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Biomedical subjects

G G Stewart

Publications and source records attributed to G G Stewart.

At least 19 recordsLinked to original sources
PubMed2000

The effect of combinations of Fusarium mycotoxins (deoxynivalenol, zearalenone and fumonisin B1) on growth of brewing yeasts.

The interactive effect of combinations of the Fusarium mycotoxins deoxynivalenol (DON), zearalenone (ZEA) and fumonisin B1 (FB1) on growth of brewing yeasts was examined. Yeast growth was assessed by measurement of dry weight or relative growth, cell number, viability and conductance change of the growth medium using direct and indirect methods. The interactive effect of a combination of these mycotoxins was subject to the ratio of toxins in the mixture and the toxicity of individual toxins on yeast growth. When a combination of mycotoxins at low concentration was added into the growth medium, no significant inhibitory effect on growth was observed compared to controls. However, when a combination of high concentrations of DON and ZEA which individually inhibited yeast growth was examined, the interactive effect was shown to pass from antagonism to synergism depending on the ratio of the toxins in the mixture. As a synergistic interaction between these Fusarium mycotoxins was observed only at high concentrations, which were far higher than would be expected in good quality grain, they are not a concern when related to yeast growth under the brewing conditions studied.

Beer↗
PubMed1998

A scanning electron microscopic study of the cleansing effectiveness of three irrigating modalities on the tubular structure of dentin.

This is a scanning electron microscope study of the cleaning effectiveness of three irrigating modalities on root dentin. When hydrogen peroxide was followed by sodium hypochlorite, it effectively cleaned the dentinal tubules of the root. When RC-Prep was reacted with sodium hypochlorite, it proved to be a more efficient irrigating method than the hydrogen peroxide and sodium hypochlorite solution. When a new improved RC-Prep with 15% carbanide peroxide was reacted with sodium hypochlorite, it proved to be a superior cleansing method for root dentin.

Carbamide Peroxide↗
PubMed1996

Characteristics of maltose transporter activity in an ale and large strain of the yeast Saccharomyces cerevisiae.

Kinetic studies on maltose uptake by ale and larger yeasts showed lower Km and higher Vmax values than for laboratory yeasts. Eadie-Hofstee plots were biphasic and inhibition by sulphydryl reagents was consistent with low affinity uptake by a specific transporter rather than by non-specific adsorption. High affinity maltose transport by both strains was inhibited by galactose, CCCP, 2, 4,-DNP and NEM. In contrast, glucose and pCMBS inhibited high affinity transport by the ale yeast but not by the larger yeast. In the case of pCMBS the difference could result from a single amino acid change in the maltose transporter.

2,4-Dinitrophenol↗
PubMed1995

Gaining access to calcified canals.

Gaining entrance to calcified canals can be very difficult and at times impossible. With the aid of the EDTA-Urea preparation (RC-Prep, Premier Dental Products, Norristown, Pa.) and the surgical length contra-angle burs, the task can be facilitated. The use of the multipurpose probe reduces the problem of perforation. We may now be able to gain access and treat a greater number of calcified canals.

Aged↗
PubMed1994

Comparison of apical leakage between Ketac Endo sealer and Grossman sealer.

Forty-eight extracted human teeth were prepared for study to compare Ketac Endo cement with Grossman's cement in preventing leakage of a dye. Four groups were formed: (1) Grossman's sealer with a single gutta percha cone; (2) Grossman's sealer with lateral condensation of gutta percha; (3) Ketac Endo sealer with a single cone of gutta percha; and (4) Ketac Endo sealer with lateral condensation of gutta percha. The teeth were immersed in the dye for 10 days, after which they were rinsed in running tap water and cleared for observation. In the groups of teeth evaluated by three individual evaluators, the results consistently showed less leakage with glass ionomer sealers (groups 3 and 4) than with the Grossman's sealers (groups 1 and 2). The best results were noted when Ketac Endo sealers were used with lateral condensation.

Dental Leakage↗
PubMed1992

Thiamine secretion in yeast.

To isolate thiamine excretors and (or) overproducers, 188 cultures belonging to nine yeast and three fungal genera were screened. Nine excreted thiamine as determined by both the presence of cross-feeding zones on a thiamine-free agar medium seeded with a thiamine-requiring yeast strain and by the direct detection of excreted thiamine on agar plates. Several of these cultures produced several-fold more intracellular thiamine than the general culture population. Thiamine-requiring strains of Saccharomyces cerevisiae and S. uvarum (carlsbergensis) were identified and were tentatively assigned to 10 complementation groups.

Extracellular Space↗
PubMed1990

2-Deoxy-D-glucose resistant yeast with altered sugar transport activity.

