Dental Plaque Microorganisms Research Articles

Adhesion of Non-coccal Dental Plaque Microorganisms to Buccal Epithelial Cells: Inhibition by Saliva and Amphipathic Agents

Adhesion of Non-coccal Dental Plaque Microorganisms to Buccal Epithelial Cells: Inhibition by Saliva and Amphipathic Agents

In Vitro Assessment of Nystose as a Sugar Substitute

Nystose represents a fructooligosaccharide with two fructose molecules linked via β(1→2) bonds to the fructosyl moiety of sucrose. This tetrasaccharide was subjected to an array of in vitro tests designed for the assessment of potential sugar substitutes before animal or human studies. β-Fructosidase from yeast cleaved nystose at about 5% of the initial rate observed with sucrose. The terminal fructose was released first. Glycosyltransferase from Streptococcus mutans #620 did not utilize nystose for the formation of a glucan-type polysaccharide. Anaerobic fermentation of nystose by a suspension of mixed dental plaque microorganisms and by S. mutans NCTC 10449 was about half as fast as with sucrose. Thin-layer chromatography at various reaction times with S. mutans NCTC 10449 indicated the terminal fructose as the site of first attack. Analyses for free monosaccharides confirmed these data because free fructose exceeded free glucose at early reaction times far more than would follow from the 3:1 ratio of fructose to glucose in the nystose molecule. High pressure liquid chromatography assays demonstrated lactic and acetic acids as the main fermentation products. Carbohydrases from human jejunal mucosa did not attack nystose. However, cecal anaerobic microorganisms of the rat fermented nystose rapidly into acids.

Competition for dietary carbohydrates between streptococci in dental plaque

The predominant microorganisms in dental plaque, i.e., streptococci and actinomycetes, are carbohydrate fermenters. In the natural environment these organisms experience carbohydrate limitation interrupted by periods of substrate excess following food intake by the host. Recently, we have studied the competition between pairs of oral Streptococcus species in the chemostat under continuous glucose or sucrose limitation and under glucose pulsed conditions. In the present study we have investigated the competition for dietary carbohydrates in dental plaque of gnotobiotic rats infected with the same combinations of streptococci. The rats were exposed to similar regimes of carbohydrate administration as in the chemostat by incorporation of low molecular carbohydrates in the diet and drinking water. Addition of glucose to the diet favoured the organism with the highest qmax for glucose. This result parallels the outcome of earlier competition experiments in glucose-pulsed chemostats, which showed that the organism with the highest qmax glucose became dominant in the cultures. Previous observations that bacteriocin production and extracellular glucan synthesis are major ecological factors for oral streptococci were also confirmed in this experiment.

Studies of the Inhibitory Action of Intense Sweeteners on Oral Microorganisms Relating to Dental Health

The effects of five different intense sweeteners on the growth and metabolism of mixed cultures of dental plaque microorganisms or a pure culture of Streptococcus mutans NCTC 10449 were studied (a) in peptone liquid media, (b) in agar media by the zone inhibition method and (c) in tryptone soya medium by a modification of the minimum inhibitory concentration method. Acesulfam-K and cyclamate showed no activity. The effect of Talin was obscured by its tendency to precipitate from solution. Only aspartame and saccharin had any inhibitory action, with aspartame the more effective in the mixed plaque cultures and saccharin the more effective against S. mutans.

Cell surface hydrophobicity of dental plaque microorganisms in situ.

The cell surface hydrophobicity of bacteria obtained directly from human tooth surfaces was assayed by measuring their adherence to liquid hydrocarbons. Fresh samples of supragingival dental plaque were washed and dispersed in buffer. Adherence of the plaque microorganisms to hexadecane, octane, and xylene was tested turbidimetrically and by direct microscopic observation. The results clearly show that the vast majority of bacteria comprising dental plaque exhibit pronounced cell surface hydrophobicity. These data support the hypothesis that hydrophobic interactions play a major role in mediating bacterial adherence on tooth surfaces.

