Prevalence of faecal excretion of verocytotoxigenic Escherichia coli 0157 in cattle in England and Wales

During the decade to 1999, the incidence of human infections with the zoonotic pathogen verocytotoxin-producing Escherichia coli O157 (VTEC O157) increased in England and Wales. This paper describes the results of a survey of 75 farms to determine the prevalence of faecal excretion of VTEC O157 by cattle, its primary reservoir host, in England and Wales. Faecal samples were collected from 4663 cattle between June and December 1999. The prevalence of excretion by individual cattle was 4.2 per cent (95 per cent confidence interval [CI] 2.0 to 6.4) and 10.3 per cent (95 per cent CI 5.8 to 14.8) among animals in infected herds. The within-herd prevalence on positive farms ranged from 1.1 to 51.4 per cent. At least one positive animal was identified on 29 (38.7 per cent; 95 per cent CI 28.1 to 50.4) of the farms, including dairy, suckler and fattening herds. The prevalence of excretion was least in the calves under two months of age, peaked in the calves aged between two and six months and declined thereafter. The phage types identified most widely were 4, 34 and 2, which were each found on six of the 29 positive farms.

Mechanism and cleavage specificity of the H-N-H endonuclease colicin E9

Colicin endonucleases and the H-N-H family of homing enzymes share a common active site structural motif that has similarities to the active sites of a variety of other nucleases such as the non-specific endonuclease from Serratia and the sequence-specific His-Cys box homing enzyme I-PpoI. In contrast to these latter enzymes, however, it remains unclear how H-N-H enzymes cleave nucleic acid substrates. Here, we show that the H-N-H enzyme from colicin E9 (the E9 DNase) shares many of the same basic enzymological characteristics as sequence-specific H-N-H enzymes including a dependence for high concentrations of Mg2+ or Ca2+ with double-stranded substrates, a high pH optimum (pH 8-9) and inhibition by monovalent cations. We also show that this seemingly non-specific enzyme preferentially nicks double-stranded DNA at thymine bases producing 3'-hydroxy and 5'-phosphate termini, and that the enzyme does not cleave small substrates, such as dinucleotides or nucleotide analogues, which has implications for its mode of inhibition in bacteria by immunity proteins. The E9 DNase will also bind single-stranded DNA above a certain length and in a sequence-independent manner, with transition metals such as Ni2+ optimal for cleavage but Mg2+ a poor cofactor. Ironically, the H-N-H motif of the E9 DNase although resembling the zinc binding site of a metalloenzyme does not support zinc-mediated hydrolysis of any DNA substrate. Finally, we demonstrate that the E9 DNase also degrades RNA in the absence of metal ions. In the context of current structural information, our data show that the H-N-H motif is an adaptable catalytic centre able to hydrolyse nucleic acid by different mechanisms depending on the substrate and metal ion regime.

QT prolongation associated with azithromycin/amiodarone combination

Administration of oral azithromycin, in addition to previously well-tolerated long-term amiodarone therapy, was associated with a marked prolongation of QT interval and increased QT dispersion, both substrates for life-threatening ventricular tachyarrhythmia and torsades de pointes. This is a report of QT prolongation and increased QT dispersion associated with the use of azithromycin. The report assumes an added significance, in view of widespread empirical use of this antibiotic for the treatment of lower respiratory infections and belief of its safety in patients with cardiac diseases. Based on the authors' experience, they would like to emphasize that the combination of azithromycin with other drugs known to prolong QT or causing torsades de pointes be used with caution until the question of the proarrhythmic effect of azithromycin is resolved by further studies.

Use of proportional reporting ratios (PRRs) for signal generation from spontaneous adverse drug reaction reports

BACKGROUND

The process of generating 'signals' of possible unrecognized hazards from spontaneous adverse drug reaction reporting data has been likened to looking for a needle in a haystack. However, statistical approaches to the data have been under-utilised.

METHODS

Using the UK Yellow Card database, we have developed and evaluated a statistical aid to signal generation called a Proportional Reporting Ratio (PRR). The proportion of all reactions to a drug which are for a particular medical condition of interest is compared to the same proportion for all drugs in the database, in a 2 x 2 table. We investigated a group of newly-marketed drugs using as minimum criteria for a signal, 3 or more cases, PRR at least 2, chi-squared of at least 4.

