Home About us Contact
|
Home About us Contact | ||
|
|
||
Strain Variation (strain + variation)
Selected AbstractsLimited genetic diversity of Candida albicans in fecal flora of healthy volunteers and inpatients: a proposed basis for strain homogeneity in clinical isolatesMYCOSES, Issue 9-10 2002R. Khatib Candida albicans; Gastrointestinalflora; Molekulare Typisierung Summary. Molecular analysis of Candida albicans isolates from individual patients often yields a single strain at multiple sites. Whether this strain-limitation is due to virulence factors favoring the invasive strain or to lack of genetic diversity in the gastrointestinal reservoir is uncertain. We elected to study C. albicans genotypes in the fecal flora among healthy volunteers and inpatients. Self-obtained stool swabs or stool samples were cultured on inhibitory mold agar. From each subject with C. albicans, nine colonies were randomly selected, individually propagated, and typed utilizing random amplified polymorphic DNA. Colonies were considered identical (all bands matched), related variants (one to three unique bands), or distinct strains (more than three unique bands). Analysis showed a single clone in 33/43 (76.7%) volunteers and 6/18 (33.3%) inpatients (P = 0.018), two to four related variants in eight (18.6%) volunteers and 10 (55.6%) inpatients, and two distinct strains in two volunteers (4.6%) and two inpatients (11.1%). Strain variation was more common in females (33.5 versus 5.6%; P = 0.04) and tended to increase with age (r = 0.245, P = 0.06). These findings illustrate that most healthy subjects harbor a single strain of C. albicans in the fecal flora. This strain may undergo genetic evolution leading to minor clonal variations. The mechanisms for strain selection, maintenance and possible evolution remain to be delineated. Zusammenfassung. Molekularanalysen von Candida albicans -Isolaten von individuellen Patienten zeigen oft einen individuellen Stamm an mehreren Lokalisationen. Ob diese Beschränkung auf einer Förderung durch Virulenzfaktoren des beherbergten Stammes oder auf einem Mangel an genetischer Diversität im Gastrointestinaltrakt beruht, ist unbekannt. Wir untersuchten daher die C. albicans Genotypen in der Fäkalflora von Gesunden und von Krankenhauspatienten. Selbstgewonnene Stuhlabstriche und Stuhlproben wurden auf einem schimmelpilzhemmenden Nährmedium kultiviert. Von jedem Probanden wurden 9 Kolonien randomisiert ausgewählt, individuell subkultiviert und RAPD-typisiert. Die Kolonien wurden wie folgt bewertet: klonal identisch: sämtliche Banden identisch; klonal verwandt: 1,3 Banden nicht identisch; klonal unterschiedlich: >,3 Banden nicht identisch. Die Analyse zeigte Klonidentität bei 33/43 (77%) Gesunden und 6/18 (33%) bei Hospitalisierten (P = 0.018); Klonverwandtschaft wurde bei 8 (19%) Gesunden und 10 (56%) Hospitalisierten gefunden und zwei Hospitalisierten (11%). Klonvariation war häufiger bei Frauen (33.5 vs. 5.6%; P = 0.04) und nahm mit dem Lebensalter zu (r = 0.245, P = 0.06). Diese Resultate belegen, dass die Mehrzahl Gesunder jeweils nur einen Stamm in der Fäkalflora beherbergt. Dieser kann genetisch geringgradig klonal variieren. Die hierbei wirksamen Mechanismen bedürfen noch der Aufklärung. [source] A deconvolution method for the reconstruction of underlying profiles measured using large sampling volumesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006Y.-S. Xiong A deconvolution method for diffraction measurements based on a statistical learning technique is presented. The radial-basis function network is used to model the underlying function. A full probabilistic description of the measurement is introduced, incorporating a Bayesian algorithm based on an evidence framework. This method allows predictions of both the convolution and the underlying function from noisy measurements. In addition, the method can provide an estimation of the prediction uncertainty, i.e. error-bars. In order to assess the capability of the method, the model was tested first on synthetic data of controllable quality and sparsity; it is shown that the method works very well, even for inaccurately measured (noisy) data. Subsequently, the deconvolution method was applied to real data sets typical of neutron and synchrotron residual stress (strain) data, recovering features not immediately evident in the large-gauge-volume measurements themselves. Finally, the extent to which short-period components are lost as a function of the measurement gauge dimensions is discussed. The results seem to indicate that for a triangular sensor-sensitivity function, measurements are best made with a gauge of a width approximately equal to the wavelength of the expected strain variation, but with a significant level of overlap (,80%) between successive points; this is contrary to current practice for neutron strain measurements. [source] Epidemiology of meningococcal disease in AustraliaJOURNAL OF PAEDIATRICS AND CHILD HEALTH, Issue 2001J Jelfs Abstract: A review of the epidemiology of meningococcal