Antimicrobial effects of silver nanoparticles on planktonic and sessile communities of pathogenic bacteria

PAULA DE OÑA; VIRGINIA ROLDÁN ; AGUSTÍN MÖHLINGER ; PAOLA CAMISCIA ; YOLANDA CASTRO; ALICIA DURÁN ; PABLO FACCENDINI; CLAUDIA LAGIER; NORA PELLEGRI ; ROBERTO R GRAU

Madrid

Conferencia; III International Conference on Antimicrobial Research - ICAR2014; 2014

Formatex Research Center

In recent years, the resistance of bacteria to antimicrobials has increased due to the slapdash use of antibiotics in animal feed as growth promoters as well as their abusive utilization in medicine and veterinary. The bactericidal effects of ionic silver are known and applied since antiquity. Silver is used in several medical devices and surgical equipments such as burn dressings, scaffolds, water purification systems and medical devices. In particular, silver nanoparticles (SNPs) may damage the activity of bacterial enzymes and cell structures, which cause bacterial cells to die. Besides, the photo-induced water splitting on TiO2 electrodes when is exposed to UV light (=400 nm) generate excited electrons (ecb) that are trapped by water (H2O) or hydroxyl groups (OH) adsorbed on the surface to generate hydroxyl radicals (OH?). OH? is a powerful and indiscriminate oxidizing agent with antibacterial properties. In this work, we study the antimicrobial activity of SNPs in combination with coated TiO2 against multiresistant strains of the human-pathogenic bacteria Escherichia coli (EHEC), Staphylococcus aureus, Listeria monocytogenes, Pseudomonas aeruginosa, and spores of Clostridium perfringens and Bacillus anthracis. Our results show the efficacy of SNPs coated (meso and dense) with TiO2 to kill highly-grew cultures of planktonic pathogenic bacteria. Thus, the combination of noble metals (e.g., silver) and TiO2 may enhance the photo-catalytic efficiency and so degradation of pathogen microorganisms. In addition, these SNPs also affect the viability of stability of the bacterial biofilm. Biofilms are surface-associated bacterial communities, in which bacteria are enveloped by polymeric substances known as the biofilm matrix. In the model organism Bacillus subtilis, biofilms display persistent resistance to liquid wetting and gas penetration which probably explains the broad-spectrum of resistance and tolerance of bacterial biofilms to antimicrobial agents. We analyze the ability of B. subtilis, and isogenic mutants affected in the synthesis of the extracellular matrix (ECM), to form biofilms in the presence of AgNPs. Our results show that silver nanoparticles have a greater inhibitory effect on biofilm development that the inhibition of biofilm formation produced by the germicide compound silver nitrate. In addition, it was observed that strains defective in the formation of particular ECM components (lipids, exopolysaccharide, etc.) differentially responded to the presence of AgNPs, suggesting a selective and exclusive effect of this novel nanomaterial on biofilm architecture.