Post-infarct VT substrate ablation based on evoked delayed potential elimination as well-defined target: results from a prospective multicenter study

Background

In patients with VT after myocardial infarction (MI), substrate-based ablation is superior to approaches that target clinical and tolerated VTs only. Different substrate modification strategies have been reported. However, proposed ablation targets are prone to operator interpretation (e.g. abnormal electrograms). Accordingly, ablation results can also be operator dependent. Evoked delayed potentials (EDP) are a well-defined target. Elimination of EDP has been effective to prevent VT recurrence in a retrospective, single center cohort.

Aim

(1)To evaluate the outcome of EDP ablation in a prospective cohort of patients included on an intention-to-treat principle and (2)to assess the outcome of EDP ablation following one uniform protocol when performed in centers without prior experience with this strategy.

Methods

Consecutive patients referred for post-MI VT ablation were prospectively enrolled in one center with extensive experience in EDP ablation and 5 centers with no prior experience. Substrate mapping focused on EDP identification followed a uniform protocol across all centers. In brief, all electrograms located within the infarct area were analyzed during sinus rhythm, RV pacing at a fixed rate and during the application of one short-coupled RV extra-stimulus (S2). Sites showing low-voltage, nearfield electrograms with >10ms delay or block in response to S2 were categorized as EDP and targeted for ablation. After ablation, re-mapping to confirm EDP elimination and a complete stimulation protocol (up to 4 extra's from RV and LV) were performed. Patients were followed for VT recurrence and mortality.

Results

130 patients (69±10 years, 87% men, 42% anterior MI, LVEF 34% (IQR 24–43), 71% NYHA II–III, 42% on amiodarone, 52% ≥1 ICD shock, 22% with electrical storm or incessant VT) were included. The extra-stimulation protocol was systematically conducted in 127 (98%) patients and in 121 (93%), EDPs were identified. EDPs were successfully eliminated in 117/121 (97%) patients. After 23 (IQR 14–35) min of RF, 102 (78%) patients were rendered non-inducible. Median procedural duration was 212 (IQR 179–262) min. During follow-up of 14 (IQR 8–18) months, 36 (28%) patients had VT recurrence and 13 (10%) died or received a LVAD. VT-free survival was 79% (95% CI: 72–86) and 72% (95% CI: 63–80) at 6 and 12 months follow-up. Of note, VT-free survival at 12 month was not significantly different between patients undergoing the procedure in centers with and without prior experience in EDP ablation (76% (95% CI: 61–90) vs. 70% (95% CI: 59–81); P=0.269).

Conclusion

In a large prospective cohort of patients with post-MI VT, substrate ablation based on EDP elimination resulted in excellent long-term outcome. Of importance, procedural outcomes were similar in centers with or without experience in EDP ablation, indicating that this approach can be easily reproduced by operators previously not familiar with the technique.

Funding Acknowledgement

Type of funding sources: None.

Cell Boundary Confinement Sets the Size and Position of the E. coli Chromosome

Although the spatiotemporal structure of the genome is crucial to its biological function, many basic questions remain unanswered on the morphology and segregation of chromosomes. Here, we experimentally show in Escherichia coli that spatial confinement plays a dominant role in determining both the chromosome size and position. In non-dividing cells with lengths increased to 10 times normal, single chromosomes are observed to expand > 4-fold in size. Chromosomes show pronounced internal dynamics but exhibit a robust positioning where single nucleoids reside robustly at mid-cell, whereas two nucleoids self-organize at 1/4 and 3/4 positions. The cell-size-dependent expansion of the nucleoid is only modestly influenced by deletions of nucleoid-associated proteins, whereas osmotic manipulation experiments reveal a prominent role of molecular crowding. Molecular dynamics simulations with model chromosomes and crowders recapitulate the observed phenomena and highlight the role of entropic effects caused by confinement and molecular crowding in the spatial organization of the chromosome.

