Role of fibronectin-binding protein A in Clostridium difficile intestinal colonization

Clostridium difficile is a frequent cause of severe, recurrent, post-antibiotic diarrhoea and pseudomembranous colitis. Its pathogenicity is mediated mainly by two toxins, TcdA and TcdB. However, different adhesins have also been described as important colonization factors which are implicated in the first step of the intestinal infection. In this study, we focused our interest on one of these adhesins, fibronectin-binding protein A (FbpA), and on its role in the intestinal colonization process. A mutant of FbpA (CD Delta FbpA) was constructed in C. difficile strain 630 Delta erm by using ClosTron technology. This mutant was characterized in vitro and in vivo and compared to the isogenic wild-type strain. Adhesion of the CD Delta FbpA mutant to the human colonic epithelial cell line Caco-2 and to mucus-secreting HT29-MTX cells was examined. Surprisingly, the CD Delta FbpA mutant adhered more than the wild-type parental strain. The CD Delta FbpA mutant was also analysed in three different mouse models by following the intestinal implantation kinetics (faecal shedding) and caecal colonization (7 days post-challenge). We showed that in monoxenic mice, CD Delta FbpA shed C. difficile in faeces at the same rate as that of the isogenic wild-type strain but its colonization of the caecal wall was significantly reduced. In dixenic mice, the shedding rate was slower for the CD Delta FbpA mutant than for the isogenic wildtype strain during the first days of infection, but no significant difference was observed in caecal colonization. Similar rates of intestinal implantation and caecal colonization were observed for both strains in assays performed in human microbiota-associated mice. Taken together, our data suggest that FbpA plays a role in intestinal colonization by C. difficile.