The use of selective media for examining relationships between dental plaque microorganisms and periodontal disease in a large sample clinical investigation.

The use of selective media for examining relationships between dental plaque microorganisms and periodontal disease in a large sample clinical investigation.

In vitro hydrolysis of monofluorophosphate by dental plaque microorganisms.

Enzymic hydrolysis of sodium monofluorophosphate by suspensions of dental microorganisms has been demonstrated at pH 5.1, pH 7.0, and pH 8.4, using a fluoride-selective electrode. The extracellular medium from viable Streptococcus mutans K1R cells contained low MFPase and paranitrophenyl phosphatase activity. It is hypothesized that the enzymes responsible for MFP hydrolysis by S. mutans K1R are intracellular, and that cell disruption is necessary for hydrolysis to be manifested; this question requires further study. In vitro MFPase activity was of a magnitude consistent with the hypothesis that it may significantly raise the fluoride ion concentration of plaque within the several minutes MFP would be in the mouth during toothbrushing.

Cell-mediated immune response to fractionated products of Actinomyces viscosus cultures.

Since bacterial invasion of host tissue has not been shown to occur in the course of periodontitis, many investigators believe that products released from dental plaque microorganisms enter the tissue and elicit a series of host responses leading to the pathological condition. This study, therefore, was designed to explore the possibility that cell-free products isolated from Actinomyces viscosus cultures are able to induce cell-mediated immunological responses in experimental animals. Hartley strain guinea pigs were sensitized with concentrated cell-free products of A. viscosus culture supernatant fluids mixed with Freund complete adjuvant. After 10 to 17 days the animals responded to challenge with this material with skin reactions indicative of delayed-type hypersensitivity. Furthermore, cells isolated from sensitized animals produced mitogenic factor and macrophage migration inhibition factor (MIF) when cultured with the material. The cell-free culture products were fractionated by column chromatography and electrophoresis. Several partially purified components were shown to induce cell-mediated responses in guinea pigs as determined by skin tests and by mitogenic factor and MIF assays. It is apparent that this single microorganism associated with dental plaque is capable of producing several substances which can induce a cell-mediated immune response and subsequent tissue inflammation in laboratory animals.

Acidogenic fermentation of pentose alcohols by human dental plaque microorganisms

The potential non-cariogenicity of the pentose sugar alcohols xylitol, l-arabinitol and ribitol was estimated by determining their fermenting properties with 50 separate samples of dental plaque, collected from people of different ages. Sucrose and control cultures were included for comparison. For most subjects, sucrose was more acidogenic than the pentitols. Lactobacilli or propionibacteria which fermented xylitol were isolated in pure culture from 2 out of 50 plaque samples whereas lactobacilli which fermented l-arabinitol were purified from another. Tests were made for pentitol metabolism by saliva collected from 8 subjects: 3 carried lactobacilli or propionibacteria which fermented xylitol and at least 2 contained lactobacilli that used l-arabinitol anaerobically. Candida albicans isolated from 2 subjects metabolized xylitol aerobically. Thus xylitol-utilizing oral microorganisms may be widespread. Further research is desirable before encouraging the widespread substitution of xylitol for sucrose.

Rapid method for identification and enumeration of oral Actinomyces.

Serotype-specific antisera prepared against whole cells of Actinomyces viscosus, A. naeslundii, and A. israeli were labeled with fluorescein dye and used to detect and quantitate antigenically related microorganisms in human dental plaque. By relating the DNA content of the dental plaque microflora to the number of Actinomyces present in the plaque samples, a reproducible method was developed for specifically enumerating five serotypic representatives of this genus found in human plaque.

Cell mediated immune responses to plaque antigens during experimental gingivitis in man.