Calcium-mediated actin reset (CaAR) mediates acute cell adaptations

Actin has well established functions in cellular morphogenesis. However, it is not well understood how the various actin assemblies in a cell are kept in a dynamic equilibrium, in particular when cells have to respond to acute signals. Here, we characterize a rapid and transient actin reset in response to increased intracellular calcium levels. Within seconds of calcium influx, the formin INF2 stimulates filament polymerization at the endoplasmic reticulum (ER), while cortical actin is disassembled. The reaction is then reversed within a few minutes. This Calcium-mediated actin reset (CaAR) occurs in a wide range of mammalian cell types and in response to many physiological cues. CaAR leads to transient immobilization of organelles, drives reorganization of actin during cell cortex repair, cell spreading and wound healing, and induces long-lasting changes in gene expression. Our findings suggest that CaAR acts as fundamental facilitator of cellular adaptations in response to acute signals and stress.

DOI:http://dx.doi.org/10.7554/eLife.19850.001

Our skeleton plays a vital role in giving shape and structure to our body, it also allows us to make coordinated movements. Similarly, each cell contains a microscopic network of structures and supports called the cytoskeleton that helps cells to adopt specific shapes and is crucial for them to move around. Unlike our skeleton, which is relatively unchanging, the cytoskeleton of each cell constantly changes and adapts to the specific needs of the cell.

One part of the cytoskeleton is a dense, flexible meshwork of fibers called the cortex that lies just beneath the surface of the cell. The cortex is constructed using a protein called actin, and many of these proteins join together to form each fiber. When cells need to adapt rapidly to an injury or other sudden changes in their environment they activate a so-called stress response. This response often begins with a rapid increase in the amount of calcium ions inside a cell, which can then trigger changes in actin organization. However, it is not clear how cells under stress are able to globally remodel their actin cytoskeleton without compromising stability and integrity of the cortex.

Wales, Schuberth, Aufschnaiter et al. used a range of mammalian cells to investigate how actin responds to stress signals. All cells responded to the resulting influx of calcium ions by deconstructing large parts of the actin cortex and simultaneously forming actin filaments near the center of the cell. Wales, Schuberth, Aufschnaiter et al. termed this response calcium-mediated actin reset (CaAR), as it lasted for only a few minutes before the actin cortex reformed. The experiments show that a protein called INF2 controls CaAR by rapidly removing actin from the cortex and forming new filaments near a cell compartment called the endoplasmic reticulum.

CaAR allows cells to rapidly and drastically alter the cortex in response to stress. The experiments also show that this sudden shift in actin can change the activity of certain genes, leading to longer-term effects on the cell. The findings of Wales, Schuberth, Aufschnaiter et al. suggest that calcium ions globally regulate the actin cytoskeleton and hence cell shape and movement under stress. This could be relevant for many important processes and conditions such as wound healing, inflammation and cancer. A future challenge will be to understand the role of CaAR in these processes.

DOI:http://dx.doi.org/10.7554/eLife.19850.002

Antibiotic use during pregnancy and asthma in preschool children: the influence of confounding

BACKGROUND

A recent study suggested that early-life intestinal microbiota may play an important role in the development of childhood asthma, indicating that antibiotics taken during early life or in late pregnancy may be associated with childhood asthma.

OBJECTIVE

This study aims to assess the association between prenatal antibiotic use and asthma in preschool children using data from the prescription database IADB.nl. To assess the influence of potential confounding, we conducted both a case-sibling and a case-control study and compared the results.

METHODS

We conducted a case-sibling study in which 1228 children with asthma were compared to 1228 siblings without asthma, using data from the prescription database IADB.nl. In addition, a case-control study was conducted. Asthma in preschool children was defined as ≥ 3 prescriptions for anti-asthma medication within a year before the fifth birthday. Conditional logistic regression was used to estimate crude and adjusted odds ratios (aORs).

RESULTS

In both the case-sibling and case-control analysis, the use of antibiotics in the third trimester of pregnancy was associated with an increased risk of asthma in preschool children (aOR 1.37; 95% CI 1.02-1.83 and aOR 1.40; 95% CI 1.15-1.47). Time-trend analyses showed that results were not influenced by a time trend in antibiotic exposure. A significant association between exposure to antibiotics in any trimester of pregnancy and the development of asthma in preschool children was observed in the case-control analysis only (aOR 1.46; 95% CI 1.34-1.59).

CONCLUSION

Antibiotic use in the third trimester of pregnancy was associated with a small increased risk of asthma in preschool children. This association was robust to time-invariant confounding or exposure time trends, further supporting the important role for early-life intestinal microbiota in the development of childhood asthma.

