Identification and Experimental Verification of Protective Antigens Against Streptococcus suis Serotype 2 Based on Genome Sequence Analysis

Abstract

Streptococcus suis serotype 2 (S. suis 2) is an important zoonotic pathogen that can cause severe disease and even death in both humans and swine. No effective vaccine is clinically available. In this study, a reverse vaccinology method was first applied to identify protective antigens against S. suis 2. As a consequence, 153 genes encoding vaccine candidates were selected from the whole genome sequence by means of bioinformatics analysis, from which 10 genes were selected based on experimental evidences arising from the study of related bacteria such as Streptococcus pneumoniae, group B streptococcus, S. suis and so on. Of 10 target genes, 8 were successfully expressed in Escherichia coli Rosetta, and expressed proteins were purified and used as the immunogens for evaluating vaccine efficacy in a mouse infection model. The results have confirmed that RTX family exoprotein A (RfeA), epidermal surface antigen (ESA), immunoglobulin G (IgG)-binding protein (IBP), and suilysin (SLY) can induce a protective response of the vaccinated animals against S. suis 2, whereas RfeA, ESA, and IBP mainly induce humoral-mediated immunity, and SLY elicits a combined pattern of both humoral- and cellular-mediated immunity. Although immunoprotection of SLY against S. suis 2 was reported previously, RfeA, ESA, and IBP were explored first in this study.

Streptococcus suisinfection

“…Of note, most of the remaining 10 protein antigens were elucidated by research groups in China. In 2009, in addition to identification of the known protective antigen SLY, Liu’s report verified three more new protective antigens that are RTX family exoprotein A (RfeA), epidermal surface antigen (ESA), and immunoglobulin G (IgG)-binding protein (IBP) 172 . Two different research groups from China confirmed that enolase, an enzyme of central metabolism, acts as a protective antigen displayed on bacterial surface 96 , 129 .…”

HtpS, a novel immunogenic cell surface-exposed protein of Streptococcus suis, confers protection in mice

“…The HtpS protection test was performed as described previously (Liu et al , 2009), with some modifications. Briefly, 4‐week‐old, SPF grade female BALB/c mice (SLAC, China) were divided into two groups (10 mice per group).…”

Streptococcus suisEnolase Functions as a Protective Antigen Displayed on the Bacterial Cell Surface

“…Two days after inoculation, 15 of 15 mice in the negative control group had died, but the mice immunized with suilysin or enolase survived and did not show any clinical signs of SS2 infection (eg, ruffled hair, absentmindedness, and poor appetite) (Table 1). Therefore, we conclude that, for mice, enolase can confer a level of protection similar to that of suilysin, a well-known protective antigen [36,38]. To better understand the molecular mechanism by which enolase functions as a protective antigen, we used a bioinformatics approach to dissect possible B cell epitopes and MHC II-restricted peptides of enolase (data not shown).…”