The transport of glucose and maltose in Saccharomyces cerevisiae was observed to occur by both high and low affinity transport systems. A spontaneously isolated 2-deoxy-D-glucose resistant mutant was observed to transport glucose and maltose only by the high affinity transport systems. Associated with this was an increase in the Vmax values, indicating derepression of the high affinity transport systems. The low affinity transport systems could not be detected. This mutant will be important in examining the repression regulatory and sugar transport mechanisms in yeast.

Biological Transport↗
PubMed1990

The potential of periodontal pocket formation associated with untreated accessory root canals.

Teeth that were to be extracted because of periodontic-endodontic involvement, in six patients, were treated by hemisection or root amputation. The roots were processed histologically. All cases showed the presence of accessory root canals with remnants of pulpal tissue, bacteria, and necrotic debris. It was demonstrated in the cases studied that residual necrotic tissue in untreated root canals can result in periradicular pathosis. We may speculate that if the inflammatory process persists and drainage results via the sulcus, in time, plaque and then concretions may develop.

Adult↗
PubMed1990

Expression and regulation of glucoamylase from the yeast Schwanniomyces castellii.

Expression of the 146-kilodalton (kDa) extracellular glucoamylase by the budding yeast Schwanniomyces castellii is induced by maltose and starch. By use of antiglucoamylase antisera, we found that this expression was regulated at the level of the mRNA, taking place within 30 min after exposure of yeast cells to the respective sugars. Polyacrylamide gel electrophoresis analysis of the in vitro-translated products of total RNA from maltose-treated cells established that the glucoamylase precursor was approximately 120 kDa in size. Stable glucoamylase transcript was not produced in cells exposed to glucose, 2-deoxyglucose, and heat shock. Cells exposed to these two sugars also degraded intracellular and extracellular glucoamylase. In the presence of sugars such as cellobiose, galactose, lactose, and xylose or in the absence of any carbohydrate, a low-level, constitutive-like expression of this preglucoamylase occurred. The nascent glucoamylase underwent at least two posttranslational modifications, resulting in a 138-kDa cell-associated form and the 146-kDa active form that was found free in the medium. These results suggest that glucoamylase expression is tightly regulated similarly to expression of the enzymes responsible for maltose metabolism in Saccharomyces yeasts.

Blotting, Western↗
PubMed1990

A study of ethanol tolerance in yeast.

The ethanol tolerance of yeast and other microorganisms has remained a controversial area despite the many years of study. The complex inhibition mechanism of ethanol and the lack of a universally accepted definition and method to measure ethanol tolerance have been prime reasons for the controversy. A number of factors such as plasma membrane composition, media composition, mode of substrate feeding, osmotic pressure, temperature, intracellular ethanol accumulation, and byproduct formation have been shown to influence the ethanol tolerance of yeast. Media composition was found to have a profound effect upon the ability of a yeast strain to ferment concentrated substrates (high osmotic pressure) and to ferment at higher temperatures. Supplementation with peptone-yeast extract, magnesium, or potassium salts has a significant and positive effect upon overall fermentation rates. An intracellular accumulation of ethanol was observed during the early stages of fermentation. As fermentation proceeds, the intracellular and extracellular ethanol concentrations become similar. In addition, increases in osmotic pressure are associated with increased intracellular accumulation of ethanol. However, it was observed that nutrient limitation, not increased intracellular accumulation of ethanol, is responsible to some extent for the decreases in growth and fermentation activity of yeast cells at higher osmotic pressure and temperature.

Biotechnology↗
PubMed1988

Intracellular ethanol accumulation in Saccharomyces cerevisiae during fermentation.

An intracellular accumulation of ethanol in Saccharomyces cerevisiae was observed during the early stages of fermentation (3 h). However, after 12 h of fermentation, the intracellular and extracellular ethanol concentrations were similar. Increasing the osmotic pressure of the medium caused an increase in the ratio of intracellular to extracellular ethanol concentrations at 3 h of fermentation. As in the previous case, the intracellular and extracellular ethanol concentrations were similar after 12 h of fermentation. Increasing the osmotic pressure also caused a decrease in yeast cell growth and fermentation activities. However, nutrient supplementation of the medium increased the extent of growth and fermentation, resulting in complete glucose utilization, even though intracellular ethanol concentrations were unaltered. These results suggest that nutrient limitation is a major factor responsible for the decreased growth and fermentation activities observed in yeast cells at higher osmotic pressures.

Ethanol↗
PubMed1987

Applicability of yeast extracellular proteinases in brewing: physiological and biochemical aspects.

