Vaccination with a live-attenuated small-colony variant improves the humoral and cell-mediated responses against Staphylococcus aureus

PLoS One. 2019 Dec 27;14(12):e0227109. doi: 10.1371/journal.pone.0227109. eCollection 2019.

Abstract

Staphylococcus aureus is known to produce persistent and chronic infections in both humans and animals. It is recognized that small-colony variants (SCVs), which produce higher levels of biofilm and that are capable of intracellular persistence, contribute to the chronicity or recurrence of infections and that this phenotype is inherent to the pathogenesis process. Prevention of S. aureus infections through vaccination has not yet met with considerable success. Some of the current vaccine formulations for S. aureus bovine mastitis consist of inactivated S. aureus bacteria, sometimes combined to E. coli J5. As such, the stimulation of cell-mediated immunity by these vaccines might not be optimal. With this in mind, we recently engineered a genetically stable double mutant SCV (ΔvraGΔhemB), which was highly attenuated in a mastitis model of infection. The present work describes the immune responses elicited in mice by various experimental vaccine compositions including the live-attenuated SCV double mutant and its inactivated form, combined or not with inactivated E. coli J5. The live-attenuated SCV was found to provoke a strong and balanced humoral response in immunized mice, as well as strong proliferation of ex-vivo stimulated splenocytes isolated from these animals. These splenocytes were also found to release high concentration of IL-17 and IFN-γ when compared to every other vaccination formulation. Inversely, the inactivated whole-cell vaccine, alone or in combination with the E. coli J5 bacterin, elicited lower antibody titers and failed to induce Th1 or Th17 cell-mediated responses in the splenocyte proliferation assay. Our results suggest that live-attenuated SCVs can trigger host immunity differently than inactivated bacteria and could represent a suitable vector for inducing strong humoral and cell-mediated immune responses, which are crucial for protection. This could represent an important improvement over existing vaccine formulations for preventing S. aureus bovine mastitis and other infections caused by this pathogen.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Female
  • Immunity, Cellular*
  • Immunity, Humoral*
  • Mice
  • Staphylococcal Infections / immunology
  • Staphylococcal Infections / prevention & control*
  • Staphylococcal Vaccines / pharmacology
  • Staphylococcal Vaccines / therapeutic use*
  • Staphylococcus aureus / immunology*
  • Vaccination
  • Vaccines, Attenuated / pharmacology
  • Vaccines, Attenuated / therapeutic use*

Substances

  • Staphylococcal Vaccines
  • Vaccines, Attenuated

Grants and funding

This research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC grant to FM No. 2015-05916). The authors also acknowledge support from the Canadian Bovine Mastitis and Milk Quality Research Network (Université de Montréal, St-Hyacinthe, QC, Canada) as well as from Op+lait, the FRQNT Regroupement pour un lait de qualité optimale (Université de Montréal, St-Hyacinthe, QC, Canada). JCG is grateful for receiving studentships from Op+lait and the NSERC CREATE program in Milk Quality in support of her doctoral studies. The funding agencies had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.