Pulsed high electric field causes 'all or nothing' membrane damage in Listeria monocytogenes and Salmonella typhimurium, but membrane H+-ATPase is not a primary target.

Salmonella typhimurium (CRA 1005) was more sensitive than Listeria monocytogenes (NCTC 11994) to pulsed high electric field (PHEF) treatment in distilled water (10, 15 and 20 kV/cm), 10 mM Tris-maleate buffer, pH 7.4 (15 kV/cm) and model beef broth (0.75%, w/v; 15 kV/cm). Sublethal injury could not be detected using a selective medium plating technique, indicating that bacterial inactivation by PHEF may be an 'all or nothing' event. PHEF-induced membrane permeabilisation resulted in an increase in the leakage of UV-absorbing material from the bacteria (UV-leakage) and a decreased ability of L. monocytogenes to maintain a pH gradient. A lack of correlation between the inhibition of H+-ATPase activity and PHEF treatment, cell viability or UV-leakage indicates that this enzyme is probably not a primary site of bacterial inactivation despite its role in the maintenance of internal pH.

Effects of high hydrostatic pressure on Clostridium sporogenes spores.

Spores of Clostridium sporogenes were found to be resistant to ultra high pressure, with treatments of 600 MPa for 30 min at 20 degrees C causing no significant inactivation. Combination treatments including heat and pressure applied simultaneously (e.g. 400 MPa at 60 degrees C for 30 min) or sequentially (e.g. 80 degrees C for 10 min followed by 400 MPa for 30 min) proved more effective at inactivating spores. Pressure cycling (e.g. 60 MPa followed by 400 MPa at 60 degrees C) also reduced spore numbers. Overall, these pressure treatments resulted in less than a 3 log reduction, and it was concluded that the spores could not be inactivated by pressure alone. This could indicate that for the effective inactivation of bacterial spores, high pressure technology may have to be used in combination with other preservation methods.

The effect of potential investment expansion and hot strength on the fit of full crown castings made with phosphate-bonded investment.

In an earlier investigation, it was shown that when full crowns are cast in gypsum-bonded investments, their relative inaccuracy is affected by both the investment's potential expansion and its hot strength. This study repeated the earlier one, but used a high-melting gold alloy and two phosphate-bonded investments. The investments were used under conditions which gave a range of potential expansions and hot strengths. Casting inaccuracies were determined both diametrally and axially. All castings showed distortion, which varied under the different conditions. All were oversized axially, by amounts varying from + 0.8% to +2.3%. Diametral inaccuracies ranged from -0.2% to +0.7%. Investment expansion had a strong effect on axial inaccuracy, but a negligible effect on diametral inaccuracy. Conversely, hot strength had a strong effect on diametral inaccuracy, but only a very weak effect on axial inaccuracy. With phosphate-bonded investments, both potential expansion and hot strength are important parameters of relative casting inaccuracy. In combination, these properties showed very strong correlations with both diametral and axial inaccuracies. The observed distortions were the result of anisotropic mould expansion and anisotropic alloy shrinkage. The best fit, and least distortion, occurred with an investment setting under dry conditions.

The effect of potential investment expansion and hot strength on the fit of full-crown castings made with a gypsum-bonded investment.

OBJECTIVES: It has been claimed that the strength of the investment mold at the casting temperature affects the dimensional accuracy of castings (e.g., Markley, 1953; Earnshaw, 1957; Asgar, 1972), but the relationship has not been studied quantitatively. In this investigation, the effects of both mold expansion and hot strength on the relative inaccuracy of full-crown castings have been measured and analyzed. The likelihood that a strong investment could cause distortion of the casting by non-uniform restriction of casting shrinkage (Earnshaw, 1969b) was also considered. METHODS: Castings were made with a commercial gypsum-bonded inlay investment, used both as supplied and with modifications that increased its expansion and reduced its hot strength. In both series of tests, the investments were used over a wide range of liquid/powder (L/P) ratios in casting rings fitted with dry ceramic liners, and set under dry conditions. RESULTS: Casting inaccuracy showed a significant linear correlation with total expansion and a highly significant linear correlation with the combination of total expansion and hot strength. The modified investment, with its low hot strength, gave less distortion of casting shape than did the much stronger unmodified material. However, it was found that to ensure sound castings, the hot compressive strength should not be less than 1.8MPa. SIGNIFICANCE: This investigation showed that while investment expansion is the major variable affecting casting inaccuracy, hot strength is an important modifying factor which also has to be considered when predicting casting inaccuracy from measured properties of the investment.

