Improved photoinactivation of gram-negative and gram-positive methicillin-resistant bacterial strains using a new near-infrared absorbing meso-tetrahydroporphyrin: a comparative study with a chlorine e6 photosensitizer photolon

The antimicrobial activity of new tetracationic and water-soluble meso-substituted tetrahydroporphyrin tetratosylat (BL1065) and of dicationic water-soluble chlorine e6 Photolon (BLC1013) is described. The dark toxicity and photosensitizing potentials of both photosensitizers were tested on Gram-positive (Staphylococcus aureus and MRSA) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria in phosphate-buffered saline (PBS, pH 7.4), PBS + horse serum (HS) and PBS + sheep blood (SB). The results show that BLC1065 and BLC1013 did not inhibit the growth of S. aureus in the dark, but efficiently inactivated this Gram-positive bacterium after illumination. Contrary to BLC1013, BLC1065 has a photodynamic activity toward Gram-negative bacteria as well, at least in PBS. Results suggest that tetracationic BLC1065 can bind better to both Gram-positive and Gram-negative bacterial cell envelope than the dianionic chlorine BLC1013 resulting in better efficiency of photoinactivation.