Síntese, caracterização e ação antimicrobiana de nanopartículas de prata

• Autor(a) principal: Fernandes, Patrícia érica
• Data de Publicação: 2014
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/510
• topic: Nanopartículas; Nanopartículas de prata; Efeito antimicrobiano; Nanopartículas de prata - Síntese; nanoparticles; Silver nanoparticles; Antimicrobial effect; Silver nanoparticles - Summary; CNPQ::CIENCIAS AGRARIAS::CIENCIA E TECNOLOGIA DE ALIMENTOS::CIENCIA DE ALIMENTOS

Silver nanoparticles (Ag-NPs) have been widely incorporated into various products such as textiles, household items, medical products, toiletries and food packaging because of its known antimicrobial activity and its broad spectrum of action. The antimicrobial effect of Ag-NPs is well established, however, their antimicrobial mechanism of action is not fully understood. Furthermore, it is important to better understand the effect of Ag-NP in microbial adhesion. The objectives of this study were 1) to determine the antimicrobial effect and probable mechanisms of action of Ag-NPs and Ag+ ions, from the silver nitrate (AgNO3), on species of gram-positive and gram-negative bacteria; 2) to determine the effect of subinhibitory concentrations of Ag-NPs and Ag+ ions on microbial adhesion, 3) characterize the inactivation kinetics of planktonic cells of Pseudomonas aeruginosa treated with Ag-NPs and Ag+ ions under different conditions. The Ag-NPs were synthesized with sodium citrate (Ag-NPC) or sodium borohydride (Ag-NPB) as reducing agents and coated with polyvinylpyrrolidone or carboxymethylcellulose. The characterization of Ag-NPs was made by spectroscopy in the ultraviolet and visible, dynamic light scattering (DLS), zeta potential (δ), transmission electron microscopy (TEM) and atomic absorption. Both Ag-NPs showed typical surface plasmon resonance, which confirmed their formation during the synthesis. The average particle size determined by DLS was 3.4 ± 1.2 nm for the Ag-NPC and 3.1 ± 0.9 nm for the Ag-NPB. The size of the Ag-NPC observed by TEM was 3.86 nm confirming the result obtained by DLS. The potential δ of Ag-NPC and Ag-NPB was - 31.9 ± 8.6 mV and - 33.2 ± 1.7 mV, respectively. Gram-negative bacteria are more sensitive to Ag-NPC and AgNO3 than gram-positive bacteria. The presence of Ag-NPC at subinhibitory concentrations decreased the adherence of P. aeruginosa onto polystyrene surfaces. However, subinhibitory concentrations of Ag-NPC or AgNO3 increased adhesion of gram-positive bacteria compared with the control group, probably in response to stress. Through Transmission Electron Microscopy / Energy Dispersive X-rays, it was observed that the silver penetrates in P. aeruginosa and Staphylococcus aureus cells and complex with sulfur and phosphorus, forming a condensation region in the center of the bacteria. Damage to S. aureus was less intense compared to the damage in P. aeruginosa. The Ag-NPC and the AgNO3 lost their antimicrobial activity in the presence of antioxidants agents, suggesting the involvement of reactive oxygen species (ROS) in its antimicrobial activity. However, it was not verified lipid peroxidation in cells treated with Ag-NPC or AgNO3. The results using dialysis membranes indicated that the antimicrobial activity of Ag-NPC is related to the release of Ag+ ions. The kinetics of inactivation of planktonic cells of P. aeruginosa was adjusted for biphasic model, which demonstrated heterogeneity in microbial resistance. The microbial inactivation time decreased with increasing of silver concentration and temperature. The antimicrobial activity of Ag-NPC and AgNO3 was reduced in culture medium compared to its activity in water, probably due to the complexation of Ag-NPC or AgNO3 with the medium constituents such as sulfur and phosphates.