Pectic oligosaccharide structure-function relationships: Prebiotics, inhibitors of Escherichia coli O157:H7 adhesion and reduction of Shiga toxin cytotoxicity in HT29 cells.

Shiga toxin (Stx)-producing, food-contaminating Escherichia coli (STEC) is a major health concern. Plant-derived pectin and pectic-oligosaccharides (POS) have been considered as prebiotics and for the protection of humans from Stx. Of five structurally different citrus pectic samples, POS1, POS2 and modified citrus pectin 1 (MCP1) were bifidogenic with similar fermentabilities in human faecal cultures and arabinose-rich POS2 had the greatest prebiotic potential. Pectic oligosaccharides also enhanced lactobacilli growth during mixed batch faecal fermentation. We demonstrated that all pectic substrates were anti-adhesive for E. coli O157:H7 binding to human HT29 cells. Lower molecular weight and deesterification enhanced the anti-adhesive activity. We showed that all pectic samples reduced Stx2 cytotoxicity in HT29 cells, as measured by the reduction of human rRNA depurination detected by our novel TaqMan-based RT-qPCR assay, with POS1 performing the best. POS1 competes with Stx2 binding to the Gb3 receptor based on ELISA results, underlining the POS anti-STEC properties.

Cranberry Xyloglucan Structure and Inhibition of Escherichia coli Adhesion to Epithelial Cells.

Cranberry juice has been recognized as a treatment for urinary tract infections on the basis of scientific reports of proanthocyanidin anti-adhesion activity against Escherichia coli as well as from folklore. Xyloglucan oligosaccharides were detected in cranberry juice and the residue remaining following commercial juice extraction that included pectinase maceration of the pulp. A novel xyloglucan was detected through tandem mass spectrometry analysis of an ion at m/z 1055 that was determined to be a branched, three hexose, four pentose oligosaccharide consistent with an arabino-xyloglucan structure. Two-dimensional nuclear magnetic resonance spectroscopy analysis provided through-bond correlations for the α-L-Araf (1→2) α-D-Xylp (1→6) ß-D-Glcp sequence, proving the S-type cranberry xyloglucan structure. Cranberry xyloglucan-rich fractions inhibited the adhesion of E. coli CFT073 and UTI89 strains to T24 human bladder epithelial cells and that of E. coli O157:H7 to HT29 human colonic epithelial cells. SSGG xyloglucan oligosaccharides represent a new cranberry bioactive component with E. coli anti-adhesion activity and high affinity for type 1 fimbriae.