The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners.

Measurements were made of the fit of full-crown gold-alloy castings produced with two types of pre-wetted ring liner (asbestos and cellulose) and a typical gypsum-bonded investment (Cristobalite Inlay, Sybron/Kerr Products, Romulus, MI; W/P = 0.40). Laboratory measurements were made of the effects of the liners on potential investment expansion, and properties of the lining materials considered relevant to casting accuracy were also measured. There was a wide variation in values for mean dimensional inaccuracy. One liner produced a series of castings all of whose inaccuracies lay within the range +/- 0.1%, with a mean value of + 0.01%. With the other five liners, all or most castings were undersize. With three, all or most castings showed inaccuracies worse than -0.2%. The values for casting inaccuracy with the various liners showed a probable correlation with potential investment expansion (p < 0.05); however, no correlation was found between casting inaccuracy and any apparently relevant liner properties, alone or in combination. In casting techniques which use a pre-wetted ring liner, the choice of a specific lining material is an important factor which has a significant effect on casting inaccuracy. With at least three of the six liners tested, a higher investment expansion was needed for accurate full-crown castings to be ensured.

The fit of gold-alloy full-crown castings made with ceramic casting ring liners.

Measurements were made of the fit of gold-alloy full-crown castings produced with dry ceramic ring liners. When used with vacuum investing, these liners absorb relatively large amounts of water from the investment mix (thereby reducing its original W/P ratio) and then function as wet liners, thus increasing the investment's potential expansion and giving castings which are consistently larger than when air investing is used. With four of the five liners tested, investing in air produced many castings which were unacceptably undersized (inaccuracy worse than -0.2%). The fifth liner, an industrial material 2 mm thick, gave only one casting out of 12 which was outside this limit, although all castings were undersized to a lesser extent. Vacuum investing gave improved casting accuracy; with four of the five liners, the improvement was highly significant (p < 0.001), and with the fifth, probably significant (p < 0.05). Even with vacuum investing, however, with only two of the liners did all castings show inaccuracies within +/- 0.2%. With the other three liners, some castings (ranging from 2/10 to 7/9) had inaccuracies worse than -0.2%. With both air and vacuum investing, changing from one liner to another caused changes in relative casting accuracy which were often significant (p < 0.01) or highly significant (p < 0.001). In casting techniques where a ceramic ring liner is used, the choice of specific lining material and the choice between investing in air or under vacuum are important factors which can have a major effect on the fit of castings.

A novel directly coupled gradostat.

The original bidirectional compound chemostat (gradostat) described by Lovitt and Wimpenny has been simplified by making a more compact apparatus in which chemical gradients are established by diffusion between adjacent culture chambers. The experimental model (diffusion coupled (DC) gradostat) consisted of five chambers whose contents could be agitated by turbines rotating in the horizontal plane on a common shaft. Two biological experiments were designed to reveal the value of the DC gradostat. A methylotroph (Methylophilus methylotrophus) grown in a methanol gradient showed expected changes in cell viability as a function of position in the five vessel array. Cells of two species of photosynthetic bacteria (Rhodobacter capsulata and Rhodopseudomonas marina/agilis) with different salt sensitivities could be mixed and subsequently separated by the DC gradostat operating with a NaCl gradient of 0-3% w/v.

pH gradients through colonies of Bacillus cereus and the surrounding agar.

