Contribution of hla Regulation by SaeR to Staphylococcus aureus USA300 Pathogenesis

Area of Science:

• Microbiology
• Molecular Biology
• Pathogenesis

Background:

• The SaeRS two-component system regulates virulence genes in *Staphylococcus aureus*.
• Alpha-toxin (encoded by *hla*) is a key virulence factor, but Sae's role in pathogenesis is unclear.

Purpose of the Study:

• To investigate the direct contribution of SaeR-mediated *hla* regulation to *S. aureus* pathogenesis.
• To determine the impact of SaeR-binding mutations in the *hla* promoter on alpha-toxin expression and virulence.

Main Methods:

• Site-directed mutagenesis of SaeR-binding sequences in the *hla* promoter of *S. aureus* USA300 JE2.
• Western blot analysis to quantify alpha-toxin levels.
• In vivo pathogenesis studies using rat infective endocarditis and skin/soft tissue infection models.

Main Results:

• Mutation of SaeR-binding sites drastically reduced alpha-toxin production.
• The mutation did not affect alpha-toxin regulation by Agr, MgrA, or CcpA.
• The SaeR-binding mutation did not impact pathogenesis in the endocarditis model but significantly reduced abscess size in the skin/soft tissue model.

Conclusions:

• SaeR directly influences *S. aureus* pathogenesis through *hla* regulation.
• The contribution of SaeR-mediated *hla* regulation to virulence is model-dependent.