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Biomedical subjects

J M Parry

Publications and source records attributed to J M Parry.

At least 163 records · Page 9Linked to original sources
PubMed1979

Severe clinical conditions associated with Bacillus cereus and the apparent involvement of exotoxins.

Twenty-one cases of infection with Bacillus cereus are summarised. The histories supplied showed that at least 15 of these were associated with severe or potentially severe symptoms including two deaths. Analysis of the production of exotoxins, including haemolysin and phospholipase, by these strains is given, and the relevance of these metabolites to the severity of the condition is discussed. Three incidents of bovine mastitis resulting from B. cereus and involving three deaths are also included. The observations presented here together with those of previous reports which are reviewed indicate that B. cereus may be of clinical importance, not just an opportunist but also as an agent of potentially severe infections in its own right.

Bacillus cereus↗
PubMed1979

Detection of mitotic and meiotic aneuploidy in the yeast Saccharomyces cerevisiae.

A number of genetic systems are described which involve the use of the yeast Saccharomyces cerevisiae. The systems may be used to detect the production of aneuploid cells produced during both mitotic and meiotic cell division in the presence of genetically active chemicals. During mitotic cell division, monosomic colonies (2n - 1) may be detected by plating upon selective medium. Increases in such monosomic colonies are produced by exposure of cells to a number of chemical mutagens such as ethyl methane-sulfonate and mitomycin C. More importantly, monosomic colonies are also induced by nonmutagens such as sulfacetamide and saccharin, which suggests that such chemicals are capable of inducing aneuploidy (aneugenic) in the absence of mutagenic activity. Genetic analysis of aneuploid colonies produced on nonselective medium indicate that at least a proportion of the monosomic colonies were the result of mitotic nondisjunction. During meiotic cell division, disomic cells (n + 1) produced by chromosome nondisjunction may be detected by plating on selective media. The frequency of disomic cells has been shown to increase after exposure to p-fluorophenylalanine.

Aneuploidy↗
PubMed1978

The modification of induced genetic change in yeast by an amino acid analogue.

Treatment of diploid yeast cultures with the amino acid analogue, para-fluorophenylalanine (PFPA), at concentrations which caused inhibition of growth, resulted in up to 5 fold increases in the frequency of mitotic gene conversion at two different heteroallelic loci. With haploid yeast cultures, growth in PFPA increased the rate of forward mutation to canavanine resistance by at least 2 fold. Growth of diploids in PFPA prior to exposure to the deaminating agent nitrous acid, the cross-linking agent mitomycin C, the alkylating chemical ethylmethanesulphonate (EMS) and UV light resulted in significant changes in the potency of these diverse mutagens to induce intragenic recombination. For all four mutagens, increased frequencies of gene convertants/viable cell were observed in those cultures which had been exposed to the amino acid analogue prior to mutagen treatment. In haploid WT yeast cells, amino acid analogue incorporation resulted in an enhanced frequency of UV induced forward mutation to canavanine resistance whilst in a DNA repair deficient rad 6 mutant this interaction between UV and PFPA was abolished. The results have been interpreted on the basis of incorporation of the analogue into enzymes involved with DNA replication with a consequent loss of fidelity of such enzymes and increased errors in base incorporation.

Alleles↗
PubMed1978

Cell-cycle variation in the induction of lethality and mitotic recombination after treatment with UV and nitrous acid in the yeast, Saccharomyces cerevisiae.

Exponentially growing yeast cultures separated into discrete periods of the cell cycle by zonal rotor centrifugation show cyclic variation in both UV and nitrous acid induced cell lethality, mitotic gene conversion and mitotic crossing-over. Maximum cell survival after UV treatment was observed in the S and G2 phases of the cell cycle at a time when UV induction of both types of mitotic recombination was at a minimum. In contrast, cell inactivation by the chemical mutagen nitrous acid showed a single discrete period of sensitivity which occurred in S phase cells which are undergoing DNA synthesis. Mitotic gene conversion and mitotic crossing-over were induced by nitrous acid in cells at all stages of the cell cycle with a peak of induction of both events occurring at the time of maximum cell lethality. The lack of correlation observed between maximum cell and the maximum induction of mitotic intragenic recombination suggest that other DNA-repair mechanisms besides DNA-recombination repair are involved in the recovery of inactivated yeast cells during the cell cycle.

Cell Cycle↗
PubMed1977

The use of yeast cultures for the detection of environmental mutagens using a fluctuation test.

