Gold nanoparticles as alternative therapy for antibiotic-resistant bacterial strains

ROCCA DIAMELA; BECERRA M. CECILIA; AIASSA V; SILVERO JAZMÍN; J.C. SCAIANO

Costa da Caparica (Lisbon)

Conferencia; II International Caparica Conference in Antibiotic Resistance - IC2AR 2017; 2019

A strategy to combat infections by bacteria resistant to antibiotics is the development of nanomaterials with photosensitizing activity. In our group, gold nanoparticles (NPS) stabilized with amoxicillin (amoxi@AuNPs) were obtained1. They have the advantage of being synthesized in a single step and in a few minutes. The evaluation of the antibacterial activity against methicillin-sensitive Staphylococcus aureus (MSSA ATCC 29213) and a methicillin-resistant clinical strain (MRSA 9455) was carried out by irradiation with white light LEDs (to cover the absorption of the different shapes of NPs) and subsequent counting in solid medium of the colony forming units. The eradication of biofilms from clinical strains of MRSA and Pseudomonas aeruginosa (PAE) treated with amoxi@AuNPs was quantified. The biomass of the biofilm was quantified in the clinical strains MRSA 771 and 773 and in the clinical strains PAE 191150 and 189718, by the staining test with crystal violet. Metabolic activity was determined by reducing the XTT reagent and SEM images. To investigate the mechanism of action of the amoxi@AuNPs, the generation of reactive oxygen species (ERO) in S. aureus was measured using the dihydrorhodamine 123 (DHR) probe. Results suggest that maximum antibacterial effect was achieved at 30 min of irradiation, with a concentration of 1.5 μg/mL amoxi@AuNPs. A marked reduction in the metabolic activity of the biofilms treated with amoxi@AuNPs and irradiated was obtained. The metabolic activity was reduced with respect to its untreated controls. The results were corroborated by SEM images. Fluorescence microscopy with temporal resolution evaluated the activity of the mentioned NPs in co-cultures of bacteria and eukaryotic cells. These NPs possess bactericidal activity and an excellent biocompatibility in co-cultures. In order to give a step towards the application of this technology, we have synthesized in just one step a gel containing AuNPs plus an antimicrobial peptide (AMP). Casein was the chosen AMP because it is a small biocompatible molecule, relatively cheap and with gelation properties. SEM images showed spherical NPs (10 ± 2 nm diameter) and were stabilized between the casein net. They have an absorption peak at 544 nm and inhibit the growth of pathogenic strains as Klebsiella pneumoniae and S. aureus after only 15 min with green LEDs. This is possible because of the combination effect of the AMP and the plasmon excitation.The application of these nanoparticles for Photodynamic Antimicrobial Therapy is promising to treat infections resistant to antibiotics given its high stability in vivo, cytocompatibility and also because, until now, the development of resistance has not been registered.