Education and Awareness on Antimicrobial Resistance in the WHO African Region: A Systematic Review

This review documents the status of AMR education and awareness in the WHO African region, as well as specific initiatives by its member states in implementing education and awareness interventions, as a strategic objective of the Global Action Plan on AMR, i.e., improve knowledge and understanding on AMR through effective communication, education, and training. A systematic search was conducted in Google Scholar, PubMed, and African Journals Online Library according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines, for articles published in English. Retrieval and screening of articles was performed using a structured search protocol following a pre-set inclusion/exclusion criterion. Eighty-five published articles reporting 92 different studies from 19 Member States met inclusion criteria and were included in the final qualitative synthesis. Nigeria (21) and Ethiopia (16) had most of the studies, while the rest were distributed across the remaining 17 Member States. The majority of the articles were on knowledge, attitude, and practices with regard to AMR and antimicrobial use and most of them documented a general lack and suboptimal knowledge, poor attitude and practices, and widespread self-medication. This review shows low levels of knowledge of AMR coupled with extensive misuse of antimicrobial medicines by different target audiences. These findings underscore the urgent need for enhanced and context-specific educational and positive behavioural change interventions.

Global Antimicrobial Resistance and Use Surveillance System on the African continent: Early implementation 2017–2019

Background

Antimicrobial resistance (AMR) is becoming a critical public health issue globally. The World Health Organization launched the Global Antimicrobial Resistance and Use Surveillance System (GLASS) to support the strengthening of the AMR evidence base.

Objective

The article describes the evolution of national AMR surveillance systems and AMR data reporting of countries in the African continent between 2017 and 2019, and the constraints, perceived impact and value of the participation in GLASS.

Methods

Data on implementation of national surveillance systems and AMR rates were submitted to GLASS between 2017 and 2019 and summarised though descriptive statistics. The information on constraints and perceived impact and value in GLASS participation was collected though a set of questionnaires.

Results

Between 2017 and 2019, Egypt, Ethiopia, Madagascar, Malawi, Mali, Mozambique, Nigeria, South Africa, Sudan, Tunisia, Uganda and Zambia submitted data to GLASS. The main constraints listed are linked to scarce laboratory capacity and capability, limited staffing, budget issues, and data management. Moreover, while the data are not yet nationally representative, high resistance rates were reported to commonly-used antibiotics, as the emerging resistance to last treatment options.

Conclusion

Despite the limitations, more and more countries in the African continent are working towards reaching a status that will enable them to report AMR data in a complete and systematic manner. Future improvements involve the expansion of routine surveillance capacity for several countries and the implementation of surveys that allow to effectively define the magnitude of AMR in the continent.

Antimicrobial use among hospitalized patients: A multi-center, point prevalence survey across public healthcare facilities, Osun State, Nigeria

INTRODUCTION

In order to inform sub-national action plan for control of antimicrobial resistance (AMR) and benchmark interventions to improve antibiotic use, it is essential to define situations on antibiotic use using standardized tools. We sought to assess quality of antimicrobial prescription across all government healthcare facilities with capacities for in-patient care in the first of the 36 states in Nigeria as part of ongoing state-wide situation analysis on AMR.

METHODS

A survey was conducted between 10-27 June 2019 using the WHO methodology for point prevalence survey on antibiotic use in hospitals. Data was collected from hospital administrators and records of hospitalized patients. Data analysis was done using Microsoft Excel 2010 (Redmond Washington).

RESULTS

Prevalence of antibiotic use amongst all 321 included patients was 76.6% (246/321). Of all indications recorded, the highest was surgical prophylaxis (96/260, 36.9%) for which there were multiple doses beyond 24 hours in almost all cases (91/96, 94.8%). The largest volume of prescribing took place in the surgical wards, and the most common prescriptions were metronidazole (142/564, 25.2%), cefuroxime (104/564, 18.4%), and ceftriaxone (77/564, 13.7%). Overall, 46.3% of the antibiotics used belong to Access group, 53.5% to watch and only 0.2% to Reserve. Treatment in almost all instances 544/563 (96.6%) was empiric.

