Serotype-specific role of antigen I/II in the initial steps of the pathogenesis of the infection caused by Streptococcus suis

Sarah Chuzeville,Daniel Grenier,Audrey Dumesnil,Nahuel Fittipaldi,Jean-Philippe Auger,Sonia Lacouture,Marcelo Gottschalk,David Roy

doi:10.1186/s13567-017-0443-4

Abstract

Streptococcus suis is one of the most important post-weaning porcine bacterial pathogens worldwide. The serotypes 2 and 9 are often considered the most virulent and prevalent serotypes involved in swine infections, especially in Europe. However, knowledge of the bacterial factors involved in the first steps of the pathogenesis of the infection remains scarce. In several pathogenic streptococci, expression of multimodal adhesion proteins known as antigen I/II (AgI/II) have been linked with persistence in the upper respiratory tract and the oral cavity, as well as with bacterial dissemination. Herein, we report expression of these immunostimulatory factors by S. suis serotype 2 and 9 strains and that AgI/II-encoding genes are carried by integrative and conjugative elements. Using mutagenesis and different in vitro assays, we demonstrate that the contribution of AgI/II to the virulence of the serotype 2 strain used herein appears to be modest. In contrast, data demonstrate that the serotype 9 AgI/II participates in self-aggregation, induces salivary glycoprotein 340-related aggregation, contributes to biofilm formation and increased strain resistance to low pH, as well as in bacterial adhesion to extracellular matrix proteins and epithelial cells. Moreover, the use of a porcine infection model revealed that AgI/II contributes to colonization of the upper respiratory tract of pigs. Taken together, these findings suggest that surface exposed AgI/II likely play a key role in the first steps of the pathogenesis of the S. suis serotype 9 infection.

Highlights

Streptococcus suis is one of the most important postweaning bacterial pathogens of pigs and a major economic problem for the porcine industry [1]
antigen I/ II (AgI/II) proteins have been extensively described in oral pathogenic streptococci as multimodal adhesion proteins and immunostimulatory components implicated in host upper respiratory tract and oral cavity persistence and dissemination [11]
These proteins have been described in pyogenic streptococci, such as S. pyogenes and S. agalactiae, but they have never been identified in Streptococcus pneumoniae [11]

Summary

Introduction

Streptococcus suis is one of the most important postweaning bacterial pathogens of pigs and a major economic problem for the porcine industry [1]. Septicemia with sudden death, meningitis, arthritis, and endocarditis are the most frequent clinical signs caused by S. suis in pigs [2]. S. suis is a zoonotic agent responsible for numerous human cases of meningitis, septicemia, and streptococcal toxic shock-like syndrome [2]. The first S. suis serotype 9 human case of infection was reported in 2015 [7]. The upper respiratory tract of pigs, the tonsils and nasal cavities, are important reservoirs of S. suis [1]. S. suis has been shown to be present in nearly half of the submaxillary lymph node samples of clinically healthy pigs [9]. Bacterial loads in saliva swab and tonsillar brush samples are similar, indicating that S. suis is a natural inhabitant of the oral cavity [10]

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Results

Conclusion