Role of volatile fatty acids in colonization resistance to Clostridium difficile in gnotobiotic mice

Clostridium difficile is an agent involved in the development of antibiotic-associated pseudomembranous colitis. The purpose of this work was to investigate the role of volatile fatty acids (VFAs) in resistance to colonization by C. difficile by using a gnotobiotic animal model. Accordingly, germfree mice were associated with different hamster flora, and the VFAs in their cecal contents were measured by gas chromatography. The results showed that VFAs were produced mainly by the intestinal flora, especially by the strictly anaerobic bacteria. In these associated mice, the concentrations of acetic, propionic, and butyric acids were higher than those of other acids, but at pH 6.8 the MICs of these three acids in vitro for C. difficile were more than 200 mu eq/ml. In gnotobiotic mice monoassociated with C. difficile and in the isolated ceca of these mice, VFAs did not inhibit the growth of C. difficile. In gnotobiotic mice which were diassociated with C. difficile and C. butyricum and given drinking water with a lactose concentration of 20%, the cecal contents included about the same amount of butyric acid as did those of the monoassociated mice, although the population of C. difficile remained the same. Therefore, it is suggested that VFAs alone cannot inhibit intestinal colonization by C. difficile and that, consequently, other inhibitory mechanisms are also present.