On the release of fluoride from biofilm reservoirs during a cariogenic challenge: an in situ study

Abstract

Biofilm fluoride reservoirs may be a source of fluoride to the fluid phase during a sugar challenge reducing tooth mineral loss. However, the evidence for that is conflicting and has not been studied in biofilms containing different fluoride levels. In order to test fluoride release from biofilms with distinct fluoride concentrations, biofilms were grown in situ exposed to a combination of placebo, calcium and fluoride rinses forming biofilms with no (fluoride-free rinses), low (fluoride-only rinses) or high (calcium followed by fluoride rinses) fluoride concentrations, and collected before and 5?min after a sucrose challenge. Rinsing with fluoride increased fluoride concentration in the biofilm (p?<?0.05), mainly when a calcium pre-rinse was used before the fluoride (p?<?0.05). However, after a sugar challenge, no significant increase in the biofilm fluid fluoride concentration was observed, even in the fluoride-rich biofilms (p?>?0.05). Fluoride-rich biofilms do not release fluoride to the fluid phase during a sugar challenge.     

Virulence and pathogenicity of Candida albicans is enhanced in biofilms containing oral bacteria

This study examined the influence of bacteria on the virulence and pathogenicity of candidal biofilms. Mature biofilms (Candida albicans-only, bacteria-only, C. albicans with bacteria) were generated on acrylic and either analysed directly, or used to infect a reconstituted human oral epithelium (RHOE). Analyses included Candida hyphae enumeration and assessment of Candida virulence gene expression. Lactate dehydrogenase (LDH) activity and Candida tissue invasion following biofilm infection of the RHOE were also measured. Candida hyphae were more prevalent (p < 0.05) in acrylic biofilms also containing bacteria, with genes encoding secreted aspartyl-proteinases (SAP4/SAP6) and hyphal-wall protein (HWP1) up-regulated (p < 0.05). Candida adhesin genes (ALS3/EPA1), SAP6 and HWP1 were up-regulated in mixed-species biofilm infections of RHOE. Multi-species infections exhibited higher hyphal proportions (p < 0.05), up-regulation of IL-18, higher LDH activity and tissue invasion. As the presence of bacteria in acrylic biofilms promoted Candida virulence, consideration should be given to the bacterial component when managing denture biofilm associated candidoses.     

Sampling plan for Diaphania spp. (Lepidoptera: Pyralidae) and for hymenopteran parasitoids on cucumber

The objective of this work was to determine the best technique, sampling unit, and the number of samples to compose a conventional sampling plan for the cucurbit borers, Diaphania spp. (Lepidoptera: Pyralidae), and for hymenopteran parasitoids on cucumber. This research was carried out in 10 commercial cucumber crops fields from July to December 2000 in Tocantins, Minas Gerais State, Brazil (21 degrees 11' 15" S; 42 degrees 03' 45" W; altitude 363 m). The sampling methods studied were beating on a tray, direct counting of insects on the lower leaf surface, and whole leaf collection. Three sampling units also were studied: leaves from a branch located in the apical, median, or basal third of the canopy. The best sampling systems, which included the best technique and sampling unit, were determined based on the relative variance and the economic precision of the sampling. Once the best sampling systems were established, the numbers of samples to compose the conventional sampling plans were determined. The more suitable sampling system for the larvae of Diaphania spp. in cucumber plants was beating a leaf of the median third of the canopy on a plastic tray. One leaf must be sampled for every 50 plants in a crop. The more suitable sampling system for hymenopteran parasitoids in cucumber plants was to directly count the adults on one leaf of the median third of the canopy. One leaf must be sampled for every 74 plants in a crop.     

