Effect of Organic Matter on the Photoeradication of Pseudomonas aeruginosa by Means of a Cationic Tetraaryl-porphyrin

The Photodynamic therapy is emerging as a an antimicrobial alternative approach; the concomitant presence of a photosensitizer (PS) and visible light induces lethal oxidative damages to bacterial cells. Among Gram-negative bacteria, Pseudomonas aeruginosa seems to be one of the least susceptible to photodynamic inactivation. In this study, we evaluated the influence of some experimental conditions on photoeradication of a planktonic culture of P. aeruginosa PAO1 by means of a tetracationic meso-arylsubstituted porphyrin (RM24). Our findings suggest that the photo-oxidative stress induced by RM24 is strictly correlated to the amount of PS bound to the cells that in turn decreases with the increasing concentrations of organic compounds. The photoeradication is dependent on PS concentrations, cellular density and light dose. The standardized experimental conditions of the photo-spot test permitted to evidence intraspecific PDT sensitivity differences among three strains of P. aeruginosa. Furthermore RM24 was able to induce oxidative stress by means of singlet oxygen formation, although ROS formation cannot be ruled out.