Cell surface characteristics of nontypeable isolates of Streptococcus suis.

Streptococcus suis is a worldwide cause of various swine infections and is also an important agent of zoonosis. Strains of S. suis are classified according to their serotype, and currently, 35 serotypes are recognized. The aim of this study was to characterize nontypeable isolates of S. suis with regard to their cell surface properties and compare them with serotype 2 strains, the most frequently associated with infections. The seven nontypeable strains of S. suis isolated from infected animals demonstrated a stronger capacity to adhere to a fibronectin-coated polystyrene surface than the serotype 2 isolates. Three nontypeable strains were also tested for their ability to adhere to endothelial cells and were found to attach in higher amounts compared with the serotype 2 isolates. Electron microscopy analysis revealed the absence of a capsule in the seven nontypeable isolates, which correlated with a much higher cell surface hydrophobicity than that of serotype 2 isolates. All nontypeable isolates of S. suis also showed the capacity to form a biofilm while serotype 2 isolates were unable to do so. In conclusion, the nontypeable isolates of S. suis examined in this study possess surface properties different from those of serotype 2 isolates.