Specific molecular weight and glycosidic linkage diversity of dextran-type exopolysaccharides determine their anti-adhesion bioactivity against enterotoxigenic Escherichia coli (ETEC)

Bacterial exopolysaccharides (EPS) can inhibit enterotoxigenic Escherichia coli (ETEC) adhesion to intestinal mucin. This inhibition prevents intestinal colonization and toxin production by ETEC thus mitigating the severity of diarrhea. Here, we investigated the effect of molecular weight (Mw) distribution towards anti-adhesion bioactivity of dextran (α-1,6-linked glucan)-like EPS against ETEC. EPS samples from Leuconostoc sp. were partially hydrolyzed with dextranase resulting in products with various Mw. Two EPSs, namely commercial HMW-dextran (primarily linear dextran from Leuconostoc mesenteroides B512; Mw ∼220 kDa) and EPS-LmWN (∼95% α-1,6-linked dextran from L. mesenteroides WN; Mw ∼969 kDa), did not show anti-adhesion bioactivity against ETEC when they had Mw >200 or <0.5 kDa. Partially hydrolyzed HMW-dextran with Mw ∼0.5–120 kDa showed significant anti-adhesion bioactivity, with the strongest bioactivity observed from dextran fractions with a degree of polymerization (DP) 80–220 (Mw ∼14–35 kDa). EPS-LmWN only showed anti-adhesion bioactivity when it was partially hydrolyzed with dextranase resulting in polydisperse dextran fractions that covered DP80–220. EPS-LcTR (mixed-linkages dextran from Leuconostoc citreum , Mw ∼529 kDa) did not show anti-adhesion bioactivity even after lowering the Mw with dextranase. Our finding indicates that an optimal Mw range and primarily α-1,6-linked glucan are important structural features for anti-adhesion bioactivity of dextran against ETEC F4.