PubMed Health⌕ Search

Biomedical subjects

C G Mitchell

Publications and source records attributed to C G Mitchell.

At least 19 recordsLinked to original sources
PubMed2001

Prevention for positives: challenges and opportunities for integrating prevention into HIV case management.

Despite nearly 20 years of HIV prevention efforts, rates of new HIV infection persist at an alarming rate. As successful antiretroviral medications enable many HIV infected persons to live longer, healthier lives, interventions are necessary to support ongoing prevention and reduced risk behaviors. This article describes a survey that was used to assess the opportunities and challenges related to the integration of prevention screening into the work of HIV/AIDS case managers. The article describes the survey, reports the findings (N = 101), and concludes with a discussion of issues that must be addressed prior to incorporating prevention screening into HIV/AIDS case management.

Adult↗
PubMed2000

Enhanced binding of Aspergillus fumigatus spores to A549 epithelial cells and extracellular matrix proteins by a component from the spore surface and inhibition by rat lung lavage fluid.

BACKGROUND: Aspergillus fumigatus is a pathogenic fungus which causes a range of diseases, particularly in the human lung. The pathological mechanism is unknown but may involve a complex mixture of biomolecules which can diffuse from the spore surface. This material is known as A fumigatus diffusate (AfD) and has previously been shown to have a range of immunosuppressive functions. It is hypothesised that AfD may influence the binding of spores to extracellular matrix (ECM) proteins and lung epithelial cells, thereby affecting the ability of the fungus to cause infection. METHODS: The binding of spores to ECM proteins and to epithelial cells was carried out using a direct binding assay in microtitre plates and spores were counted by phase contrast microscopy. Rat bronchoalveolar lavage (BAL) fluid was enriched for surfactant protein D (SP-D) using maltose agarose affinity chromatography. The effects of AfD and the SP-D enriched BAL fluid were assessed by pre-incubation with ECM proteins or epithelial cells in the direct binding assay. RESULTS: AfD enhanced the binding of spores to laminin by 137% and to A549 epithelial cells by 250%. SP-D enriched BAL fluid inhibited spore binding to ECM proteins and epithelial cells. Pre-incubation of ECM proteins and epithelial cells with SP-D enriched BAL fluid prevented the enhancement of spore binding by AfD, and pre-incubation of ECM proteins and epithelial cells with AfD prevented the inhibition of spore binding by SP-D enriched BAL fluid. This pretreatment did not prevent the enhancement of spore binding, giving an increase of 95% for collagen I, 80% for fibronectin, 75% for laminin, and 150% for A549 cells. CONCLUSIONS: The hypothesis that AfD would affect spore binding to ECM proteins and epithelial cells was confirmed. Rat BAL fluid, with SP-D as the possible bioactive agent, prevented this enhancement. The in vivo significance is unclear but the enhanced binding of spores may increase the chance of fungal infection in the lung which could be prevented by the protective effects of lung surfactant components (possibly SP-D). The results suggest that there may be competition between AfD and a BAL fluid component (possibly SP-D) for the same or similar binding sites on ECM proteins and epithelial cells. Whether this competition occurs in vivo requires further investigation.

Animals↗
PubMed1998

Pathology attributed to Mycobacterium chelonae infection among farmed and laboratory-infected Atlantic salmon Salmo salar.

This study was promoted following concern over increasing mortality on 2 farms rearing Atlantic salmon Salmo salar in the Shetland Isles, Scotland. A Mycobacterium sp. was isolated from moribund, market-sized Atlantic salmon. Biochemical tests, lipid analysis and PCR (polymerase chain reaction) techniques confirmed the bacterium to be Mycobacterium chelonae. Multiple greyish-white miliary granuloma-like nodules were observed in several tissues. Dense hard-packed nodules contained abundant acid-fast bacteria. Atlantic salmon injected with M. chelonae remained sub-clinically infected, demonstrating the chronic nature of this disease. The source of the pathogen was not identified.

