Effect of Light on the Antibacterial Property of Silver Diamine Fluoride

Objective: The study aimed to evaluate the antibacterial effect of shortened time and lightcuring on the biofilm of silver diamine fluoride (SDF) applied lesions.Materials and methods: Twenty dentin specimens (3 x 3 x 2 mm3) were prepared fromtwenty primary molar teeth with caries extended to the middle third of dentin. The specimens wererandomly allocated into 4 groups (n = 5/group); 1) distilled water (DW, negative control), 2) SDF10 seconds, 3) SDF 10 seconds with light curing (LC) for 20 seconds and 4) SDF 1 minute (AAPDrecommendation) and then were treated following the assigned group. Treated specimens wereindividually placed in 24-well plates with Streptococcus mutans (S. mutans) culture (approximately6 x 108 colony-forming-unit (CFU)/mL) and incubated at 37°C, 5% CO2 for 24 hours to form biofilm.The biofilm was removed from the specimens by a pipette tip and underwent serial 10-fold dilutions.The diluted solutions were then plated on agar. After incubation, the colonies were counted andpresented as CFU/mL.Results: There was no difference in the number of bacteria that remained on the specimenstreated with SDF for 10 seconds, SDF for 10 seconds with LC, and SDF for 1 minute (0, 284 ± 284,and 0 CFU/mL, respectively; mean ± standard error). However, all three groups had significantlyfewer bacterial counts than the DW treatment (8.39 x 106 ± 4.94 x 106 CFU/mL), (p < 0.05).Conclusion: The antibacterial activity of shortening the duration of SDF application with orwithout light curing was not different from the conventional 1-minute application.Keywords: Antibacterial agents, Biofilms, Dental curing lights, Silver diamine fluoride, Streptococcusmutans SWU Dent J. 2021;15(1):86-92

Genome-Wide Identification of Host Genes Required for Toxicity of Bacterial Cytolethal Distending Toxin in a Yeast Model

BackgroundAggregatibacter actinomycetemcomitans, a periodontal pathogen, secretes a cytolethal distending toxin (AaCDT) that causes host cell cycle arrest and cell death. Although CDT could be an important virulence factor, it is unclear how it enters the nucleus to exert its cytotoxicity.ObjectiveTo investigate the mechanisms of AaCDT by genome-wide screening for host mutations that confer resistance to the catalytic subunit, AaCdtB, in a Saccharomyces cerevisiae model.MethodsWe transformed the yeast haploid deletion library, a collection of yeast mutants with single gene deletions of virtually all non-essential ORFs in the genome, with plasmids carrying galactose-inducible AaCdtB. Yeast mutants that showed resistance to AaCdtB were selected and rescreened by a spotting assay. AaCdtB expression was confirmed by western blot analysis; any mutants that showed no or weak expression of AaCdtB were omitted from the analysis. The lists of genes whose mutations confer resistance to AaCdtB were analyzed for Gene Ontology (GO) term enrichments. Localization of AaCdtB-EGFP was examined using fluorescent microscopy. Nuclear localization relative to EGFP control was calculated and compared to wild-type.ResultsOut of approximately 5,000 deletion mutants, we isolated 243 mutants that are resistant to AaCdtB. GO analyses indicated that genes associated with organic anion transport are significantly enriched (16 genes). Furthermore, several genes associated with the nucleus and endoplasmic reticulum (ER) were identified. Localization studies of AaCdtB, in mutants with the deletion of genes associated with the GO term organic anion transport, showed lower nuclear localization than wild-type. The results suggest that these genes may be required for AaCdtB translocation into the nucleus and its cytotoxicity.ConclusionThe genome-wide screen in the yeast deletion library allowed us to identify a large number of host genes required for AaCdtB cytotoxicity. Further investigation could lead to more insights into the mechanisms of CdtB intoxication

Hydrogen peroxide masks the bitterness of chlorhexidine mouthwash without affecting its antibacterial activity

Background: Chlorhexidine (CHX) is an antiseptic mouthwash widely used as the gold standard for inhibiting plaque formation. However, the bitter taste of CHX limits patient compliance. We developed a 0.12% CHX and 1.5% hydrogen peroxide (H2O2) mouthwash that masked the bitter taste of CHX. This study evaluated the antibacterial activity and subject satisfaction of the developed mouthwash. Materials and Methods: Three mouthwashes were used as follows: (1) a commercial 0.12% CHX mouthwash, (2) a prepared 0.12% CHX mouthwash containing 1.5% H2O2, and (3) a prepared 0.12% CHX mouthwash. A disc diffusion assay was performed to determine the antibacterial activity of each mouthwash against Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans. To assess subject satisfaction with each mouthwash, a satisfaction questionnaire was completed immediately after rinsing with each mouthwash. Results: The antibacterial activities of the three mouthwashes were similar. Moreover, the questionnaire results revealed that the level of satisfaction was significantly higher for the 0.12% CHX/1.5% H2O2 mouthwash compared with the other mouthwashes. Conclusion: The 0.12% CHX/1.5% H2O2 mouthwash revealed a similar antibacterial activity as the CHX standard against periodontal disease pathogens. In addition, the subjects were more satisfied with the new formula compared with 0.12% CHX alone. These data suggest that the 0.12% CHX/1.5% H2O2 formulation is an alternative antibacterial mouthwash to avoid the unpleasant CHX side effects

Code Timing Acquisition Using an Antenna Array for Asynchronous DS-CDMA Systems in a Near-Far Environment

In this paper, an adaptive near-far resistant detector using a multiple antennas for acquiring synchronization of an asynchronous DS-CDMA system is presented. The only requirement is the prior knowledge of the user-spreading sequence of interest. Also, there is no need of a training sequence and a training period. Synchronization acquisition of asynchronous DS-CDMA signals is treated as a binaryhypothesis test. Under the binary hypotheses, an adaptive generalized maximum likelihood ratio test (GLRT) is developed to acquire the multipath code timings of a single desired user in both a fading and a near-far interference environment. The synchronization is obtained by sliding a search window in a sample-by-sample manner to perform the adaptive GLRT with the non-constrained maximum likelihood estimator (MLE) of Direction-Of-Arrival (DOA) during the symbol interval. The acquisition performance of the proposed detector is illustrated by computer simulations of an asynchronous BPSK DS-CDMA system and is shown to be potential to against multipath fading and the problems of near-far interference