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Results for “Observer Variation”

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PubMed1978

Penetration of antimicrobials into tissue culture cells and leucocytes.

When exposed to HeLa cells in tissue culture for 72 hr., antimicrobials could be categorised into three groups characterised by cell associated concentrations much lower (ampicillin, cephalexin, cloxacillin, flucloxacillin, streptomycin and trimethoprim, all 14% or less), much higher (tetracycline and polymyxins) or approximating to those extracellularly (erythromycin, lincomycin, fusidic acid and gentamicin). For kanamycin, neomycin and sulphonamides, cell associated levels were between 24 and 47% and for penicillin G and cephaloridine were 66% of those extracellularly. With mouse peritoneal macrophages and human peripheral blood leucocytes cell associated levels for representative antibiotics were all lower after 3 hr. exposure than in the tissue culture cells. However, studies on the rate of release of cell associated antibiotic and of the effects of surface active agents indicated that the differences between cell types were due to loss of cell association during washing procedures to remove extracellular antibiotic. The effects of bactericidal antibiotics on survival of bacteria phagocytosed by mouse macrophages suggested that the cell association observed in tissue culture cells represented true intracellular penetration rather than mere binding to the cell surface. Within families of antibiotics, alterations to the molecule change cell penetration and the variations observed can not be explained merely in terms of simple diffusion, molecular size, dissociation constants, lipid solubility or protein binding.

Animals↗

PubMed1991

Anisocoria. Variation and clinical observation with different conditions of illumination and accommodation.

Variations in anisocoria in light and dark conditions are used to help diagnose normal and pathologic conditions; however, there have been few observations of anisocoria in different lighting and accommodative conditions. The authors measured pupil size photographically in a group of normal subjects examined in six conditions that were controlled for illumination and accommodation. Greater variation and average extent of anisocoria were found in conditions that resulted in larger pupil size. A subset of subjects repeated several sessions. For this group, the average value of anisocoria and variability tended to be greater in dark conditions. These results show that the observation of anisocoria varies under different conditions, and they suggest careful consideration of conditions used clinically to assess pupil equality. Our analysis shows that for a given observation threshold, conditions that produce even modest changes in variability can cause dramatic changes in the probability of observing anisocoria.

Accommodation, Ocular↗

PubMed1998

Measurement of ovalocyte frequency in peripheral blood smears in defining ovalocytosis in Papua New Guinea.

Red cell oval morphology is still the only accepted basis for the clinical or epidemiological diagnosis of ovalocytosis. Therefore it is important to know the errors when detecting and counting morphological ovalocytes. In all previous studies of ovalocytosis there was no assessment of the variation which may have occurred in classification due to smearing and staining techniques or the criteria for the diagnosis of ovalocyte morphology; nor was inter or intraobserver variation assessed. We report how different peripheral blood smear methods influence the diagnosis of ovalocytosis in populations in the Madang and East Sepik Provinces in Papua New Guinea. We also examined within and between observer variation in the quantitative assessment of ovalocytosis at x 40 and x 100 microscopy powers. A modified method of making a thin malaria blood smear gave the best preservation of red cell morphology and was adopted for the quantitative ovalocytosis studies. A special haematology smear is unnecessary. Ovalocyte frequency estimations were similar when x 40 and x 100 lenses were used, but x 40 was preferable for assessing morphology. Two observers were consistent in their findings and produced very similar results for the high-quality smears from the planned Madang survey, and rather different results for the smears from the unplanned routine Sepik survey. We conclude that measurement error for ovalocytosis assessment can be quite small and unimportant, minimized by careful planning and quality control. Otherwise measurement error is substantial and threatens validity of classification and grading of ovalocytosis.

Diagnostic Errors↗

PubMed1996

The role of individual susceptibility in cancer burden related to environmental exposure.

