title: Comparative photodynamic inactivation of antibiotic resistant bacteria by first and second generation cationic photosensitizers.
abstract: Photodynamic inactivation (PDI) is an efficient approach against a wide range of microorganisms and can be viewed as an alternative for the treatment of microbial infections. In this work we synthesized "first" and "second" generation photosensitizers (PSs), the tetra-cationic porphyrin  and the new penta-cationic chlorin , respectively, and evaluated their efficiency against two antibiotic resistant bacterial strains, Staphylococcus aureus and Pseudomonas aeruginosa. The PS  was obtained in very good yield by an easy synthesis method. The PDI studies were performed in parallel with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetra-iodide (), a widely studied PS in PDI, and the obtained results were compared. Two different light ranges were used: white light (400-800 nm) and red light (530-800 nm) delivered at a fluence rate of 150 mW cm(-2). The results show that both strains, even though antibiotic resistant, were efficiently inactivated by the three PSs, chlorin  being the most effective. For the Gram positive bacterium S. aureus a 7.0 log reduction was observed after 5-10 min of irradiation, at a concentration of 0.5 μM, whereas for the Gram negative P. aeruginosa, similar photoinactivation occurred at a higher PS concentration (10 μM) and after a longer irradiation period (30 min). The synthetic chlorin  can be regarded as promising for the treatment of bacterial infections under red light, which penetrates deeper in living tissues. The results of this study open the possibility to prepare a new series of chlorin-type derivatives to efficiently photoinactivate Gram (+) and (-) antibiotic resistant bacteria. The efficient PDI with the chlorin  indicates high potential for the use of a  scaffold in the preparation of new generation PSs based on cationic chlorin derivatives.
authors.affiliation: Department of Chemistry, QOPNA, University of Aveiro, Campus of Santiago, Aveiro, Portugal.
authors.forename: Dora C S
authors.initials: DC
authors.lastname: Costa
authors.forename: Maria C
authors.initials: MC
authors.lastname: Gomes
authors.forename: Maria A F
authors.initials: MA
authors.lastname: Faustino
authors.forename: Maria G P M S
authors.initials: MG
authors.lastname: Neves
authors.forename: Angela
authors.initials: A
authors.lastname: Cunha
authors.forename: José A S
authors.initials: JA
authors.lastname: Cavaleiro
authors.forename: Adelaide
authors.initials: A
authors.lastname: Almeida
authors.forename: João P C
authors.initials: JP
authors.lastname: Tomé
mesh_terms: D024881:Drug Resistance, Bacterial; D008027:Light; D008826:Microbial Sensitivity Tests; D017319:Photosensitizing Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000528:radiation effects; D026082:Singlet Oxygen / Q000378:metabolism; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000528:radiation effects
chemical_list: D017319:Photosensitizing Agents; D011166:Porphyrins; D026082:Singlet Oxygen