FINDINGS

The database was used to examine retrospectively 15 drugs newly-marketed in the UK, with the highest levels of ADR reporting. The method identified 481 signals meeting the minimum criteria during the period 1996-8. Further evaluation of these showed that 70% were known adverse reactions, 13% were events which were likely to be related to the underlying disease and 17% were signals requiring further evaluation.

IMPLICATIONS

Proportional reporting ratios are a valuable aid to signal generation from spontaneous reporting data which are easy to calculate and interpret, and various refinements are possible.

Comparison of UK paediatric cardiac surgical performance by analysis of routinely collected data 1984-96: was Bristol an outlier?

BACKGROUND

Reports of high mortality after paediatric cardiac surgery at the Bristol Royal Infirmary, UK, led to the establishment of an independent public inquiry. A key question was whether or not the mortality statistics in Bristol were unusual compared with other specialist centres. To answer this question, we did a retrospective analysis of mortality in the UK using two datasets.

METHODS

Data from the UK Cardiac Surgical Register (CSR; January, 1984, to March, 1996) and Hospital Episode Statistics (HES; April, 1991, to December, 1995) were obtained for all 12 major centres in which paediatric cardiac surgery is done in the UK. The main outcome measure was mortality within 30 days of a cardiac surgical procedure. We estimated excess deaths in Bristol using a random-effects model derived from the remaining 11 centres. Additionally, a sensitivity analysis was done and case-mix examined.

FINDINGS

For children younger than 1 year, in open operations, the mortality rate in Bristol was around double that of the other centres during 1991-95: within the CSR, there were 19.0 excess deaths (95% interval 2-32) among 43 deaths; and in HES, there were 24.1 excess deaths (12-34) among 41 deaths recorded. There was no strong evidence for excess mortality in Bristol for closed operations or for open operations in children older than 1 year.

INTERPRETATION

Our results suggest that Bristol was an outlier, and we do not believe that statistical variation, systematic bias in data collection, case-mix, or data quality can explain a divergence in performance of this size.

Mechanisms for discordant alternans

INTRODUCTION

Discordant alternans has the potential to produce larger alternans of the ECG T wave than concordant alternans, but its mechanism is unknown.

METHODS AND RESULTS

We demonstrate by one- and two-dimensional simulation of action potential propagation models that discordant alternans can form spontaneously in spatially homogeneous tissue through one of two mechanisms, due to the interaction of conduction velocity and action potential duration restitution at high pacing frequencies or through the dispersion of diastolic interval produced by ectopic foci. In discordant alternans due to the first mechanism, the boundaries marking regions of alternans with opposite phase arise far from the stimulus site, move toward the stimulus site, and stabilize. Dynamic splitting of action potential duration restitution curves due to electrotonic coupling plays a crucial role in this stability. Larger tissues and faster pacing rates are conducive to multiple boundaries, and inhomogeneities of tissue properties facilitate or inhibit formation of boundaries.

CONCLUSION

Spatial inhomogeneities of electrical restitution properties are not required to produce discordant alternans.

A trial of biosecurity as a means to control Campylobacter infection of broiler chickens

We ran a controlled intervention trial to assess whether the risk of a broiler flock becoming infected with Campylobacter could be reduced by biosecurity measures. These were a standard method of cleansing and disinfecting the poultry house prior to stocking, and a standard hygiene protocol followed by all personnel who entered the study house during the flock's life. Thirty-nine flocks were allocated to intervention or control groups in a ratio of 1:2. Intervention flocks were asked to follow the specified biosecurity measures; all flocks were monitored weekly for Campylobacter infection. Analysis of infection at 42 days of age and over the life of the flock showed that the risk of thermophilic Campylobacter infection of broilers was reduced by over 50% in intervention flocks. Parts of the intervention identified as significant in the univariable analysis included twice weekly replenishment of boot dip disinfectant; potential independent risk factors identified included the location of ventilation fans and daily sanitisation of the water supply. The non-random allocation of 10 flocks to the control group may have introduced some study bias (the effect of which is discussed in the paper).

Pharmacovigilance: a science or fielding emergencies?

