Nurit Beyth

Alternative Antimicrobial Approach: Nano-Antimicrobial Materials

Despite numerous existing potent antibiotics and other antimicrobial means, bacterial infections are still a major cause of morbidity and mortality. Moreover, the need to develop additional bactericidal means has significantly increased due to the growing concern regarding multidrug-resistant bacterial strains and biofilm associated infections. Consequently, attention has been especially devoted to new and emerging nanoparticle-based materials in the field of antimicrobial chemotherapy. The present review discusses the activities of nanoparticles as an antimicrobial means, their mode of action, nanoparticle effect on drug-resistant bacteria, and the risks attendant on their use as antibacterial agents. Factors contributing to nanoparticle performance in the clinical setting, their unique properties, and mechanism of action as antibacterial agents are discussed in detail.

Surface antimicrobial activity and biocompatibility of incorporated polyethylenimine nanoparticles

The antimicrobial effect and biocompatibility of insoluble cross-linked quaternary ammonium polyethylenimine (PEI) nanoparticles incorporated at 1 or 2%w/w in a resin composite were assayed. The antimicrobial effect against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Pseudomonas aeruginosa and Escherichia coli was tested using the direct contact test (DCT), agar diffusion test (ADT) and scanning electron microscopy (SEM). Biocompatibility was tested by assessing macrophage viability, and TNFalpha secretion. Samples incorporating 2%w/w nanoparticles inhibited the growth of all bacterial strains tested. Reducing the amount of the added nanoparticles to 1%w/w resulted in complete inhibition of S. aureus and E. faecalis, and decreased growth of S. epidermidis, P. aeruginosa and E. coli (p<0.0001). The DCT results were confirmed by SEM. However, ADT showed no inhibition halo in all test bacteria, indicating the antimicrobial nanoparticles are not diffusing into the agar milieu. Biocompatibility tests revealed macrophage viability, and TNFalpha secretion was not altered by the presence of the nanoparticles in the resin. Incorporation of PEI nanoparticles in a resin composite had a long lasing antimicrobial effect against a wide range of bacteria with no measured effect on biocompatibility.

Polyethyleneimine nanoparticles incorporated into resin composite cause cell death and trigger biofilm stress in vivo

Incorporation of cross-linked quaternary ammonium polyethylenimine (QPEI) nanoparticles in dental resin composite has a long-lasting and wide antimicrobial effect with no measured impact on biocompatibility in vitro. We hypothesized that QPEI nanoparticles incorporated into a resin composite have a potent antibacterial effect in vivo and that this stress condition triggers a suicide module in the bacterial biofilm. Ten volunteers wore a removable acrylic appliance, in which two control resin composite specimens and two resin composite specimens incorporating 1% wt/wt QPEI nanoparticles were inserted to allow the buildup of intraoral biofilms. After 4 h, the specimens were removed and tested for bacterial vitality and biofilm thickness, using confocal laser scanning microscopy. The vitality rate in specimens incorporating QPEI was reduced by > 50% (p < 0.00001), whereas biofilm thickness was increased (p < 0.05). The ability of the biofilm supernatant to restore bacterial death was tested in vitro. The in vitro tests showed a 70% decrease in viable bacteria (p < 0.05). Biofilm morphological differences were also observed in the scanning electron microscope micrographs of the resin composite versus the resin composite incorporating QPEI. These results strongly suggest that QPEI nanoparticles incorporated at a low concentration in resin composite exert a significant in vivo antibiofilm activity and exhibit a potent broad spectrum antibacterial activity against salivary bacteria.

Surface Characterization and Biocompatibility of Restorative Resin Containing Nanoparticles

Composite resins that are used to restore hard tissues have several drawbacks including the accumulation of biofilm on teeth and restorations. Recently, quaternary ammonium poly(ethylene imine) (QA-PEI) nanoparticles were developed for additional antibacterial activity of restorative composite resins. QA-PEI nanoparticles were synthesized from cross-linked poly(ethylene imine) that was N-alkylated with octyl halide, followed by quaternary methylation with methyl iodide. QA-PEI particles that were embedded in restorative composite resin at 1% w/w resulted in the complete growth inhibition of Streptococcus mutans. Moreover, the antibacterial activity was retained for at least 3 months. The active substances on the surface of the restorative composite resin that were incorporated with QA-PEI particles were detected by X-ray photoelectron spectroscopy (XPS) and confocal microscopy measurements. The in vitro cytotoxicity tests showed a similar effect on the viability of the cell line that was tested with composites including modified and unmodified dental composite resins. In vivo toxicity studies, which were assessed on Wistar rats by the implantation of modified composite specimens, revealed no inflammation response 1 week after the implantation of restorative composite resin that was embedded with up to 2% w/w QA-PEI.

