FIG. 4.

In vitro C. difficile toxin-neutralizing activity in prechallenge sera of vaccinated hamsters. Sera from hamsters either primed (a) or boosted (b) by various mucosal routes with C. difficile culture filtrate toxoid were analyzed for neutralizing activity against toxin A (solid bars) or toxin B (hatched bars) as determined by inhibition of toxicity in the cell culture assay described in Materials and Methods. Each bar represents the geometric mean titer and standard error of samples from five animals.