The Effect of Silver Nanoparticles Against Formation of Enterococcus Faecalis Biofilms

The main factor of bacteria pathogenicity is the ability to organize biofilm, which increases the resistance to antibacterial agents. Nanomaterials are promising substances with antimicrobial activity due to their unique physicochemical properties such as ultra-small sizes, large surface-area-to-mass ratio, and increased chemical reactivity[1]. The aim of this study was to evaluate the antibacterial efficacy of silver nanoparticles (AgNPs) against Enterococcus faecalis. AgNPs were prepared by the chemical reduction method with PVP as a capturing agent. Antibacterial properties were examined with the determination of the Minimum Inhibitory Concentration (MIC), and Minimum Bactericidal Concentration (MBC). The influence of AgNPs on biofilm formation was evaluated by detecting the biofilm mass inhibition (with gentian violet assay) and determining the AgNPs' effect on the biofilm ultrastructure with Scanning Electron Microscopy. AgNPs demonstrated appropriate antibacterial properties with inhibition of bacterial growth at concentrations $\mathbf{5}\ \boldsymbol{\mu} \mathbf{g}/\mathbf{ml}$ (MIC) and killing bacteria at concentrations of $\mathbf{10} \boldsymbol{\mu} \mathbf{g}/\mathbf{ml}$ (MBC). AgNPs do not affect bacteria attachment at these concentrations. Increasing concentrations up to $\mathbf{40}\ \boldsymbol{\mu} \mathbf{g}/\mathbf{ml}$ lead to decreasing biomass quantity on 1- and 2-day biofilms compared to the control. We did not find the changes in biomass quantity of 5-day biofilm, but reviled the structural changes in the bacteria cell wall. We demonstrated that AgNPs could be used for effective treatment and prevention of infections caused by Enterococcus faecalis at concentrations varied from 10 to $\mathbf{40} \boldsymbol{\mu} \mathbf{g}/\mathbf{ml}$ .