Identification of Dutch children diagnosed with atopic diseases using prescription data: a validation study

Purpose

The aim of this study is to validate medication proxies for the identification of children diagnosed with atopic disorders that can be applied in various types of epidemiological research.

Methods

Records of 7439 children, aged between 0 and 10 years, in the period 2001 until 2010, were retrieved from the Registration Network Groningen database, a general practitioners database in the north-eastern part of the Netherlands. The sensitivity and positive predictive value (PPV) of 22 medication proxies for the identification of children diagnosed with atopic disorders (asthma, atopic dermatitis, and allergic rhinitis) were computed using the registered diagnoses as gold standards. In addition, different capture periods (1 year, half year, and length of study period) for the detection of prescriptions were tested for all the medication proxies.

Results

The highest PPV (0.84, 95 % CI 0.81–0.87) in combination with a sufficient sensitivity value (0.54, 95 % CI 0.50–0.57) for the identification of children diagnosed with asthma was yielded for the medication proxy, ≥2 prescriptions for anti-asthma medication within 1 year, including 1 inhaled steroid. PPV and sensitivity were even higher in the age group 6–10 years. The proxies designed for the identification of children diagnosed with atopic dermatitis and allergic rhinitis yielded only high PPVs (≥0.75) in combination with low sensitivity values (≤0.22). Altering the capture period for the detection of prescriptions to half a year or the length of the study period only affected sensitivity values.

Conclusion

Children diagnosed with asthma can be identified reliably with a range of medication proxies. The use of prescription data for the identification of children diagnosed with atopic dermatitis and allergic rhinitis is questionable.

Prenatal exposure to acid-suppressive drugs and the risk of allergic diseases in the offspring: a cohort study

BACKGROUND

Recent studies reported increased risks for the development of asthma in children after prenatal exposure to acid-suppressive drugs. As a result of common pathogenesis, associations could also be present for other allergic diseases.

METHODS

Using the prescription database IADB.nl, we conducted a cohort study amongst 33 536 children in the Netherlands, with a maximum follow-up of 8 years. Maternal exposure was defined as ≥1 dispensed prescription for proton pump inhibitors (PPIs) and/or Histamine 2-antagonists (H2As) during pregnancy. Children were considered to have a drug-treated allergic disease if they received either ≥2 prescriptions for dermal (atopic dermatitis), inhaled (asthma) or nasal (allergic rhinitis) steroids within a 12-month period. Clustered Cox proportional hazard regression was used to estimate crude and adjusted hazard ratios (aHR) with 95% confidence intervals (95% CI).

RESULTS

The aHR for the development of any allergic disease was 1.37 (95% CI: 1.14-1.66) for children exposed to PPIs or H2As. Prenatal exposure to PPIs and/or H2As was associated with atopic dermatitis, asthma and allergic rhinitis with aHRs of 1.32 (95% CI 1.06-1.64), 1.57 (95% CI 1.20-2.05) and 2.40 (95% CI 1.42-4.04), respectively. The aHR for the development of two or more (aHR 2.13 95% CI: 1.43-3.19) and three allergic diseases (aHR 5.18 95% CI: 2.16-12.42) were even more elevated after prenatal exposure to PPIs or H2As.

CONCLUSION

Prenatal exposure to PPIs and H2As appeared associated with an increased risk for the development of atopic dermatitis, asthma and allergic rhinitis in the offspring, especially with the development of multiple allergic diseases. Because our study has limitations inherent to observational studies, prospective studies are now warranted to confirm our findings.

Simultaneous increase of Cryptosporidium infections in the Netherlands, the United Kingdom and Germany in late summer season, 2012

Binary file ES_Abstracts_Final_ECDC.txt matches

Simultaneous increase of Cryptosporidium infections in the Netherlands, the United Kingdom and Germany in late summer season, 2012

Starting August 2012, an increase in Cryptosporidium infections was reported in the Netherlands, the United Kingdom and Germany. It represented a 1.8 to 4.9-fold increase compared to previous years. Most samples were C. hominis IbA10G2. A case–control study was performed in the Netherlands but did not identify an endemic source. A case–case study in the north of England found travel abroad to be the most common risk factor.

