Identification, purification, and characterization of a thiol-activated hemolysin (suilysin) of Streptococcus suis

Abstract

The present report describes the identification, purification, and characterization of a hemolysin produced by Streptococcus suis type 2. The hemolysin was purified from the culture supernatant by using different filtration steps, Superose-12 column chromatography, and selective (NH4)2SO4 precipitation. The purified hemolysin, designated suilysin, had an apparent molecular mass of 54,000 Da and exhibited a specific activity of 0.7 x 106 hemolytic units per mg. Suilysin appeared to belong to a family of toxins known as the thiol-activated toxins, with which it had several characteristics in common: loss of activity upon oxidation, reactivation upon reduction, and inhibition of activity by small amounts of cholesterol. The N-terminal amino acid sequence of suilysin showed many similarities with parts of the deduced N-terminal amino acid sequences of perfringolysin 0, streptolysin 0, listeriolysin 0, alveolysin, and pneumolysin. Mice immunized with a vaccine containing purified suilysin appeared to be completely protected against a lethal S. suis type 2 challenge, indicating that suilysin is an important factor and that the neutralization of this single factor is sufficient to protect mice against the detrimental effects of an S. suis type 2 infection. Most of the different (serotype) strains appeared to secrete hemolytic activity which was biochemically and immunologically indistinguishable from suilysin into the culture supernatant in vitro, indicating that suilysin might be a cross-protection factor.

Epithelial invasion and cell lysis by virulent strains of Streptococcus suis is enhanced by the presence of suilysin

“…A lytic ability in other streptococci has been attributed to heamolysins [21]. S. suis has an identi¢ed thiolactivated haemolysin, SLY [12,13]. A contribution by SLY to the lytic process was con¢rmed by the antibody inhibition of lysis.…”

“…A greater ability to invade may be conferred on virulent strains by speci¢c bacterial factors not expressed by the less virulent strains. Three proteins have been identi¢ed which are associated with virulence, extracellular factor (EF), muraminidase released protein (MRP) [11] and suilysin (SLY) [12,13]. No speci¢c activity or role has been assigned to EF and MRP and the virulence is not attenuated by mutation of the genes encoding these proteins in one animal model [14] although they correlate strongly with virulence among European isolates.…”

Pro-inflammatory cytokine and chemokine release by human brain microvascular endothelial cells stimulated by Streptococcus suis serotype 2

“…Comparative studies of cytokine induction by S. suis strain S735 and its unencapsulated mutant 2A were always done in parallel [4]. In separate experiments, cells were stimulated with di¡erent concentrations of pu-ri¢ed CPS, cell wall or suilysin, puri¢ed as previously described [17,27,30]. Endothelial cells stimulated with lipopolysaccharide (LPS) from E. coli 0127:B8 (Sigma-Aldrich) (10 Wg ml 31 for BMEC and 1 Wg ml 31 for HU-VEC) served as a positive control.…”

“…Adhesion of S. suis to BMEC may have di¡erent consequences which may lead to increased permeability of the BBB. For example, some strains produce a toxin (suilysin) [12,17], that was reported as being toxic for BMEC and other cells [6,21]. However, only European strains of S. suis produce this hemolysin [12].…”

Characterisation of the gene encoding suilysin from Streptococcus suis and expression in field strains

“…Thiol-activated cytolysins (TACY) are a family of pore-forming toxins produced by members of the Streptococcus, Listeria, Bacillus, and Clostridium genera [4]. Recently, a new TACY was isolated from Streptococcus suis and designated suilysin [5]. In contrast to other extracellular antigens, suilysin can protect pigs from virulent challenge after vaccination [6].…”