The purpose of the present investigation was to evaluate the ability of antigens of human dental plaque microorganisms to stimulate peripheral blood lymphocytes (PBL) from humans during the development and recovery from experimental gingivitis.Eleven healthy dental students (22–36 years) participated in the study. At the start of the experiment, they exhibited clean teeth and clinically healthy gingivae. They then abstained from all oral hygiene measures for four weeks according to the model proposed by Löe et al. (1965). At the start, after 1, 2, 3 and 4 weeks of abolished oral hygience and 2 weeks following reinstitution of oral hygiene, the oral conditions were assessed, using the critieria of the Plaque Index system (Löe & Silness 1964) and the Gingival Index system (Löe & Silness (1963).At each examination triplicate microcultures, each containing 2 × 105 viable PBL in .2 ml TC 199 with glutamine and antibiotics containing 10% fetal calf serum, were stimulated with four concentrations of sonicates from V. alcalescens, F. nucleatum, B. melaninogenicus, A. viscosus, A. naeslundii, S. sanguis and pooled dental plaque all obtained from the previsouly performed experimental gingivitis. The cultures were incubated for 78 hours at 37°C in 5% CO2. 3H‐thymidine was added for the final 8 hours.Only A. viscosus was able to stimulate PBL to undergo blastogenesis during the development of experimental gingivitis. A. viscosus stimulated the PBL of 3 subjects after one week but all subjects after 2 weeks of abolished oral hygiene. The stimulation indices (SI) remained >2.5 for the rest of the experimental period. Following 2 weeks of reinstituted oral hygiene, the SI reached preexperimental levels.These results suggest that A. visocus is capable of inducing a specific cellular immune response during the development of experimental gingivitis and may be important as a causative plaque constituent. Further research is indicated to study this association.

Activation of the complement system by some Gram-positive oral bacteria

Actinomyces viscosus 19246, T 14V and T 14AV, Streptococcus mutans and Streptococcus sanguis consumed complement in vitro. Complement (C) profile analysis revealed that C 4 and C 3–9 were consumed concomitantly in unadsorbed human serum. In serum from which naturally occurring agglutinating antibodies had been removed, the same microorganisms caused C 3–9 consumption in the absence of a demonstrable loss of C 4 activity. Congenitally C 4-deficient guinea-pig serum (C 4D) supported a similar consumption of C 3–9. The Gram-positive plaque microorganisms tested activated serum complement by the classical as well as the alternate pathways. Dental plaque microorganisms may cause a similar activation of gingival crevicular fluid complement in vivo, thus resulting in complement-mediated inflammatory processes.

Development of dental plaque on epoxy resin crowns in man. A light and electron microscopic study.

A method was presented to fabricate epoxy resin crowns to be worn by human subjects requiring full crown restorations. These crowns were utilized in six young adults to study the internal structure of plaque after plaque formation periods of 1 and 3 days, 1 and 3 weeks and 2 months. This study confirmed previous findings that early plaque contains primarily coccal forms, with a shift to predominantly filamentous forms by 3 weeks. Early plaque growth seems to occur by the formation of columnar microcolonies which coalesce and grow by cell division within the colony in a direction perpendicular to the crown surface. Filamentous microorganisms appear in large numbers by 1 week. They appear to colonize the surface of the predominantly coccal plaque, eventually growing into it and replacing the coccal forms. The subgingival, mature plaque contains many motile forms including bacteria with unusual cell wall ultrastructures. Certain bacteria combine into distinctive bacterial aggregations resembling "corn cobs" and "test tube brushes," the latter occurring exclusively in subgingival plaque. Spirochetes appear to grow preferentially on the external surface of subgingival plaque in close contact to the gingival tissue of the deepened sulcus. Their high concentration in the external layer of subgingival plaque suggests that because of their strategic location they may play an important role in the etiology of periodontal disease. Studies of well preserved plaque, possibly combined with the use of serological markers, can serve a useful role in identifying certain microorganisms in dental plaque. Because of their numbers and/or location in relation to periodontal tissues, some of these bacteria may warrant further studies as potential etiologic agents of certain forms of periodontal disease.

