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Biomedical subjects

D R Morgan

Publications and source records attributed to D R Morgan.

At least 19 recordsLinked to original sources
PubMed1995

Chloroplast gene sequence data suggest a single origin of the predisposition for symbiotic nitrogen fixation in angiosperms.

Of the approximately 380 families of angiosperms, representatives of only 10 are known to form symbiotic associations with nitrogen-fixing bacteria in root nodules. The morphologically based classification schemes proposed by taxonomists suggest that many of these 10 families of plants are only distantly related, engendering the hypothesis that the capacity to fix nitrogen evolved independently several, if not many, times. This has in turn influenced attitudes toward the likelihood of transferring genes responsible for symbiotic nitrogen fixation to crop species lacking this ability. Phylogenetic analysis of DNA sequences for the chloroplast gene rbcL indicates, however, that representatives of all 10 families with nitrogen-fixing symbioses occur together, with several families lacking this association, in a single clade. This study therefore indicates that only one lineage of closely related taxa achieved the underlying genetic architecture necessary for symbiotic nitrogen fixation in root nodules.

Base Sequence↗
PubMed1995

Intake of carbohydrate and its components--international comparisons, trends over time, and effects of changing to low-fat diets.

Carbohydrate constitutes the major source of dietary energy for all peoples of the world. However, it has been difficult to make accurate determinations of intakes of carbohydrate and its constituents because of lack of individual assessments in which carbohydrate components are included. For many countries, only food balance information is available and values for total carbohydrate are often derived by difference. Available information indicates that carbohydrate consumption decreased in many industrialized nations as prosperity led to an increased consumption of fat. Fat intakes have fallen over the past two decades and carbohydrate intakes have increased, but still do not approach the 60-70%contribution of carbohydrate to total energy in developing countries. A negative image for carbohydrate has led to a reluctance to accept it as a legitimate dietary component, particularly in North America. New evidence of the beneficial effects of starch in the diet indicates that increased consumption of carbohydrate, especially in the form of starch, should be promoted in Western countries.

Adult↗
PubMed1995

Effect of green lentils on colonic function, nitrogen balance, and serum lipids in healthy human subjects.

Green lentils are an increasingly popular food, but their effects on human colonic function and serum lipids have been studied little. Nine healthy males aged 19-38 y consumed for 3-wk periods a controlled Western diet and the same diet supplemented with 130 g dry lentils/d [which contained 11.8 g non-starch polysaccharide (NSP)] incorporated into loaves, cakes, and soups. Protein was equilibrated with soy protein isolate and carbohydrate with soft drinks. Radioopaque markers were used to calculate mean transit time (MTT) and to correct fecal weight for infrequency of bowel movements. Feces were collected throughout the study and blood was taken on 2 d at the end of each period. Lentils increased fecal weight from 131 +/- 12 g/d (means +/- SEM) to 189 +/- 17.4 g/d (44.9%) (P < 0.005). MTT was unchanged: 46 +/- 6 h for the control diet and 43 +/- 4 h for the lentils (NS). Fecal nitrogen was increased to 2.49 +/- 0.08 g/d for lentils compared with 1.74 +/- 0.09 g/d for the control diet (P < 0.001) and urine nitrogen decreased to 15.31 +/- 0.52 g/d with the lentils compared with 15.90 +/- 0.51 g/d for the control diet (P < 0.05); nitrogen balance was unaffected. Serum lipids were unchanged by addition of lentils to the diet. Green lentils were effective in increasing fecal weight and can therefore make a valuable contribution to a healthy diet.

Adult↗
PubMed1994

A high-throughput assay for cyclic nucleotide phosphodiesterases.

The search for cyclic nucleotide phosphodiesterase inhibitors in large chemical and natural product libraries is limited by assay throughput. A high-throughput assay that can monitor different phosphodiesterase activities would be useful for these inhibitor searches. We have developed a sensitive phosphodiesterase assay which is based on the selective precipitation of the radiolabeled 5'-nucleotide product by zinc and barium. This assay is unique to previous precipitation methods in that it measures product formed, either GMP or AMP. The procedure was adapted to a microtiter plate format for high-throughput, making it possible to perform in excess of 960 assays per day. This method was used to determine accurate enzyme kinetic constants for three different phosphodiesterases. The results agree favorably with literature values. Using the cyclic guanosine 3',5'-monophosphate-specific phosphodiesterase, IC50 values for the inhibitors M&B 22,948 and 3-isobutyl-1-methylxanthine were also determined. Demonstration of appropriate Km and inhibitor IC50 values verifies the ability of this new assay to identify selective cyclic nucleotide phosphodiesterase inhibitors.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1992

Motility as a factor in the colonisation of gnotobiotic piglets by Helicobacter pylori.

Non-motile variants of Helicobacter pylori (strain 26695) occurred with a frequency of 1.6 (SD 0.4) x 10(-4) variants/cell/division cycle, and reversion to the motile form occurred with a frequency of less than 10(-7) variants/cell/division cycle. The two forms remained greater than 90% pure for up to 50 cell divisions and differed only in the presence or absence of motility and flagella. Bacteria were recovered from nine of 10 gnotobiotic piglets inoculated orally with motile H. pylori, but from only two of eight inoculated with the non-motile variant. The motile form survived for 21 days in infected piglets, but the non-motile variant survived for only 6 days. Bacteria recovered from piglets inoculated with the non-motile variant were non-motile. These data support the hypothesis that motility is a colonisation factor for H. pylori.

