Acid formation by mixed cultures of dental plaque bacteria Actinomyces and Veillonella

The metabolism of glucose by mixtures of resting cells of Actinomyces and Veillonella resulted in propionic and acetic acids. Lactic and succinic acids produced by Actinomyces from carbohydrates were further degraded by Veillonella, thus forming a food chain.     

The lactate metabolism of the oral bacterium Veillonella from human saliva

Lactate is metabolized by Veillonella via the methylmalonyl-coenzyme A (CoA) pathway to propionate and, by further pathways, to acetate. Whereas pyruvate and oxaloacetate are metabolized via the pyruvate-formate lyase reaction, lactate acts as a donor of hydrogen allowing the reduction of oxaloacetate to malate in the methylmalonyl-CoA pathway. Succinate, believed to be an intermediate in lactate metabolism of Veillonellae is readily decarboxylated to propionate by these organisms, but a severe, progressive substrate inhibition occurs at concentrations above 12–16 mmol/l.     

Lactate degradation by polysaccharide-producing Neisseria isolated from human dental plaque

Saccharolytic and polysaccharide-producing Neisseria, isolated from human dental plaque, degrade lactate mainly to acetate and CO₂. The citric acid cycle is involved with lactate degradation via pyruvate to a variable extent. Lactate degradation in these strains is very similar to that of Neisseria sp. (strain Ne-15), the lactate degradation pathway of which we have reported previously.     

Lactate degradation by a strain of Neisseria isolated from human dental plaque.

An oral Neisseria strain Ne-15 degraded lactate under aerobic conditions. Most of the lactate, both the l(+) and d(?) forms, was converted via pyruvate to acetate, and it seems that ATP may be generated through this pathway. Part of the lactate was converted to acetate directly. A small portion of pyruvate was further metabolized by the way of the citric acid cycle after CO₂ fixation or after conversion to acetyl-CoA, and was utilized for synthesis of cell components. The addition of the Neisseria in a mixed incubation with Streptococcus murans caused no change in glucose utilization but a reduced lactate concentration.     

Diffusion of sugars and carboxylic acids through human dental plaque in vitro

Diffusion through plaque was measured with an apparatus consisting of 3 identical diffusion cells contained in an aluminium alloy block thermostatically controlled at 35 °C. In two of the cells, measurements were made of diffusion through a composite membrane consisting of 18 h dental plaque contained between bacteriological grade filters and support screens. In the third cell, diffusion occurred through a reference membrane from which the bulk of the plaque was absent. Subtraction of the diffusion resistance of this reference membrane allowed calculation of apparent tracer diffusion coefficients in the bulk of the plaque alone. Diffusion of ¹⁴C-labelled sugars and carboxylic acids was compared with that of tritiated water using dual-channel liquid scintillation counting. The diffusion coefficient of tritiated water in the plaque samples varied from 0.81 to 1.02 × 10^?9 m²s^?1 depending on the wet wt used, with coefficients of variation of ~ 15 per cent. This is between $\text{1}\text{4}$ and $\text{1}\text{3}$ of the value in aqueous solution. Diffusion coefficients relative to that of tritiated water in plaque ranged from 0.154 ± 0.014 for sucrose to 0.363 ± 0.029 for acetate. Permselectivity was low, and diffusion coefficients of I he test molecules were all between $\text{1}\text{4}$ and $\text{1}\text{5}$ of their values in free aqueous solution.     

Xylitol fermentation by human dental plaque

The aim of the present study was to examine xylitol metabolism by dental plaque collected immediately after the use of xylitol gum. Plaque was collected from 12 individuals immediately before and after xylitol exposure. The effect on xylitol metabolism by dental plaque of a 3 d discontinuation of the xylitol exposure was also examined. Xylitol metabolism by the plaque suspensions was initiated by adding [¹⁴C]xylitol and analyzed by HPLC. The results showed increased xylitol metabolism after 11 wk of chewing xylitol-containing gum. The ability to metabolize xylitol was rapidly reduced after the discontinuation of the xylitol exposure. It is suggested that an induction of enzymes in one or more of the species of plaque bacteria may have caused this effect. Glucose metabolism, which also was studied in the plaque samples, was decreased after xylitol exposure, but increased again 3 d after cessation of the xylitol exposure. It is suggested that the reduced glycolysis was caused by accumulation of intracellular xylitol-5-phosphate in some plaque bacteria during the xylitol exposure.     