Pharmacovigilance involves the assessment of risks and benefits of medicines. There are legal and regulatory aspects of this process, and the licensing of a new medicine is always provisional. The systems, in the past, have had limited statistical involvement, either in terms of personnel who are statistically trained, or in terms of statistical methods. This is changing. The high profile activities of pharmacovigilance have often been emergencies, though most is routine activity. Application of statistical thinking and of techniques is being done to help detect adverse effects of medicines rather earlier so that some emergencies may be avoided.

Alternans and the onset of ventricular fibrillation

Ventricular fibrillation (VF) remains a major cause of death in the industrialized world. Alternans (a period-doubling bifurcation of cardiac electrical activity) have recently been causally linked to the progression from ventricular tachycardia (VT) to VF, a more spatiotemporally disorganized electrical activity. In this paper, we show how alternans and thus VT degenerate to chaos via multiple, specific dynamical routes, largely associated with spatial components of VF dynamics, explaining failures of many recently proposed antiarrhythmic drugs. Identification of dynamical mechanisms for the onset of VF should lead to the design of future experiments and consequently to more effective antiarrhythmic drugs.

Steroid hormones use non-genomic mechanisms to control brain functions and behaviors: a review of evidence

Progestins, estrogens, androgens, and corticosteroids are capable of modifying brain functions and behaviors by mechanisms that involve the classic genomic model for steroid action. However, experimental evidence indicates that some responses to steroid hormones use non-classical, non-genomic mechanisms. This paper reviews the evidence that steroids can bind to receptors in the plasma membrane, activate cell signaling pathways, and regulate responses on a time scale of seconds or a few minutes. The existence of these alternative regulatory pathways for steroid hormones should make endocrinologists and neurobiologists change how they think about steroid hormones. It is no longer valid to assume that minute-to-minute changes in steroid concentrations are not regulating biologically important, short-term responses, or that the only steroids with biological functions are the ones that bind with high affinity to intracellular steroid receptors.

A longitudinal study of campylobacter infection of broiler flocks in Great Britain

One hundred flocks associated with five integrated poultry companies were monitored for one production cycle to investigate risk factors for campylobacter infection of poultry broiler flocks. Bacteriological samples were collected from one house of birds on each site at weekly intervals from 3 to 4 weeks of age until the birds were infected with campylobacter or the flock was depopulated (whichever was sooner). Environmental samples were obtained from 20 houses after cleansing and disinfection of the site before chick arrival. Conventional methods were used for the isolation of campylobacter. Questionnaires were used to collect information on potential risk factors for campylobacter infection. Discrete-time survival analysis was used to assess the influence of various exposures on the age at which the flock was infected with campylobacter. More than 40% of flocks were infected with campylobacter by the time the chicks were 4 weeks old and >90% by 7 weeks. Infection spread rapidly to most birds in a flock. Infection was not predictable by campylobacter status of the last flock reared on the site. (However, because most flocks were infected, the power to detect such an association was poor.) There was no evidence of environmental survival of campylobacters in broiler houses after adequate cleansing and disinfection. The most important predictors of protection from campylobacter were related to effective hygiene barriers (such as housing birds in buildings in a good state of repair, appropriate usage of disinfectant boot dips and a high standard of cleansing and disinfection of the drinking-water equipment). There was no evidence that rodents were a source of infection (but most sites operated effective vermin-control programmes).

A subset of kappa opioid ligands bind to the membrane glucocorticoid receptor in an amphibian brain

Previous studies demonstrated that a membrane receptor for glucocorticoids (mGR) exists in neuronal membranes from the roughskin newt (Taricha granulosa) and that this receptor appears to be a G protein-coupled receptor (GPCR). The present study investigated the question of whether this mGR recognizes nonsteroid ligands that bind to cognate receptors in the GPCR superfamily. To address this question, ligand-binding competition studies evaluated the potencies of various ligands to displace [3H]corticosterone (CORT) binding to neuronal membranes. Initial screening studies tested 21 different competitors and found that [3H]CORT binding was displaced only by dynorphin 1-13 amide (an endogenous kappa-selective opioid peptide), U50,488 (a synthetic kappa-specific agonist) and naloxone (a nonselective opioid antagonist). Follow-up studies revealed that the kappa agonists bremazocine (BRE) and ethylketocyclazocine (EKC) also displaced [3H]CORT binding to neuronal membranes, but that U69,593 (a kappa specific agonist) and nor-BNI (a kappa specific antagonist) were ineffective. The Ki values measured for the opioid competitors were in the subnanomolar to low micromolar range and had the following rank-order: dynorphin > U50,488 > naloxone > BRE > EKC. Because these ligands displaced, at most, only 70% of [3H]CORT specific binding, it appears that some [3H]CORT binding sites are opioid insensitive. Kinetic analysis of [3H]CORT off-rates in the presence of U50,488 and/or CORT revealed no differences in dissociation rate constants, suggesting that there is a direct, rather than allosteric, interaction with the [3H]CORT binding site. In summary, these results are consistent with the hypothesis that the high-affinity membrane binding site for [3H] CORT is located on a kappa opioid-like receptor.

