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Biomedical subjects

K M Schilling

Publications and source records attributed to K M Schilling.

8 recordsLinked to original sources
PubMed1996

A modified chemostat system to study the ecology of oral biofilms.

Previously, we developed a chemostat system to study the behaviour and properties of a community of up to 10 species of oral bacteria. The present study describes modification of this system to incorporate removable and replaceable hydroxyapatite (the major mineral in human dental enamel) disks on which biofilms could develop. Hydroxyapatite disks were immersed in the chemostat for known time periods, and the bacterial content of biofilms determined by viable counting. Initial deposition rates were rapid, with all 10 species detected after 1 h, and the numbers of bacteria in biofilms continued to increase for 21 d. The species composition of biofilms reflected that of the surrounding fluid phase, and showed only limited signs of the type of 'species succession' which is observed in developing dental plaque in vivo, although anaerobic species increased in proportion in older biofilms. Four-day biofilms showed the least variability and were chosen as the 'standard biofilm' for more detailed study. Variability in the bacterial composition of 4-d biofilms was comparable both within a single chemostat run and between independent chemostat runs. Glucose pulsing in the absence of pH control resulted in the selection of cariogenic species; the disruption of the biofilm community was less marked than that of the equivalent planktonic culture. The model system has considerable potential in studying the effects of a variety of factors on biofilm development, as well as in comparing the efficacy of antimicrobial systems against biofilms.

Bacteria↗
PubMed1996

Characterization of glucosyltransferase of human saliva adsorbed onto hydroxyapatite surfaces.

Activities of glucosyltransferases (Gtf)-B, -C and -D adsorbed on the surface of saliva-coated hydroxyapatite were compared with those of Gtfs of donor whole saliva. Antiserum raised against a mixture of the three Gtfs reduced the activity of GtfB only, and had no effect on donor Gtf activities. GtfB, and not the Gtfs of the donors, was stimulated in the presence of starch hydrosylates. GtfD and GtfC activities were enhanced on the surfaces, as were the Gtf activities of donor salivas. The activities of GtfD and GtfB, but not GtfC, were stimulated by dextran. The donor Gtf activities were unaffected by dextran. Therefore, Gtf activity in pellicles has properties similar to those of GtfC.

Adsorption↗
PubMed1995

Mutacin II, a bactericidal antibiotic from Streptococcus mutans.

Mutacin II is an antibiotic that is produced by group II Streptococcus mutans. It inhibits the growth of other streptococci as well as many other gram-positive microorganisms by a hitherto unknown mechanism. Mutacin II possess bactericidal activity against susceptible cells. It transiently depolarizes the transmembrane electrical potential (delta psi) and the transmembrane pH gradient (delta pH) and partially inhibits amino acid transport. However, it rapidly depletes the intracellular ATP pool in glucose-energized cells and prevents the generation of ATP. It is concluded that mutacin II does not belong to the group of pore-forming antibiotics (type A) or to the type B antibiotics, which inhibit phospholipases or interfere with peptidoglycan biosynthesis. Mutacin II acts by inhibiting essential enzyme functions at the level of metabolic energy generation, an activity that has not yet been classified for antibiotics.

Adenosine Triphosphate↗
PubMed1992

Glucans synthesized in situ in experimental salivary pellicle function as specific binding sites for Streptococcus mutans.

Many researchers have suggested that the role of glucan-mediated interactions in the adherence of Streptococcus mutans is restricted to accumulation of this cariogenic bacterium following its sucrose (i.e., glucan)-independent binding to saliva-coated tooth surfaces. However, the presence of enzymatically active glucosyltransferase in salivary pellicle suggests that glucans could also promote the initial adherence of S. mutans to the teeth. In the present study, the commonly used hydroxyapatite adherence assay was modified to include the incorporation of glucosyltransferase and the synthesis of glucans in situ on saliva-coated hydroxyapatite beads. Several laboratory strains and clinical isolates of S. mutans were examined for their ability to adhere to experimental pellicles, either with or without the prior formation of glucans in situ. Results showed that most strains of S. mutans bound stereospecifically to glucans synthesized in pellicle. Inhibition studies with various polysaccharides and fungal dextranase indicated that alpha 1,6-linked glucose residues were of primary importance in the glucan binding observed. Scanning electron microscopic analysis showed direct binding of S. mutans to hydroxyapatite surface-associated polysaccharide and revealed no evidence of trapping or cell-to-cell binding. S. mutans strains also attached to host-derived structures in experimental pellicles, and the data suggest that the bacterial adhesins which recognize salivary binding sites were distinct from glucan-binding adhesins. Furthermore, glucans formed in experimental pellicles appeared to mask the host-derived components. These results support the concept that glucans synthesized in salivary pellicle can promote the selective adherence of the cariogenic streptococci which colonize human teeth.

Bacterial Adhesion↗
PubMed1988

The activity of glucosyltransferase adsorbed onto saliva-coated hydroxyapatite.

This study aimed to determine physical and kinetic properties of glucosyltransferase (GTF) adsorbed onto hydroxyapatite (HA) surfaces. For development of a solid-phase enzyme assay, 4.0-mg samples of washed HA powder were exposed to centrifuged whole saliva (WSHA) or buffer, and subsequently exposed to a GTF solution. The activities of GTF adsorbed to HA and that remaining in solution were measured. WSHA was more effective in adsorbing GTF than was naked HA. Enzyme activity on the surface of WSHA was enhanced; more activity was detected on WSHA than was apparently removed from solution. A similar effect was observed when GTF was adsorbed to naked HA from a mixture with lysozyme or saliva; however, no enhancement was seen when GTF was adsorbed from a mixture with albumin. Compared with GTF in solution, adsorbed GTF displayed activity over a much wider range of pH values. Temperature-activity profiles indicated that GTF adsorbed to surfaces had a lower temperature optimum (40 degrees C) than did soluble enzyme (45 degrees C), and that the bound enzyme was more resistant to adverse effects of heat at elevated temperatures. The majority of glucan made by GTF adsorbed to parotid saliva-coated HA remained attached to the surface. The activity of lysozyme adsorbed to HA was reduced by adsorption of GTF to the same surface and was almost completely abolished by formation of glucans by the adsorbed GTF. These results suggest that soluble bacterial enzymes found in saliva can be incorporated into pellicle, interact with host-derived molecules on the surfaces of teeth, express enzymatic activity, and potentially influence the biological properties of pellicle.

Adsorption↗
PubMed1983

Card pull in projective testing.

Card pull, the tendency of the test stimuli to evoke or predispose certain cognitive and affective responses in the subject, is essential to the understanding and practice of projective testing. The basic instruction in projective testing employs the subjunctive mood to catalyze the dialectic between actuality and potentiality inherent in the projective stimulus. The subject is encouraged to play with the stimulus, to modify fact, to forsake the literal and the concrete, and to toy with the reality-stuff of the stimulus. Various conceptions of projective stimuli are reviewed and considered nondefinitive of projective testing. Projective testing is tentatively defined as a state of mind, a temporary but adaptive collusion shared between tester and subject which involves the former inviting the latter to modify a sample of reality.

Journal Article↗
PubMed1980

Toward a construct validation of the Rorschach.

The debate over the validity of the Rorschach has been lengthy but unresolved. Major reasons for the lack of consensus and conclusion are the absence of agreement about, how validation research should be conducted and the failure to identify appropriate criteria for subsequent evaluation. A construct validation model for the Rorschach is presented, with guidelines for proper implementation. The difficulties in establishing the optimal relationship between theory, research design, and clinical practice arc discussed. Recommendations for a resolution of these difficulties are presented.

Journal Article↗