In recent years, multidrug-resistant (MDR) bacteria have increased rapidly, representing a major threat to human health. This problem has created an urgent need to identify alternatives for the treatment of MDR bacteria. The aim of this study was to identify the antibacterial activity of selenium nanoparticles (SeNPs) and selenium nanowires (SeNWs) against MDR bacteria and assess the potential synergistic effects when combined with a conventional antibiotic (linezolid). SeNPs and SeNWs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, and UV-visible analysis. The antibacterial effects of SeNPs and SeNWs were confirmed by the macro-dilution minimum inhibitory concentration (MIC) test. SeNPs showed MIC values against methicillin-sensitive S. aureus (MSSA), methicillin-resistant S. aureus (MRSA), vancomycin-resistant S. aureus (VRSA), and vancomycin-resistant enterococci (VRE) at concentrations of 20, 80, 320, and >320 μg/mL, respectively. On the other hand, SeNWs showed a MIC value of >320 μg/mL against all tested bacteria. Therefore, MSSA, MRSA, and VRSA were selected for the bacteria to be tested, and SeNPs were selected as the antimicrobial agent for the following experiments. In the time-kill assay, SeNPs at a concentration of 4X MIC (80 and 320 μg/mL) showed bactericidal effects against MSSA and MRSA, respectively. At a concentration of 2X MIC (40 and 160 μg/mL), SeNPs showed bacteriostatic effects against MSSA and bactericidal effects against MRSA, respectively. In the synergy test, SeNPs showed a synergistic effect with linezolid (LZD) through protein degradation against MSSA and MRSA. In conclusion, these results suggest that SeNPs can be candidates for antibacterial substitutes and supplements against MDR bacteria for topical use, such as dressings. However, for use in clinical situations, additional experiments such as toxicity and synergistic mechanism tests of SeNPs are needed.

Bacterial infection is closely associated with the failure of endodontic treatment, and use of endodontic sealer with antimicrobial activity and biological compatibility is necessary for the success of root canal treatment. The purpose of this study was to investigate and to compare the antibacterial effect of two calcium silicate-based root canal sealers (Endoseal and EndoSequence BC sealer) as recent development sealers and with three conventional root canal sealers (AH Plus, Sealapex, and Tubli-Seal), before or after setting, on Porphyromonas endodontalis, Porphyromonas gingivalis, and Enterococcus faecalis. The sealers were soaked in phosphate buffered saline to elute its compositions after and before setting, and the elutes were performed the antimicrobial assay. Also, X-ray fluorescence analysis was carried out to compare compositions of two calcium silicate-based sealers. The conventional root canal sealers have strong antibacterial activity against the Gram-negative bacteria, P. endodontalis and P. gingivalis. Endoseal sealer showed antibacterial activity against not only the Gram-negative bacteria, but also against the Gram-positive bacteria, E. faecalis. However, Endosequence BC sealer exhibited a weak antibacterial effect on all bacteria in this study. X-ray fluorescence analysis exhibited that Endoseal contained more types and more amount of the oxide compound known to have strong antimicrobial activity such as Al2O3, Fe2O3, MgO, Na2O, NiO, and SO2 than Endoseqeunce BC. Endoseal, which contains various types of oxide compounds, seems to be a suitable sealer for preventing bacterial infection in both treated and untreated root canals.

Streptococcus mutans is associated with dental caries. A cariogenic biofilm, in particular, has been studied extensively for its role in the formation of dental caries. Herbal extracts such as Cudrania tricuspidata, Sophora flavescens, Ginkgo biloba, and Betula Schmidtii have been used as a folk remedy for treating diseases. The purpose of this study was to evaluate and compare the antibacterial activity of herbal extracts against normal oral streptococci, planktonic and biofilm of S. mutans. Streptococcus gordonii, Streptococcus oralis, Streptococcus salivarius, Streptococcus sanguinis, and S. mutans were cultivated with brain heart infusion broth and susceptibility assay for the herbal extracts was performed according to the protocol of Clinical and Laboratory Standard Institute. Also, S. mutans biofilm was formed on a polystyrene 12-well plate and 8-well chamber glass slip using BHI broth containing 2% sucrose and 1% mannose after conditioning the plate and the glass slip with unstimulated saliva. The biofilm was treated with the herbal extracts in various concentrations and inoculated on Mitis-Salivarius bacitracin agar plate for enumeration of viable S. mutans by counting colony forming units. Planktonic S. mutans showed susceptibility to all of the extracts and S. mutans biofilm exhibited the highest level of sensitivity for the extracts of S. flavescens. The normal oral streptococci exhibited a weak susceptibility in comparison to S. mutans. S. oralis, however, was resistant to all of the extracts. In conclusion, the extract of S. flavescens may be a potential candidate for prevention and management of dental caries.

Tannerella forsythia is considered a pathogen of periodontitis and forms a biofilm with multi-species bacteria in oral cavity. Lipopolysaccharide is a powerful immunostimulator and induces inflammation and shock. The purpose of this study was to investigate the characteristics of T. forsythia LPS in its co-cultivation with Fusobacterium nucleatum or Porphyromonas gingivalis. T. forsythia was co-cultured in the presence and absence of F. nucleatum and P. gingivalis and then T. forsythia LPS was extracted. The extracts were analyzed by SDS-PAGE and NF-κB reporter CHO cell lines. THP-1 cells were treated with the LPS and evaluated induction of cytokine expression by real-time RT-PCR and ELISA. For analysis of the bioactivity of T. forsythia LPS, the binding assay on LPS-binding protein (LBP) and CD14 was processed. The extracts did not contaminate other molecules except LPS and showed TLR4 agonists. Co-cultured T. forsythia LPS with P. gingivalis exhibited a lower level of induction of TNF-α, IL-1β, and IL-6 expression than singleor co-cultured T. forsythia LPS with F. nucleatum in the conditions of human serum. However, the three T. forsythia LPS did not show difference of cytokine induction in the serum free conditions. Co-cultured T. forsythia LPS with P. gingivalis exhibited a lower affinity to LBP and CD14 as binding site of O-antigen and attached at a lower level to THP-1 cells compared to single- or co-cultured T. forsythia LPS with F. nucleatum. The virulence of T. forsythia LPS was decreased by co-culturing with P. gingivalis and their affinity to LBP and CD14 was reduced, which may due to modification of O-antigen chain by P. gingivalis.

Electrolyzed water has antimicrobial activity against oral microbes. The purpose of this study was to investigate the effects of a denture cleaning device that uses electrolyzed water on Candida biofilm on denture base-material and the physical properties of the denture material. Denture base-resin disks were prepared with Polymethyl methacrylate. After the formation of Candida albicans biofilm on the resin disks, the antimicrobial activity of the denture cleaning device and the chemical cleanser against C. albicans biofilm was compared. The resin disks were also treated with the cleaning device and the chemical cleanser for 150 days, and the physical properties were analyzed by an atomic force microscope, Vickers hardness tester, and colorimeter. The denture cleaning device and the chemical cleanser reduced the levels of C. albicans biofilm on the denture resin. Upon immersing of the resin disks for 150 days, the electrolyzed water of the denture cleaning device did not significantly change the surface roughness of the specimens, but significantly reduced its Vickers hardness compared to the initial value. The color changes of the resin disk were 0.477 ± 0.076, 0.612 ± 0.095 and 0.562 ± 0.096 after treating with tap water, the chemical cleanser, and the denture cleaning device, respectively. The denture cleaning device may be suitable for use by the elderly to clean dentures without side effects caused by the misuse of chemical cleanser.