pH-sensitive microelectrodes, constructed with a tip diameter of about 4 microns, were deployed through 24 h and 48 h colonies of Bacillus cereus incubated on CYS medium (Casamino acids, yeast extract, salts), with and without glucose. Measurements of pH were used to construct pH profiles through the colony and the surrounding agar. pH gradients could be detected for at least 800 microns into the agar beneath a 24 h colony, and to approximately 10 mm horizontally away from the edge of the colony. In older colonies, the lateral gradient extended for over 20 mm. The pH of the underlying agar was increased by up to 1.45 pH units after 48 h growth without glucose. When colonies were grown with glucose, a significant area of acidification was observed within the colony in addition to a zone of alkalinization present at its periphery. Acidification was thought to be due to the anaerobic fermentation of glucose producing organic acids whilst alkalinization was due to the aerobic oxidation of amino acids releasing ammonia.

Inhibition of Salmonella typhimurium and Escherichia coli in an Infant Milk Formula by an Activated Lactoperoxidase System.

A glucose/glucose oxidase activated lactoperoxidase system (LP-S) delayed the onset of exponential growth of Salmonella typhimurium and Escherichia coli in infant formula milk. Addition of urea peroxide with the LP-S reduced the initial population size and prevented growth of S. typhimurium and extended the lag period before the onset of exponential growth of E.coli .

The effect of casting ring liners on the potential expansion of a gypsum-bonded investment.

Cellulose paper (used wet) and ceramic paper (used dry) are replacing asbestos paper as cushioning ring liners in dental casting. A study was made of the effects of all three of these materials on the setting and subsequent thermal expansion of a gypsum-bonded cristobalite casting investment (W/P = 0.40). Thermal expansion measurements were made on the same specimens that were produced during the setting expansion tests. Control specimens setting against a smooth dry surface showed a total expansion of 1.7%. Specimens setting against dry ceramic liners had similar total expansions, in the range 1.6 to 1.7%. Specimens setting against either of the wet lining materials showed an increased total expansion (in the range 2.2 to 2.3%), by virtue mainly of a large increase in setting expansion. In order for reproducible setting expansion results to be obtained with wet liners, it was necessary to control the amount of absorbed water carefully. Dry asbestos and dry cellulose liners gave higher expansions than pre-wetted ones, since they abstracted water from the mix, reducing its effective W/P ratio (giving a thicker mix), and then functioned as wet liners. These results suggest that, at least as far as potential investment expansion is concerned, wet cellulose liners have an effect similar to that of the traditional wet asbestos liners. Dry ceramic liners give a much lower investment expansion, and when these liners are used, an investment with an increased measured expansion could be an advantage.

The bioavailability and metabolism of trilostane in normal subjects, a comparative study using high pressure liquid chromatographic and quantitative cytochemical assays.

High pressure liquid chromatographic (HPLC) analysis of plasma taken over 8 h from ten normal male subjects medicated with 120 mg of trilostane revealed that the drug is rapidly metabolised into at least one metabolite, 17-keto trilostane. Both compounds were detected in the blood stream at concentrations greater than 2 X 10(-7) M within an hour and were cleared from the blood by 6-8 h. Approximately 3 times the concentration of metabolite was detected compared to the parent compound in most samples analysed. There were large subject to subject variations in the handling of drug. Standard curves of pure 17-keto trilostane and trilostane were parallel as assessed by cytochemical bioassay. This assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase activity in unfixed tissue sections of the dioestrous rat ovary. The relative potency of the metabolite compared to trilostane was 1.71 (95% confidence 1.5-2.0) over the dose range 0.15-1.5 microM. Thus, the metabolite may be the major active agent when trilostane is administered for clinical purposes. In a further 4 volunteers, who also received 120 mg trilostane and were sampled over an 8 h period, plasma was analysed independently by HPLC and cytochemical assays. In the majority of cases the bioactivity recorded (relative to a trilostane standard curve) was substantially higher than the molar sum of circulating trilostane and 17-keto-trilostane (as assessed by HPLC). However, if the relative potency of 17-keto-trilostane is taken into consideration, correlation between the two assays was excellent (r = 0.947, n = 18, P less than 0.001). This also suggests that no further active metabolites were present in the plasma samples. The drug profiles seen in the second study were essentially the same as described for the first 10 volunteers. The combination of a bioassay, which detects trilostane-like bioactivity, and HPLC, which reveals the type of metabolism, should aid our understanding of the clinical value of this potentially important drug.

