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Biomedical subjects

R Allman

Publications and source records attributed to R Allman.

28 records · Page 2Linked to original sources
PubMed1994

Rapid estimation of bacterial antibiotic susceptibility with flow cytometry.

Bacterial antibiotic susceptibility was rapidly estimated for Escherichia coli and Staphylococcus spp. by flow cytometry. This was achieved by measuring the uptake of a negatively charged membrane potential sensitive dye bis-(1,3-dibutyl-barbituric acid) trimethine oxonol and observing changes in low-angle light scatter (excitation light scattered by up to 15 degrees). Estimations of ampicillin, gentamicin and ciprofloxacin susceptibilities were possible within 2-5 h from a plate culture, depending on the species and antibiotic used. This includes the time necessary to establish steady-state growth in liquid culture.

Anti-Bacterial Agents↗
PubMed1994

Age, race, and gender variation in the utilization of coronary artery bypass surgery and angioplasty in SHEP. SHEP Cooperative Research Group. Systolic Hypertension in the Elderly Program.

OBJECTIVE: To assess variability in the use of coronary artery bypass grafting (CABG) and percutaneous transluminal angioplasty (PTCA) in the Systolic Hypertension in the Elderly Program (SHEP) cohort with incident coronary heart disease (CHD) by age, sex, and race. DESIGN: Retrospective analysis of a multicenter prospective cohort study. SETTING: Community-based ambulatory population in academic centers. PATIENTS: Among 4736 subjects initially enrolled in SHEP, there were 432 incident cases of CHD, excluding those patients who experienced rapid or sudden cardiac death. MAIN OUTCOME MEASURE: Incident cases of CHD who underwent CABG or PTCA. RESULTS: Of those participants > or = 60 and < 75 years of age, 7.3% underwent PTCA, compared with 3.9% of those > or = 75 years (P = 0.14). 15.4% of those < 75 underwent CABG surgery, compared with 7.8% of those 75 and older (P = 0.018). When both of these endpoints, CABG and PTCA, were combined, 22.4% of those < 75 underwent a procedure, while only 11.7% of the older cohort did (P = 0.005). Twenty-six percent of men underwent either CABG or PTCA, while only 9.1% of women did (P < 0.001). Of those < 75 years of age, 31.1% of men and 12.3% of women underwent CABG or PTCA (P < 0.001). In the 75 and older age category, 19.5% of men underwent these interventions, compared with 5.9% of women (P = 0.005). Active treatment group was significantly associated with decreased use of procedures in participants < 75 year old with CHD. Race, activity limitations, number of comorbid conditions, education level, marital status, employment status, and social support were not significantly associated with CABG or PTCA use. When the variables studied were entered into a logistic regression model, increased age and female sex remained independently associated with decreased CABG and PTCA use. CONCLUSION: In the SHEP trial older patients and women, regardless of comorbid conditions, socioeconomic status, and social support, underwent less intensive cardiovascular interventions than did younger patients and men when they developed CHD.

Age Factors↗
PubMed1994

Ultrasound enhanced phase partition of microorganisms.

Aqueous two-phase partition is an established technique for the separation of many biological particles or solutes. Similarly, ultrasound is finding application in the harvesting of cell populations. We have combined the two methodologies to produce an elegant technique for separating and concentrating biological particles or solutes in an enclosed environment which is non-destructive and minimally perturbing to the objects being separated. Megahertz frequency ultrasonic standing wave fields produced either axially or radially from piezo-ceramic transducers dramatically reduce the time for completion of partition to about 1 min as demonstrated using Saccharomyces cerevisiae and Escherichia coli. The system described is competitive with established methods of cell separation and concentration.

Biotechnology↗
PubMed1994

Ultrasonic manipulation of particles and cells. Ultrasonic separation of cells.

