We examined the role of the collagen-binding function of CNA in a mouse model of septic arthritis by comparing the virulence of isogenic strains of S. aureus expressing (1) wild-type CNA, (2) a truncated form of CNA (CNA35) with a higher affinity for collagen than the wild type, (3) CNA35 containing a single point mutation resulting in loss of collagen binding, (4) CNA lacking the collagen-binding domain, and (5) the collagen-binding domain of ACE (adhesin of collagen from Enterococcus faecalis).