CONCLUSIONS

The majority of patients received multiple antibiotics mostly without compliance to guidelines. There was low prescribing of Access antibiotics and excessive use of antibiotics in the Watch group. Antibiotics were used most commonly for surgical prophylaxis but inappropriately. Inappropriate use of antibiotics in this study underscores the crucial need for an action plan incorporating antimicrobial stewardship.

Diabetic mitochondria are resistant to palmitoyl CoA inhibition of respiration, which is detrimental during ischemia

The bioactive lipid intermediate palmitoyl CoA (PCoA) can inhibit mitochondrial ADP/ATP transport, though the physiological relevance of this regulation remains unclear. We questioned whether myocardial ischemia provides a pathological setting in which PCoA regulation of ADP/ATP transport would be beneficial, and secondly, whether the chronically elevated lipid content within the diabetic heart could make mitochondria less sensitive to the effects of PCoA. PCoA acutely decreased ADP‐stimulated state 3 respiration and increased the apparent K_m for ADP twofold. The half maximal inhibitory concentration (IC₅₀) of PCoA in control mitochondria was 22 µM. This inhibitory effect of PCoA on respiration was blunted in diabetic mitochondria, with no significant difference in the K_m for ADP in the presence of PCoA, and an increase in the IC₅₀ to 32 µM PCoA. The competitive inhibition by PCoA was localised to the phosphorylation apparatus, particularly the ADP/ATP carrier (AAC). During ischemia, the AAC imports ATP into the mitochondria, where it is hydrolysed by reversal of the ATP synthase, regenerating the membrane potential. Addition of PCoA dose‐dependently prevented this wasteful ATP hydrolysis for membrane repolarisation during ischemia, however, this beneficial effect was blunted in diabetic mitochondria. Finally, using ³¹P‐magnetic resonance spectroscopy we demonstrated that diabetic hearts lose ATP more rapidly during ischemia, with a threefold higher ATP decay rate compared with control hearts. In conclusion, PCoA plays a role in protecting mitochondrial energetics during ischemia, by preventing wasteful ATP hydrolysis. However, this beneficial effect is blunted in diabetes, contributing to the impaired energy metabolism seen during myocardial ischemia in the diabetic heart.

Preventing and managing antimicrobial resistance in the African region: A scoping review protocol

Introduction

Antimicrobial resistance (AMR) constitutes a significant threat to global health and food security, typically associated with high morbidity and mortality rate. The high burden of infectious diseases coupled with the weak health systems in most countries of Africa magnifies the risk of increasing AMR and its consequences thereof. This scoping review will be aimed at mapping the evidence on interventions used to prevent and manage antimicrobial resistance in Africa, guided by the “One Health” concept.

Methods

We will consider interventions targeting multiple sectors such as health care systems, the agricultural and veterinary sectors. The outcomes to be considered include reduction of AMR decreased morbidity and mortality due to infectious diseases, increased awareness for rational use of antimicrobials and reduced antibiotic consumption. We will include all types of studies regardless of study designs conducted within the context of the WHO African region. Studies will be excluded if they are not conducted in Africa and if they are literature reviews, only describing the concept of AMR without mentioning interventions.

We will include studies identified through a comprehensive search of peer-reviewed and grey literature databases. In addition, we will search the reference lists of included studies and relevant reviews. Finally, we plan to do a citation search for included studies. Findings of this review will be narratively synthesized.

A review of policies and programmes for human organ and tissue donations and transplantations, WHO African Region

Several resolutions, endorsed by the World Health Assembly and the United Nations General Assembly, articulate the need to improve the availability, quality and safety of organ and tissue donation and transplantation, as well as to prevent and combat trafficking in human organs. Here we assessed the implementation of these resolutions pertaining to organ and tissue donations and transplantations by sending out a questionnaire to all 47 countries in the World Health Organization African Region. From 33 countries that provided data, we identified several obstacles and challenges. Compared to other regions, there are very limited data on organ donation and transplantation. Most countries are lacking legal and regulatory frameworks, since they did not yet establish a specific or comprehensive legislation covering donation and transplantation of human organs and tissues. Countries also have a poor national capacity to perform organ and tissue transplantations and the organization and management of national programmes are weak. Funding, both from domestic and external sources, is insufficient to implement effective transplantations programmes and patients have inadequate financial protection. To address these challenges, we propose that countries and partners should develop and implement policies, strategies, plans and regulatory frameworks for all aspects of organ and tissue donations and transplantations, including fighting against organ trafficking and transplant tourism. Where donation and transplantation programmes exist, stakeholders should develop the skills of human resources, adopt technical standards and quality management procedures to improve donation and transplantation of human organs and tissues.

