# A conserved glycan motif induces broadly reactive functional antibodies against the zoonotic pathogen Streptococcus suis

## TL;DR

Researchers found a common sugar structure in the bacteria Streptococcus suis that can trigger protective antibodies, offering a new approach for vaccine development.

## Contribution

The study identifies a conserved glycan core as a novel vaccine target for S. suis.

## Key findings

- Two glycan variants were characterized, differing in glucose presence due to allelic variation in a glycosyltransferase gene.
- Deleting the variable glycosyltransferase revealed a conserved glycan core affecting bacterial morphology and lysozyme resistance.
- Immunizing pigs with the glycan core induced antibodies that recognized diverse S. suis strains and triggered complement deposition.

## Abstract

Streptococcus suis is a largely neglected but emerging bacterial zoonotic pathogen of global concern for animal welfare, antibiotic resistance development, and human health. No effective vaccines are now available. Here, we identified and characterized the function and structure of two cell wall polysaccharide variants in pathogenic S. suis strains using genetic deletion and (heterologous) complementation, lectin staining, glycan composition analysis, and specialized NMR spectroscopy. Both glycan variants were anionic polymers that differed in the presence of glucose in the side chain as a result of allelic variation in a glycosyltransferase gene. Deletion of this variable glycosyltransferase revealed an identical glycan “core” and affected S. suis morphology and lysozyme resistance. Immunization of pigs with this core domain elicited antibodies that recognized antigenically diverse pathogenic S. suis strains and induced complement deposition on encapsulated pathogenic S. suis strains. This study provides valuable insights for developing next-generation glycoconjugate vaccines, whereby a single-glycan target could protect against the emerging zoonotic pathogen S. suis.

Identification of a conserved and immunogenic glycan core as a vaccine target for the zoonotic pathogen Streptococcus suis.