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P Mehl

Publications and source records attributed to P Mehl.

7 recordsLinked to original sources
PubMed1993

Bactericidal activity of the fluoroquinolone WIN 57273 against high-level gentamicin-resistant Enterococcus faecalis.

The fluoroquinolone WIN 57273 showed identical bactericidal activities (MBC for 90% of the strains = 0.25 micrograms/ml) for bacteremic strains of Enterococcus faecalis with and without high-level gentamicin resistance. WIN 57273 was bactericidal in time-kill measurements with highly gentamicin-resistant, ciprofloxacin-susceptible strains of E. faecalis. However, WIN 57273 was indifferent with penicillin for gentamicin-resistant E. faecalis and was not bactericidal for ciprofloxacin-resistant E. faecalis.

Anti-Infective Agents↗
PubMed1990

Theoretical prediction of devitrification tendency: determination of critical warming rates without using finite expansions.

Previously, critical warming rates vcr above which ice did not have enough time to crystallize had been roughly evaluated for many wholly amorphous aqueous solutions. These evaluations were obtained by extrapolation of the linear variation of the devitrification temperature Td with log v, where v is the warming rate, observed experimentally between 2.5 and 80 degrees C/min. Theory also gives such a linear variation, but only using the first term of a finite expansion. The other terms can be neglected only for small variations of Td. These evaluations were sufficient for classification of the solutions, but large errors were made in vcr. A new and more accurate method of determination of the variation of Td with v is presented here. The general equation giving in our models the derivative of the quantity of ice formed versus temperature T is differentiated, instead of integrated using a finite expansion. This gives an explicit expression of v versus Td assuming that the ratio xd of the quantity of ice formed at Td to the total quantity of ice formed on warming is constant. Experimentally, xd is constant within a good approximation. Theoretical curves representing the variation of Td with v have been drawn for solutions of 35 or 45% (w/w) 1,2-propanediol in water. Td never reaches the temperature of the end of melting Tm, but as v tends toward infinity, Td tends toward an asymptotic value of 0.96Tm for 35% solute. For that solution, above about 10(3) degrees C/min, Td deviates appreciably from linearity with log v, but 1/Td remains almost linear with log v up to Td congruent to 0.95Tm. Therefore, systematic comparison of the theoretical variation of Td with v with a linear variation of 1/Td with log v has been done, varying the parameters of the equations within the entire experimental range. Similar conclusions can be given for all the solutions. Experimentally for Td = 0.95Tm, the quantity of ice crystallized is generally less than 0.1% of the solution, reaching 1% only once. Therefore, a new definition of the critical warming rate vcr has been used, corresponding to extrapolation of the linear variation of 1/T with log v up to Td = 0.95Tm. New values of vcr have been calculated for all the binary systems previously studied. The order of the solutions is almost the same, but the new values of vcr are significantly smaller than the former.

Cryopreservation↗
PubMed1988

Cryoprotection of red blood cells by 1,3-butanediol and 2,3-butanediol.

1,3-Butanediol and 2,3-butanediol have been used in buffered solutions with 20, 30, or 35% (w/w) alcohol to cool erythrocytes to -196 degrees C at different cooling rates between 1 to 3500 degrees C/min, followed by slow or rapid rewarming. 1,3-butanediol shows the same shapes of red blood cell survival curves as 1,2-propanediol. Having nearly the same physical properties, they have comparable effects on cell survival. The classical maximum of survival for intermediate cooling rates and an increase for the highest cooling rates are observed. This increase seems to be correlated with the glass-forming tendency of the solution. After the fastest cooling rates, a warming rate of 5000 degrees C/min is sufficient to avoid cell damage, but a warming rate of 100-200 degrees C/min is not. Yet both of these rates would be insufficient to avoid the intracellular ice crystallization on warming. The damage on warming after fast cooling seems once again to be correlated with the transition from cubic to hexagonal ice. For all our results, 1,3-butanediol is like a "second" 1,2-propanediol and could be useful as a cryoprotectant for preservation by total vitrification. 2,3-Butanediol always gives extremely low survival rates, though it presents good physical properties. The crystallization of its hydrate seems to be lethal on cooling or on rewarming.