Xpert MTB/RIF®, a novel automated polymerase chain reaction-based tool for the diagnosis of tuberculosis

There is an urgent need for new point of care tests for tuberculosis (TB). Xpert MTB/RIF® is a real-time polymerase chain reaction-based system that detects Mycobacterium tuberculosis DNA and rifampicin (RMP) resistance modulating mutations directly from clinical samples in 2 h. The sensitivity for detecting M. tuberculosis in culture-positive samples was 93.8% (60/64) and exceeded smear microscopy (40/64, 62.5%). The specificity for detecting M. tuberculosis was 92.0% (23/25) and for RMP resistance it was 100% (8/8). The test is simple to conduct and requires basic sputum handling facilities only. These characteristics render it a promising close-to-patient test for TB in various settings.

Size and shape of excluded volume polymers confined between parallel plates

A number of recent experiments have provided detailed observations of the configurations of long DNA strands under nano-to-micrometer-sized confinement. We therefore revisit the problem of an excluded volume polymer chain confined between two parallel plates with varying plate separation. We show that the nonmonotonic behavior of the overall size of the chain as a function of plate separation, seen in computer simulations and reproduced by earlier theories, can already be predicted on the basis of scaling arguments. However, the behavior of the size in a plane parallel to the plates, a quantity observed in recent experiments, is predicted to be monotonic, in contrast to the experimental findings. We analyze this problem in depth with a mean-field approach that maps the confined polymer onto an anisotropic Gaussian chain, which allows the size of the polymer to be determined separately in the confined and unconfined directions. The theory allows the analytical construction of a smooth crossover between the small-plate-separation de Gennes regime and the large-plate-separation Flory regime. The results show good agreement with molecular dynamics simulations in the presence of a Langevin heat bath and confirm the scaling predictions.

Cerebrovascular accidents in adult patients with congenital heart disease

OBJECTIVE

To investigate the prevalence and characteristics of cerebrovascular accidents (CVA) in a large population of adults with congenital heart disease (CHD).

METHODS AND RESULTS

In a retrospective analysis of aggregated European and Canadian databases a total population of 23 153 patients with CHD was followed up to the age of 16-91 years (mean 36.4 years). Among them, 458 patients (2.0%) had one or more CVA, with an estimated event rate of 0.05% per patient-year. Permanent neurological sequelae were noted in 116 patients (25.3%). The prevalence of CVA in selected diagnostic categories was as follows: open atrial septal defect 93/2351 (4.0%); closed atrial or ventricular septal defect 57/4035 (1.4%); corrected tetralogy of Fallot 52/2196 (2.4%); Eisenmenger physiology 24/467 (5.1%); other cyanotic 50/215 (23.3%); mechanical prostheses (29/882 (3.3%). Associated conditions in patients with CVA were absence of sinus rhythm (25%), transvenous pacemakers (7%), endocarditis (2%), cardiac surgery (11%) and catheter intervention (2%), but with the exception of absent sinus rhythm these were not significantly more prevalent in patients with CVA.

CONCLUSION

CVA are a major contributor to morbidity in this young population despite absence of classical cardiovascular risk factors. Although the prevalence of CVA in patients with CHD appears low, it is 10-100 times higher than expected in control populations of comparable age. Residua occur in a strong minority of patients. The subjects at highest risk are those patients with CHD with cyanotic lesions, in whom the prevalence is over 10-fold above the average.

Non-specific interactions are sufficient to explain the position of heterochromatic chromocenters and nucleoli in interphase nuclei

The organization of the eukaryote nucleus into functional compartments arises by self-organization both through specific protein-protein and protein-DNA interactions and non-specific interactions that lead to entropic effects, such as e.g. depletion attraction. While many specific interactions have so far been demonstrated, the contributions of non-specific interactions are still unclear. We used coarse-grained molecular dynamics simulations of previously published models for Arabidopsis thaliana chromatin organization to show that non-specific interactions can explain the in vivo localization of nucleoli and chromocenters. Also, we quantitatively demonstrate that chromatin looping contributes to the formation of chromosome territories. Our results are consistent with the previously published Rosette model for Arabidopsis chromatin organization and suggest that chromocenter-associated loops play a role in suppressing chromocenter clustering.

