Niacin Limitation Promotes Candida glabrata Adhesion to Abiotic Surfaces

Candida glabrata is a prevalent fungal pathogen in humans, which is able to adhere to host cells and abiotic surfaces. Nicotinic acid (NA) limitation has been shown to promote the adherence of C. glabrata to human epithelial cells. Clinically, the elderly and hospitalized patients who are prone to C. glabrata–related denture stomatitis often suffer from vitamin deficiency. This study aimed to investigate C. glabrata adhesion to abiotic surfaces, including acrylic resin (a denture material) surfaces, cell surface hydrophobicity and adhesion gene expression. C. glabrata CBS138 was grown in media containing decreasing NA concentrations (40, 0.4, 0.04 and 0.004 µM). Adherence of C. glabrata to glass coverslips and acrylic resin was analyzed. C. glabrata adhesion to both surfaces generally increased with decreasing NA concentrations. The highest adhesion was found for the cells grown with 0.004 µM NA. The cell surface hydrophobicity test indicated that NA limitation enhanced hydrophobicity of C. glabrata cells. Quantitative PCR showed that of all adhesion genes tested, EPA1, EPA3 and EPA7 were significantly up-regulated in both 0.004 µM NA and 0.04 µM NA groups compared to those in the 40 µM NA group. No significant up- or down-regulation under NA limitation was observed for the other tested adhesion genes, namely AWP3, AWP4, AWP6 and EPA6. NA limitation resulted in increased expression of some adhesion genes, higher surface hydrophobicity of C. glabrata and enhanced adhesion to abiotic surfaces. NA deficiency is likely a risk factor for C. glabrata–related denture stomatitis in the elderly.

Exploring the role of oral microorganisms in the pathogenesis of mucositis by assessing their impact on metabolic activity and reproductive capacity of epithelial cells in vitro

Purpose

Clinical and in vitro studies showed selected oral microorganisms to be related to delayed wound healing and ulcerative oral mucositis. However, it is not known whether this effect is due to reduced metabolism and/or the reduced reproductive capacity of epithelial cells. Therefore, we studied the influence of the oral microorganisms Porphyromonas gingivalis, Candida glabrata, and Candida kefyr on cell metabolism and reproductive capacity of oral epithelial cells, aimed to further unravel the pathogenesis of oral mucositis.

Methods

Oral epithelial cells were exposed to different concentrations of P. gingivalis, C. glabrata, and C. kefyr as mono-infections or mixed together. An MTT assay was performed to determine the effect on cell metabolism. A clonogenic assay was used to study the effect on the reproductive capacity of oral epithelial cells.

Results

The metabolism of oral epithelial cells was reduced when the microorganisms were present in high concentrations: P. gingivalis at a multiplicity of infection (MOI) of 1000 and the Candida spp. at MOI 100. No statistical difference was observed in the ability of a single epithelial cell to grow into a colony of cells between control and P. gingivalis, C. glabrata, and C. kefyr, independent of the concentrations and combinations used.

Conclusion

P. gingivalis, C. glabrata, and C. kefyr lowered the metabolic activity of oral epithelial cells in high concentrations, yet they did not influence the reproductive capacity of epithelial cells. Their impact on ulcerative oral mucositis is likely due to an effect on the migration, proliferation, and metabolism of epithelial cells.

Efficacy of probiotics: clinical and microbial parameters of halitosis

BACKGROUND & AIM

Halitosis is defined as an offensive breath odour of whatever source and therefore may affect a person's social interactions. Intra-oral halitosis is a result of bacterial activity. Therefore, probiotics may offer an appropriate and biological solution as a part of the therapy of intra-oral halitosis. The aim of this systematic review was to study the effect of the administration of probiotics alone or as an adjunct to other treatments on the level of halitosis as measured by volatile sulphur compound (VSC) levels, organoleptic scores (ORG) or hydrogen sulphide, methyl mercaptan and dimethyl sulphide levels. In addition, the effect of probiotic usage on oral microbial composition was summarised.

METHODS

The MEDLINE-PubMed and Embase databases were searched up to September 2017 with language restricted to English. Eligible papers were selected according to pre-set criteria; the data was extracted and analysed descriptively.

