Charles F. Schachtele

Comparison of Methods for Monitoring Changes in the pH of Human Dental Plaque

Changes in human dental plaque pH can be used to obtain estimates of the acidogenic potential of ingested foods. The presence of acid in plaque is influenced by a large number of host, microbial, and substrate factors. Several useful methods have been developed for monitoring changes in plaque pH. Plaque sampling involves repeated removal of small samples of plaque from a number of teeth at intervals after food ingestion, dispersion of the sample, and in vitro measurement of pH. Touch electrode methods utilize glass or antimony microelectrodes, which are placed onto plaque in situ where direct readings can be obtained. Telemetry methods involve placement of glass microelectrodes or ion-sensitive field effect transistors within the dentition. Plaque is allowed to accumulate, and pH changes can subsequently be transmitted with radio or wire. Each of the methods has clear advantages and limitations. The methods have been simultaneously compared in human volunteers using solutions of fermentable carbohydrate. Inter-method differences in response were observed depending upon the site of measurement. Data obtained from caries-prone surfaces via telemetry showed lower pH minima and retarded returns to resting pH levels. The technology is available for controlled comparative plaque pH studies, with the method of choice depending upon the goals of the investigation. It is essential that the results be compared to data obtained with other models designed to evaluate the cariogenic potential of foods.

Rapid Filter Paper Assay for the Dextransucrase Activity from Streptococcus mutans

A convenient, sensitive, and reliable assay for the conversion of radiolabeled sucrose to alcohol-insoluble dextran by the Streptococcus mutans dextransucrase has been developed.

Effect of pH on the Growth and Proteolytic Activity of Porphyromonas gingivalis and Bacteroides intermedius

The effect of pH on the growth and proteolytic activity of the type strain and fresh isolates of Porphyromonas gingivalis and Bacteroides intermedius was investigated. B. intermedius strains grew with and without glucose at a pH as low as 5.0. These bacteria grew almost as well as Streptococcus mutans at pH 5.0 and better than Actinomyces viscosus at pH 5.5 and 5.0. Some B. intermedius strains raised the culture pH when grown at a low pH without glucose. In contrast, P. gingivalis strains grew only at pH 6.5 to 7.0. The P. gingivalis strains had proteolytic activities against azocoll, azocasein, and azoalbumin, while the B. intermedius strains degraded azocasein and azoalbumin, but not azocoll. B. intermedius showed maximum proteolytic activity at pH 7.0, and high activity over a wide pH range. In contrast, the optimum pH of proteolytic activity in P. gingivalis was pH 7.5 to 8.0. The P. gingivalis activities were more sensitive than those of B. intermedius to low pH. The capacity of B. intermedius to degrade proteins to more readily metabolizable substrates at low pH might explain the growth of this bacterium in an acidic environment. These differences between B. intermedius and P. gingivalis could explain their capacity to survive at different sites in the oral cavity and indicate how B. intermedius might positively influence the growth of P. gingivalis in subgingival plaque.

Plaque sampling and telemetry for monitoring acid production on human buccal tooth surfaces

The plaque sampling method and wire telemetry using miniature, glass pH electrodes on the buccal surface of mandibular first permanent molars, compared human dental plaque pH responses to a 10 per cent solution of sucrose. Nine subjects abstained from oral hygiene and were tested in morning sessions on 5 consecutive days. The mean resting plaque pH value for all sessions by plaque sampling was 6.60 +/- 0.18 (mean +/- SD) and by telemetry was 6.56 +/- 0.19. After a 1 min sucrose rinse, 1-day-old plaque showed a decrease in pH approx. 5.5 by both methods. The 2-, 3-, 4- and 5-day-old plaque, the mean minimum pH achieved was 4.69 +/- 0.28 as measured by sampling and 3.94 +/- 0.49 as determined by telemetry. The times taken to reach minimum pH as determined by the two methods were almost identical. The electrode calibration data showed that all the telemetry electrodes responded consistently for all 5 days of study. Scanning electron microscopy and microbiological analysis of electrode tips and enamel replicas revealed that plaque accumulated on glass at the same rate with a similar bacterial composition to plaque formed on clean enamel. It is proposed that glass microelectrodes and wire telemetry are a reasonable means for continuously monitoring plaque pH in situ. Comparison with plaque sampling suggested that telemetric responses reflect the type of plaque which accumulates at particular sites on the dentition.

Phosphoenolpyruvate-Dependent Glucose Transport in Oral Streptococci

Streptococcus mutans, S sanguis, and S salivarius use a phosphoenolpyruvate (PEP)-dependent phosphotransferase system that results in phosphorylation of glucose at carbon 6. This enzyme system is not sensitive to fluoride. Glucose uptake into resting cell suspensions is sensitive to fluoride because of inhibition of intracellular PEP production. The glucose phosphotransferase system is constitutive in oral streptococci.

The Acidogenic Potential of Reference Foods and Snacks at Interproximal Sites in the Human Dentition

Telemetry was used to evaluate changes in plaque pH at interproximal sites in the dentition of five human subjects following the ingestion of a variety of reference foods and snacks. Short-term telemetry (30 min) revealed that most of the substrates yielded both pH minima and total responses similar to that obtained with a 10% sucrose rinse. Aged Cheddar cheese and skim milk were much less acidogenic than were the other foods.

