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Biomedical subjects

L C Thomas

Publications and source records attributed to L C Thomas.

At least 19 recordsLinked to original sources
PubMed2006

Development of a real-time Staphylococcus aureus and MRSA (SAM-) PCR for routine blood culture.

The notification of "Gram-positive cocci, possibly staphylococcus" in a blood culture drawn from a seriously ill patient is responsible for a large amount of vancomycin prescribing in institutions where methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of bacteraemia. A duplex real-time TaqMan polymerase chain reaction targeting the species-specific nuc gene, and the mecA gene encoding methicillin-resistance, was developed as a tool for rapid identification and detection of S. aureus and methicillin-resistance, and optimised for immediate as-needs testing. Three different DNA extraction methods achieved varying DNA quality, with PCR inhibition the main problem. Serial blood cultures (n=120) identified as possible staphylococci on Gram stain from our clinical laboratory were examined. There was one false negative result for a methicillin-resistant Staphylococcus epidermidis, which was positive on repeat testing, and one false negative result due to DNA extraction failure for MRSA from peritoneal dialysate inoculated into blood culture medium. Sensitivity and specificity of 97% and 100%, respectively, were obtained for mecA; and sensitivity and specificity of 98% and 100%, respectively, for nuc. Detection of slow-growing coagulase-negative staphylococci as co-infecting strains may be reduced. The assay quickly and reliably identified S. aureus in mixed infection, and identified methicillin resistance in both S. epidermidis and S. aureus strains.

Bacterial Proteins↗
PubMed2000

Frames of reference for the display of battlefield information: judgment-display dependencies.

In 2 experiments, U.S. Army soldiers viewed computer-generated displays that presented battlefield information from 3 different frames of reference: a 2D plan view display (with contour lines), a 3D exocentric perspective display, and an interactive 3D immersed display. In Experiment 1, soldiers made geographical judgments. The results suggested that both 3D displays suffered from ambiguity of distance estimates but that the 3D immersed display was most accurate for judging whether a location is directly visible from another. In Experiment 2, the 3D exocentric display was compared with a 3D immersed view, coupled with a small 2D inset map, in a more continuous battlefield scenario in which judgments of enemy activity were made. The findings of 3D ambiguity were replicated from Experiment 1. The accuracy of judgments of enemy activity suffered with the immersed display when information necessary to answer correctly did not appear in the initial forward view and required panning to acquire, reflecting the cognitive demands of integration across different views. This display also hindered soldiers' ability to report changes in enemy activity from one scene to the next. The results of this research will help to provide guidelines for the appropriate choice of computer display technology to assist in designing battlefield visualization aids. Caution should be exercised in choosing immersive viewpoints.

Computer Systems↗
PubMed1999

A discussion of the principles and applications of Modulated Temperature DSC (MTDSC).

The benefits of Modulated Temperature DSC (MTDSC) over conventional differential scanning calorimetry (DSC) for studying thermal transitions in materials are reviewed by means of examples. These include the separation of overlapping phenomena such as melting/recrystallization in semi-crystalline materials, the heat capacity variation and enthalpic relaxation at the glass transition, and transitions from the different components of a blend. In addition, examples are presented demonstrating the ability of MTDSC to detect subtle transitions more readily and without loss of resolution. The possibility of measuring heat capacity in quasi-isothermal conditions and the evaluation of the thermal conductivity of a material are explained.

Algorithms↗
PubMed1999

Effects of Mycoplasma fermentans incognitus on differentiation of THP-1 cells.

Mycoplasma fermentans incognitus has been isolated from human tissue in patients both with and without AIDS who died of systemic infection. M. fermentans incognitus and other strains of M. fermentans have been associated with rheumatoid arthritis. While cell extracts of M. fermentans incognitus can induce changes in murine and human cells of the monocytic lineage, little is known about interactions of viable organisms with such cells. Because of the central role of macrophages in chronic inflammation, we examined the effects of M. fermentans incognitus on surface markers and functions of THP-1 cells, a well-characterized human monocytic cell line. This cell line has been used extensively in studies of macrophage differentiation, especially following exposure to phorbol esters. Changes in cell morphology, phagocytosis, rate of cell division, and selected surface markers were evaluated in cultures of THP-1 cells exposed to phorbol myristate acetate (PMA), M. fermentans incognitus, or both. As reported by other investigators, PMA induced THP-1 cells to differentiate into cells resembling tissue macrophages. M. fermentans incognitus only minimally affected changes induced by PMA, slightly increasing the percentage of cells positive for FCgammaRI and major histocompatibility complex (MHC) class II antigens. M. fermentans incognitus alone induced an incomplete arrest in the cell cycle at G0 phase, increased phagocytic ability, and enhanced expression of FCgammaRI, CR3, CR4, and MHC class II antigens.