Molecular and epidemiological investigations of cryptosporidiosis in Cuban children

Molecular and epidemiological studies of Cryptosporidium infections amongst 28 Cuban children (aged 2-8 years) with diarrhoea are described. As few of the younger infected children but most of the older infected children had been breastfed, short-term protection from maternal antibodies passed to infants during breastfeeding may result in a lack of cryptosporidial infection in infancy. This protection of breastfeeding children may, however, result in such children developing less anti-Cryptosporidium immunity of their own (than their bottle-fed counterparts), so that, by school age, the children who had been breastfed are those most likely to be found infected. In the present study, in contrast with the observations made during a previous study of cryptosporidiosis in Cuban children, vomiting was rare (7%) whereas abdominal pain was common (57%). These differences in expression of symptoms between studies may be age-related. As seen in other studies from similar countries, including those of the Caribbean and Latin America, C. hominis was found to predominate, the results of the successful molecular analyses revealing 10 C. hominis infections but no C. parvum. Subgenotyping (at the gp60 locus) indicated that the C. hominis infections included a wide range of subtypes, with isolates from three subtype families (Ia, Ib and Id) being detected.

Giardia infections in Cuban children: the genotypes circulating in a rural population

Stool samples containing Giardia duodenalis cysts were collected from 95 primary-school children in central Cuba, and preserved by storing at -20 degrees C in 70% ethanol. Clinical data were collected for each child. Although 57% of the children were asymptomatic, the remaining 43% each reported between one and three symptoms. Following cyst quantification and isolation, molecular analyses were attempted on all cyst isolates, with the focus on the parasite's beta-giardin and glutamate-dehydrogenase (gdh) genes. Unfortunately, the cyst-preservation procedure appeared to have a deleterious effect on the cysts, since genotyping data could only be obtained for 20 of the 95 isolates. These data indicated, however, an approximately equal distribution between assemblage A (nine isolates) and assemblage B (11 isolates). Children found to be excreting relatively large numbers of cysts were more likely to be symptomatic than children who were excreting fewer cysts, and children with Giardia isolates from assemblage B were more likely to have symptomatic infections than children with isolates from assemblage A. Although considerable sequence variability was seen in the assemblage-B isolates, the assemblage-A isolates were relatively genetically homogeneous. This is the first publication from the Caribbean in which the Giardia genotypes circulating within the population have been identified, the first from the Americas providing information on associations between clinical presentation and the assemblage of the infecting Giardia, and the first to indicate that levels of cyst excretion may have clinical significance.

Aetiology and presentation of HIV/AIDS-associated pulmonary infections in patients presenting for bronchoscopy at a referral hospital in northern Tanzania

OBJECTIVES

To determine the aetiological agents of pulmonary infections in HIV-infected Tanzanians and to correlate the causative agents with clinical, radiographic features, and mortality.

DESIGN

A prospective study.

SETTING

Kilimanjaro Christian Medical Centre (KCMC), Tanzania.

SUBJECTS

Bronchoalveolar lavage fluid (BAL) were obtained from 120 HIV infected patients with pulmonary infections. BAL for causative agents was analysed and correlated with clinical and radiographic features, and one-month outcome.

RESULTS

Causative agents were identified in 71 (59.2%) patients and in 16 of these patients, multiple agents were found. Common bacteria were identified in 35 (29.2%) patients, Mycobacterium tuberculosis in 28 (23.3%), Human Herpes Virus 8 (HHV8) in 12 (10%), Pneumocystis jiroveci in nine (7.5%) and fungi in five (4.2%) patients. Median CD4 T cell count of the patients with identified causes was 47 cells/microl (IQR 14-91) and in the 49 patients with undetermined aetiology was 100 cells/ microl (IQR 36-188; p = 0.01). Micronodular chest radiographic lesions were associated with presence of M. tuberculosis (p = 0.002). The one-month mortality was 20 (16.7%). The highest mortality was associated with HHV8 (41.7%) and M. tuberculosis (32.1%). Mortality in patients with undetermined aetiology was 11.3%. No death occurred in patients with PCP.