A general screening survey for expression of extracellular acid proteinase production was performed on over 100 cultures belonging to the genus Saccharomyces. Although two strains of Saccharomyces cerevisiae showed positive extracellular proteinase phenotypes in plate tests, it was not possible to demonstrate proteolytic activities in cell-free culture supernatants in assays performed at beer pH values. Of several yeasts from other genera examined, Saccharomycopsis fibuligera and Torulopsis magnoliae produced extracellular proteinases with desirable properties. Proteolytic activities were detected in assays performed at beer pH values and at lower temperature. Brewer's wort served as a highly inducing medium for extracellular proteinase production, with T. magnoliae yielding enzyme of highest specific activity. In fact, commencement of enzyme production was detected shortly after the onset of exponential growth in brewer's wort. Inclusion of crude enzyme preparations in brewer's wort inoculated simultaneously with brewer's yeast reduced final ethanol yields slightly and was found to be effective in reducing chill haze formation in bottled beer.

Journal Article↗
PubMed1986

Chelation and flotation in endodontic practice: an update.

The removal of broken instruments and silver points, as well as pulp tissue, may be accomplished by careful instrumentation, irrigation, and flotation. Flotation and recapitulation with smaller instruments and irrigation with copious amounts of sodium hypochlorite can clean out microorganisms and the organic matter from the tubular structure which provides a more ideal surface for sealing the root canal system. A sterile environment was obtained by removing the substrate and creating a more ideal environment for better healing.

Carbamide Peroxide↗
PubMed1985

Phenotypic expression of Kluyveromyces lactis killer toxin against Saccharomyces spp.

The secretion of killer toxins by some strains of yeasts is a phenomenon of significant industrial importance. The activity of a recently discovered Kluyveromyces lactis killer strain against a sensitive Saccharomyces cerevisiae strain was determined on peptone-yeast extract-nutrient agar plates containing as the carbon source glucose, fructose, galactose, maltose, or glycerol at pH 4.5 or 6.5. Enhanced activity (50 to 90% increase) was found at pH 6.5, particularly on the plates containing galactose, maltose, or glycerol, although production of the toxin in liquid medium was not significantly different with either glucose or galactose as the carbon source. Results indicated that the action of the K. lactis toxin was not mediated by catabolite repression in the sensitive strain. Sensitivities of different haploid and polyploid Saccharomyces yeasts to the two different killer yeasts S. cerevisiae (RNA-plasmid-coded toxin) and K. lactis (DNA-plasmid-coded toxin) were tested. Three industrial polyploid yeasts sensitive to the S. cerevisiae killer yeast were resistant to the K. lactis killer yeast. The S. cerevisiae killer strain itself, however, was sensitive to the K. lactis killer yeast.

Fructose↗
PubMed1985

Identification and characterization of antimicrobial activity in two yeast genera.

A general screening test for the expression of antibacterial activity was performed on over 400 cultures belonging to 31 yeast genera. Of these cultures, only two, Kluyveromyces thermotolerans and Kloeckera apiculata, were found to produce zones of inhibition of bacterial growth on Diagnostic Sensitivity Test Agar medium supplemented with 0.002% methylene blue. Of nine bacteria used as test organisms, only Lactobacillus plantarum and Bacillus megaterium were inhibited. No antibacterial activity was evident against four gram-negative bacteria used in this study. Optimal activities were found to be expressed after yeasts were grown at pH 6. A requirement for cultivation in the presence of methylene blue added to culture media for the expression of apparent antibacterial activity was demonstrated.

Anti-Bacterial Agents↗
PubMed1984

Susceptibility of Saccharomyces spp. and Schwanniomyces spp. to the aminoglycoside antibiotic G418.

Industrially useful polyploid yeasts such as the brewing yeasts do not possess any auxotrophic genetic markers and hence are not easily amenable to plasmid-mediated DNA transformations. In an attempt to obtain genetic markers, a number of useful Saccharomyces sp. strains and some amylolytic Schwanniomyces sp. strains were tested for their susceptibility to the antibiotic Geneticin G418 , a 2-deoxystreptamine reported to be active against bacteria, yeasts, and plant and animal cells. All of the Saccharomyces sp. strains, including the brewing strains, were found to be susceptible to G418 in the concentration range of 150 to 500 micrograms/ml. Of the three Schwanniomyces species investigated, only Schwanniomyces castellii (strain 1402) was found to be resistant to G418 at concentrations up to 1 mg/ml. Resistance was exhibited both in liquid media and on glycerol-peptone-yeast extract agar plates. This finding is interesting in view of the possibility of using this strain as a DNA donor for transformations aimed at introducing the amylolytic capability into brewing yeasts.

Anti-Bacterial Agents↗