Carcinogens↗
PubMed1996

Metastases of unknown primary site.

Despite the fact that effective therapy does not currently exist for the majority of patients presenting with metastases of unknown primary site, the last decade has witnessed significant advances in the approach to this heterogeneous disease. The use of modern pathologic techniques that frequently provide better diagnostic precision and the recognition of specific subgroups with a favorable prognosis and responsiveness to treatment has improved the outcome for some patients. Currently the diagnostic strategy should emphasize the rapid identification of patients likely to benefit from available therapy, whereas clinical research should focus on the development of more effective treatments for those patients with unresponsive tumors. In the future, continued improvements in the molecular characterization of these tumors will likely enhance understanding of the metastatic process, allow for more specific definitions of cell lineage, and provide insights for better therapy.

Cell Lineage↗
PubMed1991

Quantitative measurements via co-elution and dual-isotope detection by gas chromatography-mass spectrometry.

Dual-isotope measurements by gas chromatography-mass spectrometry (GC-MS) which mimic isotope dilution may suffer from irreproducibilities or unduly large uncertainties because of variations in ionization efficacies for the respective forms in the MS source. Such variations are sometimes avoided via extensive pretreatments and high-resolution GC separations. However, in some circumstances, an alternative approach is feasible which instead exploits the advantages of decreasing GC resolution. By forcing both forms of each analyte to co-elute, their ionization efficacies in the MS source will be virtually identical, thereby allowing for highly reproducible relative response ratios to be attained despite dramatically lowered GC resolution. The co-elution results described here are nearly as precise as results from moderate-resolution separations in the absence of interferents. Thus, dual-isotope GC-MS measurements with co-elution of the target analytes and their respective isotopically labeled internal standards offer a powerful alternative to the conventional approach of requiring expensive and labor-intensive additional pretreatments and separations; however, the effects of interferences may be exacerbated by the forced co-elution and must also be considered.

Anthracenes↗
PubMed1991

Measurements using gas chromatography with coelution and dual-isotope atomic emission detection.

Dual-isotope measurements by gas chromatography (GC)-atomic emission detection (AED) may enhance results for quantitative analyses. Adding a known amount of an isotopically labelled form of target analytes in each sample can compensate for irreproducibilities or uncertainties associated with sample pretreatments and sample loading. Similarly, fluctuations in AED temperatures, flows and interferants can be compensated via the added labelled forms if each target analyte and its isotopically labelled form coelute. Under these conditions they are subject to identical excitation environments and are measured from the same viewed volumes. Consequently, improved quantitative results may be attained by coelution in GC-AED methods which mimic isotope dilution.

Gas Chromatography-Mass Spectrometry↗
PubMed1991

Laser-excited fluorescence detection of gas-phase chromatography eluates.

A high-spectral-resolution laser-excited molecular fluorescence gas chromatographic (GC) detection system is evaluated. It utilizes a pulsed supersonic jet expansion to yield very-narrow-bandwidth (e.g. less than or equal to 0.1 nm) fluorescence excitation spectra that may be rapidly scanned via a tunable dye laser. A microcomputer synchronizes the entire system, collects data, performs calculations, and creates visual displays of results. The laser-excited fluorescence detection system was interfaced to a gas chromatograph to exploit both the selectivity of the chromatography and the excellent spectral selectivity of the detector. Fluorescence excitation chromatograms were acquired by monitoring fluorescence emission from selected transition wavelengths characteristic of the GC eluates. The excitation wavelengths were also programmed to change at appropriate retention times to provide greatest selectivities for individual analytes as they eluted, and to allow multiple analytes to be determined in a single elution. Response factors for the system varied appreciably from run to run, which precluded the use of external standard quantitation procedures. However, excellent stabilities for within-run relative response factors were sufficient to allow for good quantitative measurements using internal standard techniques.

Chromatography, Gas↗
PubMed1989

Mitochondrial rRNA-containing petite strains of yeast (Saccharomyces cerevisiae) show a normal nuclear-mitochondrial stringent response.

The nuclear-mitochondrial stringent response was examined in isonuclear rho+, 21S rRNA-containing rho-, and rho o strains of S. cerevisiae. By 30 min after nutritional downshift, nuclear rDNA transcription falls to 15% of control levels congruently in all strains, as assayed via whole-cell RNA or by hybrid selection of specific double-labeled transcripts. Both in vivo and in vitro, the mitochondrial stringent response is identical between the rho- strain and its parental rho+ strain, and in both, the kinetics and magnitude of the organellar response mirror those of the nuclear response. The data show that mitochondrial transcription and protein synthesis are not required for stringent regulation of either nuclear or mitochondrial rDNA transcription.

