Study of cell surface associated virulence factors of Streptococcus parauberis strains pathogenic for turbot

The cell surface characteristics of a collection of Streptococcus parauberis strains isolated from turbot were examined, including the autoagglutinating and hemagglutinating capacities and the hydrophobic character. In addition, their possible relationship with the adhesive and invasive abilities of the strains was determined. S. parauberis isolates showed only hemagglutinating activity against turbot erythrocytes indicating host specificity for this character. Although hydrophobicity results were variable depending on the method employed, a good correlation was observed between BATH (adherence to hydrocarbons) and NCF (binding to nitrocellulose filters) tests. In addition, the growth media influenced the hydrophobic character of the strains, probably due to the induction of synthesis of capsular material. On the other hand, all the isolates from turbot of S. parauberis were moderately adherent and invasive in different poikilotherm and homoiotherm cell lines. Inhibition experiments showed that lipoteichoic acids markedly reduced the adherence levels, suggesting that these molecules are implicated in the adhesive mechanism of this fish pathogen.