Enhancement of photodynamic inactivation of Staphylococcus aureus biofilms by disruptive strategies

GANDARA, LAUTARO; MAMONE, LEANDRO; BOHM, GABRIELA CERVINI; BUZZOLA, FERNANDA; CASAS, ADRIANA

LASERS IN MEDICAL SCIENCE

SPRINGER LONDON LTD

Año: 2017

0268-8921

Abstract Photodynamic inactivation (PDI) has been used toinactivate microorganisms through the use of photosensitizersand visible light. On the one hand, near-infrared treatment(NIRT) has also bactericidal and dispersal effects on biofilms.In addition, dispersal biological tools such as enzymes havealso been employed in antibiotic combination treatments. Theaim of this work was to use alternative approaches to increasethe PDI efficacy, employing combination therapies aimed atthe partial disruption of the biofilms, thus potentially increasingphotosensitizer or oxygen penetration and interaction withbacteria. To that end, we applied toluidine blue (TB)-PDItreatment to Staphylococcus aureus biofilms previously treatedwith NIRT or enzymes and investigated the outcome of thecombined therapies. TB employed at 0.5 mM induced per se2-log drop in S. aureus RN6390 biofilm viability. Each NIRT(980-nm laser) and PDI (635-nm laser) treatment induced afurther reduction of 1-log of viable counts. The combinationof successive 980- and 635-nm laser treatments on TB-treatedbiofilms induced additive effects, leading to a 4.5-log viablecount decrease. Proteinase K treatment applied to S. aureus ofthe Newman strain induced an additive effect on PDI mortality,leading to an overall 4-log decrease in S. aureus viability.Confocal scanning laser microscopy after biofilm staining with a fluorescent viability test and scanning electron microscopyobservations were correlated with colony counts. TheNIRT dose employed (227 J/cm2) led to an increase from 21to 47 °C in the buffer temperature of the biofilm system, andthis NIRT dose also induced 100% keratinocyte death. Furtherwork is needed to establish conditions under which biofilmdispersal occurs at lower NIRT doses