Contribution of different adherent properties of Granulicatella adiacens and Abiotrophia defectiva to their associations with oral colonization and the risk of infective endocarditis

Granulicatella adiacens (G. adiacens) and Abiotrophia defectiva (A. defectiva) colonize the oral cavity and form part of the normal flora in the intestinal and genitourinary tracts. As reported previously, the frequency of isolation of G. adiacens from the oral cavity was much higher than that of A. defectiva. However, it has been reported that compared with G. adiacens, A. defectiva was isolated at considerably higher frequencies from the blood of patients with infective endocarditis (IE). Hence, in this study, the in vitro interaction of G. adiacens and A. defectiva strains with host surfaces and biofilm formation was examined to assess whether their different adhesive properties contribute to their associations with oral colonization and IE, respectively. G. adiacens exhibited an increased binding ability to saliva-coated hydroxyapatite beads than A. defectiva following the addition of CaCl2. Furthermore, biofilm formation was observed only for G. adiacens with the use of a polystyrene tube and scanning electron microscopy analysis. Conversely, A. defectiva displayed significantly greater adherence to human umbilical vein endothelial cells and immobilized fibronectin than G. adiacens. These findings suggest that differences in binding properties to host components imply specific binding mechanisms in G. adiacens and A. defectiva, which might mediate selective colonization in the oral cavity or are associated with the pathogenicity of endocarditis.