is the main causative agent of antibiotic-associated and health care-associated infective diarrhea. Recently, there has been growing interest in alternative sources of other than patients with infection (CDI) and the hospital environment. Notably, the role of -colonized patients as a possible source of transmission has received attention. In this review, we present a comprehensive overview of the current understanding of colonization. Findings from gut microbiota studies yield more insights into determinants that are important for acquiring or resisting colonization and progression to CDI. In discussions on the prevalence of colonization among populations and its associated risk factors, colonized patients at hospital admission merit more attention, as findings from the literature have pointed to their role in both health care-associated transmission of and a higher risk of progression to CDI once admitted. colonization among patients at admission may have clinical implications, although further research is needed to identify if interventions are beneficial for preventing transmission or overcoming progression to CDI.

Clostridium difficile pathogenicity is mediated mainly by its A and B toxins, but the colonization process is thought to be a necessary preliminary step in the course of infection. The aim of this study was to characterize the Cwp84 protease of C. difficile, which is highly immunogenic in patients with C. difficile-associated disease and is potentially involved in the pathogenic process. Cwp84 was purified as a recombinant His-tagged protein, and specific antibodies were generated in rabbits. Treatment of multiple-band-containing eluted fractions with a reducing agent or with trypsin led to accumulation of a unique protein species with an estimated molecular mass of 61 kDa, corresponding most likely to mature autoprocessed Cwp84 (mCwp84). mCwp84 showed concentration-dependent caseinolytic activity, with maximum activity at pH 7.5. The Cwp84 activity was inhibited by various cysteine protease inhibitors, such as the specific inhibitor E64, and the anti-Cwp84-specific antibodies. Using fractionation experiments followed by immunoblot detection, the protease was found to be associated with the S-layer proteins, mostly as a nonmature species. Proteolytic assays were performed with extracellular matrix proteins to assess the putative role of Cwp84 in the pathogenicity of C. difficile. No degrading activity was detected with type IV collagen. In contrast, Cwp84 exhibited degrading activity with fibronectin, laminin, and vitronectin, which was neutralized by the E64 inhibitor and specific antibodies. In vivo, this proteolytic activity could contribute to the degradation of the host tissue integrity and to the dissemination of the infection.