Abiotrophia defectiva adhere to saliva-coated hydroxyapatite beads via interactions between salivary proline-rich-proteins and bacterial glyceraldehyde-3-phosphate dehydrogenase.

Abiotrophia defectiva is a species of nutritionally variant streptococci that is found in human saliva and dental plaques and that has been associated with infective endocarditis. In our previous study, it was found that A. defectiva could bind specifically to saliva-coated hydroxyapatite beads (SHA). This study identified a cell surface component of A. defectiva that promotes adherence to SHA beads. The binding of A. defectiva to SHA was reduced in the presence of antibodies against human proline-rich protein (PRP); these results suggested that PRP may be a critical component mediating interactions between A. defectiva and the salivary pellicle. Two-dimensional gel electrophoresis of whole A. defectiva cells followed by Far-Western blotting was conducted by probing with synthetic peptides analogous to the binding region of PRP known as PRP-C. The results indicate that an A. defectiva protein of 37 kDa interacts with PRP-C. The results of amino-terminal sequencing of the adhesive A. defectiva protein revealed significant similarity to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Recombinant GAPDH bound to immobilized PRP-C in a dose-dependent manner and binding of A. defectiva to SHA or to PRP was reduced in the presence of anti-GAPDH antiserum. Western blotting or electron immunomicroscopic observations with anti-GAPDH antiserum revealed that this protein was expressed in both cytosolic and cell wall fractions. These results suggest that A. defectiva could specifically bind to PRP via interactions with cell surface GAPDH; the findings suggest a mechanism underlying A. defectiva-mediated adherence to saliva-coated tooth surfaces.

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.

Infective endocarditis caused by Granulicatella elegans originating in the oral cavity.

We studied the pheno- and genotypes of an oral Granulicatella elegans strain in comparison with those of a blood-derived isolate which caused infective endocarditis. The two isolates exhibited identical biochemical characteristics and had the same drug MICs. Their genotypes were indistinguishable, indicating that these were from the same clone. The transmission of G. elegans from the oral cavity thus should be noted as a possible cause of infective endocarditis.

Characterization and molecular cloning of a glutamyl endopeptidase from Staphylococcus epidermidis.

A novel extracellular endopeptidase, designated GluSE, was purified from Staphylococcus epidermidis ATCC 14990 cultured by the dialysis membrane technique, and the structural gene (gseA) was cloned. GluSE was a 27kDa, glutamic acid-specific protease, and the optimal pH was 8.0. The proteolytic activity was specifically inhibited with diisopropyl fluorophosphate, indicating that it is a serine protease. The gseA encoded a single polypeptide of 282 amino acids with a deduced molecular weight of 30,809, in which the first 19 N-terminal amino acids completely matched the deduced sequence starting at Val-67, suggesting that GluSE is synthesized with a propeptide. The amino acid sequence of GluSE exhibited 50.5% identity to Staphylococcus aureus V8-protease (GluV8). Although GluSE lacks a C-terminal 12 repeats of the PBN/PBZ tripeptide of GluV8, a catalytic triad of His-117, Asp-159 and Ser-235 was conserved in GluSE. Southern hybridization analysis revealed that gseA exists as a single copy on the chromosomal DNA. The finding that production of GluSE was obviously observed in the adherent culture conditions of the dialysis membrane technique, but not in the planktonic culture conditions, strongly suggests that GluSE could be involved in an important etiologic process in S.epidermidis infection leading to multiple tissue damages.