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Biomedical subjects

D H Dean

Publications and source records attributed to D H Dean.

103 records · Page 6Linked to original sources
PubMed1974

Buoyant density heterogeneity in spores of Bacillus subtilis: biochemical and physiological basis.

The biochemical and physiological basis of density heterogeneity in Renografin of Bacillus subtilis W23 spores was determined by analysis of metals, macromolecules, and dipicolinic acid in the two density classes of the population. Germination rate and heat resistance were measured in both density classes. Atomic absorption spectrophotometry revealed that heavy spores (density = 1.335 g/ml) have 30% more calcium than light spores (density = 1.290 g/ml). Other metals found in greater amounts in heavy spores were manganese and potassium. However, light spores had more sodium than heavy spores. The amounts of carbohydrates, nucleic acids, and proteins were the same in both types of spores, but light spores contained more lipids, whereas heavy spores had 30% more dipicolinic acid than light spores. Calcium and lipid were excluded as causes of the heterogeneity in density in that alteration of their contents in spores did not detectably affect the density of these spores. Spores of two densities were genetically similar. Furthermore, light density spores arose earlier during sporulation than heavy spores as determined by releasing refractile forespores at various times during sporulation. We concluded that light spores represent an incomplete stage in development because they became heavy when reinoculated into spent sporulation medium. This must involve the additional accretion or synthesis of dipicolinic acid.

Bacillus subtilis↗
PubMedDate not supplied

Exploration of receptor binding of Bacillus thuringiensis toxins.

Wild type and mutant toxins of Bacillus thuringiensis delta-endotoxins were examined for their binding to midgut brush border membrane vesicles (BBMV). CryIAa, CryIAb, and CryIAc were examined for their binding to Gypsy moth (Lymantria dispar) BBMV. The binding of CryIAa and CryIAc was directly correlated with their toxicity, while CryIAb was observed to have lower binding than expected from its toxicity. The latter observation confirms the observation of Wolfersberger (1990). The "rule" of reciprocity of binding and toxicity is apparently obeyed by CryIAa and CryIAc, but broken by CryIAb on L. dispar. Alanine substitutions were made in several positions of the putative loops of CryIAa to test the hypothesis that the loops are intimately involved in binding to the receptor. The mutant toxins showed minor shifts in heterologous binding to Bombyx mori BBMV, but not enough to conclude that the residues chosen play critical roles in receptor binding.

Amino Acid Sequence↗
PubMedDate not supplied

Condition of toothbrushes in use: correlation with behavioral and socio-economic factors.

Toothbrushes and questionnaires from 94 adult dentate individuals were analyzed. More than 97% of respondents said they brushed their teeth at least once a day, while 48% used more than one toothbrush (such as one at home and another at work). Only 47% said they preferred a soft nylon bristle, while 41% preferred medium and 10% a hard nylon bristle. More than 73% of subjects said they used their brushes for 3 months or longer. Examination of collected brushes by both objective and subjective criteria revealed a wide variation in wear; however, the majority of brushes did not appear to be 'worn-out'. No significant correlation was found between objective wear-index and the educational level of the user, annual household income of the user, or reported time in use of the brush. A significant (p less than 0.01) correlation was found between brush wear-index and the ability of the user to judge toothbrush wear.

Adult↗
PubMedDate not supplied

Toothbrushes with graduated wear: correlation with in vitro cleansing performance.

A display set of toothbrushes with graduated natural wear was shown to 268 adult respondents who were asked to indicate which brushes were "worn out." The same brushes were then compared against each other for their ability to remove artificial plaque in models of interproximal and facial surface cleansing effectiveness. Despite pronounced differences in the degree of wear among the toothbrushes, no correlation was found between visual estimation of toothbrush effectiveness and its cleansing ability in the models tested. It is possible that other variables (toothbrushing technique, force applied, manual skills) exert a greater influence on plaque removal than brush wear and explain the results of this experiment.

Dental Plaque↗