Quaternary ammonium polyethyleneimine: antibacterial activity

Quaternary ammonium polyethyleneimine- (QA-PEI-) based nanoparticles were synthesized using two synthetic methods, reductive amination and N-alkylation. According to the first method, QA-PEI nanoparticles were synthesized by cross-linking with glutaraldehyde followed by reductive amination with octanal and further N-methylation with methyl iodide. The second method is based on crosslinking with dialkyl halide followed by N-alkylation with octyl halide and further N-methylation with methyl iodide. QA-PEI nanoparticles completely inhibited bacterial growth (<106 bacteria), including both Gram-positive, that is, Staphylococcus aureus at 80 µg/mL, and Gram-negative, that is, Escherichia coli at 320 µg/mL. Activity analysis revealed that the degree of alkylation and N-methylation of the QA-PEI nanoparticles plays a significant role in antibacterial activity of the reagent. The most potent compound was octyl alkylated QA-PEI alkylated at 1 : 1 mole ratio (primary amine of PEI monomer units/alkylating agent). Also, cytotoxicity studies on MAT-LyLu and MBT cell lines were performed with QA-PEI nanoparticles. These findings confirm previous reports that polycations bearing quaternary ammonium moieties inhibit bacterial growth in vitro and have a potential use as additives in medical devices which need antibacterial properties.

Targeting Enterococcus faecalis Biofilms with Phage Therapy

ABSTRACT Phage therapy has been proven to be more effective, in some cases, than conventional antibiotics, especially regarding multidrug-resistant biofilm infections. The objective here was to isolate an anti-Enterococcus faecalis bacteriophage and to evaluate its efficacy against planktonic and biofilm cultures. E. faecalis is an important pathogen found in many infections, including endocarditis and persistent infections associated with root canal treatment failure. The difficulty in E. faecalis treatment has been attributed to the lack of anti-infective strategies to eradicate its biofilm and to the frequent emergence of multidrug-resistant strains. To this end, an anti-E. faecalis and E. faecium phage, termed EFDG1, was isolated from sewage effluents. The phage was visualized by electron microscopy. EFDG1 coding sequences and phylogeny were determined by whole genome sequencing (GenBank accession number KP339049), revealing it belongs to the Spounavirinae subfamily of the Myoviridae phages, which includes promising candidates for therapy against Gram-positive pathogens. This analysis also showed that the EFDG1 genome does not contain apparent harmful genes. EFDG1 antibacterial efficacy was evaluated in vitro against planktonic and biofilm cultures, showing effective lytic activity against various E. faecalis and E. faecium isolates, regardless of their antibiotic resistance profile. In addition, EFDG1 efficiently prevented ex vivo E. faecalis root canal infection. These findings suggest that phage therapy using EFDG1 might be efficacious to prevent E. faecalis infection after root canal treatment.

Antibacterial effect of polyethyleneimine nanoparticles incorporated in provisional cements against Streptococcus mutans