Mitochondria↗
PubMed1987

Ultraviolet spectrometric detection for gas chromatography of polynuclear aromatic compounds with repetitive spectral scans using absorbance and concurrent fluorescence measurements.

A computer-controlled ultraviolet spectrometric detection system for gas chromatography (GC) is described which acquires absorption spectra of gas-phase GC effluents at rates up to two 62-nm scans per s. Concurrent fluorescence measurements enhance the selectivity of this detection system, providing additional qualitative information. The system has been designed to preserve chromatographic resolution and is selective for aromatic compounds. This multi-mode GC detection is demonstrated through GC separations of polynuclear aromatic compounds with limits of detection ranging from 30 to 70 ng for absorbance measurements. The spectral information obtained with this detection system may be used for compound identification, enhancement of the selectivity and for resolving co-eluting GC eluites.

Chromatography, Gas↗
PubMed1987

Determinations of polychlorinated biphenyl isomers by response factor calibration.

Quantitative measurement of polychlorinated biphenyl (PCB) isomers by response factor calibration (RFC) is evaluated with gas chromatography and the Hall electrolytic conductivity detector. The procedure requires neither isomer identification nor reference compounds identical to each measured PCB isomer. Weight percent chlorine is determined for five Aroclor mixtures by RFC and compared within a few percent of expected values. Individual PCB isomers are measured and quantitatively compared for Aroclor mixtures. Also, RFC determinations for ten PCB isomers contained in a test material reference solution are compared to the supplier's stated concentrations. These RFC measurements provide quantitative analyses in the absence of a standard for each measured component.

Chromatography, Gas↗
PubMed1982

Aortic stenosis associated with systemic lupus erythematosus.

Hemodynamically significant valvular lesions have been rarely reported sequelae of Libman-Sacks endocarditis complicating systemic lupus erythematosus (SLE). Furthermore, embolic phenomena associated with these vegetations have not been clearly documented. We present a report of critical aortic stenosis associated with SLE in a patient who had received corticosteroid treatment for several years. An embolus, histologically identical with the aortic valve vegetation, was found in the left anterior descending artery at necropsy. There was no evidence of rheumatic heart disease, bacterial endocarditis or a bicuspid aortic valve. Recent reports suggest an increased incidence of significant valvular dysfunction in patients with SLE who have received long-term corticosteroid treatment.

Adult↗
PubMed1982

An outbreak of pyomyositis in a large refugee camp in Thailand.

During a 2-month period, 17 cases of pyomyositis were seen in the hospital population of a large refugee camp for Cambodians in Thailand. The temporal clustering of the cases suggests an epidemic pattern. Patients in this series were generally young and otherwise healthy. All had gram-positive cocci demonstrated in abscess pus, and all responded to surgical drainage. Fourteen (82%) of the cases were initially misdiagnosed by volunteer physicians who were unfamiliar with the disease. The authors suggest that a mosquito-borne virus predisposes to the development of the pyomyositis abscess.

Abscess↗
PubMed1979

Metabolic fate of aromatic hydrocarbons in aquatic organisms: analysis of metabolites by thin-layer chromatography and high-pressure liquid chromatography.

Aquatic organisms convert aromatic hydrocarbons into a variety of conjugated and nonconjugated derivatives. Analytical techniques based on thin-layer chromatography (TLC) and high-pressure liquid chromatography (HPLC) were employed to separate, identify and quantitate individual metabolites from fish exposed to radiolabeled naphthalene and 2,6-dimethylnaphthalene. Significant differences in profiles of individual metabolites were found in relation to the type of biological sample analyzed. Liver of naphthalene-exposed salmonids contained eight polar derivatives, as shown by HPLC. Two nonconjugates (1-naphthol and 1,2-dihydro-1,2-dihydroxynaphthalene) and three conjugates (1-naphthyl glucuronic acid, 1-naphthyl sulfate and 1-naphthyl glucoside) were identified. HPLC revealed that brain of 3H-naphthalene-exposed trout contained essentially the nonconjugated derivatives, 1-naphthol and 1,2-dihydro-1,2-dihydroxynaphthalene. TLC showed that the metabolites from trout urine were 1-naphthol, 1,2-dihydro-1,2-dihydroxynapthalene, and 1-naphthyl glucuronic acid (99% of the total metabolites detected). Major components of the metabolite fractions of tissues and biological fluids were 1,2-dihydro-1,2-dihydroxy and glucuronic acid derivatives. Dihydrodiol derivatives arise from the corresponding arene oxides, some of which have been shown to be cytotoxic to certain mammalian systems.

Animals↗