الفهرس 
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Abstract
It is well known that the presence of lactobacilli is important for the maintenance of the intestinal microbial ecosystem. Lactic acid bacteria possess inhibitory activity toward the growth of pathogenic bacteria such as Listeria monocytogenes, Escherichia coli, Salmonella spp. and others. This inhibition could be due to the production of inhibitory compounds such as organic acids, hydrogen peroxide, bacteriocins, or reuterin or to competitive adhesion to the epithelium. This study aimed to induce recombinants in lactobacilli via conjugation to enhancing their antagonism against pathogenic bacteria, as well as, to improve the conversion of lactose–whey to lactic acid. The performed experiments have given promising results can be summarized as follow: 1- Lactobacillus strains were varied in their resistance to antibiotics and heavy metals. These variations were used as genetic markers in conjugation experiments. 2- All Lactobacillus strains were resistant to metronedazol, neomycin and kanamycin, as well as, Co, Ni, Pb, Zn, Fe and Al. 3- All Lactobacillus strains were sensitive to erythromycin, amoxycillin, pinicillin, chloramephenicol, refambcin and cephotax as well as Hg. 4- The differences in sensitivity between Lactobacillus strains were found in gentamycin, ampicillin, tetracyclin, streptomycin, norflaxacin, cefradin and cefadroxil as well as, Cu, Cd and Cr. 5- All matings between Lactobacillus strains were successed except for the mating between Lac14411 with Lac56223 and Lac19226 which dose not appeared any transconjugants. 6- Three whey media were used in this study; whey medium (I), whey + 4 g/L yeast extract (II) and whey + 8 g/L yeast extract (III) for testing the conversion efficiency of lactose-whey to lactic acid and biomass of cells. 7- Both transconjugants; Tr8 and Tr10 resulted from the mating between Lac44958 with Lac14411 appeared significant increase in lactose conversion efficiency in whey medium (I) more than other isolates. 8- All transconjugants appeared hybrid vigor in lactic acid production in all media except for Tr20 however; Tr17 did not appeared hybrid vigor in biomass of cells in whey medium No. III. 9- Media types, as well as, Lactobacillus strains were significantly affected on lactic acid production and biomass of cells. 10- The interaction between media and Lactobacillus strains appeared significant effect on lactic acid production and biomass of cells. 11- Data revealed significant variation in the inhibitory action between Lactobacillus strains against E. coli, Staphylococcus epidermis, Bacillus cereus and Klebsiella sp. 12- All transconjugants appeared significant inhibitory effect toward all pathogenic bacteria than their parents. 13- Transconjugants; Tr14, Tr28, Tr29, Tr¬¬31, Tr35 appeared significant differences in antagonistic activity against all pathogenic bacteria in relation to the parental strains. 14- Wild type strains of Lactobacillus treated with 52 oC appeared elimination of neomy, metro, Co and Ni resistance genes in some Lactobacillus strains. 15- All resistance markers were eliminated at 57 oC except for Zn and Al. 16- All strains lost their antagonistic activity against pathogenic bacteria at 57oC, except for Lac44958. 17- The antagonistic activity of Lac19226 strain was stable against Ec1885, Ec2463 and Ec2494 after treated with 57 oC. However, similar trend was also obtained by Lac34587 against Bacillus cereus and Klebsiella pneumoniae after treated with 57 oC. 18- The results indicated that treatment of Lactobacillus strains with high levels of temperature (57 oC) has been shown to result plasmid free cells in most strains for all markers tested. 19- The importance of this study was related to human healthy because of the antagonistic activity of Lactobacillus recombinants against some pathogenic bacteria, as well as, converting lactose-whey to lactic acid.