The bactericidal efficiency of various positively and negatively charged silver nanoparticles has been extensively evaluated in literature, but there is no report on efficacy of neutrally charged silver nanoparticles. The goal of this study is to evaluate the role of electrical charge at the surface of silver nanoparticles on antibacterial activity against a panel of microorganisms. Three different silver nanoparticles were synthesized by different methods, providing three different electrical surface charges (positive, neutral, and negative). The antibacterial activity of these nanoparticles was tested against gram‐positive (i.e., Staphylococcus aureus, Streptococcus mutans, and Streptococcus pyogenes) and gram‐negative (i.e., Escherichia coli and Proteus vulgaris) bacteria. Well diffusion and micro‐dilution tests were used to evaluate the bactericidal activity of the nanoparticles. According to the obtained results, the positively‐charged silver nanoparticles showed the highest bactericidal activity against all microorganisms tested. The negatively charged silver nanoparticles had the least and the neutral nanoparticles had intermediate antibacterial activity. The most resistant bacteria were Proteus vulgaris. We found that the surface charge of the silver nanoparticles was a significant factor affecting bactericidal activity on these surfaces. Although the positively charged nanoparticles showed the highest level of effectiveness against the organisms tested, the neutrally charged particles were also potent against most bacterial species.

Introduction: Persistent infections of human root canals play a fundamental role in the failure of endodontic treatment. The purpose of this study is to determine the chemical composition of Myrtus communis (M. communis) essential oil and to assess its antimicrobial activity against Enterococcus faecalis, Staphylococcus aureus and Candida albicans compared to that of sodium hypochlorite (NaOCl) and chlorhexidine (CHX). Materials and Methods: Gas chromatography-mass spectrometry (GC-MS) was used to determine the chemical composition of essential oil from M. communis leaves. A micro-dilution susceptibility assay and disk diffusion methods were utilized to evaluate the antimicrobial activity [minimum inhibitory concentration (MIC) and minimum lethal dose concentration] of the tested solutions against selected microorganisms. Results: GC-MS analyses revealed that M. communis contained 1, 8-Cineole (28.62%), α-Pinene (17.8%), Linalool (17.55%), and Geranylacetate (6.3%) as the major compounds and Geraniol (1.6%), α-Humulene (1.5%), eugenol (1.3%), isobutyl-isobutyrate (0.8%), and methyl chavicol (0.5%) as minor components. Chlorhexidine had the lowest MIC value among all medicaments tested. M. communis oil had less MIC values than NaOCl against both bacteria, but it had more MIC value against C. albicans. Conclusion: M. communis essential oil with the minimum inhibitory concentration in the range of 0.032-32 μg/mL was an effective antimicrobial agent against persistent endodontic microorganisms.

This study successfully developed a positively charged silver nanocomplex as a nanocarrier for chlorhexidine (CHX) using ionic liquids. This nanocomplex can interestingly deliver the antibacterial agent with a synergistic effect. In this study, we synthetized and characterized a positively charged silver nanocomplex (AgNPs⁺) and CHX‐loaded positively charged silver nanoparticles (CHX@AgNPs⁺) using UV‐visible spectroscopy, transmission electron microscopy, X‐ray diffractometer, Fourier transform infrared spectroscopy, and Zetasizer. Then, the loading efficiency and release profile of XHX from nanocomplex were evaluated. The antibacterial activity was evaluated by employing two standard microdilution tests to obtain the minimum bactericidal and inhibitory concentrations. The average sizes of 27.43 nm and 29.66 nm were obtained for AgNPs⁺ and CHX@AgNPs⁺, respectively. The CHX@AgNPs⁺ showed a constant release of CHX, making them a more effective antibacterial agent against Enterococcus faecalis (E. faecalis) than CHX or AgNPs⁺ alone. Antibacterial assays showed that CHX@AgNPs⁺ significantly reduced the viability of the bacterial strain compared to CHX as the standard irrigant. AgNPs⁺ had an antibacterial effect similar to CHX only at intermediate concentrations (12 and 25 μg/mL), and their effects were significantly less than those of CHX at other concentrations (3, 6, 50, and 100 μg/mL). The effects of CHX@AgNPs⁺ were statistically greater than those of AgNPs⁺ at all concentrations tested. The MIC values of CHX@AgNPs⁺ and CHX were 50 and 100 μg/mL. However, AgNPs⁺ were not showed MIC value at tested concentrations. Therefore, the designed nanocomplex can be regarded as a potential root canal disinfectant with clinical applications for bacterial infections.