Cells or particles suspended in a sonic standing wave field experience forces which concentrate them at positions separated by half a wavelength. The aims of the study were: (1) To optimise conditions and test theoretical predictions for ultrasonic concentration and separation of particles or cells. (2) To investigate the scale-up of experimental systems. (3) To establish the maximum acoustic pressure to which a suspension might be exposed without inducing order-disrupting cavitation. (4) To compare the efficiencies of techniques for harvesting concentrated particles. The primary outcomes were: (1) To design of an acoustic pressure distribution within cylindrical containers which led to uniformly repeating sound pressure patterns throughout the containers in the standing wave mode, concentrated suspended eukaryotic cells or latex beads in clumps on the axis of wide containers, and provided uniform response of all particle clumps to acoustic harvesting regimes. Theory for the behaviour (e.g. movement to different preferred sites) of particles as a function of specific gravity and compressibility in containers of different lateral dimensions was extended and was confirmed experimentally. Convective streaming in the container was identified as a variable requiring control in the manipulation of particles of 1 micron or smaller size. (2) Consideration of scale-up from the model 10 ml volume led to the conclusion that flow systems in intermediate volume containers have more promise than scaled up batch systems. (3) The maximum acoustic pressures applicable to a suspension without inducing order-disrupting cavitation or excessive conductive streaming at 1 MHz and 3 MHz induce a force equivalent to a centrifugal field of about 10(3) g. (4) The most efficient technique for harvesting concentrated particles was the introduction of a frequency increment between two transducers to form a slowly sweeping pseudo-standing wave. The attractive inter-droplet ultrasonic standing wave force was employed to enhance the rate of aqueous biphasic cell separation and harvesting. The results help clarify the particle size, concentration, density and compressibility for which standing wave separation techniques can contribute either on a process engineering scale or on the scale of the manipulation of small particles for industrial and medical diagnostic procedures.

Bacteria↗
PubMed1992

Characterization of bacteria by multiparameter flow cytometry.

An arc-lamp based flow cytometer was used to obtain high resolution measurements of the light scattering characteristics and DNA contents of eight different bacteria. Light scatter profiles of bacteria are a useful first step when flow cytometry is used to characterize organisms. Scanning and transmission electron microscopy of the bacterial samples demonstrate that the structural basis of the light scattering profiles is not always clear, i.e. some organisms appear to have anomalous light scattering characteristics. The use of a third measurement parameter, DNA content, allowed much better discrimination of the organisms. Flow cytometry shows great promise as a method for the rapid discrimination and identification of bacterial populations.

Bacteria↗
PubMed1991

Cell cycle parameters of Escherichia coli K-12.

A computer simulation routine was used to calculate the DNA distributions of exponentially growing cultures of Escherichia coli K-12. Simulated distributions were compared with distributions obtained experimentally by flow cytometry. Durations of the DNA replication period (C) and the postreplication period (D) were found by minimizing the difference between theoretical and experimental DNA histograms. It was demonstrated that the K-12 strains AB1157 and CM735 had C and D periods that differed widely from each other and from those of the previously measured strain B/rA, while strain MC1000 was shown to have the same durations of the C and D periods as strain B/rA. The variation between K-12 strains may explain the divergence in the literature regarding their C and D periods. Strains W3110 and AB1157 recA1 had DNA histograms that could not be adequately simulated by the classical Cooper-Helmstetter model, which is consistent with the asymmetrically located origin and terminus for W3110 and the asynchrony of initiation for AB1157 recA1.

Cell Cycle↗
PubMed1990

Growth of Azotobacter vinelandii with correlation of Coulter cell size, flow cytometric parameters, and ultrastructure.

When Azotobacter vinelandii is grown under nitrogen-fixing conditions, the mean cell volume fluctuates from 2.7 to 6.6 microns 3 as determined using a Coulter counter. When NH4Cl is supplied as nitrogen source, the mean cell volume fluctuates from 4.6 to 7.4 microns3. Parallel experiments using flow cytometric measurements show similar characteristic fluctuations in the narrow forward angle light scattering signal and also in cellular protein content as determined using fluorescein isothiocyanate (FITC) fluorescence. Fluctuations in the perpendicular light scatter signal during batch growth are similar for both sets of growth conditions. Changes in cell morphology and ultrastructure are also similar for both sets of growth conditions, as demonstrated by electron microscopic examination. We conclude that narrow forward angle light scatter is a close correlate of cell size, whereas right angle scatter is an indicator of morphological variations other than size.

Ammonium Chloride↗
PubMed1984

Computer-assisted instruction and diagnosis of radiographic findings.

Recent advances in computer technology, including high bit-density storage, digital imaging, and the ability to interface microprocessors with videodisk, create enormous opportunities in the field of medical education. This program, utilizing a personal computer, videodisk, BASIC language, a linked textfile system, and a triangulation approach to the interpretation of radiographs developed by Dr. W. L. Thompson, can enable the user to engage in a user-friendly, dynamic teaching program in radiology, applicable to various levels of expertise. Advantages include a relatively more compact and inexpensive system with rapid access and ease of revision which requires little instruction to the user.

Computer-Assisted Instruction↗