Saccharomyces boulardii protease inhibits the effects of Clostridium difficile toxins A and B in human colonic mucosa

Infect Immun. 1999 Jan;67(1):302-7. doi: 10.1128/IAI.67.1.302-307.1999.


Saccharomyces boulardii is a nonpathogenic yeast used in the treatment of Clostridium difficile diarrhea and colitis. We have reported that S. boulardii inhibits C. difficile toxin A enteritis in rats by releasing a 54-kDa protease which digests the toxin A molecule and its brush border membrane (BBM) receptor (I. Castagliuolo, J. T. LaMont, S. T. Nikulasson, and C. Pothoulakis, Infect. Immun. 64:5225-5232, 1996). The aim of this study was to further evaluate the role of S. boulardii protease in preventing C. difficile toxin A enteritis in rat ileum and determine whether it protects human colonic mucosa from C. difficile toxins. A polyclonal rabbit antiserum raised against purified S. boulardii serine protease inhibited by 73% the proteolytic activity present in S. boulardii conditioned medium in vitro. The anti-protease immunoglobulin G (IgG) prevented the action of S. boulardii on toxin A-induced intestinal secretion and mucosal permeability to [3H]mannitol in rat ileal loops, while control rabbit IgG had no effect. The anti-protease IgG also prevented the effects of S. boulardii protease on digestion of toxins A and B and on binding of [3H]toxin A and [3H]toxin B to purified human colonic BBM. Purified S. boulardii protease reversed toxin A- and toxin B-induced inhibition of protein synthesis in human colonic (HT-29) cells. Furthermore, toxin A- and B-induced drops in transepithelial resistance in human colonic mucosa mounted in Ussing chambers were reversed by 60 and 68%, respectively, by preexposing the toxins to S. boulardii protease. We conclude that the protective effects of S. boulardii on C. difficile-induced inflammatory diarrhea in humans are due, at least in part, to proteolytic digestion of toxin A and B molecules by a secreted protease.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antitoxins / pharmacology
  • Bacterial Proteins*
  • Bacterial Toxins / metabolism
  • Bacterial Toxins / toxicity*
  • Binding Sites / immunology
  • Clostridioides difficile / immunology*
  • Colon / enzymology
  • Colon / immunology
  • Colon / microbiology*
  • Culture Media, Conditioned
  • Cytotoxins / metabolism
  • Cytotoxins / toxicity
  • Enterocolitis, Pseudomembranous / immunology
  • Enterocolitis, Pseudomembranous / microbiology
  • Enterocolitis, Pseudomembranous / prevention & control
  • Enterotoxins / metabolism
  • Enterotoxins / toxicity*
  • HT29 Cells
  • Humans
  • Hydrolysis
  • Immunoglobulin G / pharmacology
  • Intestinal Mucosa / enzymology
  • Intestinal Mucosa / immunology
  • Intestinal Mucosa / microbiology*
  • Male
  • Metalloendopeptidases / immunology
  • Metalloendopeptidases / pharmacology*
  • Microvilli / enzymology
  • Microvilli / immunology
  • Microvilli / metabolism
  • Protein Synthesis Inhibitors / immunology
  • Rats
  • Rats, Wistar
  • Saccharomyces / enzymology*
  • Saccharomyces / immunology


  • Antitoxins
  • Bacterial Proteins
  • Bacterial Toxins
  • Culture Media, Conditioned
  • Cytotoxins
  • Enterotoxins
  • Immunoglobulin G
  • Protein Synthesis Inhibitors
  • tcdA protein, Clostridium difficile
  • toxB protein, Clostridium difficile
  • Metalloendopeptidases
  • pseudolysin, Pseudomonas aeruginosa