Individual susceptibility to cancer may result from host factors including differences n metabolism, DNA repair, altered expression of protooncogenes and tumor suppressor genes, and nutritional status. Since most carcinogens require metabolic activation before binding to DNA, variations in an individual's metabolic phenotype that have detected in enzymes involved in activation and detoxification should play an essential role in the development of environmental cancer. This phenotypic metabolic variation has now been related to genetic polymorphisms, and many genes encoding carcinogen-metabolizing enzymes have been identified and cloned. Consequently, allelic variants or genetic defects that give rise to the observed variation and new polymorphisms have been recognized. Development of simple polymerase chain reaction (PCR)-based assays has enabled identification of an individual's genotype for a variety of metabolic polymorphisms. Thus, recent knowledge of the genetic basis for individual metabolic variation has opened new possibilities of studies focusing on increased individual susceptibility to environmentally induced cancer, which are reviewed with special reference to smoking-induced lung cancer. Cancer susceptibility due to chemical exposure is likely to be determined by an individual's phenotype for a number of enzymes (both activating and detoxifying) relevant to that of a single carcinogen or mixtures of carcinogens. Given the number and variability in expression of carcinogen-metabolizing enzymes and the complexity of chemical exposures, assessment of a single polymorphic enzyme (genotype) may not be sufficient. Mutations in the p53 gene are among the most common genetic changes in human cancer. The frequency and type p53 mutations can act as a fingerprint of carcinogen exposure and may therefore provide information about external etiological agents, intensity of exposure, and host factors affecting the tumorigenesis process. In human lung cancer, p53 mutations (both the mutation pattern and frequency) have been linked with tobacco smoking; the type of mutation most frequently observed is G:C to T:A transversion, a mutation preferentially induced by benzo[a]pyrene diol epoxide. An association between the presence of this transversion and the genotype deficient in glutathione S-transferase M1-mediated detoxification has been observed in lung cancer. Taken together, these findings suggest that determination of metabolic at risk genotypes in combination with levels of DNA adducts in target (surrogate) tissues and the p53 mutation pattern should allow the identification of susceptible individuals and subgroups in carcinogen-exposed populations.

Carcinogens, Environmental↗

PubMed2005

Thromboxane synthase (TBXAS1) polymorphisms in African-American and Caucasian populations: evidence for selective pressure.

Thromboxane synthase (TBXAS1), a cytochrome P450 enzyme, converts prostaglandin H2 into thromboxane A2, a potent vasoconstrictor and inducer of platelet aggregation. Thromboxane A2 has been implicated in modulating cell cytotoxicity and in tumor growth and metastasis. Twelve coding-region variants were identified in the human TBXAS1 gene in 48 African-American and 46 Caucasian individuals, of which eight were amino-acid substitutions. The latter were confirmed in an independent Caucasian population (n=94 unrelated individuals). We performed an evolutionary analysis of patterns of nucleotide diversity and identified patterns of amino acid replacement in human-mouse comparisons consistent with purifying selection on an inter-species time scale using the McDonald-Kreitman test. We also observed patterns of nucleotide diversity within humans consistent with purifying selection acting on existing polymorphism using Tajima's D within coding regions. These evolutionary tests suggest that some of the rare coding variations observed in the human population are deleterious. We used two sequence-homology-based software programs and molecular modeling to predict the potential impact of these polymorphisms on TBXAS1 function. The c.772C>T (p.Lys258Glu), c.1249C>G (p.Gln417Glu), and c.1348G>A (p.Glu450Lys) substitutions are predicted as most likely to alter protein function; another, c.1352C>A (p.Thr451Asn), may also affect function. Given the evolutionary evidence, these variants may be functional and therefore of relevance for disease endpoints related to inflammation and angiogenesis, as well as for the pharmacogenetics of non-steroidal anti-inflammatory drugs.

Black or African American↗

PubMed1998

Observer and biological variation of a rapid whole blood D-dimer test.

In consecutive patients with suspected venous thromboembolism the interobserver variability of the SimpliRED D-dimer test was evaluated by two observers who independently scored one plate, the between assay variation was performed simultaneously by a third independent observer, who assessed a second plate. The biological variation was studied, 1-4 hours later by an independent evaluation. A total of 155 patients entered the study, venous thromboembolism was present in 42 patients (28%). The interobserver variability was 2/83 samples, with a kappa of 0.95 (95% confidence interval 0.88-1.0). The between assay variation was 2/98, with a kappa value of 0.96 (95% confidence interval 0.90-1.0). When testing the biological variation the observers disagreed in 2 of 69 patients (3%). The SimpliRED D-dimer assay has a good to excellent interobserver variability, between assay variation and reproducibility.