Objective ranges of soil-to-dust transfer coefficients for lead-impacted sites

Residential yard soil and indoor dust datasets from eight communities near historical mining, smelting, and refining operations were used to quantify soil track-in, an important factor in evaluating indoor exposures to soil metals and to set residential soil cleanup levels. Regression analyses were used to derive slopes that represent mass soil-to-dust transfer coefficients or MSDs. Lead concentration data were available for all datasets. Arsenic data were available for six of the eight datasets. Cadmium and zinc data were available for one dataset, allowing limited comparison of MSDs for lead with other metals. Covariates that could indicate potential indoor sources of metals, such as house age and indoor heating source, were examined by multivariate regression analysis when available (three datasets). Covariates that could affect soil track-in, such as the amount of bare soil in the yard or having pets, were examined by stratified linear regression analysis when available (two datasets). Most of the R-squared values for lead, cadmium and zinc indicate a good to moderate fit (≥0.25), but for arsenic most indicate a poor fit (<0.25). Significant MSDs for models with a good to moderate fit range from 0.14 to 0.47 for lead, and 0.12 to 0.43 for the other metals (arsenic, cadmium, and zinc). The treatment of outliers was a significant methodological factor affecting the slope of the regressions. Substantial variability is expected among soils at residences due to both physical characteristics of each property and the ways in which residents interact with their home. Survey data providing information on various factors affecting soil track-in help to refine MSD estimates. For three of the datasets, covariate data were available that improved model fit by multivariate or stratified regression analysis for lead. When multivariate or stratified regression analyses were performed, the estimated MSD varied as little as <1% to as great as 200% depending on the dataset, but all estimates were below 0.4. Notably, the MSDs were lowest for the three datasets with the highest soil lead concentrations, i.e., those with average soil lead concentrations greater than 300 mg/kg after outlier removal. For five of the six datasets that had both arsenic and lead sampled, arsenic MSDs were much less than the lead MSDs; however, only two of the sites' arsenic models had significant MSDs and adequate fit. Cadmium and zinc were only included in one dataset, limiting our ability to draw any conclusions from comparison to those MSDs. The results of our study are consistent with prior studies suggesting that MSDs for metals without internal sources are 0.3-0.4, and application of MSDs in that range will provide more reliable exposure estimates than the 0.7 default value used by the United States Environmental Protection Agency in the Integrated Exposure Uptake Biokinetic (IEUBK) Model.

Regulation of the cardiac sodium pump

In cardiac muscle, the sarcolemmal sodium/potassium ATPase is the principal quantitative means of active transport at the myocyte cell surface, and its activity is essential for maintaining the trans-sarcolemmal sodium gradient that drives ion exchange and transport processes that are critical for cardiac function. The 72-residue phosphoprotein phospholemman regulates the sodium pump in the heart: unphosphorylated phospholemman inhibits the pump, and phospholemman phosphorylation increases pump activity. Phospholemman is subject to a remarkable plethora of post-translational modifications for such a small protein: the combination of three phosphorylation sites, two palmitoylation sites, and one glutathionylation site means that phospholemman integrates multiple signaling events to control the cardiac sodium pump. Since misregulation of cytosolic sodium contributes to contractile and metabolic dysfunction during cardiac failure, a complete understanding of the mechanisms that control the cardiac sodium pump is vital. This review explores our current understanding of these mechanisms.

Marginal ulceration after laparoscopic gastric bypass: an analysis of predisposing factors in 260 patients

BACKGROUND

Marginal ulceration after Roux-en-Y gastric bypass (RYGB) is diagnosed in 1% to 16% of patients. The factors predisposing patients to marginal ulceration are still unclear.

