Subunit Vaccine Targeting Phosphate ABC Transporter ATP-Binding Protein, PstB, Provides Cross-Protection against Streptococcus suis Serotype 2, 7, and 9 in Mice

Abstract

Streptococcus suis is a significant pathogen in pigs and a newly emerging zoonotic agent in humans. The presence of multiple serotypes and strains with diversified sequence types in pig herds highlights the need for the identification of broadly cross-reactive universal vaccine antigen targets, capable of providing cross-protection against S. suis infection. Subunit vaccines based on the conserved proteins shared between different S. suis serotypes are potential candidates for such a universally protective vaccine. In the present study, phosphate ABC transporter ATP-binding protein PstB (PstB), an immunogenic protein of the S. suis bacterium, was expressed and purified, and then subjected to cross-protection evaluation in mice. The PstB protein showed nearly 100% amino acid similarity across a panel of 31 S. suis isolates representing different serotypes, which were collected from different countries. A recombinant PstB (rPstB) protein (S. suis serotype 2) was recognized by rabbit sera specific to this serotype, and induced high levels of IFN-γ and IL-4 in mice immunized with the recombinant protein. These cytokines are considered important for protection against S. suis infection. Immunization of mice with rPstB resulted in an 87.5% protection against challenge with S. suis serotype 2 and 9 strains, suggesting a high level of cross-protection for S. suis serotypes 2 and 9. A lower protection rate (62.5%) was observed in mice challenged with the S. suis serotype 7 strain. These data demonstrate that PstB is a promising target antigen for development as a component of a universal subunit vaccine against multiple S. suis serotypes.

Bovine Herpesvirus-4 Based Vaccine Provides Protective Immunity against Streptococcus suis Disease in a Rabbit Model

“…Cells were incubated at 37 °C in a normal atmosphere supplemented with 5% CO 2 and used for the reconstitution of recombinant BoHV-4/GMD and BoHV-4/SLY BACs and preparation of virus stocks. SS2 (ZY05719 strain), SS7 (SH04815 strain), and SS9 (SH26 strain) were in-house field isolates previously recovered from diseased pigs in China [ 32 ]. All S. suis isolates were grown in tryptone soya broth (OXOID, Basingstoke, UK) supplemented with 5% fresh sheep blood under static condition at 37 °C.…”

“…Cells were incubated at 37 • C in a normal atmosphere supplemented with 5% CO 2 and used for the reconstitution of recombinant BoHV-4/GMD and BoHV-4/SLY BACs and preparation of virus stocks. SS2 (ZY05719 strain), SS7 (SH04815 strain), and SS9 (SH26 strain) were in-house field isolates previously recovered from diseased pigs in China [32]. All S. suis isolates were grown in tryptone soya broth (OXOID, Basingstoke, UK) supplemented with 5% fresh sheep blood under static condition at 37 • C. To count SS2, first aspirate 100 µL of SS2 bacterial solution, dilute into a pre-prepared 900 µL sterile PBS solution, dilute to 10 −6 at a 10-fold ratio, apply 100 µL dilution on Colombian blood agar plates, replicate 4 times per dilution, invert in a 37 • C constant temperature incubator, and record the number of colonies on the plates the next day.…”

Immunogenicity and Protective Capacity of Sugar ABC Transporter Substrate-Binding Protein against Streptococcus suis Serotype 2, 7 and 9 Infection in Mice

“…Blood samples were collected from mice at times indicated for the analysis of antibodies against the recombinant S-ABC proteins with an ELISA, as described previously [13]. Briefly, purified rS-ABC or rS-ABC-epitope proteins were coated onto ELISA plates at 1 µg per well and incubated at 4 • C overnight.…”

“…In the past decade, a number of surface-associated immunogenic proteins of S. suis have been identified and evaluated as potential universal subunit vaccine candidates [6,12]. There are several proteins, such as muramidase-released protein (MRP), extracellular protein factors, parvulin-like peptidylprolyl isomerases (PrsA), phosphate ABC transporter ATP-binding protein (PstB), enolase, and Sao, have all been evaluated in mouse and pig models for the induction of protective immunity against homologous as well as heterologous strains of S. suis [13][14][15][16][17][18].…”

Development of a Universal Multi-Epitope Vaccine Candidate against Streptococcus suis Infections Using Immunoinformatics Approaches

“…S. suis outbreak prevention in a particular farm is mainly achieved through autogenous (bacterins) vaccines; however, vaccine cross-protection between different strains is limited and data regarding vaccine safety are lacking [ 10 ]. In the past two decades, various immunogenic proteins that are highly conserved across different serotypes have been shown to elicit immune responses in animal models [ 11 , 12 , 13 , 14 ]. The development of a vaccine composed of multiple protein antigens is probably an attractive strategy to control infections caused by a broad range of serotypes through the targeting of several important virulence factors [ 15 , 16 ].…”