Adolescent↗

PubMed1997

Retrospective correction of surface coil MR images using an automatic segmentation and modeling approach.

The use of surface coils in magnetic resonance imaging offers significant improvements in the signal-to-noise ratio over volume coils for many applications. However, the inhomogeneous reception profile of surface coils hampers their usefulness by introducing significant nonuniformities or intensity variations which can vary by greater than six-fold across the sample. In this study, we evaluated an automatic technique for retrospective correction of intensity variations observed in a high-resolution surface coil MR image of the rat brain obtained using an adiabatic magnetic resonance imaging sequence. The images are shown to have a coefficient of variation less than 12% following application of this correction algorithm. This image intensity correction technique can be applied retrospectively to all data sets and corrects both sample/patient dependent effects (e.g. attenuation of overlying tissue) or sample independent effects (e.g. coil geometry or position). This approach should also prove valuable in improving regions of interest analysis, volume histograms and thresholding techniques.

Animals↗

PubMed1999

A quantitative trait locus of Agaricus bisporus resistance to Pseudomonas tolaasii is closely linked to natural cap color.

A quantitative trait locus (QTL) of resistance to Pseudomonas tolaasii was detected in Agaricus bisporus using a cross between a wild strain from the Sonoran desert and a cultivated strain. The resistance QTL was strongly linked with the brown color allele of PPC1. This QTL explained about 30% of the variation observed for living bacteria-induced symptoms. The use of bacterial toxin did not reproduce living bacteria symptoms but revealed the same QTL. The latter QTL was not affected by environmental variation. No relation was found between the resistance QTL and the tyrosinase gene, which is involved in the browning process.

Agaricus↗

PubMed2001

Seasonal variation of antioxidant and biotransformation enzymes in barnacle, Balanus balanoides, and their relation with polyaromatic hydrocarbons.

Seasonal variations in the antioxidant enzymes (catalase, superoxide dismutase [SOD], NADH-DT diaphorase), biotransformation enzyme, glutathione-S-transferase (GST) and microsomal lipid peroxidation in digestive tissue of barnacle, Balanus balanoides, from polluted and non-polluted populations have been evaluated. Relationships with accumulated polyaromatic hydrocarbon (PAH) concentration in barnacle tissues and environmental parameters (water temperature, salinity, dissolved oxygen concentration, water pH) were determined. As a general trend, maximum antioxidant enzyme and GST activities were detected in the pre-monsoon period or summer (March-June) followed by a gradual decrease during the monsoon (July October) with a minimum in the post-monsoon period or winter (November February). This pattern was similar to tissue concentrations of PAHs, resulting in a significant positive correlation with antioxidant enzymes, mainly catalase and SOD. Microsomal lipid peroxidation exhibited an almost reverse trend of seasonal variation to that of antioxidant enzyme activities indicating an enhanced susceptibility of barnacle tissues to oxidative stress. Among the environmental parameters, only water temperature seemed to have a significant effect on observed variations of antioxidant enzymes and GST activities. The barnacles from polluted and non-polluted populations exhibited seasonal differences in the activities of all the enzymes studied, particularly catalase, SOD and GST, suggesting the possibility of some biochemical adaptation in organisms from a chronically polluted environment. The results indicated that antioxidant defense components, catalase and SOD, are sensitive parameters that could be useful biomarkers for the evaluation of contaminated aquatic ecosystems. The results also suggested the potentiality of barnacle, B. balanoides, as a bioindicator organism against organic pollution.

Animals↗

PubMed2006

A shortened, 2-hour rifampin test: a useful tool in Gilbert's syndrome.

