Identification of two proteins associated with virulence of Streptococcus suis type 2

Abstract

The protein profiles of various cell fractions of 180 strains of Streptococcus suis type 2, which were isolated from diseased pigs, from healthy pigs when they were slaughtered, and from human patients, were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The isolates from diseased pigs contained two proteins that were absent in most of the isolates from healthy pigs. One of these proteins was a 136-kDa protein that was previously identified as the muramidase-released protein (MRP). This protein was predominantly detected in protoplast supernatants and culture supernatants. The second protein was a 110-kDa protein that was detected only in culture supernatants and therefore was provisionally called extracellular factor (EF). Three phenotypes of S. suis type 2 strains were recognized. Isolates from organs of diseased pigs mainly belonged to the MRP+ EF+ phenotype (77%), while isolates from tonsils of healthy pigs mainly had the MRP- EF- phenotype (86%). Most of the isolates from human patients contained MRP (89%); 74% had the MRP+ EF- phenotype. These findings confirm the results of previous investigations which demonstrated that S. suis type 2 strains differ in virulence. Monoclonal antibodies raised against the 110-kDa EF recognized proteins with higher molecular weights in culture supernatants of all of the strains with the MRP+ EF- phenotype. However, none of the strains with the MRP+ EF+ phenotype produced these high-molecular-weight proteins. Our results demonstrate that MRP and EF are associated with virulence. This suggests that one or both of these proteins are virulence factors that play a role in the pathogenesis of S. suis type 2 infections in pigs and human patients.

Probing genomic diversity and evolution of Streptococcus suis serotype 2 by NimbleGen tiling arrays

“…significantly variant genes, respectively, including 88 genes shared by all three avirulent strains (additional file 3). The virulence-related epf gene cluster [10,11], which encodes extracellular protein factor (EF; a putative virulence marker that widely exists in virulent strains) was absent in the avirulent strains [12]. Consistent with previous research, this gene cluster is present in all of the analyzed virulent strains.…”

“…The S. suis strains used in this study are listed in Table 1. The virulent strains were isolated from diseased patients or swine, and the avirulent strains were isolated from healthy swine and were identified as avirulent in a pig model [4,12,14]. Cells were cultured in Todd-Hewitt broth (THB) (Difco Laboratories, Detroit, MI) medium.…”

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

“…The LDH released into the medium was determined using the Cytotox'96 assay kit (Promega) according to the manufacturer's instructions. In some assays, monoclonal antibodies to SLY or EF [11] were added. In these cases, serial dilutions of the antibody in culture medium were prepared.…”

“…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.…”

Vaccines in Veterinary Medicine: A Brief Review of History and Technology

“…In some cases, such as with influenza virus, canine distemper virus, and herpesvirus vaccines, nonneutralizing antibody may be produced that does not contribute to the blocking of infection or enhancing clearance of the infectious agent. 24,26 For this reason, correlates or surrogates of protection should be linked to protective mechanisms; this can be done through retrospective analysis of data from efficacy and immunogenicity studies or through associational studies in immune populations (such as with primary vaccinates in an efficacy study).…”