Abstract
Streptococcus suis serotype 2 is an important porcine and human pathogen. Lipoteichoic acid (LTA) from S. suis has been suggested to contribute to its virulence, and absence of d-alanylation from the S. suis LTA is associated with increased susceptibility to cationic antimicrobial peptides. Here, using high-resolution NMR spectroscopy and MS analyses, we characterized the LTA structures from three S. suis serotype 2 strains differing in virulence, sequence type (ST), and geographical origin. Our analyses revealed that these strains possess-in addition to the typical type I LTA present in other streptococci-a second, mixed-type series of LTA molecules of high complexity. We observed a ST-specific difference in the incorporation of glycosyl residues into these mixed-type LTAs. We found that strains P1/7 (ST1, high virulence) and SC84 (ST7, very high virulence) can attach a 1,2-linked α-d-Glcp residue as branching substituent to an α-d-Glcp that is 1,3-linked to glycerol phosphate moieties and that is not present in strain 89-1591 (ST25, intermediate virulence). In contrast, the latter strain could glycosylate its LTA at the glycerol O-2 position, which was not observed in the other two strains. Using LTA preparations from WT strains and from mutants with an inactivated prolipoprotein diacylglyceryl transferase, resulting in deficient lipoprotein acylation, we show that S. suis LTAs alone do not induce Toll-like receptor 2-dependent pro-inflammatory mediator production from dendritic cells. In summary, our study reveals an unexpected complexity of LTAs present in three S. suis serotype 2 strains differing in genetic background and virulence.
Highlights
Activation of DCs with LTA preparations from Lgt-deficient mutants of the three S. suis strains led to a complete abrogation of proinflammatory mediator production, regardless of the concentration of LTA used (p Ͻ 0.001) (Fig. 8). These results suggested that the co-purified LPs, but not the LTA, are the main activators of DCs when using LTA preparations from the S. suis strains P1/7, SC84, and 89-1591
We investigated three different serotype 2 strains: P1/7 (ST1), SC84 (ST7), and 89-1591 (ST25)
To destroy the TLR2 activity caused by potentially co-purified LPs, LTA preparations were treated with 1% H2O2 for 24 h at 37 °C followed by dialysis as described previously [23]
Summary
Streptococcus suis serotype 2 is an important porcine and human pathogen. Lipoteichoic acid (LTA) from S. suis has been suggested to contribute to its virulence, and absence of D-alanylation from the S. suis LTA is associated with increased susceptibility to cationic antimicrobial peptides. Using high-resolution NMR spectroscopy and MS analyses, we characterized the LTA structures from three S. suis serotype 2 strains differing in virulence, sequence type (ST), and geographical origin. Our study reveals an unexpected complexity of LTAs present in three S. suis serotype 2 strains differing in genetic background and virulence. We chose ST1, ST7, and ST25 strains for our analyses because of their importance as predominant virulent S. suis serotype 2 strains, which are responsible for most porcine and human infections worldwide [3]. We describe the structural analysis of LTA isolated from three S. suis serotype 2 strains of different background as representatives of the most clinically and epidemiologically important STs using chemical degradations, high-resolution MS analysis, as well as one- and two-dimensional, homo- and heteronuclear NMR spectroscopy. The immunostimulatory properties of these well-characterized LTA preparations were evaluated to understand their role in the activation and modulation of the host innate immune response by S. suis
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