الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Two hundred and fifty random samples of raw milk, Ultra heat treated milk (UHT milk), milk powder, Talaga cheese and Kareish cheese (50 each) were randomly collected from different localities in Beni-Suef Governorate (Egypt). we found that the Enterobacteriaceae count, Coliforms count and Escherichia coli count were higher in the examined raw milk, Kareish cheese and Talaga cheese, respectively. We were able to isolate both Escherichia coli and Y. enterocolitica in a percentages of 2%, 0%, 14%, 2% and 0% of the examined raw milk, UHT milk, Kareish cheese, Talaga cheese and milk powder samples, respectively for E. coli and in a percentages of 2%, 0%, 6%, 2% and 0%of the examined samples respectively for Y. enterocolitica. We failed to isolate Escherichia coli O157:H7, Enterobacter sakazakii and Salmonella from any of the examined samples.
Investigating the effect of molecule(s) secreted by probiotic bacteria on EHEC O157:H7 virulence and their role in quorum sensing (QS) were assesed by using Cell-free spent media (CFSM) of five probiotic bacteria grown on sugar-free whey protein (proTrainer) medium. Their effects have been measured on LEE promoter activity using two E. coli luminescent constructs (LEE1::lux or LEE2::lux). Lactobacillus acidophilus La-5 CFSM showed the greatest effect on both LEE1 and LEE2 expression. Size exclusion chromatography was then performed on the most active CFSM (L. acidophilus La-5) to partially purify the active fractions. Pooled active fractions were then tested by reverse transcription real-time PCR to confirm their effects on expression of several virulence genes of E. coli O157:H7. The results showed that these fractions were able to down-regulate several virulence genes of EHEC including stxB2, qseA, luxS, tir, ler, eaeA and hlyB. Another animal model study was done and we approved that probiotic Lactobacillus acidophilus La-5 exerts good properties against the colonization of E.coli O157H7 to the GI tract of balb/c mice as well as down regulation of the pro-inflammatory cytokines such as TNF- α.