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Biomedical subjects

G Holt

Publications and source records attributed to G Holt.

At least 91 records · Page 5Linked to original sources
PubMed1980

Co-synthesis of penicillin following treatment of mutants of Aspergillus nidulans impaired in antibiotic production with lytic enzymes.

Mycelia from four mutants of Aspergillus nidulans impaired in penicillin production at separate genetic loci were treated with an enzyme complex capable of lysine cell walls, then mixed in all possible paired combinations and grown in osmotically buffered penicillin production media, containing 2-deoxyglucose and an unrefined mixture of polyoxins to prevent cell wall regeneration. The culture filtrates were assayed after 6 d and significant penicillin yields were observed in four of the six possible combinations. None of these pairs produced penicillin when grown together as normal mycelium, suggesting that intermediates of the penicillin biosynthetic pathway unable to diffuse from untreated mycelium could do so from enzyme-treated mycelium when cell wall regeneration was inhibited. A general method is thus available for examining biochemical pathways with mutants accumulating intermediates unable to cross the cell wall barrier.

Anti-Bacterial Agents↗
PubMed1979

Aspergillus nidulans as a test organism for assessing radio-induced chromosomal non-disjunction.

A genetically marked heterozygous diploid of Aspergillus nidulans was synthesized and the feasibility of using this system for the simultaneous estimation of radio-induced mitotic crossing-over and non-disjunction has been investigated. In the case of the latter, serious experimental problems have been encountered. Nevertheless, induction curves for non-disjunction with 15-MeV electrons, 50-kVp X-rays, beta-particles and alpha-particles are presented showing an increase in non-disjunction with increasing LET.

Aspergillus nidulans↗
PubMed1979

The ability of ionizing radiations of different LET to induce chromosomal deletions in Aspergillus nidulans.

Conidia, derived from a strain of Aspergillus nidulans known to carry a specific chromosomal duplication, were irradiated. The duplicated segment had genetic markers, which, when eliminated from the genome, allowed the easy detection of deletion mutants. Survival curves derived following 15 MeV electron and gamma-ray irradiation were characterised by the presence of an appreciable shoulder, whilst 50 kvp X-rays gave a much smaller shoulder. Irradiation with beta-particles and alpha-particles gave rise to exponential survival curves. The RBE values for these radiations, based on the D37 value were for gamma-rays, 1.0, 15 MeV electrons 1.0, 50 kvp X-rays 1.9, beta-particles 2.1 and alpha-particles 3.4. With the exception of gamma-rays the radiations described were compared with respect to their ability to induce chromosomal deletions. When the number of deletants amongst survivors was plotted against dose, a linear relationship was found for electrons, X-rays and beta-particles. The response recorded for alpha-particles was essentially linear but with a biphasic component. The RBE values for the radiations, based on a value of unity for 15 MeV electrons were as follows: X-rays 1.3, beta-particles 0.8, alpha-particles above 7.5 krad 2.3 and below 7.5 krad 3.5. When these same data were re-plotted with number of deletants amongst survivors against log survival, electrons appeared the most efficient radiation at producing deletants amongst survivors, with an "m value" of 283 X 10(-5). Tritiated water was least efficient, the corresponding value being 182 X 10(-5). The number of deletants per 10(4) conidia plated, when plotted against dose yielded a curve which increased to a peak and then decreased linearly for all radiations. The peaks for electrons, X-rays and alpha-particles each had a value of about 14 deletants per 10(4) conidia plated and the peaks roughly corresponded with the point at which the survival curve became exponential and was clearly indicative of the accumulation of sub-lethal damage. However, for beta-particles the peak had a value of 7 deletants per 10(4) conidia plated. A non-DNA target has been implicated for cellular death following beta-particle irradiation.

Americium↗
PubMed1979

Ecological effects of antibiotic production by dermatophyte fungi.

Antibiotic production by dermatophyte fungi has been demonstrated in vivo in the lesions of patients with dermatomycoses. Patients infected with antibiotic-producing strains more frequently carried cocci resistant to penicillin and other antibiotics than did patients infected with non-producer strains. The total bacterial load was less in lesions caused by producer fungi. In vitro studies demonstrated the selection of penicillin-resistant S. aureus from mixed populations of resistant and sensitive cells.

Anti-Bacterial Agents↗
PubMed1979

Genetic and biochemical studies of mutants of Penicillium chrysogenum impaired in penicillin production.