Animals↗
PubMed1998

Perceptions of empathy and client satisfaction with managed behavioral health care.

Managed care continues to revolutionize the provision of mental health services in the United States. Long-term, open-ended therapies have been replaced by short-term, highly focused interventions. Increasingly, managed care organizations rely on standardized preferred practice guidelines to give direction and focus to social work and other therapeutic interventions. Critics argue that changes effected by managed care, particularly the use of treatment guidelines, depersonalize the client-worker relationship and significantly reduce the role of empathy in the therapeutic process. Moreover, these critics suggest that overall client satisfaction with mental health services has deteriorated. This article presents a study that examined clients' perceptions of empathy and overall satisfaction with managed behavioral health care when the clients were in unstructured individual therapy or in time-limited standardized group therapy. The results reveal no significant difference in the clients' perception of empathy or of their overall satisfaction regardless of the type of treatment they received. This article describes the rationale and design of the study, presents the results, and discusses the implications for social work practice.

Empathy↗
PubMed1997

Diffusible component from the spore surface of the fungus Aspergillus fumigatus which inhibits the macrophage oxidative burst is distinct from gliotoxin and other hyphal toxins.

BACKGROUND: The fungus Aspergillus fumigatus, whose spores are present ubiquitously in the air, causes a range of diseases in the human lung. A small molecular weight (< 10 kD) heat stable toxin released from the spores of clinical and environmental isolates of A fumigatus within minutes of deposition in aqueous solution has previously been described. A key effect of the toxin was to inhibit the oxidative burst of macrophages as measured by superoxide anion release. It was hypothesised that the toxin was one of the commonly found A fumigatus hyphal toxins such as gliotoxin. This inhibitor may be an important factor which allows the fungus to colonise the lung. METHODS: The spore derived inhibitor was shown to inhibit the respiratory burst of rat alveolar macrophages, as measured by the generation of superoxide anion. Samples of the spore diffusate were subject to reversed phase high performance liquid chromatography (HPLC), thin layer chromatography (TLC), high performance thin layer chromatography (HPTLC), or organic extraction followed by TLC or HPLC to identify the presence of gliotoxin, fumagillin, helvolic acid, fumigaclavine-C, and aurasperone-C. Commercially obtained preparations of the toxins gliotoxin, fumagillin and helvolic acid and extracts enriched for fumigaclavine-C and aurasperone-C were used as internal and external standards and in the respiratory burst measurements. RESULTS: Gliotoxin, fumagillin, helvolic acid, fumigaclavine-C, and aurasperone-C were not detected in spore derived diffusate using PHLC or TLC. Using extraction procedures with solvents known to extract gliotoxin from A fumigatus culture supernatants, no gliotoxin was detected in the spore derived diffusate. Commercial gliotoxin, fumagillin, and helvolic acid or extracts enriched for fumigaclavine-C and aurasperone-C did not inhibit the oxidative burst of macrophages. CONCLUSIONS: The hypothesis that the spore derived toxin is one of the toxins derived from hyphae such as gliotoxin, helvolic acid, fumagillin, fumigaclavine-C, or aurasperone-C is not proved. The spore toxin may exert its effect through its ability to diffuse rapidly into the lung lining fluid, diminish the macrophage oxidative burst, and play a part in allowing A fumigatus to persist in the lung and manifest its well known pathogenic effects.

Animals↗
PubMed1996

Identification of a multienzyme complex of the tricarboxylic acid cycle enzymes containing citrate synthase isoenzymes from Pseudomonas aeruginosa.

A multienzyme complex of tricarboxylic acid cycle enzymes, catalysing the consecutive reactions from fumarate to 2-oxoglutarate, has been identified in extracts of Pseudomonas aeruginosa prepared by gentle osmotic lysis of the cells. The individual enzyme activities of fumarase, malate dehydrogenase, citrate synthase, aconitase and isocitrate dehydrogenase can be used to reconstitute the complex. The citrate synthase isoenzymes, CSI and CSII, from this organism can be used either together or as the individual activities to reconstitute the complex. No complex can be reformed in the absence of CSI or CSII. Which CS isoenzyme predominates in the complex depends on the phase of growth at which the cells were harvested and the extract prepared. More CSI was found in the complex during exponential growth, whereas CSII predominated during the stationary phase. The results support the idea of a 'metabolon' in this organism, with the composition of the CS component varying during the growth cycle.