CONCLUSION

In this population of severely immunosuppressed HIV-infected patients with pulmonary infection a variety of causative agents was identified. Micronodular radiographic lesions were indicative of TB. High mortality was associated with M. tuberculosis or HHV8. No death occurred in patients with P. jiroveci infection.

Sphere size distributions from finite thickness sections: a forward approach employing a genetic algorithm

We formulate, implement and test a robust method of determining sphere size distributions from finite thickness planar sections. The method uses a forward approach in which populations of proposed distributions are tested against the input data and refined using a genetic algorithm. This method is then applied to a real-world data set concerning endo- and exocytotic vesicles in the apical region of tip growing pollen tubes of Arabidopsis thaliana.

Rapid drug susceptibility testing of mycobacteria by culture on a highly porous ceramic support

BACKGROUND

Phenotypic, culture-based methods for drug susceptibility testing (DST) of Mycobacterium tuberculosis are relatively simple and may be particularly appropriate for resource-limited settings where tuberculosis (TB) is most prevalent. However, these methods can be slow and generate significant amounts of infectious waste. Low-cost digital imaging and a unique porous ceramic support for cell culture (Anopore) may offer opportunities to improve this situation.

OBJECTIVE

To test a rapid DST method based on fluorescence microscopy of mycobacteria grown for a few generations on Anopore.

DESIGN

Mycobacteria were cultured with and without drugs, and the resulting microcolonies were heat-killed and stained with the fluorogenic dye Syto16. Microscopy, image-capture with a charge-coupled device camera and digital processing were used to quantify the inhibition of growth by drugs. Rapid DST for rifampicin and isoniazid was performed for clinical isolates.

RESULTS

Mycobacteria could be cultured, killed, stained and imaged on Anopore. For DST, the Anopore method gave an accurate result in 3 days.

CONCLUSION

This is an unprecedented speed for culture-based DST for this group of organisms and results in minimal infectious waste (<20,000 colony forming units). Analysis of mycobacteria by fluorescence and electron microscopy on Anopore also opens up research possibilities.

Prevalence, characterisation and clinical profiles of Shiga toxin-producing Escherichia coli in The Netherlands

Detection of Shiga toxin-producing Escherichia coli (STEC) in The Netherlands is traditionally limited to serogroup O157. To assess the relative importance of STEC, including non-O157 serogroups, stool samples submitted nationwide for investigation of enteric pathogens or diarrhoea were screened with real-time PCR for the presence of the Shiga toxin genes. Patients were selected if their stool contained blood upon macroscopic examination, if they had a history of bloody diarrhoea, were diagnosed with haemolytic uraemic syndrome, or were aged <6 years (irrespective of the bloody aspect of the stool). PCR-positive stools were forwarded to a central laboratory for STEC isolation and typing. In total, 4069 stools were examined, with 68 (1.7%) positive PCR results. The highest prevalence was for stools containing macroscopic blood (3.5%), followed by stools from patients with a history of bloody diarrhoea (2.4%). Among young children, the prevalence (1.0%) was not significantly higher than among random, non-bloody, stool samples from diarrhoeal patients (1.4%). STEC strains were isolated from 25 (38%) PCR-positive stools. Eleven O-serogroups were detected, including five STEC O157 strains. As serogroup O157 represented only 20% of the STEC isolates, laboratories should be encouraged to use techniques enabling them to detect non-O157 serogroups, in parallel with culture, for isolation and subsequent characterisation of STEC strains for public health surveillance and detection of outbreaks.

The cellulose synthase complex: a polymerization driven supramolecular motor

We present a biophysical model for the propulsion of the cellulose synthase complex, the motile transmembrane protein complex responsible for the biosynthesis of cellulose microfibrils, the dominant architectural component of the cell walls of higher plants. Our model identifies the polymerization and the crystallization of the cellulose chains as the combined driving forces and elucidates the role of polymer flexibility and membrane elasticity as force transducers. The model is elaborated using both stochastic simulations and a simplified analytical treatment. On the basis of the model and approximate values for the relevant physical constants, we estimate the speed of the cellulose synthase complex to be in the range v(p) approximately 10(-9)-10(-8) m/s, consistent with the recently reported experimental value of 5.8 x 10(-9) m/s.