Effects of Parafilm and cheese chewing on human dental plaque pH and metabolism

The effects of chewing Parafilm and cheese following sucrose rinsing on human dental plaque pH and plaque fluid organic and amino acid concentrations were investigated. Immediate increases in plaque pH were observed following chewing with concomitant decreases in lactate and acetate concentrations and increases in the concentration of formate and many amino acids. Chewing with cheese when compared with Parafilm resulted in significantly higher (p less than 0.05) plaque fluid concentrations of most amino acids, although significant decreases (p less than 0.05) in phosphate, succinate, and acetate concentrations were observed. However, no significant difference in the levels of formate, lactate, and propionate were found between the two chewing treatments.     

Measurement of pH in human dental plaque in vivo with an ion-sensitive transistor electrode

A transistor pH electrode mounted on a removable partial denture was used to measure the pH of 2- and 4-day-old approximal and occlusal plaques in 2 adults. Direct application or a mouth-rinse of sucrose, glucose or maltose to the plaque covering the electrode caused the pH to fall within 2–3 min to approx. 4.4–5.2 in both subjects. Glucosylsucrose and lactose also lowered the pH, but not below 5.5. The transistor pH electrode was found suitable to record the pH of dental plaque in vivo, and to evaluate the fermentability of sugar substitutes.     

Neutrophil chemotactic activity elaborated by human dental plaque

In the present investigation an in vivo method is described for studying the chemotactic activity elaborated by factors in human dental plaque. Plaque was sampled from the buccal and lingual surfaces of teeth from dental students, who had refrained from mechanical tooth cleansing during one 4 and one 8 day period. The plaque samples were suspended in 0.15 M NaCl, homogenized, and centrifuged at 12,100 × g for 30 minutes at 4°C. The plaque supernatant was then separated from the cellular pellet and sterile filtered through a 0.45 μ Millipore filter. The chemotactic activity elaborated by the filtrates was examined in (i) Boyden's in vitro chamber (ii) a wound chamber model described by Lundgren and Lindhe (1970). The results showed (i) that the wound chamber method is well suited for studying leukocyte chemotactic activity elaborated by dental plaque (ii) that factors in dental plaque stimulate the emigration mainly of neutrophils (iii) that there is no increase in the amount of chemotactic factors/mg plaque with increasing age of the plaque. Data from the wound chamber experiments further revealed that the plaque filtrates tested do not markedly influence the permeability to plasmaproteins and water of granulation tissue vessels.     

Immunoglobulins in human dental plaque

Immunoglobulins have been found previously in human gingiva, gingival fluid, serum and smeas of dental plaque. In the present study their presence and distribution in situ have been studied by immunofluorescence on the approximal surfaces of childen's teeth extracted due to caries or for orthodontic reasons. There wee also preliminary investigations of S. mutans distribution and of plaque immunoglobulins in grossly carious adult teeth. Positive fluorescence was in the order total Ig > IgG > IgA > IgM. S mutans (serotype c) was found in two of seven samples. Fluorescence was most marked at the apical plaque border, especially in relation to the contact area. This may relate to the prevalence of lysed organisms in this region. The topography and distribution of the different immunoglobulins correlate with previous studies suggesting gingival fluid (via plasma and gingival plasma cells) as the main source of the plaque immunoglobulin at the site of onset of approximal caries and chronic inflammatory periodontal disease.     

Colonization and cariogenic potential in hamsters of the bacterium Streptococcus sanguis isolated from human dental plaque

Strains of Strep. sanguis, freshly isolated from human dental plaque, were successfully implanted into albino hamsters. Transmission of the organisms from infected to uninfected animals occurred naturally. The transfer was as effective between unrelated hamsters as between dams and their offspring. Three of the strains tested did not cause caries in hamsters. Laboratory strains of Strep. sanguis did not colonize the hamsters. Two morphological variants of Strep. sanguis with different abilities to adhere to whale dentine in vitro, could infect hamsters; the more adhering phenotype was detected earlier and more frequently.     

Lipoproteins and lipids of human dental plaque

Host-derived lipoproteins have not yet-been detected in human dental plaque. In this microarea only lipids and lipoprotein polysaccharides known to derive from gram-positive and gram-negative bacterias, were detected. The results of this work show that in human dental plaque there are some components analogous to human serum lipoproteins. The presence of alpha-lipoproteins was established, while beta-lipoproteins could not be detected. The studies of lipids in plaque show that plaque samples contain lipid components similar of serum free cholesterol, free fatty acids, three glycerides and cholesterol esters. Phospholipids were present in extremely small amounts. The results were discussed from the aspect of the possible origin of these lipoprotein constituents as well as from the aspect of specificity and sensitivity of procedures applied in their detection.