disease (MD) in Australia was undertaken, with particular emphasis on the 1990s, when national strain differentiation data became available. The data included a review of clinical and laboratory notification data and published reports on clusters and outbreaks. There have been considerable changes in the patterns of MD in the 1990s. In some cases, these changes can be related to the dominance of a particular phenotype. In the early 1990s, widely scattered urban and rural clusters were associated with the phenotype C:2b:P1.2 and strains were closely genetically related. Larger urban clusters and increased numbers of cases in adolescents and young adults were most obvious in New South Wales in the mid-1990s and were associated with a phenotype C:2a:P1.5. This ET-15 clone of the ET-37 complex caused similar patterns of MD to those seen in other countries as part of the global spread of the clone. In contrast, the B:4:P1.4 phenotype, with close genetic similarities to New Zealand strains, did not cause the hyperendemic disease seen in New Zealand this decade. The epidemiology of MD will continue to exhibit considerable variation due, at least in part, to the genetic flexibility of meningococci. Information about strain variation expands our understanding of changing patterns of disease. [source] Determination of the In Vitro Susceptibility of Feline Tritrichomonas foetus to 5 Antimicrobial AgentsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 5 2007Elizabeth J. Kather Background: The nitroimidazole, ronidazole, has been demonstrated to have in vitro and in vivo activity against the protozoan Tritrichomonas foetus in cats. The purpose of this study was to evaluate the in vitro susceptibility of feline T foetus isolates obtained from naturally infected cats to 5 antimicrobial agents and to compare the in vitro time kill of ronidazole and metronidazole. Hypothesis: We hypothesized that nitroimidazoles have in vitro activity against T foetus, whereas furazolidone, omeprazole, and paromomycin do not. Animals: Fecal specimens were cultured from 4 naturally infected Bengal cats with a history of T foetus -associated diarrhea. Methods: A 24-hour susceptibility assay was performed on all 4 isolates for the 5 antimicrobial agents. A time-kill microdilution method was performed on 2 isolates for metronidazole and ronidazole. Results: Paromomycin and omeprazole showed no in vitro effect at concentrations ±80 ,g/mL. There was no significant difference in 24-hour susceptibilities among metronidazole, ronidazole, and furazolidone. In addition, only the results of the highest concentration tested (80 ,g/mL) and concentrations of 1.25 and 2.5 ,g/mL revealed significant differences in the rate of trophozoite killing, with ronidazole having a faster reduction in trophozoite survival. Conclusions and Clinical Importance: Time-kill assays demonstrated ronidazole had a higher lethal activity compared with metronidazole. These findings contrast with a previously published report and may reflect strain variation, different methodologies, or both. The lack of clinical response seen with metronidazole administration to treat feline trichomoniasis may not reflect inherent resistance but rather in vivo events involving drug distribution and pharmacokinetics. [source] A review of molecular techniques to type Candida glabrata isolatesMYCOSES, Issue 6 2010S. Abbes Summary Candida glabrata has emerged as a common cause of fungal infection causing mucosal and systemic infections. This yeast is of concern because of its reduced antifungal susceptibility to azole antifungals such as fluconazole. A clear understanding of the epidemiology of Candida infection and colonisation required a reliable typing system for the evaluation of strain relatedness. In this study, we discuss the different molecular approaches for typing C. glabrata isolates. Recent advances in the use of molecular biology-based techniques have enabled investigators to develop typing systems with greater sensitivities. Several molecular genotypic approaches have been developed for fast and accurate identification of C. glabrata in vitro. These techniques have been widely used to study diverse aspects such as nosocomial transmission. Molecular typing of C. glabrata could also provide information on strain variation, such as microvariation and microevolution. [source] The tectonic regime along the Andes: Present-day and Mesozoic regimesGEOLOGICAL JOURNAL, Issue 1 2010Victor A. Ramos Abstract The analyses of the main parameters controlling the present Chile-type and Marianas-type tectonic settings developed along the eastern Pacific region show four different tectonic regimes: (1) a nearly neutral regime in the Oregon subduction zone; (2) major extensional regimes as the Nicaragua subduction zone developed in continental crust; (3) a Marianas setting in the Sandwich subduction zone with ocean floored back-arc basin with a unique west-dipping subduction zone and (4) the classic and dominant Chile-type under compression. The