Light Induced Antimicrobial Properties of a Brominated Boron Difluoride (BF₂) Chelated Tetraarylazadipyrromethene Photosensitizer

Herein we describe a new antimicrobial photodynamic therapeutic (PDT) agent based upon the brominated BF(2) chelated tetraarylazadipyrromethene photosensitizer class. Bis-ammonium salt substitution of the photosensitizer promoted a rapid 10 min uptake into Gram-positive and -negative bacterial strains and pathogenic yeasts. A photosensitizer and light dose response analysis for methicillin-sensitive S. aureus showed an impressive antibacterial efficacy with 1, 2, and 5 μg/mL 6. Specifically, light activation with a dose of 16 J/cm(2) and 5 μg/mL 6 resulted in a 6.8 and 3.4 log(10) reduction of S. aureus and a clinically defined methicillin-resistant Staphylococcus aureus (MRSA) strain, respectively. Encouragingly, a broad spectrum pathogen response (using 5 μg/mL 6 and 75 J/cm(2)) was observed with 3.6 and 5.7 log(10) decreases in viable cell numbers achievable for Gram-negative bacterium E. coli and the pathogenic yeast C. albicans, respectively. The photophysical and cell eradicating characteristics of this bis-cationic PDT agent suggest that it has broad potential in antimicrobial therapeutics.