title: Toluidine blue-mediated photodynamic effects on staphylococcal biofilms.
abstract: Staphylococci are important causes of nosocomial and medical-device-related infections. Their virulence is attributed to the elaboration of biofilms that protect the organisms from immune system clearance and to increased resistance to phagocytosis and antibiotics. Photodynamic treatment (PDT) has been proposed as an alternative approach for the inactivation of bacteria in biofilms. In this study, we have investigated the effect of the photodynamic action of toluidine blue O (TBO) on the viability and structure of biofilms of Staphylococcus epidermidis and of a methicillin-resistant Staphylococcus aureus strain. Significant inactivation of cells was observed when staphylococcal biofilms were exposed to TBO and laser simultaneously. The effect was found to be light dose dependent. Confocal laser scanning microscopic study suggested damage to bacterial cell membranes in photodynamically treated biofilms. In addition, scanning electron microscopy provided direct evidence for the disruption of biofilm structure and a decrease in cell numbers in photodynamically treated biofilms. Furthermore, the treatment of biofilms with tetrasodium EDTA followed by PDT enhanced the photodynamic efficacy of TBO in S. epidermidis, but not in S. aureus, biofilms. The results suggest that photodynamic treatment may be a useful approach for the inactivation of staphylococcal biofilms adhering to solid surfaces of medical implants.
authors.affiliation: Department of Biochemistry, University of Pavia. Pavia 27100, Italy. msharma@cat.ernet.in
authors.forename: Mrinalini
authors.initials: M
authors.lastname: Sharma
authors.forename: Livia
authors.initials: L
authors.lastname: Visai
authors.forename: Francesca
authors.initials: F
authors.lastname: Bragheri
authors.forename: Ilaria
authors.initials: I
authors.lastname: Cristiani
authors.forename: Pradeep Kumar
authors.initials: PK
authors.lastname: Gupta
authors.forename: Pietro
authors.initials: P
authors.lastname: Speziale
mesh_terms: D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D008027:Light; D016106:Methicillin Resistance; D018613:Microscopy, Confocal; D017319:Photosensitizing Agents / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D014048:Tolonium Chloride / Q000494:pharmacology*
chemical_list: D002614:Chelating Agents; D017319:Photosensitizing Agents; D014048:Tolonium Chloride; D004492:Edetic Acid