Mechanistic Insight into the Photodynamic Effect Mediated by Neutral Red and a New Azine Compound in Staphylococcus...

Area of Science:

• Photochemistry
• Microbiology
• Dye Chemistry

Background:

• Photodynamic inactivation (PDI) is a promising antimicrobial strategy.
• Neutral Red (NR) and its derivatives are azine dyes with photosensitizing potential.
• Understanding PDI mechanisms is crucial for optimizing antimicrobial efficacy.

Purpose of the Study:

• To investigate the photodynamic activity of Neutral Red (NR) and a novel monobrominated NR against Staphylococcus aureus.
• To elucidate the mechanisms of photodynamic inactivation by evaluating the protective effects of mannitol and sodium azide.
• To differentiate the reactive species involved in the PDI mediated by NR and its halogenated analog.

Main Methods:

• Photodynamic inactivation assays using Staphylococcus aureus suspensions.
• Treatment with Neutral Red and monobrominated Neutral Red (25 μm).
• Evaluation of protective effects of mannitol and sodium azide against photosensitization.

Main Results:

• Both mannitol and sodium azide provided complete protection against NR-mediated photosensitization, indicating a Type I mechanism involving radical species.
• Monobrominated NR showed protection with mannitol, but incomplete protection with sodium azide.
• The results suggest monobrominated NR involves reactive oxygen species and potentially singlet molecular oxygen.

Conclusions:

• Neutral Red primarily acts via a Type I mechanism, generating radical species.
• Monobrominated Neutral Red exhibits a mixed mechanism involving reactive oxygen species and possibly singlet molecular oxygen.
• The distinct mechanisms explain the observed differences in photodynamic inactivation of Staphylococcus aureus by these azine photosensitizers.