Aconitate Hydratase↗
PubMed1996

Inhibition of the alveolar macrophage oxidative burst by a diffusible component from the surface of the spores of the fungus Aspergillus fumigatus.

BACKGROUND: Aspergillus fumigatus is a fungus that grows on dead and decaying organic matter in the environment and whose spores are present ubiquitously in the air. The fungus causes a range of diseases in the human lung. A study was undertaken to demonstrate and partially characterise an inhibitor of the macrophage respiratory burst from the surface of A fumigatus spores that could be an important factor in allowing the fungus to colonise the lung. METHODS: The spore-derived inhibitor of the respiratory burst of rat alveolar macrophages, as measured by generation of superoxide anion, was demonstrated in Hank's balanced salt solution extracts of four clinical isolates and an environmental isolate of A fumigatus. The time course of the release of the inhibitor into aqueous solution was assessed and the cytotoxic potential of the spore-derived inhibitor towards macrophages was tested using the propidium iodide method. An oxygen electrode was used to confirm the superoxide anion measurements. Molecular weight cutoff filters were used to determine the size of the inhibitor as assessed in the respiratory burst assay and also by its ability to inhibit macrophage spreading on glass. The crude diffusate from the spore surface was fractionated by reversed phase high pressure liquid chromatography (HPLC) and the fractions analysed for inhibitory activity, protein, and carbohydrate content. RESULTS: A small molecular weight (< 10 kD) heat stable toxin was released from the spores of clinical and environmental isolates of A fumigatus within minutes of deposition in aqueous solution. The key effect of the toxin demonstrated here was its ability to inhibit the oxidative burst of macrophages as measured by superoxide anion release. The inhibition was not due to cell death or detectable loss of membrane integrity as measured by permeability to propidium iodide. The toxin was not a scavenger of superoxide anion. Oxygen electrode studies suggested indirectly that the inhibitor acted to inhibit the assembly of the macrophage NADPH-oxidase complex. Fractions of < 10 kD also inhibited the spreading of alveolar macrophages, confirming that the toxin had an additional effect on macrophages that leads to loss of adherence or impairment of cytoskeletal function. In reversed phase HPLC fractions the inhibitory activity eluted with an associated carbohydrate, although the exact chemical nature of the toxin remains to be elucidated. CONCLUSIONS: This spore toxin may, through its ability to diffuse rapidly into lung lining fluid, diminish the macrophage respiratory burst and play a part in allowing A fumigatus to persist in the lung and manifest its well known pathogenic effects. Future research will be focused on further molecular characterisation of the toxin and elaboration of the effect of the toxin on intracellular signalling pathways involved in the activation of alveolar macrophages.

Animals↗
PubMed1995

Purification and characterization of citrate synthase isoenzymes from Pseudomonas aeruginosa.

Two types of citrate synthase (CS) have been purified from Pseudomonas aeruginosa, a 'large' form (CSI) and a 'small' form (CSII). The M(r)s of the CSI and CSII isoenzymes were determined to be 240,000 +/- 16,000 (mean +/- S.E.M.) and 80,300 +/- 3800 respectively. Chemical cross-linking of the native enzymes with either dimethyl suberimidate or glutaraldehyde followed by electrophoretic analysis by SDS/PAGE showed that CSI is a hexamer and CSII is a dimer. SDS/PAGE showed that CSI and CSII each consist of a single subunit type, of M(r) 42,000 +/- 2000 and M(r) 36,500 +/- 2000 respectively. CSI and CSII were also shown to be distinct kinetically, immunologically and in terms of their regulatory properties. It is suggested that the CS isoenzymes are products of different structural genes.

