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 5.8e9.3 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 19.6e29.1 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