Entropy-driven spatial organization of highly confined polymers: lessons for the bacterial chromosome

Despite recent progress in visualization experiments, the mechanism underlying chromosome segregation in bacteria still remains elusive. Here we address a basic physical issue associated with bacterial chromosome segregation, namely the spatial organization of highly confined, self-avoiding polymers (of nontrivial topology) in a rod-shaped cell-like geometry. Through computer simulations, we present evidence that, under strong confinement conditions, topologically distinct domains of a polymer complex effectively repel each other to maximize their conformational entropy, suggesting that duplicated circular chromosomes could partition spontaneously. This mechanism not only is able to account for the spatial separation per se but also captures the major features of the spatiotemporal organization of the duplicating chromosomes observed in Escherichia coli and Caulobacter crescentus.

Continuum description of the cytoskeleton: ring formation in the cell cortex

Motivated by the formation of ringlike filament structures in the cortex of plant and animal cells, we study the dynamics of a two-dimensional layer of cytoskeletal filaments and motor proteins near a surface by a general continuum theory. As a result of active processes, dynamic patterns of filament orientation and density emerge via instabilities. We show that self-organization phenomena can lead to the formation of stationary and oscillating rings. We present state diagrams that reveal a rich scenario of asymptotic behaviors and discuss the role of boundary conditions.

Monte Carlo study of hard pentagons

How does a liquid freeze if the geometry of its particles conflicts with the symmetry of the crystal it should naturally form? We study this question in the simplest model system of particles exhibiting such a symmetry mismatch: hard pentagons in two dimensions. Using isobaric and isotensic Monte Carlo simulations we have studied the phase behavior of hard pentagons. On increasing the pressure from the homogeneous and isotropic low-density phase, the system first exhibits a rotator phase (plastic solid) with a triangular lattice structure. At higher densities it undergoes a weak first-order phase transition into a "striped" phase composed of alternating rows of oppositely pointing particles. This phase is analogous to the "striped" phase in the compressible antiferromagnetic Ising model on a triangular lattice and is an example of systems in which frustration due to the mismatch in symmetries is released by an elastic coupling to the lattice. In order to pursue this analogy we also consider hard heptagons, showing that in this case the decrease in symmetry mismatch indeed leads to a shift in the transition densities to higher values and a weakening of the transition.

Plasmodium falciparum transmission blocking immunity under conditions of low and high endemicity in Cameroon

Transmission blocking immunity (TBI) was studied in relation to age, gametocyte density and transmission intensity. subjects with high gametocytaemias were selected in a hypo-endemic urban district and a hyper-endemic rural area in South Cameroon. TBI was determined in blood from gametocyte carriers in a bioassay (Direct Membrane Feeding Assay), with either autologous plasma (OWN) or control serum (AB). Mosquito infection rates (IR) were compared. infection rates correlated positively with gametocyte and oocyst densities. Three TBI indicators were analysed: the proportion of transmission reducers (IRAB > IROWN, P < 0.01), the mean intensity of TBI (IRAB - IROWN), and the contribution of TBI to total inhibition [(IRAB-IROWN)/(100-IROWN)]. we could not discriminate between areas with regard to either the proportion of transmission reducers (urban 15% and rural 29%) or the mean levels of TBI (urban 10% and rural 9%), or contribution of TBI to total inhibition (urban 10% and rural 13%). there was no relationship between TBI indicators and age, but a trend of increasing values was observed with rising gametocytaemia, which was considered as a confusing factor. a multivariable analysis showed that the probability of being a reducer was 4.6 fold higher in the rural area than in the urban district.

Origin of Plasmodium falciparum malaria is traced by mitochondrial DNA

The origin and geographical spread of Plasmodium falciparum is here determined by analysis of mitochondrial DNA sequence polymorphism and divergence from its most closely related species P. reichenowi (a rare parasite of chimpanzees). The complete 6 kb mitochondrial genome was sequenced from the single known isolate of P. reichenowi and from four different cultured isolates of P. falciparum, and aligned with the two previously derived P. falciparum sequences. The extremely low synonymous nucleotide polymorphism in P. falciparum (pi=0.0004) contrasts with the divergence at such sites between the two species (kappa=0.1201), and supports a hypothesis that P. falciparum has recently emerged from a single ancestral population. To survey the geographical distribution of mitochondrial haplotypes in P. falciparum, 104 isolates from several endemic areas were typed for each of the identified single nucleotide polymorphisms. The haplotypes show a radiation out of Africa, with unique types in Southeast Asia and South America being related to African types by single nucleotide changes. This indicates that P. falciparum originated in Africa and colonised Southeast Asia and South America separately.

