Abstract
Streptococcus suis, more particularly serotype 2, is a major swine pathogen and an emerging zoonotic agent worldwide that mainly causes meningitis, septicemia, endocarditis, and pneumonia. Although several potential virulence factors produced by S. suis have been identified in the last decade, the pathogenesis of S. suis infections is still not fully understood. In the present study, we showed that S. suis produces membrane vesicles (MVs) that range in diameter from 13 to 130 nm and that appear to be coated by capsular material. A proteomic analysis of the MVs revealed that they contain 46 proteins, 9 of which are considered as proven or suspected virulence factors. Biological assays confirmed that S. suis MVs possess active subtilisin-like protease (SspA) and DNase (SsnA). S. suis MVs degraded neutrophil extracellular traps, a property that may contribute to the ability of the bacterium to escape the host defense response. MVs also activated the nuclear factor-kappa B (NF-κB) signaling pathway in both monocytes and macrophages, inducing the secretion of pro-inflammatory cytokines, which may in turn contribute to increase the permeability of the blood brain barrier. The present study brought evidence that S. suis MVs may play a role as a virulence factor in the pathogenesis of S. suis infections, and given their composition be an excellent candidate for vaccine development.
Highlights
Bacterial membrane vesicles were first discovered some five decades ago in Gram-negative bacteria [1]
We hypothesized that S. suis produces membrane vesicles (MVs) that may play an important role in the pathogenesis of S. suis infections
We hypothesized that S. suis produces MVs as it has been observed with other pathogenic streptococci [20, 21]
Summary
Bacterial membrane vesicles were first discovered some five decades ago in Gram-negative bacteria [1]. These globular structures, which range in diameter from 10 to 200 nm, result from outer membrane blebbing and are called outer membrane vesicles (OMV). Many roles have been assigned to OMVs, including intercellular communication [3], response to environmental stresses [4], biofilm formation [5], pathogenic processes [6], and horizontal gene transfer [7]. The rising interest in bacterial membrane vesicles lead to the creation of EVpedia, a web-based database that collects published data.
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