CPA1 and bacterial arthritis: In the genetically closely related Streptococcus pyogenes (S. pyogenes), the adhesin Cpa has been shown to mediate attachment to tissues containing collagen type I. Furthermore, patients with a recent history of septic arthritis or osteomyelitis caused by S. pyogenes had increased anti-Cpa-titers, suggesting a role for this virulence factor in the pathogenesis of OAIs [15].