Resumo:
Introduction: The endodontic treatment aims to eliminate pathogenic microorganisms in the pulp complex. Even though this treatment has well-defined protocols, persistent infections, mainly caused by Enterococcus, have become a challenge for a successful treatment. Considering the antimicrobial potential of biogenic silver nanoparticles (AgNPs), this study aimed to evaluate the activity of these compounds on reference strains and clinical isolates of Enterococcus faecalis and Enterococcus faecium, as well as on their biofilms. Methods: Reference strains and clinical isolates of Enterococcus were obtained from patients who showed no response to the pulp sensitivity test and chronic reaction. These were submitted to AgNPs sensitivity tests through broth microdilution assays. Minimum inhibitory concentrations (MICs100) and minimum bactericidal concentrations (MBCs100) were determined. The inhibitory activity of AgNPs on biofilm formation and activity on consolidated biofilms was also tested. Scanning electron microscopy (SEM) was used for the morphological analysis of Enterococcus treated with AgNPs. Results: AgNPs showed 100% bacteriostatic effect for all strains and clinical isolates, except one clinical isolate of E. faecium, at concentrations ranging from 31.25 to 125 ug/mL. Regarding the bactericidal effect, only one clinical isolate and the reference strain of E. faecium were not 100% inactivated by AgNPs. All strains and clinical isolates analyzed herein were moderate biofilm producers. AgNPs were able to interfere with the formation of biofilm by the Enterococcus, with a maximum of 55% interference for E. faecalis, and 40% for E. faecium. There was an interference in the consolidated biofilm at levels ranging from 20 to 40%. SEM analysis confirmed the antibacterial activity of AgNPs through morphological changes in cells. Conclusion: AgNPs proved to be an antimicrobial agent with significant bacteriostatic and bactericidal capacity on reference strains and clinical oral isolates of E. faecalis and E. faecium, as well as showing inhibition properties in biofilm formation and disruption.
