In vitro adherence properties of Lactobacillus rhamnosus DR20 and Bifidobacterium lactis DR10 strains and their antagonistic activity against an enterotoxigenic Escherichia coli

Adhesion and colonisation properties of three probiotic strains namely Lact obacillus rhamnosus DR20, L. acidophilus HN017, and Bifidobacterium lactis DR10, were determined in vitro using the differentiated human intestinal ce ll-lines including HT-29, Caco-2, and HT29-MTX, and compared with propertie s of L. acidophilus LA-I and L. rhamnosus GG (two commercial probiotic stra ins), Two independent methods were employed to quantitate the "adhesiveness " of each strain. In the first method, the bacteria adhered to human cells were detected by Gram staining and counted in different fields under a micr oscope. Bacteria were also radio-labelled and extent of adhesion determined by scintillation counting. All three strains showed strong adhesion with t he human intestinal cell lines in vitro. Adhesion indices of the three stra ins to two cell lines, i.e. HT-29. and Caco-2 varied between 99 +/- 17 and 219 +/- 36. With mucus-secreting cell-line HT29-MTX, the adhesion indices o f all the strains were 2-3 times higher. The adhesion indices of L. acidoph ilus LA-I and L. rhamnosus GG were comparable to the other three probiotic strains. We also investigated the inhibitory effect of adhering strains against the intestinal cell monolayer colonization by a known enterotoxigenic strain of Escherichia coli (strain O157:H7). Pre-treatment of E. coli O157:H7 with 2 .5-fold concentrated cell-free culture supernatants from L. acidophilus HN0 17, L. rhamnosus DR20 and B. lactis DR10 reduced the culturable E. coli num bers on TSB plates and also reduced the invasiveness and cell association c haracteristics of this toxic strain. The inhibitory molecules secreted into the spent media by these strains were partially affected by treatments wit h lactate dehydrogenase, trypsin and proteinase K suggesting that overall i nhibition may be due to a synergistic action of lactic acid and proteinaceo us substances. (C) 2001 Elsevier Science B.V. All rights reserved.