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Abstract Bacteriocins are ribosomally synthesized antimicrobial compounds that are produced by many different bacterial species including many members of the lactic acid bacteria .The purpose of this study was isolation and selection of some lactic acid bacteria (LAB) belonging to the genera Lactobacillus spp. from raw milk and Ras cheese and study its ability to produce bacteriocins, with respective biology activity against pathogenic bacteria. The studies presented in this thesis include: 1- Screening of LAB isolated from raw milk and dry cheese for the production of bacteriocins. Only 4 strains out of sixteen isolates, belonging to the species L. fermentum, L. acidophilus, L. acidophilus and L. pentosus, showed activity towards indicator strains with disk well diffusion and teterazolum chloride test method. It is the first time that baceriocin activity is reported in E.coli ATCC 25922 and Bacillus subtilis NCIB3610. 2- Detection and identification of known strains by using different methods such as biochemical tests, API system and using RAPD PCR for detection the relationship between four strains. 3- Evaluation of bacteriocins production in liquid media from four strains such as: A- Influence of different media on the bacteriocins production: a maximum bacteriocin activity was shown (3200 AU/ml) in medium C by L. acidophilus CH1 against Bacillus subtilis NCIB3610, but the minimum bacteriocin activity obtained by all strains was 0.0 AU/ml in all media against E.coli ATCC 25922 except MRS mediun. Summary 118 B- Effect of different temperature on bacteriocins production: the highest activity was obtained with L.acidophillus CH1 (1600AU/ml against E.coli ATCC 25922 and 2100 AU/ml Bacillus subtilis). C- Effect of different levels of pH on bacteriocins production activity: The best pH for bacteriocin activity was pH=6. The highest activity was obtained with L.acidophillusCH1 (2800AU/ml against E.coli ATCC 25922 and 3300 AU/ml against Bacillus subtilis). D- Effect of medium composition on bacteriocin production activity: the highest bacteriocin activity was 2700AU/ml when the medium was supplemented with K2HPO4 (1%) using L.acidophillusCH1 against B. subtilis. The lowest activity 0.0 AU/ml was shown in different concentrations from (2-3%) with other media components. 4- Different parameters of characterization of bacteriocins such as: A- Effect of different concentrations of NaCl on crude bacteriocins activity: L. fermentum M1 produced 1500 AU/ml against B. subtilis. The lowest bacteriocins activity obtained was 0.0 AU/ml for all strains at 10% NaCl against E.coli and B.subtilis. B- Effect of different concentrations of amino acids on crude bacteriocin activity: The best activity was obtained at control (without addition of amino acids) for Lactobacillus acidophilus CH1 (1600 AU/ml) against B. subtilis. The smallest activity value was 0.0 AU/ml at concentration of 8% amino acids for all tested strains against B. subtilis. C- Effect of different vitamins on crude bacteriocins activity: The best bacteriocins activity was 1400 AU/ml for L. fermentum M1and L. Summary 119 acidophillus CH1 against E.coli ATCC 25922 but most tested strains showed no activity with B12 against E.coli. D- Effect of different temperatures on the crud bacteriocins activity: 1- L. fermentum M1 showed the highest inhibition percentage was (76.08%) at 60ºC/30min against E.coli but the smallest activity was (30.01%) at 30ºC/30min against B.subtilis. 2- The strain L. acidophilus M2 showed the highest growth inhibition (87.34%) at 60ºC/30min against E.coli and the smallest activity was 11.12% at 90ºC/30min against E.coli. 3- L.acidophilusCH1 with highest activity was 87.08% at 30ºC/30min against B.subtilis and smallest activity was 18.08% at 90ºC/30min against B.subtilis. 4- L. pentosus CH2 which showed the highest activity of growth inhibition 85.98% at 60ºC/30min against B.subtilis but the smallest activity was at 90ºC/30min against E.coli. E- Effect of surfactant on crude bacteriocins activity: 1- L. fermentum M1 showed the highest bacteriocins activity, growth inhibition was 73.56% with Tween 80 against E.coli but the lowest activity was -30.81% with ETDA against E.coli. 2- L. acidophilus M2 which showed the highest growth inhibition percentage (78.59) with SDS against B.subtilis but the lowest activity was -8.37% with ETDA against E.coli. 3- L.acidophilus CH1 showed the highest activity (78.29%) with Tween 80 against E.coli but showed the lowest activity (-23.70%) with ETDA against E.coli. Summary 120 4- L. pentosus CH2 showed the higest activity ( 80.59%) with CTAB against E.coli but the smallest activity was -85.11% with Tween80 against E.coli. F- Effect of some mineral salts on crude bacteriocins activity: 1- L. fermentum M1 showed the highest bacteriocins activity (87.2%) with FeSO4 against B.subtilis but the smallest activity was -64.5% with AgNO3 and CuSO4 against E.coli. 2- L. acidophilus M2 which showed the highest growth inhibition percentage (95.57) with FeSO4 against B.subtilis but the smallest activity was -62.96% with ZnSO4 against E.coli. 3- L.acidophilusCH1 showed the highest activity of growth inhibition (97.92%) with FeSO4 against E.coli, but showed the smallest activity (-81.03%) with ZnSO4 against E.coli. 4- Strain L. pentosus CH2 showed the highest activity of growth inhibition (97.17%) with FeSO4 against B.subtilis but the smallest activity was -82.96% with MnCl2 against E.coli. G- Effect of some solvents on crude bacteriocins activity: 1- L. fermentum M1 showed the highest bacteriocins activity of growth inhibition percentage (93.85%) with Isoamylchloride against B.subtilis but the smallest activity was 0.0% against E.coli. 2- L. acidophilus M2, showed the highest growth inhibition percentage (87.69) with ethanol against B.subtilis but the smallest activity was -33.7% with Isoamylchloride against B.subtilis. 3- L.acidophilusCH1, showed the highest activity of growth inhibition (88.93%) with Isopropanol against B.subtilis but showed the smallest activity (-48.15%) with chloroform against E.coli. |