Abstract
Streptococcus suis serotype 2 is an important porcine bacterial pathogen associated with multiple pathologies in piglets. Bacterial lipoproteins (LPPs) have been described as playing important roles in the pathogenesis of the infection of other Gram-positive bacteria as adhesins, pro-inflammatory cell activators and/or virulence factors. In the current study, we aimed to evaluate the role of the prolipoprotein diacylglyceryl transferase (Lgt) and lipoprotein signal peptidase (Lsp) enzymes, which are responsible for LPP maturation, on the pathogenesis of the infection caused by two different sequence types (STs) of S. suis serotype 2 strains (virulent ST1 and highly virulent ST7). Through the use of isogenic Δlgt, Δlsp and double Δlgt/Δlsp mutants, it was shown that lack of these enzymes did not influence S. suis adhesion/invasion to porcine respiratory epithelial cells. However, in the absence of the Lsp and/or Lgt, a significant reduction in the capacity of S. suis to activate phagocytic cells and induce pro-inflammatory mediators (in vitro and in vivo) was observed. In general, results obtained with the double mutant did not differ in comparison to single mutants, indicating lack of an additive effect. Finally, our data suggest that these enzymes play a differential role in virulence, depending on the genetic background of the strain and being more important for the highly virulent ST7 strain.
Highlights
Streptococcus suis is one of the most important swine pathogens, causing meningitis, endocarditis, arthritis or septicemia with sudden death in weaned piglets
We showed that growth of the ∆lgt and ∆lsp S. suis mutant strains presented a normal growth in plasma, which is considered closer to in vivo conditions
Results from the current study indicate that S. suis mutants defective in LPP maturation are able to adhere to and invade porcine respiratory epithelial cells at similar rates when compared to their respective wild-type strains, suggesting that the LPP maturation enzymes are not essential for these bacterial-cell interactions
Summary
Streptococcus suis is one of the most important swine pathogens, causing meningitis, endocarditis, arthritis or septicemia with sudden death in weaned piglets. It is an emerging zoonotic agent causing disease in humans with clinical manifestations similar to those observed in piglets [1]. ST1 strains are virulent and are mostly associated with disease in both pigs and humans in Europe and Asia. The most important toxin produced by S. suis, plays different roles during the pathogenesis of the infection but is not a critical virulence factor, at least for infection in pigs [7]. An arsenal of surface proteins has been proposed as being important for virulence, most of these have not been confirmed [5]
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