dairy products, did not have negative effect on the functions of liver and kidney.