Regulation of Staphylococcus aureus alpha-toxin gene (hla) expression by agr, sarA, and sae in vitro and in experimental infective endocarditis

J Infect Dis. 2006 Nov 1;194(9):1267-75. doi: 10.1086/508210. Epub 2006 Sep 27.


Background: The Staphylococcus aureus global regulators--agr, sarA, and sae--coordinately control alpha-toxin gene (hla) expression in vitro. However, their relative in vivo contributions to hla expression, particularly in endovascular infections, have not been defined.

Methods: A plasmid-based hla-promoter:green fluorescent protein reporter system was constructed in 2 genetically related S. aureus strains: RN6390 (a natural sigma factor B [sigB]-deficient mutant), SH1000 (a sigB-repaired variant of RN6390 lineage), and their respective agr, sarA, agr/sarA, and sae mutants. These strain sets were used to quantify hla expression in vitro and in an experimental infective endocarditis (IE) model using flow cytometry.

Results: In vitro, hla expression was positively modulated by all 3 regulons (sae > agr/sarA > agr and sarA) in both RN6390 and SH1000 backgrounds. In the IE model, hla expression in cardiac vegetations was lower in all single mutants than in the respective parental strains (P<.05 for sae mutant) but was maintained at near-parental levels in the agr/sarA double mutant in both backgrounds. A similar finding was also observed in kidneys and spleens.

Conclusions: These results indicate that, although several distinct regulatory circuits can affect hla expression in vitro and in vivo, sae appears to play a crucial role in this context.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism*
  • Endocarditis, Bacterial / microbiology*
  • Gene Expression Regulation, Bacterial*
  • Genes, Bacterial / genetics*
  • Sigma Factor / metabolism
  • Staphylococcus aureus / genetics*
  • Staphylococcus aureus / metabolism*
  • Trans-Activators / metabolism*
  • Type C Phospholipases / genetics*


  • Agr protein, Staphylococcus aureus
  • Bacterial Proteins
  • SarA protein, Staphylococcus aureus
  • SigB protein, Bacteria
  • Sigma Factor
  • Trans-Activators
  • Type C Phospholipases