The Clostridium difficile Exosporium Cysteine (CdeC)-Rich Protein Is Required for Exosporium Morphogenesis and Coat Assembly

Clostridium difficile is an important nosocomial pathogen that has become a major cause of antibiotic-associated diarrhea. There is a general consensus that C. difficile spores play an important role in C. difficile pathogenesis, contributing to infection, persistence, and transmission. Evidence has demonstrated that C. difficile spores have an outermost layer, termed the exosporium, that plays some role in adherence to intestinal epithelial cells. Recently, the protein encoded by CD1067 was shown to be present in trypsin-exosporium extracts of C. difficile 630 spores. In this study, we renamed the CD1067 protein Clostridium difficile exosporium cysteine-rich protein (CdeC) and characterized its role in the structure and properties of C. difficile spores. CdeC is expressed under sporulation conditions and localizes to the C. difficile spore. Through the construction of an Delta cdeC isogenic knockout mutant derivative of C. difficile strain R20291, we demonstrated that (i) the distinctive nap layer is largely missing in Delta cdeC spores; (ii) CdeC is localized in the exosporium-like layer and is accessible to IgGs; (iii) Delta cdeC spores were more sensitive to lysozyme, ethanol, and heat treatment than wild-type spores; and (iv) despite the almost complete absence of the exosporium layer, Delta cdeC spores adhered at higher levels than wild-type spores to intestinal epithelium cell lines (i.e., HT-29 and Caco-2 cells). Collectively, these results indicate that CdeC is essential for exosporium morphogenesis and the correct assembly of the spore coat of C. difficile.