Staphylococcus aureus Superantigen-Like Protein SSL1: A Toxic Protease

Area of Science:

• Microbiology
• Ophthalmology
• Protein biochemistry

Background:

• Staphylococcus aureus causes severe corneal infections leading to vision impairment.
• Bacterial toxins contribute to tissue damage, inflammation, and scarring in the cornea.
• Identifying virulence factors is crucial for developing effective treatments.

Purpose of the Study:

• To characterize a novel secreted toxin from Staphylococcus aureus involved in corneal pathogenesis.
• To investigate the enzymatic activity and role of this toxin in ocular infections.

Main Methods:

• Purification and N-terminal sequencing of the novel toxin from S. aureus Newman strain.
• Cloning the gene encoding the toxin and producing the recombinant protein.
• Testing the recombinant toxin and a deletion mutant in a rabbit cornea infection model.

Main Results:

• The identified toxin, SSL1 (23 kDa), is a homodimeric protease (46 kDa) with activity against substrates like collagens and cytokines (IL-17A, IFN-γ, IL-8).
• SSL1 activity is inhibited by serine protease inhibitors.
• An S. aureus mutant lacking the ssl1 gene showed significantly reduced corneal virulence compared to wild-type and rescued strains, without affecting bacterial growth.

Conclusions:

• SSL1 is a novel staphylococcal protease contributing to corneal virulence.
• SSL1 targets host defense and structural proteins, playing a key role in S. aureus-induced eye infections.
• The prevalence of the ssl1 gene in ocular isolates suggests its clinical relevance.