INTRODUCTION: Diagnosis of Gilbert's disease often involves unnecessary testing and patient anxiety. Rifampin test can support the diagnosis; it has been described in short series and lacks standardization in dose, collection times, result presentation and interpretation. Our objective was to compare the response to oral rifampin in a series of patients with Gilbert's disease, 2 and 4 h after drug administration. PATIENTS AND METHODS: Eighty-nine patients with Gilbert's disease (elevated total bilirubin with no hepatopathy or hemolysis) were recruited. After a basal blood collection, 900 mg rifampin were administered per os and new samples were drawn 2 and 4 h later. Total and esterified bilirubin were measured in every sample. Haptoglobin concentration was also analyzed. RESULTS: When expressed as relative increase with respect to basal values, variations observed 2 h after rifampin intake were all above 15%. A significant correlation (r = 0.902; p = 0.000) was found between relative increases 2 and 4 h after drug administration. No significant variations were found in haptoglobin concentrations. CONCLUSION: Rifampin test is useful in diagnosing Gilbert's disease, but variations in total bilirubin concentrations (basal and post-rifampin) make that no absolute cut-off value can be used. Correlation between 2- and 4-h relative increases suggests that a shortened version could simplify the test.

Adult↗

PubMed1991

Amino acid substitutions at tryptophan-51 of cytochrome c peroxidase: effects on coordination, species preference for cytochrome c, and electron transfer.

Amino acid replacements of an aromatic residue, Trp-51, which is in contact with the heme of yeast cytochrome c peroxidase have a number of significant effects on the kinetics and coordination state of the enzyme. Six mutants at this site (W51F, W51M, W51T, W51C, W51A, and W51G) were examined. Optical and EPR spectra show that each of these mutations introduces a shift from the 5-coordinate to 6-coordinate form, and slightly increases the asymmetry of the heme ligand field. Conversion from a 6-coordinate high-spin form at pH 5 to a 6-coordinate low-spin form at pH 7 is observed for several of the variants (W51F, W51T, and W51A), while W51G and W51C appear as predominantly low-spin species between pH 5 and 7. Addition of 50% glycerol prevents the facile conversion to the low-spin conformation for W51F, W51T, and W51A, and only W51F can be stabilized in a 5-coordinate configuration by glycerol. For the oxidation of cytochrome c by H2O2, three of the variants (W51F, W51M, and W51T) exhibit values of kcat(app) that are greater than for the wild-type enzyme, while the other mutations give decreased rates of enzyme turnover. Unlike the wild-type enzyme, which functions more efficiently with cytochrome c from yeast than with the horse heart protein, the mutant W51F does not show a preference for substrate from its native organism. The three mutants which exhibit increased values of kcat(app) show a pH optimum at 6.8 compared with that of 5.25 for the wild-type enzyme when measured with horse heart cytochrome c. This shift in pH optimum is not observed with yeast cytochrome c. Construction of single and multiple mutations at Trp-51, Ile-53, and Gly-152 shows that these kinetic properties are not due to natural amino acid variations observed at these sites. Pre-steady-state kinetics show that the bimolecular rate constant for the fast phase of the reaction of the enzyme with H2O2 is only slightly decreased from 3.03 (0.09) X 10(7) to 2.2 (0.1) X 10(7) M-1 s-1 for W51F and to 1.5 (0.1) X 10(7) M-1 s-1 for W51A. The slow phase of the reaction (4.9 s-1) which contributes approximately 30% to the amplitude of the change for the wild-type enzyme is not observed for W51F or W51A.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗

PubMed2005

Toward a biotic ligand model for freshwater green algae: surface-bound and internal copper are better predictors of toxicity than free Cu2+-ion activity when pH is varied.