Animals↗
PubMed1991

Biotype and macromolecular profiles of cytotoxin-producing strains of Helicobacter pylori from antral gastric mucosa.

Biotype, genome, protein and plasmid profile diversity amongst 40 epidemiologically unrelated strains of Helicobacter pylori was studied. Strains were API Zym biotypes II, III and IV but most (87%) were biotype II. Four subsets of strains were defined on a combination of motility (56% positive) and cytotoxin production (44% positive). A close association (P = 0.45) between these two features was observed for 69% of strains. Each strain of H. pylori had a unique DNA type defined by either HaeIII or HindIII total digest patterns and by ribopatterns, except for DNA of the rare strains not cut by these endonucleases. Strain diversity was confirmed by one-dimensional SDS-PAGE electrophoretic protein patterns. No consistent associations between cytotoxin activity and overall ribopattern or band subsets within a ribopattern were detected. Some strains (39%) contained a plasmid but the presence of plasmids was not consistently associated with either cytotoxin activity, biotype, motility or ribopattern. We conclude that the cytotoxin-producing strains of H. pylori were genomically as diverse as the non-cytotoxin producing strains.

Bacterial Proteins↗
PubMed1991

Differentiation of strains of Helicobacter pylori by numerical analysis of 1-D SDS-PAGE protein patterns: evidence for post-treatment recrudescence.

Twenty-three pre- and post-treatment isolates of Helicobacter pylori from the antral mucosa of eight patients with dyspepsia and gastritis were compared using 1-D SDS PAGE of proteins. The protein patterns were highly reproducible and were used as the basis for two numerical analyses. The first, based on the total protein patterns, showed that a number of the strains did not cluster with their respective patient set. This was thought to be due to differences in both mobility and intensity of proteins in the major band region. The second analysis, based on partial patterns, excluding the major band region (51-68 kDa), divided the clinical isolates into clearly defined groups corresponding to the patient sets. Although there was a degree of heterogeneity with respect to protein pattern between the pre- and post-treatment isolates of some patients, there was nonetheless clear evidence that each patient was harbouring strains of only a single type. These results suggested that patients were not being reinfected with a different strain but that there was recrudescence of the pre-treatment strain. Protein 'fingerprints' provided a precise and reproducible means of strain differentiation, and revealed that in each patient the same strain persisted after drug therapy even though there was marked patient-to-patient strain variation.

Bacterial Proteins↗
PubMed1991

Essential role of urease in pathogenesis of gastritis induced by Helicobacter pylori in gnotobiotic piglets.

A mutant strain of Helicobacter pylori with weak urease activity was created by using N-methyl-N'-nitro-N-nitrosoguanidine. The urease activity of the mutant (0.036 +/- 0.009 nmol of urea per micrograms of bacterial protein per min) was 0.4% of that of the parental strain (8.20 +/- 2.30 nmol of urea per micrograms of bacterial protein per min). The mutant was otherwise indistinguishable from the parental strain. Both demonstrated prominent catalase and oxidase activities, and both produced vacuolating cytotoxin. Restriction endonuclease and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns and ultrastructure were identical for the two strains. The mutant was fully motile, as evaluated by spreading in soft agar and by direct microscopic examination. Growth rate and colony size and morphology were identical for the mutant and parental strains. Seventeen gnotobiotic piglets were challenged with either the mutant or the parental strain and sacrificed 3 or 21 days after challenge. Gastric tissue was examined histologically and cultured for H. pylori. Of seven piglets challenged with the parental strain, all became infected. H. pylori was not recovered from any of 10 piglets challenged with the urease-negative strain. Lymphofollicular gastritis was present in all seven piglets challenged with the parental strain but in none of the piglets challenged with the urease-negative strain. These results suggest that prominent urease activity is essential for colonization by H. pylori.

Animals↗
PubMed1991

Comparison of isolates of Helicobacter pylori and Helicobacter mustelae.

On the basis of analysis of protein profiles, isolates of Helicobacter pylori and Helicobacter mustelae were less than 40% similar. Cytotoxin produced by H. pylori was not detected in isolates of H. mustelae. Both bacterial species agglutinated human erythrocytes. These results substantiate a taxonomic difference between H. pylori and H. mustelae.

Bacterial Proteins↗
PubMed1991

Gastritis associated with infection by Helicobacter pylori in humans: geographical differences.

