In Vitro Assessment of Probiotic Potential of Lactobacillus acidophilus and Antagonistic Activity Against Escherichia coil O157：H7

The antagonistic activity of Lactobacillus acidophilus KLDS1.0901, KLDS1.0902, KLDSI.1003 and NCFM against Escherichia coli O157 ： H7 were investigated in this study. The culture supematants of all the L. acidophilus stains showed high bacteriostatic activities against E. coli O 157 ： H7 and the bacteriostatic substances of their Cell-Free Supernatants （CFS） were preliminarily determined from organic acids. The bacteriostatic activity from CFS or viable L. acidophilus against E. coli O157 ： H7 was also assessed by using co-incubation methods, CFS had high bactericidal activity against E. coli O157 ： H7, no viable E. coli O157 ： H7 was detected when 5×10^7 CfU ofE. coli O157 ： H7 was added to 5 mL of CFS and incubated at 37℃ for 2 h. However, L. acidophilus themselves had no bacteriostatic activity after directly contacted with E. coli O157 ： H7. The inhibition E. coli O157 ： H7 adhesion and colonization of L. acidophilus were also investigated based on competition, exclusion and displacement assays. L. acidophilus KLDS1.0901, KLDSI.1003 and NCFM strains were effective to displace E. coli O157 ： H7 from a Caco-2 cell layer in competition and exclusion assays. However, in displacement assay, all of the strains showed no significant antagonistic activities. Meanwhile, the probiotic potential of L. acidophilus strains was investigated based on adhesion assay to Caco-2 cells and anti- inflammatory effects by IL-8 produced in Caco-2 cells. The adhesion ability and anti-inflammatory effects of L. acidophilus strains showed a strain-dependent manner. In general, L. acidophilus KLDS 1.0901 and NCFM showed better probiotic potential than KLDS1.0902 and KLDSI.1003. Thus, the use ofL. acidophilus KLDS1.0901 and NCFM to prevent or treat of diseases associated induced E. coli O157 ： H7 in vivo was suggested.