Abstract
Streptococcus suis (SS) is a zoonotic pathogen that causes severe disease symptoms in pigs and humans. Biofilms of SS bind to extracellular matrix proteins in both endothelial and epithelial cells and cause persistent infections. In this study, the differences in the protein expression profiles of SS grown either as planktonic cells or biofilms were identified using comparative proteomic analysis. The results revealed the existence of 13 proteins of varying amounts, among which six were upregulated and seven were downregulated in the Streptococcus biofilm compared with the planktonic controls. The convalescent serum from mini-pig, challenged with SS, was applied in a Western blot assay to visualize all proteins from the biofilm that were grown in vitro and separated by two-dimensional gel electrophoresis. A total of 10 immunoreactive protein spots corresponding to nine unique proteins were identified by MALDI-TOF/TOF-MS. Of these nine proteins, five (Manganese-dependent superoxide dismutase, UDP-N-acetylglucosamine 1-carboxyvinyltransferase, ornithine carbamoyltransferase, phosphoglycerate kinase, Hypothetical protein SSU05_0403) had no previously reported immunogenic properties in SS to our knowledge. The remaining four immunogenic proteins (glyceraldehyde-3-phosphate dehydrogenase, hemolysin, pyruvate dehydrogenase and DnaK) were identified under both planktonic and biofilm growth conditions. In conclusion, the protein expression pattern of SS, grown as biofilm, was different from the SS grown as planktonic cells. These five immunogenic proteins that were specific to SS biofilm cells may potentially be targeted as vaccine candidates to protect against SS biofilm infections. The four proteins common to both biofilm and planktonic cells can be targeted as vaccine candidates to protect against both biofilm and acute infections.
Highlights
Streptococcus suis (SS) is a major worldwide pathogen and colonizes the respiratory tract of pigs, the tonsils and nasal cavities [1]
Comparative Proteomics 2DGE of proteins from SS grown as biofilms or planktonic cells was performed to characterize the differences in protein expression between the two groups
A total of 15 dominant protein spots were different between SS grown as biofilms or planktonic cells
Summary
Streptococcus suis (SS) is a major worldwide pathogen and colonizes the respiratory tract of pigs, the tonsils and nasal cavities [1]. Some studies have demonstrated that SS has the ability to form biofilms [6,7]. The biofilm mode of growth affords SS several advantages over its planktonic counterparts, including the capability of ECM to trap nutrients and protect against both antimicrobial agents and the host immune responses [6,7]. Our previous studies indicate that SS maybe achieve persistent infections in vivo by forming biofilms [8] and SS infections might be difficult to treat. It has been postulated that an altered metabolism and changes in gene expressions and protein amounts in biofilms may be responsible for drug resistance, cell adherence and virulence. Recent results indicate that biofilm cells have an active, altered cell metabolism [10,11]. Considerable investigation is required to gain a better understanding of biofilm formation
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