Hard-sphere solids near close packing: testing theories for crystallization

The freezing transition of hard spheres has been well described by various versions of density-functional theory (DFT). These theories should possess the close-packed crystal as a special limit, which represents an extreme testing ground for the quality of such liquid-state based theories. We therefore study the predictions of DFT for the structure and thermodynamics of the hard-sphere crystal in this limit. We examine the Ramakrishnan-Yussouff (RY) approximation and two variants of the fundamental-measure theory (FMT) developed by Rosenfeld and co-workers. We allow for general shapes of the density peaks, going beyond the common Gaussian approximation. In all cases we find that upon approaching close packing, the peak width vanishes proportionally to the free distance a between the particles and the free energy depends logarithmically on a. However, different peak shapes and next-to-leading contributions to the free energy result from the different approximate functionals. For the RY theory, within the Gaussian approximation, we establish that the crystalline solutions form a closed loop with a stable and an unstable branch both connected to the close-packing point at a=0, consistent with the absence of a liquid-solid spinodal. That version of FMT that has previously been applied to freezing, predicts asymptotically steplike density profiles confined to the cells of self-consistent cell theory. But a recently suggested improved version which employs tensor weighted densities yields wider and almost Gaussian peaks that are shown to be in very good agreement with computer simulations.

Computer-controlled flow resistance

A computer-controlled flow resistance (CCR), to be used in a computer-controlled lung model, is presented. Flow is forced through a slit between a cylinder and a sleeve around the cylinder. The resulting flow resistance depends on the width, circumferences and the variable length of the slit. The variation in the length is computer-controlled by the position of the sleeve with respect to the cylinder. The total flow resistance also depends on inlet and outlet resistance at both sides of the slit and on flow. The dependence on flow is primarily due to the shape of the inlet of the slit. The resistance of the slit itself is almost independent of flow. The resistance is calculated during a calibration phase at different positions of the sleeve, for flow values from 0.05 to 1.0 litre.s-1 (inflow) and from -0.05 to -1.0 litre.s-1 (outflow). To simulate a required resistance pattern, as, for instance, will occur during breathing, at each moment the set position of the sleeve is calculated by means of an interpolation from the relationship between flow resistance and position of the sleeve. The internal diameter of the sleeve is fixed. To tune the resistance range for a specific simulation, the cylinder is changed for one with different diameter, changing the width of the slit.

Plasmodium falciparum: membrane feeding assays and competition ELISAs for the measurement of transmission reduction in sera from Cameroon

The effect of natural malaria transmission-blocking factors in the blood of Plasmodium falciparum gametocyte carriers was assessed in two types of functional bioassays. In the direct membrane feeding assay (DMFA), a comparison is made between the infectivity of gametocytes from a naturally infected gametocyte carrier in the presence of autologous plasma and the infectivity in the presence of replacement plasma from nonimmune donors. In the standard membrane feeder assay (SMFA), cultured NF54 gametocytes are used to measure the capacity of endemic sera to block transmission. In the DMFA, 18 out of 48 sera (37.5%) from Cameroonian gametocyte carriers reduced transmission significantly, while in the SMFA 22 out of 48 sera (45.8%) produced transmission reduction. There was a positive correlation between both assays (r + 0.41, P < 0.05). Antibodies against epitopes of transmission-blocking target antigens Pfs48/45 and Pfs230 were measured in competition ELISAs and compared with the results of DMFA and SMFA. Serological reactivity in competition ELISAs against three epitopes of Pfs48/45 was significantly higher in the group of transmission-reducing sera in both the DMFA and the SMFA, especially for epitope III. No significant difference was found for Pfs230 antibodies (epitope I). Sensitivity of the serological assays was approximately 60%, with a specificity of around 70%. Serological tests cannot replace the functional bioassay in field situations as yet, but can contribute in the selection of sera for SMFA evaluation.