METHODS

A total of 260 patients who underwent laparoscopic RYGB were retrospectively reviewed. Data regarding demographics, comorbidities, body mass index (BMI), Helicobacter pylori infection, gastrojejunal (GJ) anastomotic leaks, postoperative bleeding, operative time, type of suture material, and marginal ulcer formation were collected. Fisher's exact test was used for statistical analysis of discrete variables, and Student's t-test was used for continuous variables. Statistical significance was set at an alpha of 0.05.

RESULTS

The overall marginal ulceration rate was 7%. Demographic data (age, gender distribution, BMI) did not differ significantly between patients who experienced marginal ulceration and those who did not (p > 0.05). Similarly, technical factors (choice of permanent or absorbable suture for the GJ anastomosis, attending as primary surgeon, robotic GJ, operative time, postoperative hematocrit drop) were not statistically different between the two groups (p > 0.05). Finally, the prevalence of comorbidities (diabetes, hypertension, obstructive sleep apnea, musculoskeletal complaints, dyslipidemia, gastroesophageal reflux disease [GERD] and peptic ulcer disease [PUD]) did not differ significantly between the two groups (p > 0.05). However, preoperative H. pylori infection, although adequately treated, was twice as common among the patients who had marginal ulceration (32%) as among those who did not (12%) (p = 0.02). All the patients who experienced marginal ulcers had complete resolution of symptoms with proton pump inhibitors and sucralfate. No reoperations were required for marginal ulceration.

CONCLUSION

Helicobacter pylori may potentiate marginal ulcer formation. The authors hypothesize that H. pylori damages the mucosal barrier in a way that persists postoperatively, which may precipitate marginal ulceration even when the organism has been medically eradicated.

Genome of the bacterium Streptococcus pneumoniae strain R6

Streptococcus pneumoniae is among the most significant causes of bacterial disease in humans. Here we report the 2,038,615-bp genomic sequence of the gram-positive bacterium S. pneumoniae R6. Because the R6 strain is avirulent and, more importantly, because it is readily transformed with DNA from homologous species and many heterologous species, it is the principal platform for investigation of the biology of this important pathogen. It is also used as a primary vehicle for genomics-based development of antibiotics for gram-positive bacteria. In our analysis of the genome, we identified a large number of new uncharacterized genes predicted to encode proteins that either reside on the surface of the cell or are secreted. Among those proteins there may be new targets for vaccine and antibiotic development.

AlphaB crystallin translocation and phosphorylation: signal transduction pathways and preconditioning in the isolated rat heart

In this program of studies we have characterized in detail the translocation (assessed by Triton-insolubility) and phosphorylation (using serine-45 or -59 phosphospecific antibodies) of alphaB crystallin during myocardial ischemia [both with or without ischemic preconditioning (IPC)]. Pharmacological activators and inhibitors allowed us to characterize the signaling pathways involved in alphaB crystallin phosphorylation during ischemia. Ischemic preconditioning alone caused 30% of the heart's alphaB crystallin pool to translocate, providing a significant translocation 'head-start' in protected tissue. This enhanced translocation is coupled with increased (3-fold) alphaB crystallin phosphorylation at both serine residues. The possible role of alphaB crystallin in the protection afforded by ischemic preconditioning is supported by the signal transduction data; which showed preconditioning-induced alphaB crystallin phosphorylation can be blocked by tyrosine kinase inhibition (using genistein) and by p38 MAP kinase or PKC inhibition (using SB203580 or bisindolylmaleimide, respectively). The activation of both p38 MAP kinase and PKC are recognized requirements for the induction of preconditioning and their inhibition is known to block protection. Western immunoblotting analysis after isoelectric focusing electrophoresis, confirmed the observations made with the phosphospecific antibodies; but also showed that 27+/-4% of total cardiac crystallin was phosphorylated after 30 min of ischemia. AlphaB crystallin exists as large polymeric aggregates in cardiac tissue under basal conditions (approximately 1 MDa as determined by gel filtration chromatography). We induced phosphorylation of alphaB crystallin during aerobic perfusion by the administration of phenylephrine. However this treatment did not alter the molecular aggregate size of alphaB crystallin. It appears that alphaB crystallin molecular aggregate size is not simply regulated by phosphorylation. AlphaB crystallin may have a role to play in the myocardial protection induced by ischemic preconditioning, as both translocation and phosphorylation are both accelerated and enhanced by ischemic preconditioning.

