Rapid and effective photodynamic treatment of biofilm infections using low doses of amoxicillin-coated gold nanoparticles.

Bacterial biofilm are complex microbial communities covered by a matrix of extracellular polymeric substances, which develops when a community of microorganisms irreversibly adheres to a living or inert surface. This structure is considered an important virulence factor because it is difficult to eradicate and often responsible for treatment failures. This adherent community represents one of the greatest problems in public health due to the continued emergence of conventional antibiotic-therapy resistance. Photodynamic Antimicrobial Therapy (PACT) is a therapeutic alternative and promises to be an effective treatment against multiresistant bacteria biofilm, demonstrating a broad spectrum of action. This work demonstrates the reduction in biofilms of relevant clinical isolates (as Pseudomonas aeruginosa and Staphylococcus aureus) treated with PACT using low concentrations of amoxicillin-coated gold nanoparticles (amoxi@AuNP) as a photosensitizer. Moreover, the viability reduction of 60% in S. aureus biofilms and 70% in P. aeruginosa biofilms were obtained after three hours of irradiation with white light and amoxi@AuNP. Scanning electron microscopy analysis revealed that amoxi@AuNP could penetrate and cause damage to the biofilm matrix, and interact with bacteria cells. A strong biofilm production in P. aeruginosa was observed by confocal laser scanning microscopy using acridine orange as a probe, and a markedly decrease in live bacteria was appreciated when PACT was applied. The use of amoxi@AuNP for PACT allows the viability reduction of clinical Gram positive and Gram negative biofilms. This novel strategy needs shorter irradiation times and lower concentrations of nanoparticles than other reports described. This could be attributed to two major innovations: the selectivity for the bacterial wall given by the amoxicillin and the polydispersity of size and shapes with seems to contribute to the photo-antibacterial capacity.