Levels of alpha-toxin correlate with distinct phenotypic response profiles of blood mononuclear cells and with agr background of community-associated Staphylococcus aureus isolates

PLoS One. 2014 Aug 28;9(8):e106107. doi: 10.1371/journal.pone.0106107. eCollection 2014.

Abstract

Epidemiological studies of Staphylococcus aureus have shown a relation between certain clones and the presence of specific virulence genes, but how this translates into virulence-associated functional responses is not fully elucidated. Here we addressed this issue by analyses of community-acquired S. aureus strains characterized with respect to antibiotic resistance, ST types, agr types, and virulence gene profiles. Supernatants containing exotoxins were prepared from overnight bacterial cultures, and tested in proliferation assays using human peripheral blood mononuclear cells (PBMC). The strains displayed stable phenotypic response profiles, defined by either a proliferative or cytotoxic response. Although, virtually all strains elicited superantigen-mediated proliferative responses, the strains with a cytotoxic profile induced proliferation only in cultures with the most diluted supernatants. This indicated that the superantigen-response was masked by a cytotoxic effect which was also confirmed by flow cytometry analysis. The cytotoxic supernatants contained significantly higher levels of α-toxin than did the proliferative supernatants. Addition of α-toxin to supernatants characterized as proliferative switched the response into cytotoxic profiles. In contrast, no effect of Panton Valentine Leukocidin, δ-toxin or phenol soluble modulin α-3 was noted in the proliferative assay. Furthermore, a significant association between agr type and phenotypic profile was found, where agrII and agrIII strains had predominantly a proliferative profile whereas agrI and IV strains had a predominantly cytotoxic profile. The differential response profiles associated with specific S. aureus strains with varying toxin production could possibly have an impact on disease manifestations, and as such may reflect specific pathotypes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Toxins / metabolism
  • Bacterial Toxins / toxicity*
  • Cell Proliferation / drug effects
  • Community-Acquired Infections / blood
  • Community-Acquired Infections / microbiology*
  • Drug Resistance, Bacterial
  • Flow Cytometry
  • Humans
  • Leukocytes, Mononuclear / drug effects*
  • Phenotype
  • Staphylococcal Infections / blood*
  • Staphylococcal Infections / microbiology
  • Staphylococcus aureus / classification
  • Staphylococcus aureus / immunology
  • Staphylococcus aureus / isolation & purification*
  • Superantigens / metabolism

Substances

  • Bacterial Toxins
  • Superantigens

Grants and funding

This work was supported by grants from Karolinska Institutet (ANT), Swedish Research Council (521-2011-2540, ANT; 521-2009-3900 MS), The Swedish Research Links Programme (348-2009-6501; ANT & GA), Knut and Alice Wallenberg Foundation, European Union FP7 INFECT-project, NPP grant New INDIGO ERA Net, Hospices Civils de Lyon (GL, FV) and INSERM (GL, FV). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.