Amoxicillin coated gold nanoparticles with photo-antibacterial action on antibiotic resistant strains

Villa Carlos Paz

Congreso; XIII ELAFOT; 2017

Novel antibacterial strategies are badly needed as a consequence of the growing resistance of bacteria to conventional antibiotics. Photodynamic Antibacterial Chemotherapy (PACT) has recently proved to be an effective therapy when the photosensitizer presents selectivity for prokaryotic cells [1] . In fact, in the present work, gold nanoparticles were synthesized and stabilized with amoxicillin (amoxi@AuNP), which is a beta-lactamic antibiotic with high affinity for the bacterial wall. Amoxi@AuNP were prepared by 1-step synthesis at 50°C for 18 minutes. TEM revealed that the majority of the population is composed of nano-spheres (average 50 nm). However triangular and hexagonal micro-plates (50 to 90 nm) were also observed. The binding of amoxicillin (slightly modified) to the nanoparticle was confirmed through FT-IR and TGA. Importantly, the active site of the molecule, the beta-lactamic ring, was preserved intact [2]. The antibacterial activity of amoxi@AuNP against methicillin-sensitive Staphylococcus aureus ATCC 29213 (MSSA ATCC 29213) and methicillin-resistant clinical isolate of Staphylococcus aureus (MRSA 9455) was tested. Briefly, 100 µL of bacterial suspension (106 CFU/mL) and 100 µL of the tested solutions (37.5% PBS, 1.5 µg/mL amoxi@AuNP, 0.15 µg/mL amoxi@AuNP and amoxicillin at minimum inhibitory concentration (MIC): 2 µg/mL for MSSA and 32 µg/mL for MRSA) were mixed in a 96 wellplate. All samples were irradiated for a total of 90 min under white light (from blue, red and yellow LED combined) at 37 °C. An identical well plate was kept in the dark as a control. Aliquots of each samples were properly diluted and seeded on tryptic soy agar (TSA) plates for Colonies Forming Unit (CFU) counting. The 1.5 µg/mL amoxi@AuNP were able to inhibit bacterial growth of both MSSA and MRSA completely after just 30 min of irradiation. The same concentration of amoxi@AuNP was able to kill all the MSSA, but not the MRSA, after 90 min under dark conditions. This may be due to synergistic effect between the antibiotic and nanoparticles, because the amoxicillin itself was not bactericidal in this short period of time.In summary, this study has demonstrated that PACT with amoxi@AuNP have an excellent potential in treatment of infectious diseases. Additionally, our group have reported their high biocompatibility and non-toxic properties to the host [3]. Further research would include evaluation of their effects in biofilms.