Amino Acids↗
PubMed1989

Proteolysis of the 185,000 MW streptococcal cell wall antigen generating 4000 and 6000 MW peptides with distinct antigenic determinants.

A 185,000 MW glycoprotein antigen derived from Streptococcus mutans was digested with subtilisin. Purification by reversed phase high-powered liquid chromatography (HPLC) resulted in a homogeneous 20,000 MW protein which possesses the streptococcal antigen (SA) I and II determinants. This protein was immunogenic in mice both for the 20,000 MW and the native 185,000 MW SA. Further proteolysis with subtilisin generated four peptides of 18,000, 10,000, 6000 and 4000 MW. Whereas the 20,000, 18,000 and 10,000 MW peptides contained both SAI and SAII determinants, the 4000 MW peptide possessed only the SAI and the 6000 MW peptide the SAII determinant. The 4000-SAI peptide is of special significance, as the smallest SAI material separated in the past was 150,000 MW. This was difficult to purify and proved to be protective against dental caries on immunization of rhesus monkeys.

Antigens, Bacterial↗
PubMed1987

Recognition of carbohydrate and protein epitopes by monoclonal antibodies to a cell wall antigen from Streptococcus mutans.

The nature of the determinants recognized by a panel of monoclonal antibodies (MAbs) raised against a cell wall antigen of Streptococcus mutans (SA I/II) was investigated. Mild periodate oxidation of SA I/II showed that MAbs Guy 1, 2, 3, and 5 recognized carbohydrate epitopes on the antigen. Glycosidases were used to identify the nature of the sugars involved in their binding. Treatment with beta-glucosidase inhibited the binding of Guy 1, 2, 3, and 5 by 90%. No competition was found for any of the MAbs between SA I/II and a series of carbohydrates, including the serotype c polysaccharide from S. mutans. The results show that MAbs Guy 1, 2, 3, and 5 recognize carbohydrate epitopes on SA I/II which are distinct from the serotype polysaccharide. The other MAbs recognized protein epitopes on SA I/II.

Antibodies, Bacterial↗
PubMed1986

Separation of isoenzymes of citrate synthase and isocitrate dehydrogenase by fast protein liquid chromatography.

Fast protein liquid chromatography (FPLC) has been shown to be a rapid and effective method of separating isoenzymes of citrate synthase and isocitrate dehydrogenase in extracts of Pseudomonas aeruginosa and Acinetobacter calcoaceticus. The advantages of FPLC over conventional methods of fractionation are discussed and it is suggested that this may be a valuable and more general technique for isoenzyme resolution.

Acinetobacter↗
PubMed1986

Molecular size diversity of citrate synthases from Pseudomonas species.

Two forms of citrate synthase (EC 4.1.3.7) have been found in several species of Pseudomonas, a 'large' form (Mr congruent to 250,000) which is generally inhibited by NADH and reactivated by AMP, and a 'small' form (Mr congruent to 100,000) which is insensitive to these nucleotide effectors. Other species of Pseudomonas were found to contain either the 'large' or the 'small' form. Gel filtration and ion-exchange with the technique of fast protein liquid chromatography were used to resolve the enzymes. Where both citrate synthases were present, there did not appear to be an equilibrium between the two forms. The results reveal a new and complex diversity of citrate synthase within the genus Pseudomonas.

Chromatography, Gel↗
PubMed1983

Reversible effects of cross-linking on the regulatory cooperativity of Acinetobacter citrate synthase.

Citrate synthase was purified from Acinetobacter calcoaceticus and treated with the cleavable cross-linking reagent dithiobis(succinimidyl propionate). Cross-linking of the enzyme resulted in the abolition of the sigmoidal responses to inhibition by NADH and re-activation by AMP displayed by the native enzyme. Inhibition and re-activation were still observed but without any cooperativity. Cleavage of the disulphide bonds in the cross-links by treatment with dithiothreitol restored the sigmoidal characteristics of both inhibition and re-activation.

Acinetobacter↗