title: Antimicrobial photodynamic therapy: study of bacterial recovery viability and potential development of resistance after treatment.
abstract: Antimicrobial photodynamic therapy (aPDT) has emerged in the clinical field as a potential alternative to antibiotics to treat microbial infections. No cases of microbial viability recovery or any resistance mechanisms against it are yet known. 5,10,15-tris(1-Methylpyridinium-4-yl)-20-(pentafluorophenyl)-porphyrin triiodide (Tri-Py(+)-Me-PF) was used as photosensitizer. Vibrio fischeri and recombinant Escherichia coli were the studied bacteria. To determine the bacterial recovery after treatment, Tri-Py(+)-Me-PF (5.0 microM) was added to bacterial suspensions and the samples were irradiated with white light (40 W m(-2)) for 270 minutes. Then, the samples were protected from light, aliquots collected at different intervals and the bioluminescence measured. To assess the development of resistance after treatment, bacterial suspensions were exposed to white light (25 minutes), in presence of 5.0 microM of Tri-Py(+)-Me-PF (99.99% of inactivation) and plated. After the first irradiation period, surviving colonies were collected from the plate and resuspended in PBS. Then, an identical protocol was used and repeated ten times for each bacterium. The results suggest that aPDT using Tri-Py(+)-Me-PF represents a promising approach to efficiently destroy bacteria since after a single treatment these microorganisms do not recover their viability and after ten generations of partially photosensitized cells neither of the bacteria develop resistance to the photodynamic process.
authors.affiliation: CESAM and Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal. anabelatavares@ua.pt
authors.forename: Anabela
authors.initials: A
authors.lastname: Tavares
authors.forename: Carla M B
authors.initials: CM
authors.lastname: Carvalho
authors.forename: Maria A
authors.initials: MA
authors.lastname: Faustino
authors.forename: Maria G P M S
authors.initials: MG
authors.lastname: Neves
authors.forename: João P C
authors.initials: JP
authors.lastname: Tomé
authors.forename: Augusto C
authors.initials: AC
authors.lastname: Tomé
authors.forename: José A S
authors.initials: JA
authors.lastname: Cavaleiro
authors.forename: Angela
authors.initials: A
authors.lastname: Cunha
authors.forename: Newton C M
authors.initials: NC
authors.lastname: Gomes
authors.forename: Eliana
authors.initials: E
authors.lastname: Alves
authors.forename: Adelaide
authors.initials: A
authors.lastname: Almeida
mesh_terms: D048908:Aliivibrio fischeri / Q000187:drug effects / Q000528:radiation effects; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004307:Dose-Response Relationship, Radiation; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000528:radiation effects; D008027:Light; D049449:Luminescence; D050296:Microbial Viability; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins / Q000494:pharmacology; D013997:Time Factors; D005464:Fluorobenzenes; D005466:Fluorocarbons
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D017319:Photosensitizing Agents; D011166:Porphyrins; C549552:5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin triiodide; D005464:Fluorobenzenes; D005466:Fluorocarbons