Shiga Toxin Binding to Glycolipids and Glycans

Background: Immunologically distinct forms of Shiga toxin (Stx1 and Stx2) display different potencies and disease outcomes, likely due to differences in host cell binding. The glycolipid globotriaosylceramide (Gb3) has been reported to be the receptor for both toxins. While there is considerable data to suggest that Gb3 can bind Stx1, binding of Stx2 to Gb3 is variable. Methodology: We used isothermal titration calorimetry (ITC) and enzyme-linked immunosorbent assay (ELISA) to examine binding of Stx1 and Stx2 to various glycans, glycosphingolipids, and glycosphingolipid mixtures in the presence or absence of membrane components, phosphatidylcholine, and cholesterol. We have also assessed the ability of glycolipids mixtures to neutralize Stx-mediated inhibition of protein synthesis in Vero kidney cells. Results: By ITC, Stx1 bound both Pk (the trisaccharide on Gb3) and P (the tetrasaccharide on globotetraosylceramide, Gb4), while Stx2 did not bind to either glycan. Binding to neutral glycolipids individually and in combination was assessed by ELISA. Stx1 bound to glycolipids Gb3 and Gb4, and Gb3 mixed with other neural glycolipids, while Stx2 only bound to Gb3 mixtures. In the presence of phosphatidylcholine and cholesterol, both Stx1 and Stx2 bound well to Gb3 or Gb4 alone or mixed with other neutral glycolipids. Pre-incubation with Gb3 in the presence of phosphatidylcholine and cholesterol neutralized Stx1, but not Stx2 toxicity to Vero cells

Dietary perturbations alter the ecological significance of ingested Lactobacillus plantarum in the digestive tract

Host diet is a major determinant of the composition and function of the intestinal microbiome. Less understood is the importance of diet on ingested strains with probiotic significance. We investigated the population dynamics of exogenous Lactobacillus plantarum and its interactions with intestinal bacteria in mice undergoing switches between high-fat, high-sugar (HFHSD) and low-fat, plant-polysaccharide rich (LFPPD) diets. The survival and persistence of ingested L. plantarum WCFS1 was significantly improved during mouse consumption of HFHSD and was negatively associated with the numbers of indigenous Lactobacillus species. Diet also rapidly changed the composition of the indigenous microbiota, but with some taxa differentially affected between HFHSD periods. L. plantarum was not integrated into indigenous bacterial community networks according to co-occurrence patterns but still conferred distinct effects on bacterial species diversity and microbiota stability largely in a diet-dependent manner. Metagenome predictions supported the premise that L. plantarum dampens the effects of diet on the microbiome. This strain also consistently altered the predicted genetic content in the distal gut by enriching for genes encoding glyosyltransferases and bile salt hydrolases. Our findings demonstrate the interactions between ingested, transient probiotic bacteria and intestinal bacterial communities and how they can differ depending on host diet