Search PubMed⌕ Search

Biomedical subjects

P Gerhardt

Publications and source records attributed to P Gerhardt.

At least 127 records · Page 7Linked to original sources
PubMed1975

[Water uptake and solubility of 3 filling plastic materials in relation to hardness tests and time].

10 samples each of 0.25 mm, 0.5 mm, and 1 mm thickness of a conventional PMMA, a PMMA composite, and a Bowen composite were tested according to FDI specification no. 3 for 60 days. Sample thickness influences the rate of water uptake, and especially solubility. The sample size of 50 plus or minus 1 mm diameter and 0.5 plus or minus 0.1 mm thickness is suitable for obtaining reproducible, comparable, and clinically characteristic results. Water saturation is normally obtained after 3 to 5 days. Because of the varying sample thickness during production and due to different density of the materials, water uptake should only be expressed in per cent by volume. Solubility should not be disregarded when determining water uptake. It may simulate saturation or equilibrium. Solubility amounts to up to 2 per cent by weight after 60 days. Clinical findings regarding loss in substance may be explainable by this.

Acrylic Resins↗
PubMed1974

Antimicrobial actions of hexachlorophene: inhibition of respiration in Bacillus megaterium.

Hexachlorophene (HCP) inhibits both endogenous and exogenous respiration (oxygen uptake) in Bacillus megaterium, without sparing by any of several substrates. The inhibition is maximal when the cells are treated with 8 mug of HCP per mg of cells (dry weight), which corresponds to the minimal lethal dose. Levels as low as 2 mug/mg are inhibitory but not lethal. HCP also inhibits the respiration of isolated B. megaterium membranes and can act on several components of the electron transport chain in the membranes and on soluble enzymes. Although both forms of nicotinamide adenine dinucleotide, reduced form dehydrogenase and malic dehydrogenase are inhibited by HCP, they are less susceptible than is oxygen uptake. The site of maximal sensitivity is nearer the terminal electron acceptor, but the exact location depends on the cytochrome composition of the membranes. If cytochromes b(1), a, and a(3) are present, but not o, HCP inhibits electron transport on the substrate side of cytochrome b(1); if cytochromes b(1), a(3), and o are present, but not a, the inhibition occurs on the oxygen side of cytochrome b(1). Exogenous menadione, an analogue of menaquinone, reverses the inhibition in both circumstances. The primary lethal action of HCP thus appears to be respiratory inhibition at a site within the membrane-bound part of the electron transport chain.

Bacillus megaterium↗
PubMed1974

Hemodialysis culture of Serratia marcescens in a goat-artificial kidney-fermentor system.

Hemodialysis was employed to simulate in vivo conditions for growth in mammalian blood, but without phagocytosis, by using the goat and Serratia marcescens as a host-parasite model. The blood stream was shunted surgically via prosthetic tubing from a carotid artery through the hollow-fiber membranes in an artificial kidney hemodialyzer and back into a jugular vein. The dialysate solution concurrently was pumped from a modular fermentor through the hemodialyzer jacket outside of the membranes and back into the fermentor. Hemodialysis between the two circuits was maintained continuously. When equilibrium was attained, bacteria inoculated into the dialysate circuit multiplied first exponentially at the maximal rate and then arithmetically at a lesser rate equally well under aerobic or anaerobic conditions. When a population of about 10(9) viable bacteria/ml was exceeded, the goat reacted acutely with signs of general toxemia, pyrexia, and leukopenia, apparently because of dialyzable toxic material produced by the culture. The maximal molecular size of the toxic material was defined relative to a rigid globular protein of 15,000 in molecular weight and 1.9 nm in hydrodynamic radius or to a flexible fibrous polyglycol of 5,500 in molecular weight and 2.6 nm in hydrodynamic radius, based on determinations of the membrane porosity threshold for dialysis.

Aerobiosis↗
PubMed1974

Chemical composition and ultrastructure of native and reaggregated membranes from protoplasts of Bacillus cereus.

Conditions were defined for producing protoplasts with lysozyme and isolating the protoplast membranes from cells of Bacillus cereus T harvested late in the exponential growth phase just before sporogenesis. The membranes contained approximately 60% protein, 30% lipid, 6% carbohydrate, and 1% ribonucleic acid. Seventeen proteins were distinguished by molecular size in the membrane solubilized with sodium dodecyl sulfate, and 12 in that with phenol and acetic acid. The lipid fraction consisted of neutral lipids (28%) and phospholipids (72%). Four phospholipids were identified: diphosphatidyl glycerol, phosphatidyl ethanolamine, phosphatidyl glycerol, and lysophosphatidyl ethanolamine. Eighteen fatty acids were identified, with a predominance of branched C(15) and C(17) and of normal C(16) acids. The carbohydrate fraction consisted of neutral hexoses. A clear supernatant solution from the solubilized preparation became reaggregated into membrane by dialysis in the presence of MgCl(2). The reaggregated membrane had the same main components as the native membrane, but the amount and ratio of protein and lipid depended on the buffer and the MgCl(2) concentration. By electron microscopy, the reaggregated membranes appeared as vesicles or sheets, depending on the MgCl(2) concentration. Hexagonal lattices were occasionally detected in the negatively stained ultrastructure of both native and reaggregated membrane fragments.