Differential centrifugation separates cardiac sarcolemmal and endosomal membranes from Langendorff-perfused rat hearts

The application of subcellular fractionation protocols developed in soft tissues to fibrous organs such as the heart is unsuitable given the substantial differences in subcellular structure these tissues exhibit. The purpose of this study was to develop a simple method for the separation of sarcolemma and endosomes from isolated Langendorff-perfused rat hearts. Hearts were homogenized with either an Ultra-Turrax homogenizer or a hand-held glass tissue grinder. Quantitative immunoblots assessed the enrichment of the sarcolemmal proteins caveolin 3 and the sodium potassium ATPase and the endosomal proteins rab4 and GLUT4 in different membrane fractions. Application of homogenates to sucrose and Percoll density gradients failed to resolve membranes differentially enriched in sarcolemmal or endosomal marker proteins, indicating little difference in density between the sarcolemma and endosomes. However, successive spins of homogenates from a hand-held glass tissue grinder successfully separated the endosomes from the sarcolemma, indicating differences in masses between the two membrane fractions. Approximately 70% of total caveolin 3 and sodium potassium ATPase immunoreactivity was in membrane pellets up to 20,000g and approximately 85% of rab4 and GLUT4 in pellets from 20,000-100,000g. In addition, 86% of ouabain-sensitive ATPase activity (sodium potassium ATPase activity) was in membrane pellets up to 20,000g. Therefore, sarcolemmal membranes were pelleted up to 20,000g, and endosomal membranes between 20,000 and 100,000g. Regional ischemia (40 min) followed by reperfusion (60 min) caused the translocation of GLUT4 (but not rab4) from the endosomal membranes to the sarcolemma in the area of the heart subjected to ischemia.

X-ray diffraction from DNA fibres under tension

When DNA fibres are stretched during drying, the polymer undergoes a conformational transition. We present quantitative results from X-ray diffraction studies on such fibres held at various ambient relative humidities. These indicate that the molecules are arranged in arrays which are crystalline in projection down the fibre axis. The packing can be explained in terms of a hexagonal cell with a lattice parameter, a, of approximately 13 A which varies with humidity. The patterns contain meridional intensities at 1/3.4 A(-1) and 1/6.5 A(-1), a strong off-meridional intensity at Z=1/5.6 A(-1) and diffuse scatter at Z=1/28 A(-1).

Post-translational disruption of the delta F508 cystic fibrosis transmembrane conductance regulator (CFTR)-molecular chaperone complex with geldanamycin stabilizes delta F508 CFTR in the rabbit reticulocyte lysate

The DeltaF508 mutation of cystic fibrosis transmembrane conductance regulator (CFTR) is a trafficking mutant, which is retained and degraded in the endoplasmic reticulum by the ubiquitin-proteasome pathway. The mutant protein fails to reach a completely folded conformation that is no longer a substrate for ubiquitination ("stable B"). Wild type protein reaches this state with 25% efficiency. In this study the rabbit reticulocyte lysate with added microsomal membranes has been used to reproduce the post-translational events in the folding of wild type and DeltaF508 CFTR. In this system wild type CFTR does not reach the stable B form if the post-translational temperature is 37 degrees C, whereas at 30 degrees C the behavior of both wild type and mutant proteins mimics that observed in the cell. Geldanamycin stabilizes DeltaF508 CFTR with respect to ubiquitination only when added post-translationally. The interaction of wild type and mutant CFTR with the molecular chaperones heat shock cognate 70 (hsc70) and heat shock protein 90 (hsp90) has been assessed. Release of wild type protein from hsc70 coincides with the cessation of ubiquitination and formation of stable B. Geldanamycin immediately prevents the binding of hsp90 to DeltaF508 CFTR, and after a delay releases it from hsc70. Release of mutant protein from hsc70 also coincides with the formation of stable B DeltaF508 CFTR.

