Prevalence of Csh‐like fibrillar surface proteins among mitis group oral streptococci

Abstract

The prevalence of Csh-like fibrillar surface proteins among oral streptococci was investigated by ELISA and by immunoelectron microscopy using antiserum raised to recombinant fragments of CshA of Streptococcus gordonii DL1. The majority of S. gordonii, Streptococcus sanguis and Streptococcus oralis strains tested elaborated short (ca. 50-80 nm long) surface fibrils and reacted with antiserum to the amino acid repeat region of CshA, demonstrating the widespread nature of Csh-like proteins among these species. In contrast, reactivity with antiserum raised to the adhesion-mediating non-repetitive region of CshA was more restricted. On the basis of the ELISA results, several isolates were selected for immunogold analysis using CshA antisera. Immunogold-negative staining showed a surface distribution of 10 nm gold particles consistent with antibody binding to short fibrils. Long fibrils (>150 nm long), where present, were not significantly labelled with gold. The results suggest that some of the short peritrichous fibrils on many mitis group streptococci comprise Csh-like fibrillar protein. Further, the data are consistent with our hypothesis that the antigenically conserved amino acid repeat region of Csh-like proteins forms a scaffold for cell-distal presentation of the amino-terminal non-repetitive region that, at least in S. gordonii DL1, functions as an adhesin.

Mitis Group Streptococci Express Variable Pilus Islet 2 Pili

“…They were visualized by negative staining and described as tufts, fibrils or fimbriae, and ranged from a 30 nm to ≤700 nm that either coexisted on the bacterial cell or seemed to be mutually exclusive [60], [63]. S. oralis strains ATCC35037, ATCC10557, and 34 were described to express fibrils, but no fimbriae [64]. The molecular nature of these structures remained elusive until cross-reactive antibodies against the Csh-like protein, first identified in S. gordonii [25], detected fibrils of 50–80 nm on several S. oralis and S. sanguinis strains [64].…”

“…S. oralis strains ATCC35037, ATCC10557, and 34 were described to express fibrils, but no fimbriae [64]. The molecular nature of these structures remained elusive until cross-reactive antibodies against the Csh-like protein, first identified in S. gordonii [25], detected fibrils of 50–80 nm on several S. oralis and S. sanguinis strains [64]. CshA homologs are encoded in S. oralis and S. mitis , but due to major sequence variation in the binding domain, their function remains to be determined [64].…”

“…The molecular nature of these structures remained elusive until cross-reactive antibodies against the Csh-like protein, first identified in S. gordonii [25], detected fibrils of 50–80 nm on several S. oralis and S. sanguinis strains [64]. CshA homologs are encoded in S. oralis and S. mitis , but due to major sequence variation in the binding domain, their function remains to be determined [64]. However, the PI-2 pili described in this study were considerably longer (>700 nm), and therefore inconsistent with these fibrilar surface structures.…”

Biology of Oral Streptococci

“…Notably, instead of the general secretion machinery utilized for other surface proteins, an alternative secretion system including SecA2 and SecY2 is dedicated to the translocation of this family of serine-rich proteins (67, 75). In addition, CshA of S. gordonii and CshA-like proteins of S. oralis and S. sanguinis are multi-functional fibrillar adhesins that bind to multiple host proteins including fibronectin, as well as to other microorganisms(76, 77). …”

Adhesion determinants of the Streptococcus species

“…Moreover, antibodies raised against S. gordonii CshA recognized on the surface of S. sanguinis and S. oralis short peritrichous fibrils, demonstrating the widespread nature of Csh‐like proteins among streptococcal species, data also confirmed by sequence similarity analysis (Fig. 3) (Elliott et al. , 2003).…”