A microbial fluctuation test, modified for the detection of environmental mutagens has been evaluated using a number of strains of the yeast Saccharomyces cerevisiae. Auxotrophic diploid cultures of yeast which produce prototrophic colonies by both mitotic gene conversion and mutation have been extensively utilized for the detection and evaluation of chemicals showing genetic activity. A number of the yeast strains utilized were shown to be suitable for use in the fluctuation test although the time scales of the experiments were considerably extended (up to 16 days) compared to those involving bacteria. The yeast strains respond to doses of mutagens at least a 100-fold lower than that required in a conventional short exposure treat and plate experiment. In experiments involving the induction of mitotic gene conversion at the tryptophan-5 and histidine-4 loci in the fluctuation test significant increases in prototrophic cells were produced in the presence of the insecticide Lindex (0.05 microng/ml), the preservative Thiomersal (0.0001 microng/ml), a mahogany hair dye (0.01 microng/ml), the herbicide Paraquat (0.02 microng/ml) and the alkylating agent ethyl methane sulphonate (0.1 microng/ml). The results demonstrate that the fluctuation test provides an extremely sensitive assay for the detection of chemicals which show genetic activity in yeast at non-toxic concentrations.

Biological Assay↗
PubMed1977

Serotypes of Bacillus cereus from outbreaks of food poisoning and from routine foods.

A provisional serotyping scheme was used to type cultures of Bacillus cereus from 84 outbreaks of food poisoning in seven countries; 283 of the 337 (84%) cultures tested were typable. In 35 of the 61 outbreaks associated with a vomiting-type syndrome, foods, clinical specimens or both yielded H-serotype 1 only. Type 1 strains together with other sterotypes were isolated in seven outbreaks. In 14 outbreaks types 3, 4, 5, 8 or a mixture of serotypes were present. Untypable strains were isolated in five outbreaks. Two of the nine diarrhoeal-type outbreaks yielded serotype 1 only. Types 2, 6, 8, 9, 10 and a mixture of type 12 and an untypable strain appeared to be responsible for one outbreak each. Although 16 of the 18 recognized serotypes were present among cultures of B. cereus from various routine foods, only 156 of the 400 (39%) isolates tested were typable.

Australia↗
PubMed1976

The induction of mitotic gene conversion by chemical and physical mutagens as a function of culture age in the yeast, Saccharomyces cerevisiae.

Cultures of yeast progressing from the exponential to the stationary phase of growth show increased resistance to the lethal effects of the chemical mutagens nitrous acid, ethyl methane sulphonate and mitomycin C and increased sensitivity to the lethal effects of UV light. Induced mitotic intragenic recombination produced by gene conversion also shows variation in its response to the growth phase after mutagen treatment. Higher frequencies of recombination per surviving cell were found after nitrous acid and ethyl methane sulphonate treatment of stationary phase cells whereas identical frequencies were produced by UV and mitomycin C treatment in both growth phases. The results were consistent with the hypothesis that the more nitrous acid and ethyl methane sulphonate resistant stationary phase cells were more active in postreplication repair. The sensitivity of exponential phase cells to nitrous acid and ethyl methane sulphonate may result from both increased mutagen uptake and reduced postreplication repair activity. In contrast, irrespective of growth phase all cells surviving UV and mitomycin C treatment appear to have undergone identical levels of post-replication repair.

Cell Division↗
PubMed1976

The effects of "cell age" upon the lethal effects of physical and chemical mutagens in the yeast, Saccharomyces cerevisiae.

Yeast cultures progressing from the exponential to the stationary phase of growth showed changes in cell sensitivity to physical agents such as UV light, heat shock at 52 degrees C and the chemical mutagens ethyl methane sulphonate, nitrous acid and mitomycin C. Exponential phree chemicals. The increased resistance of exponential phase cells to UV light was shown to be dependent upon the functional integrity of the RAD50 gene. Treatment of growing yeast cultures with radioactively labelled ethyl methane sulphonate indicated the preferential uptake of radioactivity during the sensitive exponential stage of growth. The results indicated that the differential uptake of the chemical mutagens was responsible for at least a fraction of the variations in cell sensitivity observed in yeast cultures at different phases of growth.

Ethyl Methanesulfonate↗
PubMed1976

Division delay and DNA degradation after mutagen treatment of the yeast, Saccharomyces cerevisiae.

