Photodynamic inactivation of methicillin-resistant Staphylococcus aureus on skin using a porphyrinic formulation

Area of Science:

• Photomedicine
• Dermatology
• Microbiology

Background:

• Staphylococcus aureus causes skin and soft tissue infections.
• Increasing antibiotic resistance necessitates alternative treatments.
• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat.

Purpose of the Study:

• To evaluate the efficacy of antimicrobial photodynamic therapy (aPDT) with a porphyrinic formulation (FORM) for inactivating MRSA on skin.
• To assess the potential of potassium iodide (KI) and iodopovidone (PVP-I) as potentiators of FORM in aPDT.

Main Methods:

• The aPDT protocol was optimized in vitro using Phosphate Buffered Saline (PBS).
• Porcine skin explants were artificially contaminated with MRSA and treated with FORM, FORM + KI, or FORM + PVP-I under white light.
• MRSA inactivation was quantified by colony forming units (CFU) mL⁻¹.

Main Results:

• FORM demonstrated efficacy in inactivating MRSA in vitro.
• Combinations of FORM with KI or PVP-I significantly reduced irradiation time in vitro.
• On porcine skin, FORM at 50 μM achieved a 3.1 Log₁₀ CFU mL⁻¹ reduction in MRSA.
• Potentiation observed in vitro with KI and PVP-I was not replicated ex vivo on skin.

Conclusions:

• aPDT with the porphyrinic formulation (FORM) is a promising strategy for MRSA inactivation on skin.
• FORM alone demonstrates significant efficacy without the need for potentiating agents.
• Further research may explore optimized formulations or delivery methods for enhanced ex vivo efficacy.