P. burden on healthcare systems (1, 2). The economics of vaccines have been modeled, demonstrating that a vaccine against is economically viable and urgently required (3, 4). It has been proposed that a vaccine should provide coverage against several pathogenic strains, prevent gastrointestinal colonization, or block cellular toxicity by secreted toxins (5). The most advanced vaccines trialed to date have focused predominantly on the toxins alone, with some still the focus of clinical trials, whereas others having been withdrawn (5, 6). Many have suggested the development of vaccines that target the initial stages of CDI, such as colonization of the gut via adhesion to host cells, as a complementary strategy for new vaccines (7). Several surface molecules have been investigated as putative adhesion and colonization factors (8). These include, but are not limited to, members of the family of cell wall proteins (Cwp), the S-layer proteins (SLP), microbial KMT6 surface components recognizing adhesive matrix molecules (MSCRAMMs) including fibronectin-binding protein (Fbp68/FbpA) SB-568849 and collagen-binding protein (CbpA) (9). Other proteins reported to have a role in adherence are components of the flagellar apparatus, although these have been shown to function in a strain-dependent manner (10). The antigen CD0873 is annotated as a substrate-binding protein component (SBP) of an ATP-binding cassette (ABC) transporter (11) and is an immunoreactive protein in human infection (12). We have previously shown, using both genetic and cellular approaches, that CD0873 is a surface-exposed lipoprotein and an adhesin of (13). Here we used a competitive murine model to demonstrate that a CD0873-deficient strain of shows a long-term decrease in colonization fitness. We show that purified CD0873 can protect against SB-568849 long-term persistence in a conventional murine active immunization model, with a corresponding specific adaptive immune response to CD0873. We present three high-resolution structures of CD0873, which possesses a typical Class I SBP fold: a near-atomic resolution closed, ligand-bound structure, an open, ligand-bound structure, and an open, ligand-free structure. The structural and biochemical information reported in this study demonstrates that tyrosine is the ligand of CD0873. Given the importance of tyrosine metabolism in persistence, through 4-methylphenol (protein, CD0873, which should be considered as a component of future vaccines to prevent colonization. Results WT C. difficile outcompetes a CD0873 mutant in a dixenic murine model of colonization It has previously been shown that the lipoprotein CD0873 facilitates adherence of to human enterocytes (13). We therefore hypothesized that CD0873 may confer a fitness advantage to in a dixenic murine model of colonization. To test this hypothesis, germ-free mice were co-challenged with wildtype (WT, 630= 0.0043) and D15 (= 0.025) after challenge, showing a higher level of bacterial shedding in feces (Fig. 1(Fig. 1adhesion of to gut mucosa. Although nonsignificant, at D15, a partial decrease of mucosa-associated KSA1 was observed compared with the SB-568849 WT strain (Fig. 1model, WT outcompetes a CD0873 insertional mutant strain, suggesting that the lipoprotein CD0873 has a role in gut colonization. Open in a separate window Figure 1. Evaluation of intestinal colonization by in the competitive dixenic mice infected by both 630and KSA1 strains, with equivalent inoculum. mean of vegetative cells in mouse feces at D1, D2, D3, D6, D7, D10, and D15 630(mean of vegetative cells in caecal contents of mice sacrificed on D2, D7, and D15 for the 630group (mean of adherent vegetative cells on caecal mucosa of mice sacrificed on D2, D7, and D15. Data and are the mean S.E. calculated on counts obtained from mice per group.