الفهرس 
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Abstract
Two experiments were performed to know the efficacy of probiotic (L. casei) on pathogens (S. aureus and E. coli) in yoghurt. The aim of first experiment to investigate the ability of probiotic strain to inhibit foodborne pathogens using agar well diffusion method, the results are the mean of three independent replicates and revealed that L. casei inhibited all of the test indicator microorganisms either S. aureus or E. coli. L. casei had the strongest effect on E. coli followed by S. aureus where the widest inhibition zone was observed in case of E. coli and at same time the narrowest inhibition zone was observed in case of S. aureus .The results also revealed strong positive linear relationship of correlation coefficient between pH and tested pathogens at different inoculation ratios with and without the inoculation of L. casei, while the aim of the second experiment inhibition of foodborne pathogens was tested in the presence of L. casei ATCC393 during fermentation under controlled pH conditions, although starter culture was the same which adding yoghurt bacteria (S. thermophilus and L. delbrueckii ssp. bulgaricus) to yoghurt batches and pH levels of each kind of yoghurt were nearly the same, the difference in E. coli O157:H7 counts, S. aureus counts between regular yoghurt inoculated with S. aureus, E. coli only and yoghurt inoculated with S. aureus and E. coli plus L. casei may due to additional antibacterial substances from L. casei, from these results we noticed that the elimination times of E. coli, S. aureus in yoghurt with L. casei more shorter than E. coli, S. aureus alone in regular yoghurt., the results indicate that the probiotic culture is capable of delaying growth of many foodborne pathogens such as S. aureus and E. coli, so these results confirmed the antagonistic effect of co-inoculation of L. casei with yoghurt starter against S. aureus and E. coli during yoghurt manufacture.