The number of adherent cells for each C. difficile strain treated with the control serum ranged from 21.1 to 36.6 CFU per 100 Caco-2 cells , corresponding to 1-2% of the bacterial population used for the challenge. In contrast, pre-treatment with the serum from immunized mice significantly decreased the number to 5.8-9.3 CFU per 100 Caco-2 cells .Similar findings were observed in bacterial cells treated with intestinal fluid, where the number of adherent bacterial cells from each strain ranged from 25.9 to 42.0 and 19.6-29.1 CFU per 100 Caco-2 cells for control and immunized mice, respectively .The dose-dependent effects of serum and intestinal fluid on C. difficile adherence were examined using the JND13-119 strain. Notably, the number of adherent bacterial cells treated with 1- and 10-fold diluted serum significantly differed from that observed for the control serum samples, whereas the number of adherent cells treated with 100- and 1000-fold diluted serum samples was similar to that observed in case of the control serum samples . In comparison, a significant difference was observed in the number of adherent C. difficile cells treated with undiluted intestinal fluid from immunized and control mice; however, the difference between diluted intestinal fluids and the control samples was insignificant . Similar results were obtained by other C. difficile strains that were used in this study