A study of the variability of dental plaque microorganisms in littermate wistar rats retaining a natural oral flora

Similar types of bacteria, selected on the basis of their distinctive colony morphology on mitis-salivarius agar and trypticase soy agar plates, were recoverable from the plaque of weanling littermate rats. The proportional distribution of these bacteria was highly variable within a litter, irrespective of whether a pellet diet or a powdered non-cariogenic diet was fed before weaning, or whether plaque was sampled from the central and distal fissures and the approximal surfaces of lower first and second molars or from only the central fissures of these teeth. Corresponding observations were made in rats fed a cariogenic diet after weaning. In this case, the caries experience of littermates appeared to be less variable than the proportional distribution of bacteria from plaque in the central fissure of their lower first and second molars. The results preclude the extrapolation from one rat to its littermates of quantitative bacteriological data relating to plaque.

Detection and preliminary studies on dextranase-producing microorganisms from human dental plaque.

An enriched nutrient agar medium containing blue dextran has been utilized for the detection of dextranase-producing microorganisms in human dental plaque. When compared with the total viable anaerobic plaque flora, the proportion of these microbes in supragingival plaque from different individuals varied over a wide range. Preliminary characterization of some of the dextranase-producing microorganisms revealed a heterogeneous mixture of cell types with varying morphological and biochemical characteristics. Several bacterial isolates were tentatively identified as being members of the genus Actinomyces. An additional isolate appeared to belong to the genus Bacteroides. The dextran-degrading enzymes produced by these bacteria are extracellular, and a cell-free preparation from one of the isolates has been shown to cause extensive endohydrolytic cleavage of high-molecular-weight dextrans.

A special relationship between spherical and filamentous microorganisms in mature human dental plaque

A special relationship between spherical and filamentous microorganisms in mature human dental plaque

The effect of various factors on the extraction of protein from the predominant microorganisms in human dental plaque

A study was made of the effects of pH, temperature, Ca, Mg, ionic strength, osmotic shock, time of exposure to buffer, growth phase and bacterial concentration on the extraction of protein by aqueous solvents from eight representative dental plaque microorganisms in pure culture. Protein extraction was independent of bacterial concentration (0–4 mg total protein/ml), and of ionic strength (0.05–0.64), but was increased by increase in temperature (0 °–60 °C), duration of exposure to solvent and by osmotic shock. Organisms in stationary or early death phase were no more susceptible to protein extraction than were organisms in the logarithmic phase of growth. The minimum extraction was at pH 5.0 and the maximum at pH 12.7. Ca and Mg ions only reduced protein extraction at pH values of 9.0 and above and then only from certain organisms. The results are discussed in relation to the extraction of matrix from dental plaque.

Effect of erythromycin on dental plaque and plaque forming microorganisms of man.

Effect of erythromycin on dental plaque and plaque forming microorganisms of man.

Evaluation of Plating Media for the Determination of Viable Microorganisms in dental Plaque

Four agar media were evaluated to determine which one might be most suitable for the determination of the predominant number of viable microorganisms in dental plaque. The highest plate counts and uniformly larger microbial colonies were consistently obtained with Brain Heart Infusion Agar.

Studies on factors affecting the aggregation of the microorganisms in human dental plaque

Factors affecting the aggregation of the cellular and acellular components of dental plaque were studied as a function of pH. Suspensions of plaque cells were titrated between pH 10 and 3 with 0.1 N HCl and the effects on aggregation of varying the cell concentration, ionic strength and the concentration of divalent cations (calcium and magnesium) were determined. The effect of the high molecular weight components of plaque on the aggregation of the plaque cells in the presence of calcium was also determined as a function of pH. Aggregation occurred when the pH was decreased and was favoured and occurred at a higher pH when the cell concentration, the ionic strength, or the concentration of divalent cations was increased. All of the acellular components of plaque protected the cells against the aggregating effect of calcium, except for one component which enhanced aggregation. The findings in this study support the theory that a more acid pH on the surface of the teeth favours plaque formation.