The treatment of the yeast mutant TMP1-1, which is capable of incorporating low levels of 3H-thymidine-5' - monophosphate with UV light and ethyl methane sulphonate resulted in division delay when cultures were reinnoculated into fresh medium. The initiation of cell division was accompanied by the degradation of up to 20% of the nuclear DNA fraction. The period of DNA degradation correlates closely with the time at which yeast cultures undergo mitotic recombination and appears to represent the degradation of DNA during a post-replication repair process.

DNA↗
PubMed1976

The detection of monosomic colonies produced by mitotic chromosome non-disjunction in the yeast Saccharomyces cerevisiae.

A diploid yeast strain, D6 is described which monitors mitotic non-disjunction by the phenotypic expression of a set of coupled and recessive markers flanking the centromere of chromosome VII. These markers are not expressed in the heterozygous condition prevailing in D6. The left arm of chromosome VII carries a tightly centromere linked marker, leu1 (leucine requirement), distal to leu1 in this order: trp5 (tryptophan requirement), cyh2 (recessive resistance to cycloheximide) and met 13 (requirement for methionine). The right arm is marked with ade3 (simultaneous requirement for adenine and histidine). D6 is homozygous for ade2 and consequently, forms red rather than the normally white colonies. It shows no requirement for the above amino acids and it is sensitive to cycloheximide. Unmasking of all the markers on chromosome VII leads to colonies that are white because ade3 sets a block preceding the ade2 block (which causes the accumulation of a precursor of the red pigment), they require leucine, tryptophan and methionine, and grow on media with cycloheximide. Cells are plated on a cycloheximide medium where red and white colonies are formed. Colonies of spontaneous origin were tested. The majority of the white colonies expressed all the recessive markers whereas only few of the red colonies expressed all the markers on the left arm of chromosome VII. Basically expression of recessive markers on both sides of the centromere can be explained as a result of two coincident events of mitotic crossing over. However, the frequency of colonies expressing centromere linked leu1 was 14 times higher among the white types than the red ones. This suggested that the white, cycloheximide resistant, leucine requiring colonies arose by mitotic non-disjunction and not only by two coincident mitotic crossing over events. Presumptive spontaneous monosomic segregants were placed on sporulation medium. Only 8 out of 30 isolates sporulated, which showed that these eight segregants were diploid at the time of sporulation. They could have arisen by two coincident crossover events or through restoration of a normal disomic condition after non-disjunction had occurred. The genetic data thus leaves us with only its statistical argument in favour of non-disjunction. Further confirmation of monosomic nature of the white cycloheximide resistant colonies was provided by the estimates of their DNA contents. Compared to the stock wild type diploids the presumptive monosomics showed a reduction in DNA content. We have utilized D6 to investigate the possible induction of mitotic non-disjunction after treatment with gamma rays, heat shock at 52 degrees C and ultraviolet irradiation. In all cases white, cycloheximide resistant colonies were produced at levels significantly higher than that found in untreated cultures. In order to detect the production of monosomic cells, treated cultures were grown for 48 h in non-selective medium after exposure to allow for "expression" of the monosomic condition.

Chromosome Aberrations↗
PubMed1976

The genetic control of liquid-holding recovery and U.V.-induced repair resistance in the yeast, Saccharomyces cerevisiae.

Liquid-holding treatment in non-nutrient solutions after U.V.-exposure results in an increased resistance of wild-type (RAD) yeast cells to a second U.V.-treatment (repair resistance). U.V.-sensitive (rad) mutants of yeast which show variation in their response to liquid-holding treatment and a second U.V.-dose-range have been classified into two groups. Mutants of Group 1 show increased viability after post-U.V.-liquid-holding treatment and show repair resistance. In contrast, mutants of Group 2 which show reduced viability during post-U.V.-liquid-holding treatment have the same U.V.-sensitivity, both before and after liquid-holding treatment. Genetic analysis of crosses of the rad mutants to wild-type cultures indicate that the phenotype of repair resistance to U.V.-treatment is under genetic control and depends on the presence of alleles of radiation sensitivity genes, which also confer the property of liquid-holding recovery.

DNA Repair↗
PubMed1975

The genetic effects of elevated temperature in the yeast, Saccharomyces cerevisiae.

The growth of yeast cultures at supra-optimal temperatures up to 39 degrees C and exposure in non-nutrient solution up to 52 degrees C has been examined for the induction of genetic change. Both sets of conditions lead to the induction of mutation to antibiotic resistance, mitotic gene conversion, crossing-over and mitotic chromosomal non-disjunction.

Animals↗