Seventy-eight mutants of Penicillium chrysogenum strain NRRL 1951, that were impaired in penicillin production, were isolated following treatment with various mutagens. Twelve that yielded about 10% of their parental penicillin titre were studied in detail. Analyses of heterozygous diploids formed between them revealed the existence of at least five complementation groups with respect to penicillin production--V, W, X, Y and Z. Most mutants belonged to group Y. A biochemical investigation of the intracellular peptides in strains representing the five groups demonstrated the absence of the tripeptide alpha-aminoadipoylcysteinyl-valine from mutants of groups X, Y and Z. Extracts of mutants of groups W, Y and Z were able to catalyse a penicillin acyl-exchange reaction, a mutant of group V showed only a trace of activity and mutant from group X completely lacked this ability.

Amino Acids↗
PubMed1978

Antibiotic production by dermatophyte fungi.

Thirty-two clinical isolates of anthropophlic dermatophytes were examined for their capacity to produce antibiotics in liquid culture and on human stratum corneum in vitro. Antibiotics were detected and classified using agar diffusion bioassays and chromatographic analysis. Twenty-four isolates produced antibiotic substances in liquid culture filtrates; some strains produced more than one antibiotic. Only four isolates produced detectable levels of antibiotics when grown on stratum corneum unless an artificial sweat mixture was used as a nutrient supplement, when the number rose 11. Respresentatives of all species studied produced benzyl penicillin-like substances. Some Trichophyton isolates also produced streptomycin-like antibiotics, a characteristic previously unrecorded for eukaryotic organisms. Other antibiotics, which apart from azalomycin F could not be properly classified, were produced by Epidermophyton floccosum. Antibiotic production occurred over the normal skin temperature range but sometimes the type of antibiotic produced and the frequency of detection appeared to be influenced by the incubation temperature.

Anti-Bacterial Agents↗
PubMed1978

Smoking artifacts: factors of source evaluation.

Responses from 323 students in communication indicated that credibility factors associated with nonverbal smoking artifacts are not the same as those associated with verbal stimuli; a character factor was absent for nonverbal stimuli. Verbosity, however, may permit inferences regarding potential verbal behavior.

Character↗
PubMed1978

[Lead poisoning in Norwegian waterfowl (author's transl)].

In connection with routine autopsy of wild birds, liver samples from 56 waterfowl, representing 12 species, were analyzed for the content of lead. The median value for the birds examined was 0.2 microgram Pb/g wet weight. Concentrations probably causing lead poisoning were found in 1 mallard (Anas platyrhychos) with 11 microgram Pb/g liver and in 8 whooper swans (Cygnus cygnus) with 5.8--55 microgram Pb/g liver. Clinical observations and pathological findings of "typical" lead poisoning were found in 2 of the whooper swans with 25 and 55 microgram Pb/g liver, respectively. Lead was not detected (less than 0.1 microgram Pb/g liver) in 29% of the 34 whooper swans examined, while another 29% contained more than 1.0 microgram Pb/g liver. In some swans with a low liver lead concentration the autopsy findings strongly indicated an intoxication. The necessity of chemical analyses for the verification of lead poisoning is emphasized. The limited number of birds examined and the uneven selection among species prevent the drawing of general conclusions. This investigation indicates, however, that lead poisoning, especially in the whooper swan, may be a problem also in Norway, but hardly a so important one as in some other European countries and in the USA.

Animals↗
PubMed1975

[The hazard of lead-accumulation in domestic animals fed on hay from fields nearby highways in Norway (author's transl.)].

In 1971 hay was harvested from an area nearby a highway (E18) at Sande in Vestfold (Norway). On an average 9,400 cars passed this place each day during the summer season. The lead pollution of the hay was moderate. Hay taken at a distance of 2 m from the roadside contained 6.6 mu-g Pb/g dry weight. There was found no increase in the lead concentration in blood, liver, kidney, muscle, urine, or bone tissue in the experimental sheep compared with the control group. In faeces, however, a higher lead concentration was found in the experimental group compared with the control group, on an average 6.3 and 1.6 mu-g Pb/g, respectively. No increase in the lead content could be demonstrated in bone tissue from cattle which since birth had been fed on grass and hay originating from areas adjacent to the highway.

Animal Feed↗