Using surface plasmon resonance technology for initial evaluation of the antitoxin activity of dextran exopolysaccharide against Escherichia coli heat-labile enterotoxin

Enterotoxigenic Escherichia coli is the most common bacterial agent causing diarrhea by binding to the intestinal mucosa and producing heat-labile enterotoxins. The aim of this study was to elucidate the interaction of two forms of dextran exopolysaccharides (molecular weights of (11-9 kDa) and (76-60 kDa)) produced by the probiotic bacterium Leuconostoc mesenteroides with the heat-labile enterotoxin ((B-pentamer) (LTB)) by using surface plasmon resonance (SPR). According to the results of interaction kinetics at 298 K, both low and high molecular weight dextran types exhibited high affinity (KA) (1.07×106 M-1 and 0.95×106 M-1, respectively) for LTB toxin in vitro. From a thermodynamic point of view, the values calculated of the Gibbs energy were negative (ΔG <0), and also enthalpy and entropy achieved both positive values (ΔH> 0 and ΔS> 0) via the van’t Hof equation, indicating that the interaction was spontaneous, endothermic, and disordered, respectively. With these findings, hydrophobic interactions appear to be important in the interaction between dextran and LTB toxins with hydrogenic bindings. Therefore, dextran molecules are capable of binding to LTB toxin and relatively displaying antitoxin effects. To sum up, these results could provide further insights for initiating extensive research with other lactic acid-derived exopolysaccharides in bacterial interactions and also with foodborne pathogen toxins.