FIG. 2.

S. boulardii increases small intestinal IgA anti-toxin A levels following oral immunization with C. difficile toxoid A. Mice were immunized with formalin-inactivated toxoid A administered by gavage on days 0 and 7 and were sacrificed on day 21. S. boulardii was administered in the drinking water (3 × 10⁸ CFU per ml). Small intestinal IgA anti-toxin A antibody levels were measured by ELISA. Results are expressed as mean and standard error of optical density (O.D.) units (×1,000) (control, n = 32; toxoid A, n = 13; S. boulardii alone, n = 15; S. boulardii and toxoid A, n = 15). Small intestinal IgA anti-toxin A antibody levels were significantly higher in the S. boulardii plus toxoid A group compared to each of the other three treatment groups (P < 0.001 by ANOVA).