Bacillus cereus↗
PubMed1974

Porosity of the yeast cell wall and membrane.

The limiting sizes of molecules that can permeate the intact cell wall and protoplast membrane of Saccharomyces cerevisiae were determined from the inflection points in a triphasic pattern of passive equilibrium uptake values obtained with a series of inert probing molecules varying in molecular size. In the phase identified with the yeast protoplast, the uptake-exclusion threshold corresponded to a monodisperse ethylene glycol of molecular weight = 110 and Einstein-Stokes hydrodynamic radius (r(ES)) = 0.42 nm. In the cell wall phase, the threshold corresponded to a polydisperse polyethylene glycol of number-average molecular weight ( M(n)) = 620 and average radius (r(ES)) = 0.81 nm. The third phase corresponded to complete exclusion of larger molecules. The assessment of cell wall porosity was confirmed by use of a second method involving analytical gel chromatographic analyses of the molecular weight distribution for a single polydisperse polyglycol before and after uptake by the cells, which indicated a quasi-monodisperse threshold for the cell wall of M(n) = 760 and r(ES) = 0.89 nm. The results were reconciled with two situations in which much larger protein molecules previously have been reported able to penetrate the yeast cell wall.

Biological Transport↗
PubMed1972

Ultrastructure of the exosporium and underlying inclusions in spores of Bacillus megaterium strains.

Spores of selected strains of Bacillus megaterium were prepared by various methods and examined with the electron microscope. An exosporium like that of B. cereus, with a nap and basal layer, was found in spores of a B. megaterium strain that reportedly contains a capsule-like exosporium. The exosporium occasionally appeared to be doubled or have an apical opening. Pili-like filaments were discerned on the surface. Beneath the exosporium were found large deposits of planar inclusions, which in cross section appeared laminated and in surface views consisted of a patchwork of striated packets with a periodicity of approximately 5 nm. The inclusions were usually attached to the exosporium, but in ultrastructure they differed from both the exosporium and coat. In two other strains of B. megaterium, one or two coats occurred but a typical exosporium was not present.

Bacillus megaterium↗
PubMed1972

Location of calcium within Bacillus spores by electron probe x-ray microanalysis.

Spectroscopic microanalysis of the element-characteristic X rays produced by a scanning electron microprobe was employed to detect calcium and carbon in both intact and thin-sectioned spores of Bacillus cereus T and B. megaterium QM B1551. Linear scan profiles and multilinear scan images of the X-ray emissions for calcium (Ca(Kalpha)) were compared with those for carbon (C(Kalpha)) as an index of mass. Location was accomplished by stereological comparisons with secondary electron images and conventional transmission electron micrographs. Although the elements could be detected at the attogram level theoretically, spatial resolution was limited to approximately 500 to 1,000 nm in an intact spore, e.g., by the primary electron beam diameter, the electron-excited spore microvolume, and the type of specimen support. The resolution was improved to approximately 100 to 200 nm by use of thin-sectioned spores, with precautions to prevent calcium leakage from the specimen during preparations. In both intact and sectioned spores, calcium was distributed throughout the spore, similarly to carbon, and concentrated mainly in a central region corresponding to the spore protoplast.

Bacillus cereus↗
PubMed1971

Dielectric study of the physical state of electrolytes and water within Bacillus cereus spores.

Dielectric measurements revealed that dormant spores of Bacillus cereus have extremely low conductivities at high frequencies (50 MHz) and so must contain remarkably low concentrations of mobile ions both within the core and in the surrounding integuments. Activation, germination, and outgrowth were all accompanied by increases in conductivity of the cells and their suspending medium, and this result indicated that intracellular electrolytes had become ionized and leaked from the spores. High-frequency dielectric constants of spores were consistent with normal states for cell water. These values increased during successive stages of development from dormant spore to vegetative bacillus, and they could be directly related to increases in cell water content. In all, the results refuted a model of the dormant spore involving freely mobile, ionized electrolytes and supported a model involving electrostatically bound electrolytes.

Aerobiosis↗