Recent studies have considered the utility of photodynamic therapy using porphyrins as novel antimicrobials

Recent studies have considered the utility of photodynamic therapy using porphyrins as novel antimicrobials.  Photoactivation of porphyrins results in the production of ROS, such as singlet oxygen (¹O₂), that damage biomolecules associated with bacterial cells and biofilms, e.g., proteins, polysaccharides, and DNA.  There is little evidence of dark toxicity of these compounds to bacterial cells.  We  tested the effect of a cationic porphryin on P. aeruginosa PAO1 biofilms by exposing static biofilms to 5,10,15,20-tetrakis(1-methyl-pyridino)-21H,23H-porphine, tetra-p-tosylate salt  (TMP) followed by visible light irradiation. Biofilms were visualized using confocal scanning laser microscopy (CSLM) and cell viability determined using the LIVE/DEAD BacLight viability assay and standard plate counts.     Exposure to 225 µM TMP resulted in a 4.1-log₁₀ reduction in biofilm associated cells as well as the detachment of biofilms from the surface substrata.  Our results suggest that the action of photoactivated TMP on P. aeruginosa biofilms is two-fold: direct killing of individual cells within biofilms and detachment of the biofilm from the substratum. There was no evidence of porphyrin toxicity in the absence of light; however, biofilms pretreated with TMP without photoactivation were substantially more sensitive to several different classes of antibiotics than untreated biofilms.  A second novel porphyrin containing Zinc (patent pending)  was tested and found to reduce P. aeruginosa  planktonic cell populations by more than 6 logs without photoactivation.  The use of porphyrins in the eradication of bacteria on surfaces will be discussed.