الفهرس 
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Abstract
The aim of the present study
1- Isolate and identify lactic acid bacteria from some traditional Egyption fermented dairy product.
2- Study the ability of the identified isolates to produce bacteriocin – like peptides.
3- partially purify and characterize the produced bacteriocins.
Results
One hundred and thirty isolates were isolated from the three traditional fermented dairy products (Laban Zeer, Laban Rayeb and Kariesh cheese). Out of the total isolates, 46 only (35%) were characterized as lactic acid bacteria using morphological, physiological and biochemical tests. `Twenty-eight strains (61%) out of Forty-six isolates showed antagonistic activity against six food pathogens using well diffusion method. The pathogenic bacteria were (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae subsp. Pneumoniae, Staphylococcus aureus subsp. aureus, Listeria monocytogenes, and Bacillus cereus. The distribution of the 28 isolates by genus according to pre-identification was as follows: 15 isolates were Lactobacillus (53%), 8 isolates were Enterococcus (29%) and 5 isolates were belong to Lactococcus (18%).
The physical and biochemical properties of bacteriocin produced by six strains of lactic acid bacteria (Z26, Z31, K5, R38, R44 and R45) such as effect of enzymes, effect of pH and heat treatment were also studied. The results showed that the antibacterial activity was completely inactivated showing no residual activity upon treatment with α-chymotrypsin; trypsin and pepsin. The bacteriocin were stable in a wide range of PH (2.0, 4.0, 6.0, 8.0 and 10.0) and after the heat treatment at 100 °C for 5 to 30 min. Bacteriocins produced by six strains were characterized and purified. Purification of bacteriocin protein was achieved by sephadex G 15-125 Gel - permeation chromatography. The results showed that the elution profile of bacteria isolates R38; R44; K5 and Z 31 exhibited two protein peaks with different molecular weight. strains R 45 and Z26 showed three peaks.
The molecular weights of bacteriocin produced by six strains were determined by Gel Electrophoresis (SDS PAGE). The estimated molecular mass of partially purified bacteriocin was found to be ranged from 67.4 K Da – 15 K Da). Four strains only were idefined by a biolog system. The results showed that R38 identified as (Lactococcus lactis ssp lactis), R44 identified as (lactobacillus rhamnosus), R 45 identified as (Lactobacillus casei) and Z26 identified as (Lactobacillus mail).