Simulation of Spatial and Temporal Variability of Chronic Copper Toxicity to Daphnia magna and Pseudokirchneriella subcapitata in Swedish and British Surface Waters

Water Quality Criteria (WQC) for metals are usually based on single species laboratory toxicity data. The influence of water characteristics of the surface waters on bioavailability to freshwater organisms is hence neglected, along with regional and temporal variability of these water characteristics. A methodology is presented to account for regional and temporal variability in the WQC setting for copper in the United Kingdom and Sweden. Bioavailability models were applied in a Monte-Carlo approach to account for temporal variability and a Geographic Information System was used to account for geographical variability on the chronic copper toxicity to Daphnia magna and Pseudokirchneriella subcapitata. Fifth percentiles of distributions of the No Observed Effect Concentration (NOEC) for both model species were derived in both study regions. For P. subcapitata, it was demonstrated that this fifth percentile can vary by a factor 10 in the UK study region. The ratio of these NOEC fifth percentiles (D. magna percentile divided by P. subcapitata percentile) was used to compare the ecotoxicity of copper to two model species. This ratio showed the highest variability (a factor 5) within the Swedish study region. The findings of this research stress the need for the use of region-specific WQC for copper.     

Validation of a fluid-structure interaction model of a heart valve using the dynamic mesh method in fluent

Simulations of coupled problems such as fluid-structure interaction (FSI) are becoming more and more important for engineering purposes. This is particularly true when modeling the aortic valve, where the FSI between the blood and the valve determines the valve movement and the valvular hemodynamics. Nevertheless only a few studies are focusing on the opening and closing behavior during the ejection phase (systole). In this paper, we present the validation of a FSI model using the dynamic mesh method of Fluent for the two-dimensional (2D) simulation of mechanical heart valves during the ejection phase of the cardiac cycle. The FSI model is successfully validated by comparing simulation results to experimental data obtained from in vitro studies using a CCD camera.     

Part of my story. The meaning and experiences of genes and genetics for sperm donor-conceived offspring

Existing empirical research often do not explain which concepts about genetics underlie the assumption that genetic information is deemed important for donor-conceived offspring. This study focused on how donor-conceived individuals following anonymous sperm donation give meaning to and make sense of genes and genetics. Analysis is based on focus groups and interviews with adult donor-conceived offspring. Findings suggest that genes are part of their specific context of being donor-conceived but also play a role in daily life. Genes make sense on an individual level and a relational level, both on parent-child as sibling-level. On an individual level they were perceived as (1) a biological starting package, (2) their own unique combination and (3) as a reference point. On a relational level, genes were seen as (1) “person-al”, (2) connecting and (3) locating individuals. This information is essential for those supporting/counseling donor conceived offspring and families as well as for policy-members.     

Molecular characterization of <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> isolates from various healthcare institutions in Nairobi,Kenya: a cross sectional study

Background

Staphylococcus aureus (S. aureus) has established itself over the years as a major cause of morbidity and mortality both within the community and in healthcare settings. Methicillin resistant S. aureus (MRSA) in particular has been a major cause of nosocomial infections resulting in significant increase in healthcare costs. In Africa, the MRSA prevalence has been shown to vary across different countries. In order to better understand the epidemiology of MRSA in a setting, it is important to define its population structure using molecular tools as different clones have been found to predominate in certain geographical locations.

Methods

We carried out PFGE, MLST, SCCmec and spa typing of selected S. aureus isolates from a private and public referral hospital in Nairobi, Kenya.

Results

A total of 93 S. aureus isolates were grouped into 19 PFGE clonal complexes (A–S) and 12 singletons. From these, 55 (32 MRSA and 23 MSSA) representative isolates from each PFGE clonal complex and all singletons were spa typed. There were 18 different MRSA spa types and 22 MSSA spa types. The predominant MRSA spa type was t037 comprising 40.6 % (13/32) of all MRSA. In contrast, the MSSA were quite heterogeneous, only 2 out of 23 MSSA shared the same spa type. Two new MRSA spa types (t13149 and t13150) and 3 new MSSA spa types (t13182, t13193 and t13194) were identified. The predominant clonal complex was CC 5 which included multi-locus sequence types 1, 8 and 241.

Conclusion

In contrast to previous studies published from Kenya, there’s marked genetic diversity amongst clinical MRSA isolates in Nairobi including the presence of well-known epidemic MRSA clones. Given that these clones are resident within our referral hospitals, adherence to strict infection control measures needs to be ensured to reduce morbidity and mortality associated with hospital acquired MRSA infections.

