Introduction: Enterococci are opportunistic bacteria that are natural inhabitants of the cavity and intestines. Enterococcus faecalis (E.faecalis) is the most common pathogen that causes persistent infection of a root canal. The lack of response to traditional treatment is due to the formation of a biofilm inside the canal. Microorganisms in the biofilm have increased resistance to antibacterial preparations, disinfectants and the host’s immune system. Therefore, it is necessary to investigate the effectiveness of new antimicrobial agents. Silver nanoparticles (AgNPs) have been known as a powerful agent with antimicrobial activity over several decades. Therefore, we decided to investigate the influence of AgNPs on the E.faecalis biofilms formation.

Aim: To determine the effect of Ag NPs on the formation of E.faecalis biofilms.

Materials and methods: AgNPs were provided by Nano Pure Co (Poland). The strain of E.faecalis was isolated from patient. The glass slides were placed individually in Muller Hinton broth and inoculated with E. faecalis at a concentration of 10⁶ CFU/ml. Then AgNPs were added to the samples at the AgNPs concentration equals to 1 MIC and incubated for 1, 2, and 3 days. Then the samples were removed from the medium and fixed with 2,5 % glutaraldehyde and  dehydrated with a series of ethanol solution 50%, 70%, 80%, 90%/. After that the samples were coated with silver and examined by SEOSEM Inspect S50-B microscope. 

Results: In control samples there was a formation of   the structures formed by adherent bacteria and extracellular polimer matrix at 1, 2, and 3 days of incubation. The typical stages of biofilm formation are observed: adhesion, fixation, aggregation, and dispersion. In the treated samples, we revealed the different degreees of the biofilm structure formation. Coincubation of the bacteria with AgNPs within 1 day caused partial biofilm destruction. Some bacteria were still observed adhering to the glass slides. Incubating of AgNPs with E.faecalis for 2 and 3 days shown whole destruction of the biofilms and we revealed only cells with altered shape and structure. 

Conclusions. Thus, the Ag NPs prevent the formation of biofilms of E.faecalis by inhibiting their growth and reproduction. This indicates that AgNPs can be used for prophylactic biofilm formation.

Acknowledgment: This research supported by H2020 Marie Skłodowska-Curie Actions (NanoSurf 777926) and Grant of the Ministry of Education and Science of Ukraine No. 0118U003577 “Antimicrobial effectiveness of nano-complexes (Chitosannanometals) against the multi-resistant clinical strains”.