Controlling the Growth of the Skin Commensal Staphylococcus epidermidis Using d-Alanine Auxotrophy

Area of Science:

• Microbiology and Synthetic Biology
• Dermatology and Cutaneous Immunology

Background:

• The skin microbiome plays a vital role in skin health, with dysbiosis linked to various skin diseases.
• Live biotherapeutic products (LBPs) offer a promising therapeutic strategy for skin conditions.
• Controlling LBP growth without antibiotics is crucial for safety and therapeutic modulation.

Purpose of the Study:

• To design and characterize an engineered commensal bacterium, Staphylococcus epidermidis, as a live biotherapeutic product (LBP) candidate for skin diseases.
• To develop a strain with antibiotic-independent growth control for enhanced safety and modulated therapeutic exposure.
• To evaluate the in vitro efficacy and safety profile of the engineered strain.

Main Methods:

• Construction of an auxotrophic Staphylococcus epidermidis strain (SEΔΔΔ) by deleting three key d-alanine biosynthetic genes (alr1, alr2, dat).
• Assessment of SEΔΔΔ growth dependency on exogenous d-alanine in vitro, in pooled human blood, and in skin models.
• Evaluation of SEΔΔΔ colonization, human β-defensin 2 induction in human skin models, reversion propensity, and biofilm formation in vitro.

Main Results:

• The engineered SEΔΔΔ strain exhibited auxotrophy for d-alanine, restricting its growth in its absence.
• In the presence of d-alanine, SEΔΔΔ colonized human skin models and increased human β-defensin 2 expression.
• SEΔΔΔ demonstrated a low reversion rate and did not form biofilms in vitro, indicating a favorable safety profile.

Conclusions:

• The engineered d-alanine auxotroph, SEΔΔΔ, is a viable candidate for a live biotherapeutic product for skin diseases.
• Growth control via d-alanine offers a safe and effective method for modulating therapeutic exposure.
• These findings support further clinical investigation of SEΔΔΔ for human use in treating skin conditions.