Protection of Bifidobacterial cells against antibiotics by a high molecular weight exopolysaccharide of a medicinal fungus Cs-HK1 through physical interactions

This study was to assess the protective effect of exopolysaccharide (EPS) produced by a medicinal fungus Cordyceps sinensis Cs-HK1 on Bifidobacteria against antibiotic inhibition. The high-molecular weight EPS fractions showed significant protective effect on all five bifidobacterial strains against four common antibiotics, leading to a dramatic increase in the minimal inhibitory and minimal bactericidal concentrations. The protective effect of EPS on the bacteria was probably attributed to the formation of a viscous layer around the bacterial cell resisting the access by the antibiotics. The EPS layer surrounding the bacteria cell also promoted the aggregation of bacteria and formation of biofilm as observed by microscopy. EPS also enhanced the bifidobacterial adhesion to Caco-2 cell monolayer. In general, the protective effect as well as biofilm formation due to EPS was significantly correlated with the molecular weight of EPS fractions.