Mechanism of canavanine death in Escherichia coli: II. Membrane-bound canavanyl-protein and nuclear disruption

Abstract Electron microscopy of canavanine-grown Escherichia coli demonstrates two profound changes in intracellular organization. First, two to eight large electrondense bodies are found attached to the cell membrane. These canavanineinduced bodies have been isolated from the cells and shown to have an irregular, amorphous structure with pieces of cell membrane attached to them. Second, extensive physical disruption of the nuclear region is observed in cells grown with canavanine under conditions that produce death. More than 70% of the canavanyl-protein formed is attached to the heavy cell fraction containing the canavanine-induced bodies; they are largely protein in nature, and their amino acid composition is similar to that of total E. coli protein except that canavanine replaces most of the arginine. A canavanine-resistant mutant of an arginine auxotroph of E. coli is described. This mutant incorporates canavanine into protein but it remains viable in the presence of 1 mg/ml. of l -canavanine, and can subsequently produce bacteriophage upon T4 infection. Electron micrographs of this mutant show the presence of the canavanine-induced bodies, but the nuclear region remains intact. Our results suggest that the lethal action of l -canavanine involves incorporation of this analog into membrane-bound protein(s) that interrupts the normal organization and functioning of the E. coli genome.

Comparison of in vivo Human Dental Plaque pH Changes within Artificial Fissures and at Interproximal Sites

Ion-sensitive field-effect transistor (ISFET) pH electrodes were used to monitor changes in plaque pH at the base of artificial occlusal surface fissures and at interproximal sites. Bovine enamel was used to construct fissures (1.5 x 0.1 x 1.0 mm) containing a small ISFET electrode. The fissures were fixed to carrier appliances and worn by 4 human volunteers. After plaque accumulation for 4 days changes in pH were monitored by wire telemetry following 1-min rinses with 10% solutions of either sorbitol or sucrose. Results were compared to data obtained from interproximal sites in the same subjects. Responses to sorbitol in the fissure and on the proximal surfaces were minimal and showed no significant difference in minimum pH (5.9 +/- 0.4 and 6.1 +/- 0.3, respectively) and area under pH 7.0. The response to sucrose at the two sites was very different revealing unique pH profiles which were statistically significantly different with regard to minimum pH (5.0 +/- 0.3, fissure and 4.3 +/- 0.2, proximal) and area under pH 5.7. Thus, the acidogenic potential of fermentable carbohydrate at two caries-prone sites in the human dentition is significantly different and conclusions based on interproximal telemetry measurements may not be applicable to occlusal surface fissures.

Clinical Science Plaque pH Measurements by Different Methods on the Buccal and Approximal Surfaces of Human Teeth after a Sucrose Rinse

Changes in plaque pH after a sucrose rinse were simultaneously monitored by plaque sampling, touching of the plaque with antimony and glass electrodes, and telemetry. The minimum pH at approximal sites was approximately 0. 7 pH units lower than that on buccal surfaces. The pH at the approximal site remained below resting levels after 120 min, and the area under the pH response curves from this site was five times greater than that from the buccal surfaces.Changes in plaque pH after a sucrose rinse were simultaneously monitored by plaque sampling, touching of the plaque with antimony and glass electrodes, and telemetry. The minimum pH at approximal sites was approximately 0.7 pH units lower than that on buccal surfaces. The pH at the approximal site remained below resting levels after 120 min, and the area under the pH response curves from this site was five times greater than that from the buccal surfaces.

Mechanism of canavanine death in Escherichia coli: I. Effect of canavanine on macromolecular synthesis☆

Abstract Canavanine-dead Escherichia coli are unable to support the growth of T-even bacteriophage. Loss of the ability to make virus is directly related to the kinetics of canavanine death and is due to the synthesis of host protein containing canavanine. T4-infected canavanine-dead cells did not form phage-induced messenger RNA and consequently no phage-induced protein and DNA synthesis were observed. Amino acid incorporation into protein by cell-free extracts indicated a defect in the protein synthesizing system of canavanine-dead cells. It is shown that the washed ribosomes from dead cells are only slightly active while the soluble fraction is normal. Activity is restored when synthetic mRNA is supplied to ribosomes from cells rendered non-viable by canavanine. Thus, the protein synthesizing machinery in canavanine-dead E. coli appears intact and the low level of mRNA in cell extracts indicates that very little transcription takes place in the dead cells. Crude extracts from dead cells show high levels of RNA polymerase activity. However, plasmolyzed canavanine-dead cells show lowered levels of RNA synthesis in the presence of exogenous ribonucleoside triphosphates. DNA synthesis is not initiated in dead cells by supplying excess arginine followed by plasmolysis and the addition of deoxynucleoside triphosphates. Canavanine-dead cells retain the ability to oxidize glucose and generate ATP. These results are consistent with the hypothesis that, during canavanine death, proteins containing this amino acid analog are synthesized, which eventually block transcription of all DNA in the intact cell.