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Infection and Immunity, January 1999, p. 302-307, Vol. 67, No. 1
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Saccharomyces boulardii Protease Inhibits the Effects of Clostridium difficile Toxins A and B in Human Colonic Mucosa

Ignazio Castagliuolo, Martin F. Riegler, Leyla Valenick, J. Thomas LaMont, and Charalabos Pothoulakis*

Division of Gastroenterology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts

Received 13 July 1998/Returned for modification 18 August 1998/Accepted 28 October 1998

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.

* Corresponding author. Mailing address: Beth Israel Hospital, Harvard Medical School, Division of Gastroenterology, Dana 501, 330 Brookline Ave., Boston, MA 02215. Phone: (617) 667-1259. Fax: (617) 975-5071. E-mail: cpothoul{at}bidmc.harvard.edu.

Infection and Immunity, January 1999, p. 302-307, Vol. 67, No. 1
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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