A cytochemical section bioassay for plasma trilostane: an orally active inhibitor of 3 beta-hydroxysteroid dehydrogenase activity.

Trilostane is a competitive inhibitor of 3 beta-hydroxysteroid dehydrogenase activity in vitro and an orally active inhibitor of steroidogenesis in vivo. A cytochemical section bioassay for this drug (4 alpha, 5-epoxy-17 beta-hydroxy-3-oxo-5 alpha-androstane-2 alpha-carbonitrile) in human plasma has been developed. The assay is based upon the inhibition of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the corpus luteum of unfixed tissue sections (6 micron) of the mature dioestrous rat ovary. Trilostane is extracted from plasma by a simple chloroform procedure. The standard curve (0.15-2.5 mumol/l pure trilostane) exhibits a four-fold change in 3 beta-HSD activity and is constructed in the presence of extract from control plasma pools. The detection limit of the plasma assay is 2 mumol/l trilostane after allowing for dilution effects and recovery losses. This level gives a significantly different response from the zero quality control (P less than 0.05) and has an inter-assay coefficient of variation of less than 15%. No false positives have been recorded to date and the majority of samples from subjects receiving therapeutic doses of the drug have levels of greater than 2 mumol/l. Intra- and inter-assay coefficients of variation using both plasma quality controls and unknown samples are 4% (n = 15) and 13.9% (n = 27) respectively. Recovery is 80 +/- 9% (n = 13) and 79 +/- 10% (n = 10) for plasma quality controls containing 12 and 4.8 mumol/l trilostane respectively. Dilutions (up to 1:5) of plasma extracts are parallel to the standard curve and the assay throughput is approximately 16 samples/week technician.(ABSTRACT TRUNCATED AT 250 WORDS)

Experience with trilostane in the treatment of Cushing's syndrome.

Five patients with pituitary dependent Cushing's syndrome and two with adrenal carcinoma were treated with increasing doses of trilostane (up to 1440 mg daily). There was no consistent fall in serum cortisol levels. In addition there was no rise in the levels of precursors immediately preceding the proposed site of action of trilostane. These results suggest that trilostane does not effectively block the enzyme 3 beta-hydroxysteroid dehydrogenase delta 4,delta 5 isomerase in patients with Cushing's syndrome and that it should no longer be recommended for their treatment.

The effect of alginate impressions on the surface of cast gypsum. II. The role of sodium sulphate in incompatibility.

Of the materials tested only two alginates, Palginex (D), and Echo (C), show good surface reproduction when Vel-Mix (1), Ainsworth Greenstone (4), and Investo Greenstone (5) are cast against them. The above two alginates were shown to have a potassium and sulphate rich exudate. The reasonable surface produced by CA-37 (A) can be attributed to a proportional decrease in the ratio of potassium to sulphate present in the exudate, compared with Echo (C) and Palginex (D). S.S. White (B), Kromopan (E), and Tissutex (G) produce poor cast surfaces when high strength gypsum products are set against them. The exudates from these alginates were found to consist almost entirely of sodium sulphate. This study suggests that one way to improve the surface compatibility of alginates with gypsum products would be to modify the chemistry of the impression material so that a reactor other than calcium sulphate is used, to eliminate the appearance of sulphate ions in the exudate. Moreover, sources of sodium ions should also be eliminated. Therefore soluble alginates other than sodium alginate should be preferred, and a retarder other than one or other of the forms of sodium phosphate should be used. These changes would ensure that sulphate, particularly sodium sulphate, would not be produced as a by-product of the setting reaction. This in turn would eliminate the effects of incompatibility at present encountered to a greater or lesser extent with most combinations of alginate impression materials and gypsum cast materials.