Micro-SAXS and force/strain measurements during the tensile deformation of single struts of an elastomeric polyurethane foam

A microdeformation stage based on a piezoelectric crystal actuator capable of measuring the force applied to micrometre-sized polymeric samples is described. Laboratory force/strain measurements on a single strut of an elastomeric polyurethane foam have been conducted for the first time. The device has also been used on the microfocus beamline at the European Synchrotron Radiation Facility to collect microbeam small-angle X-ray scattering data simultaneously with strain and force measurements during the time-resolved tensile deformation of a single strut of elastomeric polyurethane foam.

Structural polymorphism in a tubercidin analogue of the DNA double helix

A high-angle X-ray fibre diffraction study of a tubercidin analogue of the poly[d(A-T)].poly[d(A-T)] DNA double helix has been carried out using station 7.2 at the Daresbury Laboratory synchrotron radiation source. The polymer has been studied for a wide range of salt strengths and hydration conditions and exhibits conformational polymorphism that is quite distinct from that observed for the unmodified polymer. The replacement of deoxyadenosine by deoxytubercidin in the polynucleotide causes only slight alterations to the structure of A-DNA, but significantly alters the structure of the B conformation. Additionally, the modified polymer does not, in any conditions yet identified, adopt the D conformation. In conditions which would normally favour the D conformation of poly[d(A-T)].poly[d(A-T)], the modified polymer adopts an unusual conformation which is designated here as the K conformation. These observations are important for an understanding of major groove interactions involved in the stabilisation of particular DNA conformations and also more generally for an insight into the pharmacological activity of tubercidin which following its incorporation into nucleic acids may cause stereochemical distortions of the DNA double helix.

A high-angle neutron fibre diffraction study of the hydration of deuterated A-DNA

A high-angle neutron fibre diffraction study of the hydration of A-DNA has been performed using the single-crystal diffractometer D19 at the Institut Laue-Langevin (Grenoble, France). The sample was prepared using deuterated DNA extracted from E. Coli cells cultured on deuterated nutrients. In common with our previous neutron fibre diffraction studies of DNA, this work exploits the ability to isotopically replace H2O around the DNA by D2O. However this study benefitted additionally from the fact that the hydrogen atoms which are covalently bonded to carbon atoms in the DNA sugars and bases were replaced by deuterium so that incoherent scattering and absorption effects were minimised. Successive cycles of Fourier synthesis and Fourier difference synthesis allowed water peaks to be identified and their positional and occupancy parameters to be refined against the observed diffraction data. The results confirm the main hydration features noted in our earlier studies with a clear network of water running along the inside edge of the major groove linking successive OI phosphate oxygen atoms. The central core of water running along the axis of the double helix is very much clearer in this work. Additionally this study shows chains of ordered water lying in the centre of the major groove.

Investigation of the variation in orientation and crystallinity in poly(ethylene terephthalate) containers using microfocus X-ray diffraction

The microfocus X-ray beamline at the European Synchrotron Radiation Facility has been used to investigate the variation in molecular orientation and crystallinity in the wall of a container fabricated from poly(ethylene terephthalate). Two-dimensional wide-angle X-ray scattering patterns were recorded and displayed in real time as the specimen was tracked across the incident X-ray beam enabling the measurement of textural changes to be made with a spatial resolution of ~2 mum.

Time-Resolved Simultaneous SAXS/WAXS of the Drawing of Polyethylene at the Daresbury SRS

A system has been developed which represents a significant advance in the quality and extent of small- and wide-angle X-ray scattering data (SAXS and WAXS) that can be recorded simultaneously with strain data during the drawing and annealing of polymer materials. WAXS data are recorded using a Photonic Science charge-coupled-device area detector and SAXS data using a gas-filled multiwire area detector. Strain data, for the region of the specimen from which the SAXS/WAXS data are collected, are calculated from an accurately synchronized continuously recorded video image of the specimen. The system allows X-ray and video image data to be collected as a series of frames with essentially no ;dead-time' between frames. The data are fully two-dimensional and can be collected for a wide range of d spacings. The use of this system to investigate the stress-induced orientation and phase changes during the drawing of a range of grades of commercially available polyethylene is described.