     

Comparison of the hemodynamic and thrombogenic performance of two bileaflet mechanical heart valves using a CFD/FSI model

The hemodynamic and the thrombogenic performance of two commercially available bileaflet mechanical heart valves (MHVs)--the ATS Open Pivot Valve (ATS) and the St. Jude Regent Valve (SJM), was compared using a state of the art computational fluid dynamics-fluid structure interaction (CFD-FSI) methodology. A transient simulation of the ATS and SJM valves was conducted in a three-dimensional model geometry of a straight conduit with sudden expansion distal the valves, including the valve housing and detailed hinge geometry. An aortic flow waveform (60 beats/min, cardiac output 4 l/min) was applied at the inlet. The FSI formulation utilized a fully implicit coupling procedure using a separate solver for the fluid problem (FLUENT) and for the structural problem. Valve leaflet excursion and pressure differences were calculated, as well as shear stress on the leaflets and accumulated shear stress on particles released during both forward and backward flow phases through the open and closed valve, respectively. In contrast to the SJM, the ATS valve opened to less than maximal opening angle. Nevertheless, maximal and mean pressure gradients and velocity patterns through the valve orifices were comparable. Platelet stress accumulation during forward flow indicated that no platelets experienced a stress accumulation higher than 35 dyne x s/cm2, the threshold for platelet activation (Hellums criterion). However, during the regurgitation flow phase, 0.81% of the platelets in the SJM valve experienced a stress accumulation higher than 35 dyne x s/cm2, compared with 0.63% for the ATS valve. The numerical results indicate that the designs of the ATS and SJM valves, which differ mostly in their hinge mechanism, lead to different potential for platelet activation, especially during the regurgitation phase. This numerical methodology can be used to assess the effects of design parameters on the flow induced thrombogenic potential of blood recirculating devices.     

Flow cytometric testing of green fluorescent protein-tagged Lactobacillus rhamnosus GG for response to defensins

Lactobacillus rhamnosus GG is of general interest as a probiotic. Although L. rhamnosus GG is often used in clinical trials, there are few genetic tools to further determine its mode of action or to develop it as a vehicle for heterologous gene expression in therapy. Therefore, we developed a reproducible, efficient electroporation procedure for L. rhamnosus GG. The best transformation efficiency obtained was 10(4) transformants per microg of DNA. We validated this protocol by tagging L. rhamnosus GG with green fluorescent protein (GFP) using the nisin-controlled expression (NICE) system. Parameters for overexpression were optimized, which allowed expression of gfp in L. rhamnosus GG upon induction with nisin. The GFP+ strain can be used to monitor the survival and behavior of L. rhamnosus GG in vivo. Moreover, implementation of the NICE system as a gene expression switch in L. rhamnosus GG opens up possibilities for improving and expanding the performance of this strain. The GFP-labeled strain was used to demonstrate that L. rhamnosus GG is sensitive to human beta-defensin-2 but not to human beta-defensin-1.     

Na(+)] in the subsarcolemmal 'fuzzy' space and modulation of [Ca(2+)](i) and contraction in cardiac myocytes

The strength of the heart beat depends on the amplitude and time course of the transient increase in [Ca(2+)] in the myocytes with each cycle. [Na(+)](i) modulates cardiac contraction through its effect on the Ca(2+) flux through the Na/Ca exchanger. Cardiac excitation-contraction coupling has been postulated to occur in a microdomain or 'fuzzy' space at the junction of the T-tubules and the sarcoplasmic reticulum. This 'fuzzy' space is well described for the Ca(2+) fluxes and the interaction between the L-type Ca(2+) channel, the Ca(2+) release channel of the sarcoplasmic reticulum and the Na/Ca exchanger. Co-localization of the Na(+) transporters, in particular the Na/K pump and the Na(+) channel, within this 'fuzzy' space is not as well established. The functional and morphological characteristics of the 'fuzzy' space for Na(+) and its interaction with the Ca(2+) handling suggest that this space is not strictly co-inciding with the Ca(2+) microdomain. In this space [Na(+)] can be several-fold higher or lower than [Na(+)] in the bulk cytosol. This has implications for modulation of [Ca(2+)](i) during a single beat as well as during alterations in Na(+) fluxes seen in pathological conditions.