Previous studies have indicated that infection rates of Helicobacter pylori are influenced by geographical factors. The present studies evaluate the characteristics of gastritis, associated with infection by H. pyrlori, and demonstrate relationships between different geographical locations and the extent of inflammatory cell accumulation in the gastric mucosa. Gastric biopsy specimens were obtained from patients infected with H. pylori at three clinical sites (two from North America and one from South America). Gastric inflammation was evaluated by quantitative histomorphometric techniques. Patients from South America had a more severe gastritis than did those from North America. Additionally, in South American patients the neutrophil was the predominant inflammatory cell type in the gastric mucosa. In contrast, the lymphocyte was the primary cell composing the mucosal infiltrate of infected North American subjects. Eosinophil infiltration into the mucosa correlated with the extent of mucosal atrophy; however, there were no differences between the North and South American patient populations in the extent of mucosal atrophy present in the specimens. We conclude that the characteristics (severity and cell type) of gastritis associated with infection by H. pylori are influenced by geographical factors that may be similar to those that modify infection rates for different geographical locations.

Adult↗
PubMed1991

Molecular techniques for studying the epidemiology of infection by Helicobacter pylori.

The efficacy of one-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell protein patterns for fingerprinting isolates of Helicobacter pylori was assessed by means of computerized numerical analysis. Virtually all strains were found to have unique, stable, and reproducible protein profiles. The application of this technique to a collection of isolates from eight patients showed clearly that each harboured a distinct strain that was present before treatment and persisted after treatment. This suggests that relapse was due to recrudescence of the same strain rather than re-infection with a different strain. Minor differences in protein banding profiles within sets of isolates from the same patient were evident, and this was confirmed by means of both two-dimensional PAGE protein patterns and restriction endonuclease analysis of DNA on the same strains.

DNA Fingerprinting↗
PubMed1991

Gastric spiral bacilli in captive cheetahs.

Two kinds of gastric spiral bacilli were identified in the stomachs of captive cheetahs with naturally occurring gastritis. One type was morphologically similar to 'Gastrospirillum hominis'. This organism could not be cultured in vitro. Some of these bacteria had superficial helical filaments, and others did not. The other type was morphologically, biochemically, and bacteriologically similar to Helicobacter pylori. This organism is most likely a new species of Helicobacter. One or both of these bacteria may have been responsible for the gastritis seen in these cheetahs.

Acinonyx↗
PubMed1991

Genomic variation in Helicobacter pylori: application to identification of strains.

DNA digest analysis, ribopatterns, and plasmid profiling were used to determine genomic variation in 55 strains of Helicobacter pylori from patients with gastritis in the USA, Peru, Australia, and the U.K. HaeIII-ribopatterns and total DNA digest patterns showed a high degree of heterogeneity, with at least 33 different genomic types among strains, including some sequential isolates. Plasmids, present in 51% of strains, were less useful as epidemiologic markers. Investigation of 14 multiple isolate sets showed that genotypic variants were present in pre- and post-treatment gastric mucosa, that relapse in some patients was due to reinfection by a genotypically different strain, and that the same strain persisted in most treatment failures. We conclude that molecular methods were excellent for precise identification of H. pylori, but ribopatterns had the advantages of reproducibility, high discrimination, and visual simplicity.

DNA Fingerprinting↗
PubMed1991

Simple noninvasive method to test efficacy of drugs in the eradication of Helicobacter pylori infection: the example of combined bismuth subsalicylate and nitrofurantoin.

Eradication of Helicobacter pylori infections has proved to be difficult. There is a need both for improved therapies and for ways to rapidly identify therapies that show sufficient promise to be worth pursuing. The objectives of this study were to evaluate the value of a therapeutic regimen of a bismuth salt plus nitrofurantoin for eradication of infection by H. pylori and to determine the validity/utility of the urea breath test in monitoring the progress of a clinical trial. We used an 80% eradication rule to define a promising therapeutic regimen, i.e., a regimen that eradicated the infection (no evidence of infection by H. pylori 4 wk after termination of therapy) in at least 80% of the individuals treated. Eighteen men (median age 38) with documented infection by H. pylori completed the study. At the end-of-study evaluation, H. pylori infection was eradicated (negative urea breath test, culture, and histology) in only one of 18 (5.5%) subjects; 15 were positive by the urea breath test, 16 by culture, 15 by Warthin-Starry stain, and 16 by the presence of acute-on-chronic inflammation. Using the 80% eradication rule, any one of these tests alone would have identified that the combination of antimicrobials tested was not effective in the eradication of the infection. We conclude that the urea breath test is a simple, noninvasive, cost-effective method to separate promising from unpromising candidate therapies and for the evaluation of new therapeutic concepts.

Adult↗
PubMed1990

Decontamination of instruments and control of cross infection in general practice.

OBJECTIVE: To assess the effectiveness of decontamination procedures in general practice. DESIGN: Anonymous postal questionnaire survey of 600 general practitioners randomly selected from the national register. SETTING: General practices throughout the United Kingdom. SUBJECTS: 382 General practitioners, a response rate of 65%. RESULTS: 186 General practitioners had autoclaves but 125 used hot water disinfectors or chemical disinfectants to reprocess instruments. 22% (474/2132) Of high risk instruments were inadequately decontaminated. Decontamination was performed by the practice nurse or receptionist in 306 practices. Knowledge of treatment of spillages of blood fluids was uncertain, and only 114 general practitioners used effective methods for dealing with spillages. CONCLUSIONS: A comprehensive central code of practice for control of infection is needed for primary health care staff.

Cross Infection↗