magmatic, structural and sedimentary behaviours of these four settings are discussed to understand the past tectonic regimes in the Mesozoic Andes based on their present geological and tectonic characteristics. The evaluation of the different parameters that governed the past and present tectonic regimes indicates that absolute motion of the upper plate relative to the hotspot frame and the consequent trench roll-back velocity are the first order parameters that control the deformation. Locally, the influences of the trench fill, linked to the dominant climate in the forearc, and the age of the subducted oceanic crust, have secondary roles. Ridge collisions of seismic and seismic oceanic ridges as well as fracture zone collisions have also a local outcome, and may produce an increase in coupling that reinforces compressional deformation. Local strain variations in the past and present Andes are not related with changes in the relative convergence rate, which is less important than the absolute motion relative to the Pacific hotspot frame, or changes in the thermal state of the upper plate. Changes in the slab dip, mainly those linked to steepening subduction zones, produce significant variations in the thermal state, that are important to generate extreme deformation in the foreland. Copyright © 2009 John Wiley & Sons, Ltd. [source] A finite element formulation for thermoelastic damping analysisINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2009Enrico Serra Abstract We present a finite element formulation based on a weak form of the boundary value problem for fully coupled thermoelasticity. The thermoelastic damping is calculated from the irreversible flow of entropy due to the thermal fluxes that have originated from the volumetric strain variations. Within our weak formulation we define a dissipation function that can be integrated over an oscillation period to evaluate the thermoelastic damping. We show the physical meaning of this dissipation function in the framework of the well-known Biot's variational principle of thermoelasticity. The coupled finite element equations are derived by considering harmonic small variations of displacement and temperature with respect to the thermodynamic equilibrium state. In the finite element formulation two elements are considered: the first is a new 8-node thermoelastic element based on the Reissner,Mindlin plate theory, which can be used for modeling thin or moderately thick structures, while the second is a standard three-dimensional 20-node iso-parametric thermoelastic element, which is suitable to model massive structures. For the 8-node element the dissipation along the plate thickness has been taken into account by introducing a through-the-thickness dependence of the temperature shape function. With this assumption the unknowns and the computational effort are minimized. Comparisons with analytical results for thin beams are shown to illustrate the performances of those coupled-field elements. Copyright © 2008 John Wiley & Sons, Ltd. [source] Enrichment of enhanced assumed strain approximations for representing strong discontinuities: addressing volumetric incompressibility and the discontinuous patch testINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2004J. E. Dolbow Abstract We present a geometrically non-linear assumed strain method that allows for the presence of arbitrary, intra-finite element discontinuities in the deformation map. Special attention is placed on the coarse-mesh accuracy of these methods and their ability to avoid mesh locking in the incompressible limit. Given an underlying mesh and an arbitrary failure surface, we first construct an enriched approximation for the deformation map with the non-linear analogue of the extended finite element method (X-FEM). With regard to the richer space of functions spanned by the gradient of the enriched approximation, we then adopt a broader interpretation of variational consistency for the construction of the enhanced strain. In particular, in those elements intersected by the failure surface, we construct enhanced strain approximations which are orthogonal to piecewise-constant stress fields. Contrast is drawn with existing strong discontinuity approaches where the enhanced strain variations in localized elements were constructed to be orthogonal to constant nominal stress fields. Importantly, the present formulation gives rise to a symmetric tangent stiffness matrix, even in localized elements. The present modification also allows for the satisfaction of a discontinuous patch test, wherein two different constant stress fields (on each side of the failure surface) lie in the solution space. We demonstrate how the proposed modifications eliminate spurious stress oscillations along the failure surface, particularly for nearly incompressible material response. Additional numerical examples are provided to illustrate the efficacy of the modified method for problems in hyperelastic fracture mechanics. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||