Enolase and dipeptidyl peptidase IV protein sub-unit vaccines are not protective against a lethal Streptococcus suis serotype 2 challenge in a mouse model of infection

Audrey Dumesnil,Léa Martelet,Josée Harel,Jean-Philippe Auger,Marcelo Gottschalk,Daniel Grenier,Eric Nadeau

doi:10.1186/s12917-019-2196-y

Audrey Dumesnil, Léa Martelet + Show 5 more

Open Access

https://doi.org/10.1186/s12917-019-2196-y

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Abstract

BackgroundStreptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in post-weaning piglets and is also a zoonotic agent. S. suis comprises 35 different serotypes of which the serotype 2 is the most prevalent in both pigs and humans. In the absence of commercial vaccines, bacterins (mostly autogenous), are used in the field, with controversial results. In the past years, the focus has turned towards the development of sub-unit vaccine candidates. However, published results are sometimes contradictory regarding the protective effect of a same candidate. Moreover, the adjuvant used may significantly influence the protective capacity of a given antigen. This study focused on two protective candidates, the dipeptidyl peptidase IV (DPPIV) and the enolase (SsEno). Both proteins are involved in S. suis pathogenesis, and while contradictory protection results have been obtained with SsEno in the past, no data on the protective capacity of DPPIV was available.ResultsResults showed that among all the field strains tested, 86 and 88% were positive for the expression of the SsEno and DPPIV proteins, respectively, suggesting that they are widely expressed by strains of different serotypes. However, no protection was obtained after two vaccine doses in a CD-1 mouse model of infection, regardless of the use of four different adjuvants. Even though no protection was obtained, significant amounts of antibodies were produced against both antigens, and this regardless of the adjuvant used.ConclusionsTaken together, these results demonstrate that S. suis DPPIV and SsEno are probably not good vaccine candidates, at least not in the conditions evaluated in this study. Further studies in the natural host (pig) should still be carried out. Moreover, this work highlights the importance of confirming results obtained by different research groups.

Highlights

Streptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in postweaning piglets and is a zoonotic agent
Production of dipeptidyl peptidase IV (DPPIV) and SsEno by field strains of S. suis belonging to different serotypes Antisera produced against recombinant enolase and DPPIV showed clear reactions with purified proteins of expected molecular masses of approximately 75 kDa and 100 kDa, respectively (Fig. 1A and B)
The constitutional expression of SsEno and DPPIV was evaluated in S. suis field strains by dot-blot with these mono-specific polyclonal hyperimmune rabbit sera

Summary

Introduction

Streptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in postweaning piglets and is a zoonotic agent. This study focused on two protective candidates, the dipeptidyl peptidase IV (DPPIV) and the enolase (SsEno) Both proteins are involved in S. suis pathogenesis, and while contradictory protection results have been obtained with SsEno in the past, no data on the protective capacity of DPPIV was available. Streptococcus suis (S. suis) is one of the most frequent causes of mortality in weaned piglets worldwide, causing mainly septicemia with sudden death, meningitis and arthritis [1]. It is considered an emerging zoonotic agent, mainly in South-East Asia, as an etiological agent of meningitis and septic shock [2, 3]. Serotype 2 is by far the serotype most frequently recovered from ill patients, followed by serotype 14 [6]

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