Oxidative stress on Staphylococcus aureus ATCC 29213 and Extended-spectrum beta-lactamases-producing (ESBL) Escherichia coli by AuNPs irradiated with green LEDs

SILVERO MJ; ARGÜELLO GA; BECERRA M C

Córdoba

Congreso; XIV Congreso Internacional de Fotobiología; 2014

Unión Internacional de Fotobiología y el Grupo Argentino de Fotobiología

Oxidative stress on Staphylococcus aureus ATCC 29213 and extended-spectrum beta-lactamases-producing (ESBL) Escherichia coli by AuNPs irradiated with green LEDs M. Jazmín Silvero a and Gerardo A. Arguello a, M. Cecilia Becerra b a Instituto de Investigaciones en Físico Química de Córdoba (INFIQC) CONICET-UNC, Departamento de Físico Química. Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, X5000HUA Córdoba Argentina; jsilvero@hotmail.fcq.unc.edu.ar b Instituto Multidisciplinario de Biología Vegetal (IMBIV), CONICET and Dpto. de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba. Ciudad Universitaria, 5000-Córdoba, Argentina. Previous results from our group have shown that a total inhibition of Staphylococcus aureus ATCC 29213 and an ESBL Escherichia coli growth were observed when incubated with 2mM AuNPs and irradiated with LEDs at 525 nm for 12 h. [1] Considering this potential of the AuNP in Photodynamic Antimicrobial Chemo Therapy (PACT), we wanted to elucidate which was the possible mechanism of cell death. Trasmission Electron Microscope images displayed that AuNPs selectively arranged around the outer bacteria membrane. On the other hand, pictures taken with Fluorescence Microscope probe (2´,7´-dichlorodihydrofluorescein diacetate), showed that irradiation of AuNPs (4 hours with 525 nm LED) already attached to the peptidoglican wall promotes the generation of Reactive Oxygen Species (ROS) in both strains. This could be due to the photothermal effect of plasmon excitation. In addition, bacterial macromolecules damage was evaluated through the detection of Advanced Oxidation Protein Products (AOPP) at 340 nm with KI and acetic acid. This experiment showed that after 4 hours of irradiation, the AOPP levels of ESBL E. coli and S. aureus treated with AuNPs were higher than the controls in the dark or without nanoparticles. We could conclude from this results that bacterial death caused through PACT, using AuNPs as photosensitizers, is mainly caused for an oxidative stress of bacterial macromolecules. This pathway seems to be valid for both a Gram negative bacilus and Gram positive coccus.