The freshwater green microalgae Chlorella sp. and Pseudokirchneriella subcapitata (P. subcapitata) were chronically (48 and 72 h, respectively) exposed to copper at various pH levels, i.e., pH 6-7.5 and pH 5.9-8.5, respectively. Concentrations resulting in 50% inhibition of exponential growth rate (EC50) were determined as dissolved Cu, estimated chemical activity of the free Cu2+ ion (as pCu = - log{Cu2+ activity as molarity}), and as external (surface-bound) Cu and internal Cu in the algal cells. With increasing pH, EC50dissolved decreased from 30 to 1.1 microg of Cu L(-1) for Chlorella sp. and from 46 to 18 microg of Cu L(-1) for P. subcapitata. The pH effect on copper toxicity was even more obvious when expressed as Cu2+ activity. The EC50pCu increased on average 1.4 pCu unit per pH unit for Chlorella sp. and 1.1 pCu unit per pH unit for P. subcapitata, thus indicating a marked increase of Cu2+ toxicity at higher pH (more than 1 order of magnitude per pH unit). In contrast, it was found that EC50 values expressed as surface bound or external copper (EC50external) and as internal copper (EC50internal) did not vary substantially when pH was increased. External Cu was operationally defined as the Cu fraction removable from the algal cell by short-term contact with ethylenediaminetetraacetic acid; internal copper was defined as the nonremovable fraction. For Chlorella sp. the EC50external varied between 5 and 10 fg of Cu/ cell (factor of 2 difference) and the EC50internal between 25 and 40 fg of Cu/cell (factor of 1.6 difference). For P. subcapitata the EC50external varied between 10 and 28 fg of Cu/cell (factor of 2.8 difference) and the EC50internal between 42 and 71 fg of Cu/cell (factor of 1.7 difference). Because the observed variation in EC50external and EC50internal is much less than the variation in EC50Cu2+, it is concluded that both external and internal copper are better predictors of copper toxicity than Cu2+ when pH is varied. From the perspective of toxicity modeling, this observation is the first step toward considering the use of the cell surface as the algal biotic ligand for Cu in a similar way as fish gills fulfill this role in the biotic ligand model for predicting metal toxicity to fish species.

Chlorophyta↗

PubMed2002

Genetic differentiation, gene flow and the origin of infestations of the medfly, Ceratitis capitata.

The genetic structure of natural populations of the economically important dipteran species Ceratitis capitata was analysed using both biochemical and molecular markers. This revealed considerable genetic variation in populations from different geographic regions. The nature of this variation suggests that the evolutionary history of the species involved the spread of individuals from the ancestral African populations through Europe and, more recently, to Latin America, Hawaii and Australia. The observed variation can be explained by various evolutionary forces acting differentially in the different geographic areas, including genetic drift, bottleneck effects, selection and gene flow. The analysis of the intrinsic variability of the medfly's genome and the genetic relationships among populations of this pest is a prerequisite for any control programme.

Africa↗

PubMed2004

Wing shape heritability and morphological divergence of the sibling species Drosophila mercatorum and Drosophila paranaensis.

The fruit-flies Drosophila paranaensis and Drosophila mercatorum pararepleta are sibling species belonging to the repleta group. Females of these two species are normally considered to be morphologically indistinguishable while males only differ consistently in the morphology of their genitalia. These species are sympatric throughout a large area of their geographic distribution. In this study, we investigated the degree of morphological divergence between D. paranaensis and D. mercatorum pararepleta based on morphometric analysis of their wings. The ellipse method was used to describe the placement of the longitudinal and transversal wing veins as well as the size of the wing and the shape of its outline. The heritability under laboratory and field conditions was also estimated from the parameters generated. Multivariate analysis showed that wing morphology possessed sufficient differences to discriminate between the two species with a successful classification rate of 95-98% for females and 82-87% for males. The results of the autoclassification were confirmed by a cross-validation test for females (92-96%). Most measurements possessed significant natural heritability (a mean of 0.48 for D. mercatorum and 0.88 for D. paranaensis), indicating that the variation observed was related to differences in genes acting additively. The principal difference between the two species was in the placement of the posterior transverse wing vein. However, the pattern of morphological variation in the wings of both species was similar, possibly because of shared restrictions in wing development pathways.

Animals↗

PubMed2003

The regionality of campylobacteriosis seasonality in New Zealand.