A three-species biofilm model for the evaluation of enamel and dentin demineralization

Although Streptococcus mutans biofilms have been useful for evaluating the cariogenic potential of dietary carbohydrates and the effects of fluoride on dental demineralization, a more appropriate biofilm should be developed to demonstrate the influence of other oral bacteria on cariogenic biofilms. This study describes the development and validation of a three-species biofilm model comprising Streptococcus mutans, Actinomyces naeslundii, and Streptococcus gordonii for the evaluation of enamel and dentin demineralization after cariogenic challenges and fluoride exposure. Single- or three-species biofilms were developed on dental substrata for 96?h, and biofilms were exposed to feast and famine episodes. The three-species biofilm model produced a large biomass, mostly comprising S. mutans (41%) and S. gordonii (44%), and produced significant demineralization in the dental substrata, although enamel demineralization was decreased by fluoride treatment. The findings indicate that the three-species biofilm model may be useful for evaluating the cariogenic potential of dietary carbohydrates other than sucrose and determining the effects of fluoride on dental substrata.     

Denture disinfection by microwave energy: influence of Candida albicans biofilm

doi: 10.1111/j.1741‐2358.2010.00439.x Denture disinfection by microwave energy: influence of Candida albicans biofilm Objective: This study evaluated the influence of the area of Candida albicans biofilm on denture disinfection by microwave energy. Materials and methods: Candida albicans biofilm was allowed to form for 72 h on resin discs, and three small coverage or seven large coverage discs were placed onto the palatal surface of sterile maxillary dentures. Each denture was immersed in 200 ml distilled water and individually irradiated at a power of 450, 630 or 900 W for different time intervals (1, 2 or 3 min) (n = 6). The effectiveness of disinfection was evaluated by counting the residual cells. The data were analysed by anova and Tukey’s HSD test (α = 0.05). Pearson’s correlation test was performed to determine the correlation between effectiveness of sterilisation and temperature. Results: Dentures with a larger area of biofilm demanded a longer irradiation exposure to achieve disinfection (p < 0.001), irrespective of power setting, and in this time no yeast growth was detected. Dentures with small areas of biofilm were disinfected after 1 min at 900 W and 2 min at 450 or 630 W. A positive correlation was found between water temperature and effectiveness of disinfection (r = 0.6170; p < 0.001). Conclusion: The C. albicans biofilm area influenced disinfection by microwave energy; therefore dentures with larger biofilm areas required longer irradiation exposure to be disinfected.     

Induced responses of Coffea arabica to attack of Coccus viridis stimulate locomotion of the herbivore

The green scale, Coccus viridis (Green) (Hemiptera: Coccidae), is an insect pest of coffee and several other perennial cultivated plant species. We investigated changes in alkaloid and phenolic contents in coffee plants as a response to herbivory by this insect. Greenhouse‐grown, 11‐month‐old coffee plants were artificially infested with the coccid and compared with control, uninfested plants. Leaf samples were taken at 15, 30, 45, and 60 days after infestation, and high‐performance liquid chromatography was used to identify and quantify alkaloid and phenolic compounds induced by the coccids at each sampling date. Of the compounds investigated, caffeine was the main coffee alkaloid detected in fully developed leaves, and its concentration in infested plants was twice as high as in the control plants. The main coffee phenolics were caffeic and chlorogenic acid, and a significant increase in their concentrations occurred only in plants infested by C. viridis. A positive and significant relationship was found between alkaloid and phenolic concentrations and the infestation level by adults and nymphs of C. viridis. Caffeine and chlorogenic acid applied on coffee leaves stimulated the locomotory activity of the green scale, thus reducing their feeding compared to untreated leaves. This is the first study to show increased levels of coffee alkaloids and phenolics in response to herbivory by scale insects. The elevation of caffeine and chlorogenic acid levels in coffee leaves because of C. viridis infestation seems to affect this generalist insect by stimulating the locomotion of crawlers.     

