Near-infrared therapy and photodynamic inactivation in an in vivo model of S. aureus infection

TOMÁS S, DI VENOSA G, BUZZOLA F, CASAS A, MAMONE L

Chapadmalal

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General (SAMIGE 2023); 2023

Sociedad Argentina de Microbiología General

Photodynamic Inactivation (PDI) combines a photosensitizer compound with visible light and molecular oxygen, to generate reactive species and kill microorganisms. PDI does not have specific biochemical targets, and therefore has the advantage of being effective against antibiotic-resistant strains, which makes it a promising alternative in the treatment of multiresistant bacterial species. 5-aminolevulinic acid (ALA) is a precursor in the biosynthesis of porphyrins, some of which can act as photosensitizing compounds in both eukaryotic cells and bacteria. Near-infrared therapy (NIRT) uses infrared light to deliver heat into tissues. NIRT can inactivate microorganisms and promote healing. The aim of this work was to employ a combination of NIRT and ALA-PDI (visible light irradiation after topical ALA treatment) to reduce the progression of wounds caused by Staphylococcus aureus infection, in an in vivo model in mice. CF1 mice were injected subcutaneously with a suspension of S. aureus RN6390. After 48 h, 20 mg/ml ALA solution was applied to the skin. NIRT was performed with a 980 nm laser (96 J/cm2). Porphyrins produced from ALA, and their localization, were determined by fluorescence spectroscopy and microscopy. The PDI was performed employing a 635 nm laser device (144 J/cm²). The effect of light treatments and untreated controls was determined by measuring the area of the wound caused by infection during four weeks after treatments (direct measurement and processing of acquired images). Bacterial load at the infection site was measured by counting CFUs from skin homogenates. Wounds treated with ALA-PDI reduced area sooner than the untreated control. Differences between these two groups were significant every day after irradiation (p˂0.05). Furthermore, the time required for complete wound closure in the ALA-PDI group was significantly less (p˂0.01) than in the light and untreated controls (14 vs 21 and 27 days respectively). There was no difference in wound closure time when PDI was combined with NIRT, despite the results indicating that NIR treatment increases porphyrin levels at the site of infection (the main porphyrin synthesized was Protoporphyrin IX). No statistically significant differences were detected in the bacterial load at the infection site between any of the treatments. Our results suggest that PDI is a promising option to treat superficial infections.