Blood Preservation↗
PubMed1986

Glass-forming tendency and stability of the amorphous state in the aqueous solutions of linear polyalcohols with four carbons. I. Binary systems water-polyalcohol.

All the aqueous solutions of linear saturated polyalcohols with four carbons have been investigated at low temperature. Only ice has been observed in the solutions of 1,3-butanediol and 1,2,3- and 1,2,4-butanetriol. For same solute concentration, the glass-forming tendency on cooling is highest with 2,3-butanediol, where it is comparable to that with 1,2-propanediol, the best solute reported to date. However, the quantity of ice and hydrate crystallized is particularly high on slow cooling or on subsequent rewarming. The highest stability of the amorphous state is observed on rewarming the 1,2-butanediol and 1,3-butanediol solutions. With respect to this property, these compounds come just after 1,2-propanediol and before all the other compounds studied so far. They are followed by dimethylsulfoxide and 1,2,3-butanetriol. The glass-forming tendency of the 1,3-butanediol solutions is also very high; it is third only to that of 1,2-propanediol and 2,3-butanediol. The glass-forming tendency is a little smaller with 1,2-butanediol, but it is cubic instead of ordinary hexagonal ice which crystallizes on cooling rapidly with 35% 1,2-butanediol. Cubic ice is thought to be innocuous. A gigantic glass transition is observed with 45% of this strange solute. 1,4-Butanediol, 45% also favors cubic ice greatly. Therefore, 1,2- and 1,3-butanediol with comparable physical properties are perhaps as interesting as 1,2-propanediol for cryopreservation of cells or organs by complete vitrification. Together with 1,2-propanediol, 1,2- and 1,3-butanetriol, 1,2,3-butanetriol, and perhaps 2,3-butanediol provide an interesting battery of solutions for cryopreservation by vitrification.

Alcohols↗
PubMedDate not supplied

Kinetics of medfly mortality.

A series of theoretical analyses of mortality were performed on recent data for Mediterranean fruit flies (Ceratitus capitata). Best fit computations were performed using the Marquardt-Levenburg technique on: 1) the classic Gompertz model, 2) the Johnson-Mehl-Avrami (JMA) model from chemical kinetics theory, which is formally a Weibull model, and 3) a hyperexponential gamma distribution model that we developed to help explain the relative success of the JMA model when compared with the Gompertz model. It was found that both the JMA and gamma models deviated from the data by about an order of magnitude less than the Gompertz model for the first few mean fly lifetimes. We discuss likely underlying causes for the success of these models vs. the classic model.

Aging↗
PubMedDate not supplied

Leukocyte adhesion molecules as biocompatibility markers for hemodialysis membranes.

Comparative flow cytometric measurement was used to evaluate the significance of leukocyte adhesion molecule (LAM) activity changes during hemodialysis (HD) with different cellulosic and non cellulosic membranes. Six hemodialysis patients (men) who were in a maintenance program for more than 6 months were treated consecutively with five different dialyzers (cuprophan, hemophan, 2 types of cellulose acetate, and polysulfone). During each study HD, blood was sampled from the arterial line at 0, 15, and 60 min and from the venous port at 3 min to harvest leukocytes immediately after the first cell-membrane contact. After whole blood lysis preparation, leukocytes were incubated with fluorescent antibodies to label LAM CD 11A/18 (LFA-1), CD 11B/18 (Mac-1), CD 11C/18 (p150/95), and CD 54 (ICAM-1) (Becton-Dickinson, San Jose, CA). Data were acquired for the granulocyte, monocyte, and lymphocyte population based on forward and 90 degrees scatter light measurements. Accuracy of gating was verified by CD 14/45 staining for all samples. Baseline integrin expression for the selected populations before biomaterial contact was found to be heterogeneous for different patients, but underwent changes for the same patient during HD treatment. The fluorescent intensity corresponding to specific integrins was characterized by different patterns of up/down regulation with maximal deviations occurring at 3 min. Fluorescent intensity of the granulocyte and monocyte populations sampled at 15 min was 40-50% lower as compared with those sampled immediately after the first biomaterial contact. Based on the basal fluorescence levels and values recorded after the first biomaterial contact and those at 15 min, two coefficients were generated to compare membrane properties.

Aged↗