New Zealand has one of the highest incidences of campylobacteriosis in the developed world, which leads a global trend of increasing notifications of Campylobacter infections over the last decade. Foodborne and waterborne transmission have been implicated as significant mechanisms in the complex ecology of the disease in New Zealand. We examined both regional and temporal variation in notification rates to gain some insight into the role of the New Zealand environments in modifying disease incidence. Firstly, there is a marked difference in the seasonality of campylobacteriosis between the North and South Islands of New Zealand. The Far North and much of the rural North Island were found to display relatively low summer incidence and small inter-seasonal variation. Secondly, there appears to be a dispersed grouping of North Island urban areas, including Auckland, Hamilton, Napier and their hinterlands as well as a few areas on the South Island that exhibit higher summer incidence and more seasonality than the first group. Thirdly, Christchurch, Dunedin, much of the South Island and the lower North Island cities of Wellington and Upper Hutt appear to experience the highest summer incidence and strongest inter-seasonal variation in New Zealand. These three broad groupings of campylobacteriosis seasonality, constructed using a principal components analysis, suggest that the importance of transmission routes may vary regionally in New Zealand. The observed variation in seasonal incidence indicates a complex ecology that is unlikely to be explained by a single dominant transmission route across these three groupings.

Campylobacter Infections↗

PubMed1997

Variability in PAH-DNA adduct measurements in peripheral mononuclear cells: implications for quantitative cancer risk assessment.

Biomarkers such as DNA adducts have significant potential to improve quantitative risk assessment by characterizing individual differences in metabolism of genotoxins and DNA repair and accounting for some of the factors that could affect interindividual variation in cancer risk. Inherent uncertainty in laboratory measurements and within-person variability of DNA adduct levels over time are putatively unrelated to cancer risk and should be subtracted from observed variation to better estimate interindividual variability of response to carcinogen exposure. A total of 41 volunteers, both smokers and nonsmokers, were asked to provide a peripheral blood sample every 3 weeks for several months in order to specifically assess intraindividual variability of polycyclic aromatic hydrocarbon (PAH)-DNA adduct levels. The intraindividual variance in PAH-DNA adduct levels, together with measurement uncertainty (laboratory variability and unaccounted for differences in exposure), constituted roughly 30% of the overall variance. An estimated 70% of the total variance was contributed by interindividual variability and is probably representative of the true biologic variability of response to carcinogenic exposure in lymphocytes. The estimated interindividual variability in DNA damage after subtracting intraindividual variability and measurement uncertainty was 24-fold. Inter-individual variance was higher (52-fold) in persons who constitutively lack the Glutathione S-Transferase M1 (GSTM1) gene which is important in the detoxification pathway of PAH. Risk assessment models that do not consider the variability of susceptibility to DNA damage following carcinogen exposure may underestimate risks to the general population, especially for those people who are most vulnerable.

Adult↗

PubMed1988

Genetic variants of influenza A/Taiwan/1/86 cocirculating in Canada during the winter of 1986 to 1987.

The first isolate of influenza virus in Canada during the winter of 1986 to 1987 was a genetic variant of A/Taiwan/1/86. This genetic variant type was the predominant strain obtained from several of the western provinces. The variant strains were antigenically indistinguishable from A/Taiwan/1/86 but were remarkably distinct by T1 oligonucleotide mapping. T1 mapping of individual genome segments indicated that the variants evolved from an A/Taiwan/1/86-like virus through the accumulation of point mutation or deletion or insertion events and probably do not contain foreign genes. The relative distribution of genetic variation was approximately equal among the individual genes, with the possible exception of segments 1 or 2 that were analyzed in combination and thus could not be individually associated with the observed variation.

Canada↗

PubMed1974

Deep sea sedimentation.

An important problem in the study of microparticles in the marine environment, suspended in the water column or deposited as sediment on the ocean bottom, is the determination of provenance of the microparticles-where did they come from and by what processes were they transported to the sampling location? Two techniques of possible interest to those concerned with tracing the origins and dispersion paths of asbestos particles are described. One utilizes variations in the naturally occurring rubidium-strontium isotope system and is used to characterize a bulk sample, i.e., a large number of particles. The other utilizes scanning electron microscopy to observe variations in surface texture of individual grains which, in the case of quartz particles in the natural environment, can be related to the transport processes to which they have been subjected.

Asbestos↗