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Biomedical subjects

J G Holt

Publications and source records attributed to J G Holt.

12 recordsLinked to original sources
PubMed1978

Isolation and characterization of Arthrobacter bacteriophages and their application to phage typing of soil arthrobacters.

Seventeen bacteriophages, active against 19 Arthrobacter soil isolates, were isolated from concentrated samples of river water and sewage. Attempts to isolate Arthrobacter bacteriophages from filtrates of broth cultures of the soil isolates or from ultraviolet light-irradiated cultures were unsuccessful. Bacteriophages were not detected in either concentrated or unconcentrated soil extracts. Electron microscopic studies of 11 phages showed morphologies characteristic of Bradley's groups B (exhibited by 9 phages) and C (exhibited by 2 phages). Moles percent guanine plus cytosine, calculated from the deoxyribonucleic acid density of three phages, ranged from 60.2 to 65.3. The phages were characterized by their plague and virion morphology, host range, and serological specificity.

Arthrobacter↗
PubMed1975

Energy dependence of the response of lithium fluoride TLD rods in high energy electron fields.

The energy dependence of lithium fluoride dosemeters is a complicated function of energy as well as of cavity size. In the application of TLD to charged particle dosimetry, a cavity perturbation effect may exist even though the ratios of the mass stopping powers are constant over the energies encountered. This effect was investigated for lithium fluoride rods in electron fields ranging in energy from 2-5 to 20 MeV. A 13% change of TL response per unit of absorbed dose was measured over that energy range. A semi-empirical theory was developed to account for the cavity effect, using Burlin cavity theory as a starting point. The agreement between theory and measurement is satisfactory.

Cobalt Radioisotopes↗
PubMed1975

A nutritional and taxonomic survey of Arthrobacter soil isolates.

One hundred and sixty Arthrobacter soil isolates, four groups of 40 from each of four soil types, and 17 Arthrobacter named strains were characterized on the basis of 203 different nutritional tests performed on each culture. One hundred and twenty-one compounds were examined as sole sources of carbon, 44 compounds as sole sources of nitrogen, 22 carbohydrates for the production of acid, and 16 tests were done for tolerance to various dyes. The four groups of soil arthrobacters differed markedly in acid production from carbohydrates, and in utilization of aliphatic amino acids and aromatic hydrocarbons as sole sources of carbon. The named strains did not exhibit as much nutritional diversity as any of the four groups of soil isolates. The results of the nutritional tests were subjected to a computerized taxonomic analysis. Eighty-four of the isolates were contained in nine separate clusters with 87 to 94% similarity; 39 isolates were contained in five mixed but recognizable clusters with 84 to 86% similarity; 60 isolates were randomly mixed with no recognizable clusters and similarity of 72 to 83%. All clusters were composed of nearly equal numbers of isolates from each of the four soils; the named strains were not found associated with any of the clusters of soil isolates. The results indicated that the diversity of the genus Arthrobacter is not represented by the named species already described, and the possibility of using a series of standardized tests to categorize soil arthrobacters into readily identifiable nutritional groups is discussed.

Acids↗
PubMed1975

Differentiation of Arthrobacter soil isolates and named strains from other bacteria by reations on dye-containing media.

Twenty-five gram-negative and 62 gram-positive bacterial cultures, of which 37 werearthrobacters, were tested, using a multipoint inoculation device, for responses on varying concentrations of 35 dyes. Both selective (growth vs. no growth) and differential (dye absorption) responses were obtained. It was possible to differentiate the arthrobacters from the other gram-positive bacteria tested as well as to distinguish separately each Arthrobacter-named strain. The results indicated that dyes have a greater potential for use in selective and differential media than has been presently realized; and the possibility of using dye-reactions as features in taxonomic schemes to differentiate rapidly many of the common genera of soil bacteria is discussed.

Arthrobacter↗
PubMed1975

Hereditary orotic aciduria: results of a screening survey.

Urine from 1,358 mentally retarded subjects was screened for the presence of elevated concentrations of orotic acid and orotidine. This survey was conducted in search of occult variants of hereditary orotic aciduria which might be associated with mental retardation. Although no homozygous variants were detected, 9 subjects with persistently abnormal urinary screening tests were discovered. Assays of erythrocyte orotidylate decarboxylase and phosphoribosyltransferase enzymes showed deficient activities for 2 of these subjects typically found in red cells of persons heterozygous for hereditary orotic aciduria. The same studies were conducted on urine and blood samples from the families of the affected subjects, and additional family members were also found to be affected. Detection of two unrelated heterozygotes among so small a screened population suggests, as previously noted, a higher frequency of the abnormal gene than that indicated by the extreme rarity of the homozygous condition. This study demonstrates the usefulness of the urinary screening test mass surveys and indicates the need for further study of the prevalence of the mutant gene.

Adult↗
PubMedDate not supplied

Ionization collection efficiencies of some ionization chambers in pulsed and continuous radiation beams.

The most commonly used method of calibrating high-energy photon or electron beams consists in converting cavity ionization to dose by the application of the appropriate Clambda or CE multipled by the 60Co correction factor. The correct interpretation of calibration data for pulsed photon or electron beams requires a knowledge of the charge collection efficiencies of the ionization chambers used. The results are presented of efficiency measurements for both pulsed and continuous beams made with these chambers: 0.6-cm3 Farmer, 0.5-cm3 Spokas, 3-cm3 Shonka, 1-cm3 PTW, and 1-cm3 Memorial pancake. The dependence of collection efficiency on collection voltage, dose rate, and dose per pulse is demonstrated. These results are shown to agree with Boag's formulas for collection efficiency. Attention is drawn to the fact that several kinds of dosimeters provide only minimal collection voltages for efficient collection of charge at high dose rates, especially in Linac electron beams. It is recommended to check the collection efficiency of chambers which are to be used at high dose rates, and a simple method for this purpose is described.

Cobalt Radioisotopes↗
PubMedDate not supplied

Examination of the factors Ac and Aeq for cylindrical ion chambers used in cobalt-60 beams.

The calibration of a cobalt-60 beam in a phantom with an ion chamber, which has been calibrated with respect to exposure, requires the use of a displacement correction factor which essentially corrects the photon fluence for the attenuation and scatter when the chamber with buildup cap is removed and replaced by phantom material. To determine the displacement factor, Ac, a special set of cylindrical ionization chambers with various volumes were constructed out of polystyrene. Tissue-air ratios were measured with these chambers for cobalt-60 gamma rays in a polystyrene phantom, and the ratio Ac/Aeq was experimentally determined. In order to calculate Ac from this ratio, Aeq was determined also. It was found that Ac depended on chamber diameter only, and not on field size or depth. A value of 0.990 for Aeq is recommended and a table of Ac for chambers of different outer diameters is included.

Cobalt Radioisotopes↗