Time-of-flight Laue fiber diffraction studies of perdeuterated DNA

The diffractometer SXD at the Rutherford Appleton Laboratory ISIS pulsed neutron source has been used to record high resolution time-of-flight Laue fiber diffraction data from DNA. These experiments, which are the first of their kind, were undertaken using fibers of DNA in the A conformation and prepared using deuterated DNA in order to minimise incoherent background scattering. These studies complement previous experiments on instrument D19 at the Institut Laue Langevin using monochromatic neutrons. Sample preparation involved drawing large numbers of these deuterated DNA fibers and mounting them in a parallel array. The strategy of data collection is discussed in terms of camera design, sample environment and data collection. The methods used to correct the recorded time-of-flight data and map it into the final reciprocal space fiber diffraction dataset are also discussed. Difference Fourier maps showing the distribution of water around A-DNA calculated on the basis of these data are compared with results obtained using data recorded from hydrogenated A-DNA on D19. Since the methods used for sample preparation, data collection and data processing are fundamentally different for the monochromatic and Laue techniques, the results of these experiments also afford a valuable opportunity to independently test the data reduction and analysis techniques used in the two methods.

DNA hydration studied by neutron fiber diffraction

The development of neutron high angle fiber diffraction to investigate the location of water around the deoxyribonucleic acid (DNA) double-helix is described. The power of the technique is illustrated by its application to the D and A conformations of DNA using the single crystal diffractometer, D19, at the Institut Laue-Langevin. Grenoble and the time of flight diffractometer, SXD, at the Rutherford Appleton ISIS Spallation Neutron Source. These studies show the existence of bound water closely associated with the DNA. The patterns of hydration in these two DNA conformations are quite distinct and are compared to those observed in X-ray single crystal studies of two-stranded oligodeoxynucleotides. Information on the location of water around the DNA double-helix from the neutron fiber diffraction studies is combined with that on the location of alkali metal cations from complementary X-ray high angle fiber diffraction studies at the Daresbury Laboratory SRS using synchrotron radiation. These analyses emphasize the importance of viewing DNA, water and ions as a single system with specific interactions between the three components and provide a basis for understanding the effect of changes in the concentration of water and ions in inducing conformational transitions in the DNA double-helix.

Microfocus X-ray Diffraction of Spherulites of Poly-3-hydroxybutyrate

The microfocus X-ray beamline at the European Synchrotron Radiation Facility has been used to investigate the variation in molecular orientation and crystallinity in spherulites of the organic polymer poly-3-hydroxybutyrate (PHB). This is the first report of the correlation of optical and X-ray measurements on spherulitic polymer films where X-ray diffraction patterns have been recorded and displayed continuously in real time while the specimen was tracked in steps of 10 mum across an incident X-ray beam with a diameter as small as 10 mum.

A high angle neutron fibre diffraction study of the hydration of the A conformation of the DNA double helix

A high angle neutron fibre diffraction study of the distribution of water around the A-form of DNA has been performed using the diffractometer D19 at the Institut Laue-Langevin, Grenoble. These experiments have exploited the ability to replace H2O surrounding the DNA by D2O so that isotopic difference Fourier maps can be computed in which peaks are identified with the distribution of water in the unit cell. All peaks of significant height have been accounted for by four families of water molecules whose positions and occupancies have been determined using least squares refinement. The coordinates of the water peaks making up each family do not deviate significantly from a regular helical arrangement with the same parameters as the DNA. Two of these families are of particular interest. The first consists of water molecules in the major groove linking successive charged phosphate oxygens along the polynucleotide chains. The second is associated with bases in the major groove and forms a central core of density along the helix axis. These two families provide a layer of hydration lining the interior wall of the major groove leaving a central channel to accommodate cations. The relationship between these observations and conformational stability is discussed.

Neutron fibre diffraction study of DNA hydration

Interactions with water are crucial to the conformation assumed by the DNA double helix. The location of water around the D conformation has been investigated in a neutron fibre diffraction study which shows that water is ordered in the minor groove of the DNA. The D conformation is important since its occurrence is limited to specific DNA base pair sequences which have been identified as functionally significant. This study is of particular interest because the D conformation has not been reported in single crystal studies of oligonucleotides.