Methods: We used the oral isolate MT8148 (PA+/CBP-) and blood isolate TW871 (PA+/CBP+), along with PA-defective isogenic mutant strains of MT8148 and TW871 (MT8148PD and TW871PD, respectively). Collagen-binding activity and invasion of human umbilical vein endothelial cells (HUVEC) were examined, and cellular hydrophobicity and sucrose-dependent adhesion rates were determined. Furthermore, the distribution frequency of strains expressing PA and CBP were examined among 170 S. mutans clinical isolates by western blotting with antiserum for each protein antigen.
Results: TW871PD showed significantly higher rates of collagen-binding activity and invasion to HUVEC as compared to TW871. As for MT8148 and MT8148PD, the rates of collagen-binding activity and invasion were almost negligible. Analysis of the 170 S. mutans clinical isolates revealed that the distribution frequencies of PA+/CBP-, PA+/CBP+, and PA-/CBP+, and PA-/CBP- strains were approximately 88%, 9%, 3%, and 0%, respectively. The PA-/CBP+ strains showed lower cellular hydrophobicity and sucrose-dependent adhesion rates than the PA+/CBP- strains, while most of The PA-/CBP+ strains showed high invasion activities to HUVEC.
Conclusions: Lack of PA expression in CBP-positive S. mutans strains, which are considered to have low cariogenic characteristics, may be associated with high virulence for infective endocarditis because of their collagen-binding properties and invasion activities to HUVEC.