Experimental studies on myocardial stretch and ventricular arrhythmia in hypertrophied and non-hypertrophied hearts

Hypertension affects about 5% of western populations and in the majority of cases it is of unknown aetiology. It exposes the heart to greater levels of myocardial stretch as a result of increased systolic pressure and peripheral resistance. Under certain circumstances myocardial stretch may trigger arrhythmias but the mechanisms and clinical importance of this phenomenon are unclear. This article outlines the risks of sudden cardiac death conferred by hypertension and left ventricular hypertrophy, presents the results of experiments using an animal model of myocardial stretch and discusses some possible mechanisms underlying stretch-induced arrhythmias which may be important in hypertensive patients.

Partial purification and biochemical characterization of a membrane glucocorticoid receptor from an amphibian brain

A membrane receptor for corticosterone (mGR) in the brain of the roughskin newt (Taricha granulosa) has been previously identified. This manuscript reports the evaluation of several chromatographic resins for enrichment of the newt mGR solubilized from neuronal membranes. A protein with an apparent molecular weight of 63 kDa was purified to near homogeneity following sequential purification using ammonium sulfate fractionation, wheat germ agglutinin (WGA)-agarose chromatography, hydroxylapatite chromatography, and an immobilized ligand affinity resin (Corticosterone-Sepharose). Other studies employed a novel protein differential display strategy and a photoaffinity labeling strategy to visualize candidate receptor proteins following SDS-PAGE. Both of these techniques also identified a 63 kDa protein, agreeing with the estimation of molecular weight from the purification data. Furthermore, the use of 2D SDS-PAGE following the photolabeling procedure showed the candidate 63 kDa protein to have a pI of approximately 5.0. Taken together these data suggest that the newt mGR is an acidic glycoprotein with an apparent molecular weight of 63 kDa. Because these characteristics of newt mGR are inconsistent with the characteristics of intracellular glucocorticoid receptors, these two receptor proteins are apparently distinct.

Increased waist size and weight in relation to consumption of Areca catechu (betel-nut); a risk factor for increased glycaemia in Asians in east London

Type 2 diabetes is commoner in Asians than Caucasians. Many nitrosamines are diabetogenic, causing both type 2 and type 1 diabetes. Of CD1 mice fed with betel-nut or associated nitrosamines 8.5% develop glucose intolerance with marked obesity. Glycaemia and anthropometric risk markers for type 2 diabetes were therefore examined in relation to betel usage in 993 'healthy' Bangladeshis by one bilingual research-worker (N.M.). Of these, 12% had known diabetes. A further 145 of 187 subjects 'at-risk' of diabetes (spot glucose > 6.5 mmol/l < 2 h after food, or > 4.5 mmol/l > 2 h after food) had a second blood glucose sample taken; sixty-one were confirmed as 'at-risk', and had an oral glucose tolerance test; nine new diabetics were identified. Multiple regression analysis showed that spot blood glucose values decreased with time after eating (P = 0.0005) and increased independently with waist size (P = 0.0005) and age (P = 0.0005) without relationships to other aspects of the diet, season or smoking. Waist size was strongly related to betel usage independent of other factors such as age. Betel use interacted with sex, relating to increasing glycaemia only in females. Since waist and age were the major markers of increasing glycaemia we suggest that betel chewing, a habit common to about 10% of the world population (more than 200 million people) may contribute to the risk of developing type 2 diabetes mellitus.