Background: Nanoparticles are made by different methodologies, which can affect the particle’s features. Recently, imidazolium-coated silver nanoparticles with a positive surface charge (PC Im-based AgNPs) have revealed favorable results as a root canal disinfectant. However, the antibacterial potency of these particles against biofilm form of Enterococcus faecalis, as the most resistant organism to eliminate in endodontic treatment, has not been investigated. It can be noted that removing this microorganism is associated with extremely effective disinfection. Objectives: This study investigated the antibacterial efficacy of PC Im-based AgNPs at 5.7 × 10^-8 mol L^-1 in comparison with 2.5% sodium hypochlorite (NaOCl) and 2% chlorhexidine as the two broadly used endodontic irrigation solutions against biofilm E. faecalis using quantitative real-time polymerase chain reaction. Methods: In total, 48 premolar teeth with a single root were infected with E. faecalis and then prepared with ProTaper rotary instruments. The samples were randomly allocated into 4 groups of 12 samples. Sterile saline, PC Im-based AgNPs, NaOCl, and chlorhexidine were used as irrigants. Sampling the root canals was implemented with paper points and Gates-Glidden drills. The reduction in E. faecalis counts was calculated and statistically analyzed by means of the Kruskal-Wallis and Mann-Whitney U tests. Results: Irrigation with PC Im-based AgNPs or NaOCl was significantly more effective in bacterial count reduction compared to irrigation with chlorhexidine or sterile saline (P < 0.05). There was no significant difference between PC Im-based AgNPs and NaOCl irrigants when either Gates-Glidden drills (P = 0.751) or paper points (P = 0.488) were employed. Chlorhexidine was significantly less efficient than PC Im-based AgNPs and NaOCl solutions (P < 0.001); however, it was significantly better than sterile saline in both sampling approaches (P > 0.001). Conclusions: The PC Im-based AgNP solution revealed promising results as a root canal irrigant. This solution at 5.7 × 10^-8 mol L^-1 was effectively able to eliminate biofilm E. faecalis and this was not significantly different from that of 2.5% NaOCl. Keywords: Ionic Liquids; Real Time Polymerase Chain Reaction; Root Canal Therapy; Nanoparticles; Enterococcus faecalis

Background: Finding strategies to overcome the rising trends of antimicrobial resistance against currently available antimicrobial agents has become increasingly relevant. Graphene oxide has recently emerged as a promising material due to its outstanding physicochemical and biological properties. This study aimed to validate previous data on the antibacterial activity of nanographene oxide (nGO), double antibiotic paste (DAP), and their combination (nGO-DAP). Methods: The antibacterial evaluation was performed against a wide range of microbial pathogens. Synthesis of nGO was achieved using a modified Hummers' method, and loading it with ciprofloxacin and metronidazole resulted in nGO-DAP. The microdilution method was utilized to assess the antimicrobial efficacy of nGO, DAP, and nGO-DAP against two gram-positive bacteria (S. aureus and E. faecalis), two gram-negative bacteria (E. coli, and S. typhi), and an opportunistic pathogenic yeast (C. albicans). Statistical analysis was conducted using one-sample t-test and one-way ANOVA (α = 0.05). Results: All three antimicrobial agents significantly increased the killing percent of microbial pathogens compared to the control group (P < 0.05). Furthermore, the synthesized nGO-DAP exhibited higher antimicrobial activity than nGO and DAP per se. Conclusion: The novel synthesized nGO-DAP can be used as an effective antimicrobial nanomaterial for use in dental, biomedical, and pharmaceutical fields against a range of microbial pathogens, including gram-negative and gram-positive bacteria, as well as yeasts.