The staphylococcal type VII secretion system protein EsxC impacts daptomycin sensitivity through controlling...

Area of Science:

• Microbiology
• Molecular Biology
• Drug Discovery

Background:

• The human pathogen *Staphylococcus aureus* utilizes a Type VII Secretion System (T7SS) for virulence.
• The precise roles of T7SS in *S. aureus* physiology and infection remain largely undefined.
• Understanding T7SS function is crucial for developing novel anti-staphylococcal strategies.

Purpose of the Study:

• To investigate the function of the T7SS effector EsxC in *S. aureus*.
• To determine the impact of EsxC deficiency on antibiotic sensitivity, particularly to daptomycin.
• To elucidate the mechanisms by which EsxC influences bacterial cell envelope properties.

Main Methods:

• Comparative analysis of wild-type and Δ*esxC* *S. aureus* strains.
• Scanning electron microscopy to assess cell morphology.
• Membrane fluidity assays, protein profiling, and cell wall synthesis analysis.
• Daptomycin binding assays and calcium ion interaction studies.
• In vitro and in vivo infection models (intracellular and murine skin).

Main Results:

• Δ*esxC* *S. aureus* exhibited significantly increased sensitivity to daptomycin and other membrane-acting antibiotics.
• EsxC deficiency led to altered cell surface morphology, decreased membrane fluidity, and changes in membrane protein and cell wall synthesis.
• Mutant membranes showed increased negative charge, correlating with enhanced daptomycin binding.
• Calcium ions modulated the growth and daptomycin sensitivity of the Δ*esxC* mutant, indicating EsxC's role in calcium-membrane interactions.
• Heightened susceptibility to daptomycin was observed in intracellular and murine skin infection models.

Conclusions:

• The T7SS component EsxC is critical for modulating *S. aureus* cell membrane integrity.
• EsxC influences bacterial sensitivity to membrane-targeting antibiotics like daptomycin, partly through calcium ion modulation.
• Targeting the T7SS represents a promising strategy to potentiate existing antibiotics against *S. aureus* infections.