RESULTS

The search resulted in 1104 original research articles and a final six were selected as being eligible including 129 subjects. These studies used different detection methods and combinations thereof to measure halitosis. Five studies were randomised placebo-controlled clinical trials of which two studies reported a significant reduction in ORG between probiotic and placebo groups, and two studies on the basis of total VSC levels. The two studies reporting a significant improvement in ORG did not find an improvement in total VSC levels. Three studies included a microbiological assessment. In these three studies, the probiotic strain was detected at the end of the treatment period, but no detailed data was reported on the abundance of the strain before and after the treatment period.

CONCLUSIONS

Probiotics may be beneficial in treating intra-oral halitosis. However, due to limited data and the heterogeneity of the studies, the efficacy of probiotics remains unclear. Studies with more subjects and standardised protocols need to be designed.

Effect of students' determination of testing time on their test performance

This article investigates whether giving students control over preparing for and the moment of taking a test affects their test results in comparison with when the school is in control of the amount of training followed by a predetermined test moment. The students participated in training for manual dexterity. After the training, the students performed a test. The results of the test were stored in a database. Students from the group with freedom to select the moment of the test performed much better than those in the other group who did not have the freedom to select the moment for the test, with significantly fewer students requiring three attempts to pass the test. The fact that students when given the responsibility to develop manual skills performed better than when guided by the policy of the school is hopeful in the sense that students can learn in an early stage of their study to take responsibility for learning.

The VicRK System of Streptococcus mutans Responds to Oxidative Stress

In Streptococcus mutans, virulence and cariogenicity may be modulated via the two-component regulatory system VicRK. Environmental signals, sensed by VicK, inducing this modulation are still unclear, however, and were investigated in the present study. We found that VicRK displays homology with protein-domains that, in other bacteria, are involved in redox-sensing. After constructing a VicRK-promoter GFP-reporter strain, we showed increased fluorescence intensity under oxidative stress. Potential interference of alternative signals and experimental conditions on GFP expression was excluded by the use of negative and positive control strains. Finally, we constructed a clean vicK knockout mutant, which proved to be more sensitive to H2O2 than the wild-type. In conclusion, this study showed that the VicRK system responds to and protects against oxidative stress. As a result, a link between oxidative/redox stress and the cariogenic nature of S. mutans can be hypothesized.

[Effect of three surface modification techniques of pure titanium on bacteria adhesion and ultrasonic cleaning efficacy]

OBJECTIVE

To evaluate the bacteria adhesion behavior and ultrasonic cleaning efficacy on pure titanium modified with 3 different techiques.

METHODS

Pure titanium disks with mechanically polished surfaces(MP), titania nanotube surfaces(TNT)and sandblast-large grit and acid-etched surfaces(SLA)were used as substrates. The surface characteristics of the 3 types of specimens were detected. The disks of all groups were co-cultured with Porphyromonas gingivalis(Pg)and microcosm for 1 day and 5 days respectively. The cell viabilities of bacteria attached to the 3 types of surfaces were tested. The remaining bacteria on different surfaces after ultrasonic treatment were observed through live/dead bacteria staining.

RESULTS

MP and SLA surfaces demonstrated a micro-scale structure, while TNT surfaces showed a nano-scale structure. The surface roughness of SLA specimen was the highest([1.62 ± 0.13]μm), and that of MP([0.81 ± 0.10]μm)and TNT specimen([0.792 ± 0.080]μm)were relatively lower and showed no statistical difference(P >0.05). At 1 and 5 d, the cell viability and the biomass of Pg attached to MP surfaces were as low as 1 829±210 and 13 811±3 110 and A570 value were 0.80±0.35 and 1.56±0.30 respectively. At 1 d, the cell viability of microcosm adhered on MP and TNT surfaces were lower(63 943±6 990 and 69 860±5 555)than that on the SLA surface, and the biomass of microcosm adhered on MP surfaces demonstrated the lowest value(A570 value 5.84±0.60). At 5 d, both the cell viability and biomass of micorcosm adhered on the three surfaces were of no statistical difference(P<0.05). The remaining bacteria on TNT surfaces were the least in the three groups and distributed sporadically after ultrasonic treatment. The remaining bacteria on all surfaces increased with culture time.

