Protection from Intestinal Inflammation by Bacterial Exopolysaccharides

Abstract

Host inflammatory responses against pathogenic organisms can be abrogated by commensals; however, the molecular mechanisms by which pathogenesis is prevented are still poorly understood. Previous studies demonstrated that administration of a single dose of Bacillus subtilis prevented disease and inflammation by the enteric mouse pathogen Citrobacter rodentium, which causes disease similar to the human pathogen enteropathogenic E. coli. No protection was observed when an exopolysaccharide (EPS)-deficient mutant of B. subtilis was used, suggesting that EPS are the protective factor. Here, we isolated and characterized EPS, and showed that they also prevent C. rodentium-associated intestinal disease after a single injection. Protection is TLR4-dependent, since EPS-treated TLR4 KO mice developed disease. Further, protection could be conveyed to wild-type (wt) mice by adoptive transfer of macrophage-rich peritoneal cells from EPS-treated mice. We found that EPS specifically bind peritoneal macrophages and because mice lacking MyD88 signaling in myeloid cells were not protected by EPS, we conclude that bacterial EPS prevent colitis in a TLR4-dependent manner that requires myeloid cells. These studies provide a simple means of preventing intestinal inflammation caused by enteric pathogens.

Exopolysaccharides: Sweet success with probiotic therapeutics

“…All protective strains were capable of producing EPS as part of their biofilm matrix, leading us to suggest that EPS is the protective molecule of B. subtilis. Consistent with this idea, we purified EPS from a B. subtilis strain that overproduced soluble EPS and found that it alone was sufficient to prevent disease [35] . Carbohydrate analysis revealed that B. subtilis EPS is comprised of 3 sugars, mannose (88%), glucose (11.9%) and N-acetyl-glucosamine (<0.1%) with linkages as described [35] .…”

“…Consistent with this idea, we purified EPS from a B. subtilis strain that overproduced soluble EPS and found that it alone was sufficient to prevent disease [35] . Carbohydrate analysis revealed that B. subtilis EPS is comprised of 3 sugars, mannose (88%), glucose (11.9%) and N-acetyl-glucosamine (<0.1%) with linkages as described [35] . The composition of this EPS contrasts with that reported previously [34] , and additional studies are needed to identify which sugar moieties and linkages are critical for protection.…”

“…The transfer of macrophage-rich peritoneal cells from an EPS-treated mouse to naïve mice prevented infectious colitis in recipient mice infected with C. rodentium. Further, EPStreated mice that lack MyD88 signaling in myeloid cells developed disease when infected with C. rodentium, supporting the role of macrophages in EPS-mediated protection [35] .…”

“…We found that EPS, which is administered intraperitoneally, bound F4/80 + CD11b + peritoneal macrophages [35] . The transfer of macrophage-rich peritoneal cells from an EPS-treated mouse to naïve mice prevented infectious colitis in recipient mice infected with C. rodentium.…”

“…-/-and TLR4 -/-mice and found that all of these strains were susceptible to C. rodentium after EPS treatment and were not protected from inflammatory disease ( [35] and unpublished data). These data suggest that signaling through both TLR2 and TLR4 is important for protection.…”