BACKGROUND Frequently provisional restorations require long-term permanence in the oral cavity, thus an antibacterial effect is desirable. We hypothesized that this effect may be achieved by incorporating polyethyleneimine (PEI) nanoparticles into provisional cements. METHODS The nanoparticles antibacterial effect incorporated at 0.5%, 1%, and 2% w/w into provisional cement, was studied in vitro. The antibacterial effect against Streptococcus mutans and Enterococcus faecalis was tested using direct contact test. The data was analyzed using the ANOVA test, with the Dunnett test for multiple pairwise comparisons. RESULTS A strong antibacterial effect was evident in all test groups after an aging period of 14 days against S. mutans and E. faecalis (p < 0.05). A significant effect was found between study groups 0.5% w/w and 1% w/w group, as well as between study groups 0.5% w/w and 2% w/w for E. faecalis (p < 0.05). No significant difference was found between study groups 1% w/w and 2% w/w. The growth rate graphs depict an effective bacteria inhibition starting from 1% w/w. CONCLUSION PEI nanoparticles incorporated at low concentrations in a provisional cement exhibit antibacterial effect against S. mutans and E. faecalis for a period of 14 days. The minimum effective concentration suggested is 1% w/w. CLINICAL IMPLICATIONS Incorporation of nanoparticles may prevent caries and inflammation, and thereby improve the results of the prosthetic treatment. Further investigation is necessary on the effect on mechanical properties and clinical relevance.

Antibacterial activity of dental cements containing quaternary ammonium polyethylenimine nanoparticles

Glass ionomer cements (GICs) are commonly used for cementing full cast crown restorations. Regrettably, although the dental cements fill the gap between the tooth and the crown, bacterial microleakage may occur, resulting in secondary caries. As microleakage cannot be completely prevented, GICs possessing antibacterial properties are in demand. In the present study the antibacterial activity of insoluble, cross-linked quaternary ammonium polyethylenimine (QPEI) nanoparticles incorporated at 1% w/w in two clinically available GICs were studied. The antibacterial activity was tested against Streptococcus mutans and Lactobacillus casei using the direct contact test (DCT) and the agar diffusion test (ADT). Using the direct contact test, antibacterial activity (P < 0.05) was found in both tested GICs with incorporated QPEI nanoparticles, the effect lasting for at least one month. However, the ADT showed no inhibition halo in the test bacteria, indicating that the antimicrobial nanoparticles do not diffuse into the agar. The results show that the incorporation of QPEI nanoparticles in glass ionomer cements has a long-lasting antibacterial effect against Streptococcusmutans and Lactobacillus casei. Changing the antibacterial properties of glass ionomer cements by incorporating QPEI antibacterial nanoparticles may prolong the clinical performance of dental crowns.

Anti-biofilm properties of wound dressing incorporating nonrelease polycationic antimicrobials

Polycationic nanoparticles show biocompatible, broad-spectrum bactericidal properties in vitro and in vivo when incorporated in denture lining material post-maxillectomy in head and neck cancer patients. In the present study, the synthesized Crosslinked quaternary ammonium polyethylenimine nanoparticles were found to have a strong bactericidal activity against a wide variety of microorganisms rapidly killing bacterial cells when incorporated at small concentrations into soft lining materials without compromising mechanical and biocompatibility properties. This appears advantageous over conventional released antimicrobials with regard to in vivo efficacy and safety, and may provide a convenient platform for the development of non-released antimicrobials. This is a crucial issue when it comes to giving an answer to the serious and life-threatening problems of contaminations in immunocompromised patients such as orofacial cancer patient.

Phage therapy against Enterococcus faecalis in dental root canals

Antibiotic resistance is an ever-growing problem faced by all major sectors of health care, including dentistry. Recurrent infections related to multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus, carbapenem-resistant Enterobacteriaceae, and vancomycin-resistant enterococci (VRE) in hospitals are untreatable and question the effectiveness of notable drugs. Two major reasons for these recurrent infections are acquired antibiotic resistance genes and biofilm formation. None of the traditionally known effective techniques have been able to efficiently resolve these issues. Hence, development of a highly effective antibacterial practice has become inevitable. One example of a hard-to-eradicate pathogen in dentistry is Enterococcus faecalis, which is one of the most common threats observed in recurrent root canal treatment failures, of which the most problematic to treat are its biofilm-forming VRE strains. An effective response against such infections could be the use of bacteriophages (phages). Phage therapy was found to be highly effective against biofilm and multidrug-resistant bacteria and has other advantages like ease of isolation and possibilities for genetic manipulations. The potential of phage therapy in dentistry, in particular against E. faecalis biofilms in root canals, is almost unexplored. Here we review the efforts to develop phage therapy against biofilms. We also focus on the phages isolated against E. faecalis and discuss the possibility of using phages against E. faecalis biofilm in root canals.