CONCLUSIONS

Both surface topography and roughness affect early bacteria adhesion. However, this effect can be weakened as the biofilm getting mature. The surface topography can significantly affect the mechanical cleaning efficacy of the biofilm. TNT surface reveals a lower adhesion of microcosm and a higher efficacy of ultrasonic cleaning compared to MP and SLA surfaces.

Biofilm layers affect the treatment outcomes of NaF and Nano-hydroxyapatite

During caries formation, dental biofilms function not only as acid producers but also as reservoirs and diffusion barriers for active caries-preventive components. The aim of this study was to investigate the influence of biofilms as a stagnant layer on the efficacy of NaF and nano-hydroxyapatite (nHA). Biofilms of Streptococcus mutans C180-2 were formed on the surfaces of artificially demineralized enamel in an active attachment biofilm model. After 2 days of biofilm formation, the model was subjected to a pH-cycling schedule, together with a control group without biofilms. Specimens were treated for 5 min twice daily with water, a 10% nHA slurry, or 18.4 mM NaF. At the end of the pH-cycling period, the biofilms were removed for the determination of the viable counts, the lactic acid production, and the calcium content. The mineral changes in the demineralized enamel blocks were analyzed by transversal microradiography. No differences in the biofilm viable counts and lactic acid production were found in the different treatment groups. The mean calcium content of the biofilms in the nHA group was 60.7 ± 15.3 mmol/g wet weight, which was approximately 8-fold higher than in the other 2 groups. The application of NaF resulted in net remineralization, but in the presence of a biofilm, net demineralization was observed. In contrast, nHA treatment reduced further demineralization compared with the water treatment, but the presence of a biofilm enhanced this effect. In conclusion, the presence of biofilms clearly influenced the treatment outcomes of anticaries products. Biofilms could either enhance or impede their efficacy. This result implies that biofilms should be included in the in vitro tests for the preclinical screening of caries-protective agents.

The capsule of Porphyromonas gingivalis reduces the immune response of human gingival fibroblasts

BACKGROUND

Periodontitis is a bacterial infection of the periodontal tissues. The Gram-negative anaerobic bacterium Porphyromonas gingivalis is considered a major causative agent. One of the virulence factors of P. gingivalis is capsular polysaccharide (CPS). Non-encapsulated strains have been shown to be less virulent in mouse models than encapsulated strains.

RESULTS

To examine the role of the CPS in host-pathogen interactions we constructed an insertional isogenic P. gingivalis knockout in the epimerase-coding gene epsC that is located at the end of the CPS biosynthesis locus. This mutant was subsequently shown to be non-encapsulated. K1 capsule biosynthesis could be restored by in trans expression of an intact epsC gene. We used the epsC mutant, the W83 wild type strain and the complemented mutant to challenge human gingival fibroblasts to examine the immune response by quantification of IL-1beta, IL-6 and IL-8 transcription levels. For each of the cytokines significantly higher expression levels were found when fibroblasts were challenged with the epsC mutant compared to those challenged with the W83 wild type, ranging from two times higher for IL-1beta to five times higher for IL-8.

CONCLUSIONS

These experiments provide the first evidence that P. gingivalis CPS acts as an interface between the pathogen and the host that may reduce the host's pro-inflammatory immune response. The higher virulence of encapsulated strains may be caused by this phenomenon which enables the bacteria to evade the immune system.