Effect of a denture cleanser on the concentration of volatile sulphur compounds and denture biofilm in institutionalised elderly

doi:10.1111/j.1741‐2358.2009.00341.x
Effect of a denture cleanser on the concentration of volatile sulphur compounds and denture biofilm in institutionalised elderly Objective: To determine the effectiveness of a denture cleanser in reducing the concentration of volatile sulphur compounds (VSC) and its antimicrobial action. Background: Micro‐organisms from the denture biofilm can cause local and systemic disease and halitosis. Denture cleansers are important adjuncts in oral care, but there is limited investigation on their effect in malodour compounds. Material and methods: Nineteen institutionalised elderly who wore at least an upper denture were selected; their VSC concentrations were measured and the denture biofilm was collected. In phase 1, the subjects wore their old denture and data were collected before (B₀) and after 7(A₁), 14(A₂), 28(A₃) days of continuous daily use of the denture cleanser. In phase 2, new dentures were inserted and measurements were made at 30(A_1.1), 60(A_2.2), 90(A_3.3) days of treatment. Results: The VSC concentration increased from B₀ to A₁ (p < 0.05)_, but no differences were found for the others intervals of times. Total micro‐organism data did not show a statistical difference between times in Phase I, but in Phase II, there was a statistical difference (p < 0.05) and a progressive re‐colonisation was observed. Conclusion: Within the limits of this study, it was concluded that the denture cleanser had no antimicrobial effect and VSC levels were not reduced.     

Snakebites in “Invisible Populations”: A cross-sectional survey in riverine populations in the remote western Brazilian Amazon

In the Brazilian Amazon, long distances, low healthcare coverage, common use of ineffective or deleterious self-care practices, and resistance to seeking medical assistance have an impact on access to antivenom treatment. This study aimed to estimate snakebite underreporting, and analyze barriers that prevent victims from obtaining healthcare in communities located in 15 municipalities on the banks of the Solimões, Juruá and Purus Rivers, in the remote Western Brazilian Amazon. Information on the participants’ demographics, previous snakebites, access to healthcare, time taken to reach medical assistance, use of self-care practices, and the reason for not accessing healthcare were collected through semi-structured interviews. In the case of deaths, information was collected by interviewing parents, relatives or acquaintances. A total of 172 participants who reported having suffered snakebites during their lifetime were interviewed. A total of 73 different treatment procedures was reported by 65.1% of the participants. Participants living in different river basins share few self-care procedures that use traditional medicine, and 91 (52.9%) participants reported that they had access to healthcare. Living in communities along the Juruá River [OR = 12.6 (95% CI = 3.2–49.7; p<0.001)] and the use of traditional medicine [OR = 11.6 (95% CI = 3.4–39.8; p<0.001)] were variables that were independently associated to the lack of access to healthcare. The main reasons for not accessing healthcare were the pprioritization of traditional treatments (70.4%), and the failure to recognize the situation as being potentially severe (50.6%). Four deaths from complications arising from the snakebite were reported, and three of these were from communities on the banks of the Juruá River. Only one of these received medical assistance. We found an unexpectedly high underreporting of snakebite cases and associated deaths. Snakebite victims utilized three main different healing systems: 1) self-care using miscellaneous techniques; 2) official medical healthcare generally combined with traditional practices; and 3) self-care using traditional practices combined with Western medicines. To mitigate snakebite burden in the Brazilian Amazon, an innovative intervention that would optimize timely delivery of care, including antivenom distribution among existing community healthcare centers, is needed.     

Development of Transgenic Sugarcane Resistant to Sugarcane Borer

Sugarcane borer (Diatraea saccharalis) is a major pest of sugarcane (Saccharum spp. hybrids), across the Americas. The insect is partially controlled by biological and chemical means, but still causes significant economic losses to sugarcane growers and processors. Proteins derived from Bacillus thuringiensis, Bt proteins, have been used to control sugarcane borer in maize (Zea mays) for the past decade. In sugarcane, the expression of individual Bt proteins has been reported several times. However practical use of Bt proteins requires their use as part of an Integrated Pest Management (IPM) system that includes the delivery of high doses of protein and the use of a refuge to slow the evolution of insect resistance to the protein. Here we demonstrate the feasibility of using Bt proteins to protect sugarcane from sugarcane borer in a commercial setting. We have expressed two Bt proteins with differing modes of action (Cry1Ab and Cry2Ab) in commercial sugarcane varieties, demonstrated efficacy against sugarcane borer in the field and describe a strategy for trait deployment in this tropical crop with complex genetics that limits trait introgression by backcrossing.