Effect of Psidium cattleianum leaf extract on Streptococcus mutans viability, protein expression and acid production

Plants naturally produce secondary metabolites that can be used as antimicrobials. The aim of this study was to assess the effects of Psidium cattleianum leaf extract on Streptococcus mutans. The extract (100%) was obtained by decoction of 100 g of leaves in 600 ml of deionized water. To assess killing, S. mutans biofilms were treated with water (negative control) or various extract dilutions [100, 50, 25% (v/v) in water] for 5 or 60 min. To evaluate the effect on protein expression, biofilms were exposed to water or 1.6% (v/v) extract for 120 min, proteins were extracted and submitted to 2-dimensional difference gel electrophoresis. Differentially expressed proteins were identified by mass spectrometry. The effect of 1.6% (v/v) extract on acid production was determined by pH measurements and compared to a water control. Viability was similar after 5 min of treatment with the 100% extract or 60 min with the 50% extract (about 0.03% survival). There were no differences in viability between the biofilms exposed to the 25 or 50% extract after 60 min of treatment (about 0.02% survival). Treatment with the 1.6% extract significantly changed protein expression. The abundance of 24 spots was decreased compared to water (p < 0.05). The extract significantly inhibited acid production (p < 0.05). It is concluded that P. cattleianum leaf extract kills S. mutans grown in biofilms when applied at high concentrations. At low concentrations it inhibits S. mutans acid production and reduces the expression of proteins involved in general metabolism, glycolysis and lactic acid production.

[Microbial genetics. New possibilities for the prevention and treatment of (oral) infections]

New insights in the microbial genetics of pathogenic oral micro-organisms and the development of a new array of molecular genetic techniques together have led to alternative strategies in the development of antimicrobial agents. In this article the importance of insights in microbial molecular biology for the prevention and treatment of (oral) infectious diseases is illustrated. Following the introduction of relevant terminology, the role of microbial genetics in developing of target-based anti-microbial drugs for prevention and treatment of (oral) infections is discussed. Subsequently, the impact of microbial genetics on vaccine development and several, mainly still experimental, prevention strategies are discussed.

Zinc and cadmium accumulation and tolerance in populations of Sedum alfredii

To investigate the variation of Zn and Cd accumulation and tolerance of Sedum alfredii (a newly reported Zn/Cd hyperaccumulator), field surveys and hydroponic experiments were conducted among three populations of this species: two originating from old Pb/Zn mines in Zhejiang (ZJ) and Hunan (HN) Provinces and one from a "clean" site in Guangdong (GD) Province, China. Under field conditions, up to 12,524 and 12,253 mg kg(-1) Zn, and 1400 and 97 mg kg(-1) Cd in shoots of ZJ and HN plants were recorded respectively. Under hydroponic conditions, ZJ and HN plants accumulated significantly higher Zn and Cd in their leaves and stems, and possessed significantly higher Zn and Cd tolerance than GD plants. Among the two contaminated populations, ZJ plants showed higher Cd tolerance and accumulation (in leaves) than HN plants. The present results indicate that significant differences in Zn and Cd accumulation and tolerance exist in populations of S. alfredii.

Caries-Preventive Agents Induce Remineralization of Dentin in a Biofilm Model

The aim was to study remineralization in dentin underneath a biofilm. This was done in a constant depth film fermentor (CDFF) which was modified so that two treatments can be applied simultaneously in one experiment. Forty-five Streptococcus mutans biofilms were grown in grooves in dentin. Growth medium (3.7 g/l BHI, 1.5 mM calcium and 25 mM PIPES) was administered alternately with 2% sucrose pulsing 4 x 30 min/day. Fluoride at 135 ppm as NaF only or in a mixture with 0.2% chlorhexidine was applied for 2 x 5 min/day. The treatments started 5 days after inoculation and lasted 15 days. Five specimens per group were removed at various time points. The biofilms were checked for viability (by plating) and acid content (by capillary electrophoresis). The dentin specimens were analysed for mineral loss and lesion depth (by transversal microradiography). Fluoride treatment had no effect on the viability but reduced lactic acid production by 75%. The mixture treatment reduced the viability by 80% and the lactic acid content by 93% on the first day and later reduced the two parameters to below the detection limits. Significant differences in changes in mineral loss and lesion depth were observed between the treatment groups. Partial remineralization but deeper lesions were observed in the fluoride group, while nearly complete remineralization was seen in the mixture group. In conclusion, the CDFF S. mutans biofilm model can be used as a de- and remineralization biofilm model, and the split mode is particularly suitable for testing caries-preventive agents.

Demineralization of dentin by Streptococcus mutans biofilms grown in the constant depth film fermentor

To develop a bacterial demineralization model, we grew Streptococcus mutans biofilms in a constant depth film fermentor (CDFF) and studied the effects of sucrose pulsing frequency (SPF) in time on dentin demineralization. S. mutans biofilms were grown in dentin specimens with grooves and on dentin surface specimens for 20 days. During the experiments, 2% sucrose was pulsed either 4 or 8 times per day for periods of 30 min. Diluted brain-heart infusion medium containing 25 mM PIPES buffer and 1.5 mM CaCl2 was pulsed as the alternative growth medium. Specimens with intact biofilms were taken out on days 5, 12 and 20. The model was assessed by viable counts of the biofilm, mineral loss and lesion depth in the dentin specimens (by transversal microradiography) and pH measurements in the groove (by pH microelectrode). The results showed that biofilms formed on the dentin surface specimens were constant in viable counts for the low SPF, while this parameter tended to increase with time under the high SPF. Lesions with intact surfaces were formed and the lesion size increased significantly over time and increased significantly with increasing SPF. Typical Stephan curves were found after sucrose pulsing. The pH inside the groove returned to neutral under low SPF, but remained below 6.5 under high SPF. With the CDFF S. mutans biofilm model, lesions can be created in dentin within reasonable experimental time periods, as a result of the presence of a biofilm and in response to carbohydrate challenges.

Survival of glass ionomer restorations placed in primary molars using atraumatic restorative treatment (ART) and conventional cavity preparations: 2-year results

OBJECTIVE

To compare the survival of glass ionomer cement (GIC) restorations placed in a dental clinic setting using both the atraumatic restorative treatment (ART) approach with hand instruments, and conventional cavity preparation with rotary instruments.

METHOD AND MATERIALS

Two encapsulated high-strength conventional GICs (Fuji IX GP, Ketac-Molar Aplicap) were placed in 82 Class I and 53 Class II preparations and one encapsulated non-gamma 2 amalgam alloy (GK-amalgam) was placed in 32 Class I preparations, in the primary molars of 60 Chinese children with a mean age of 7.40 +/- 1.24 (SD) years. Thus, 9 treatment groups were formed.

RESULTS

After two years, there were no significant survival differences found among 7 of the 9 treatment groups (p = 0.99). However, two groups comprising Fuji IX GP and Ketac-Molar Aplicap placed in Class II cavities prepared using the ART approach showed significantly lower restoration survivals (p < 0.001). Only 3 of the 72 initially sealed fissures adjacent to the restorations appeared to retain any GIC material.

CONCLUSIONS

In a clinic setting, both the ART hand instrument and conventional rotary instrument methods were equally suitable for high Class I restoration survival, but not for Class II restoration survival where the conventional cavity preparation method was preferable.

A study of oral health condition in individuals with no oral hygiene and its association with plaque acidogenesis

OBJECTIVE

To study the association of long-term deposited plaque, due to lack of oral hygiene, with acidogenesis of the plaque bacteria.

METHODS

Seventy-seven subjects with poor oral hygiene were selected. Debris index (DI) and calculus index (CI) were recorded. Among them, 16 were DMFS > 8, and comprised the caries active (CA) group; 27 were caries free, and comprised the caries free (CF) group. Plaque fluids in both groups were analyzed for organic acids, phosphate, and inorganic cations by use of capillary electrophoresis, while pH was measured by microelectrodes.

RESULTS

No differences were found on debris index (CF group measured 2.07-0.47, CA group measured 2.01-0.53) or calculus index (CF group measured 2.47-0.50, CA group measured 2.48-0.53) relative to carious status, although there was a positive relationship between DI and CI (r = 0.52, P < 0.001). The main finding in this study was that the quantity of lactic acid produced by sucrose exposure in these individuals with poor oral hygiene was much less (increased no more than 2 times, compared with content at rest) than in a previous report (increased 3 to 5 times, compared with content at rest) on subjects with good oral hygiene habits.

CONCLUSIONS

Long-term deposited plaque due to lack of oral hygiene may have less cariogenic capability, although patients' susceptibility to periodontal disease would increase.