Improving dideoxynucleotide-triphosphate utilisation by the hyper-thermophilic DNA polymerase from the archaeon Pyrococcus furiosus

Polymerases from the Pol-I family which are able to efficiently use ddNTPs have demonstrated a much improved performance when used to sequence DNA. A number of mutations have been made to the gene coding for the Pol-II family DNA polymerase from the archaeon Pyrococcus furiosus with the aim of improving ddNTP utilisation. 'Rational' alterations to amino acids likely to be near the dNTP binding site (based on sequence homologies and structural information) did not yield the desired level of selectivity for ddNTPs. However, alteration at four positions (Q472, A486, L490 and Y497) gave rise to variants which incorporated ddNTPs better than the wild type, allowing sequencing reactions to be carried out at lowered ddNTP:dNTP ratios. Wild-type Pfu-Pol required a ddNTP:dNTP ratio of 30:1; values of 5:1 (Q472H), 1:3 (L490W), 1:5 (A486Y) and 5:1 (Y497A) were found with the four mutants; A486Y representing a 150-fold improvement over the wild type. A486, L490 and Y497 are on analpha-helix that lines the dNTP binding groove, but the side chains of the three amino acids point away from this groove; Q472 is in a loop that connects this alpha-helix to a second long helix. None of the four amino acids can contact the dNTP directly. Therefore, the increased selectivity for ddNTPs is likely to arise from two factors: (i) small overall changes in conformation that subtly alter the nucleotide triphosphate binding site such that ddNTPs become favoured; (ii) interference with a conformational change that may be critical both for the polymerisation step and discrimination between different nucleotide triphosphates.

A read-ahead function in archaeal DNA polymerases detects promutagenic template-strand uracil

Deamination of cytosine to uracil is the most common promutagenic change in DNA, and it is greatly increased at the elevated growth temperatures of hyperthermophilic archaea. If not repaired to cytosine prior to replication, uracil in a template strand directs incorporation of adenine, generating a G.C --> A.U transition mutation in half the progeny. Surprisingly, genomic analysis of archaea has so far failed to reveal any homologues of either of the known families of uracil-DNA glycosylases responsible for initiating the base-excision repair of uracil in DNA, which is otherwise universal. Here we show that DNA polymerases from several hyperthermophilic archaea (including Vent and Pfu) specifically recognize the presence of uracil in a template strand and stall DNA synthesis before mutagenic misincorporation of adenine. A specific template-checking function in a DNA polymerase has not been observed previously, and it may represent the first step in a pathway for the repair of cytosine deamination in archaea.

Would you take blood through a venflon?

One way of saving junior doctors' time and patients' pain is to take blood samples through a venflon immediately after its insertion. This is not, however, universal practise as some believe the results, especially urea and electrolytes, are unreliable. We have surveyed junior doctors in our hospital about this practise and prospectively compared venflon and vein blood samples.

Identification of amino acid residues critical for aggregation of human CC chemokines macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and RANTES. Characterization of active disaggregated chemokine variants

Human CC chemokines macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and RANTES (regulated on activation normal T cell expressed) self-associate to form high-molecular mass aggregates. To explore the biological significance of chemokine aggregation, nonaggregating variants were sought. The phenotypes of 105 hMIP-1alpha variants generated by systematic mutagenesis and expression in yeast were determined. hMIP-1alpha residues Asp26 and Glu66 were critical to the self-association process. Substitution at either residue resulted in the formation of essentially homogenous tetramers at 0.5 mg/ml. Substitution of identical or analogous residues in homologous positions in both hMIP-1beta and RANTES demonstrated that they were also critical to aggregation. Our analysis suggests that a single charged residue at either position 26 or 66 is insufficient to support extensive aggregation and that two charged residues must be present. Solution of the three-dimensional NMR structure of hMIP-1alpha has enabled comparison of these residues in hMIP-1beta and RANTES. Aggregated and disaggregated forms of hMIP-1alpha, hMIP-1beta, and RANTES generally have equivalent G-protein-coupled receptor-mediated biological potencies. We have therefore generated novel reagents to evaluate the role of hMIP-1alpha, hMIP-1beta, and RANTES aggregation in vitro and in vivo. The disaggregated chemokines retained their human immunodeficiency virus (HIV) inhibitory activities. Surprisingly, high concentrations of RANTES, but not disaggregated RANTES variants, enhanced infection of cells by both M- and T-tropic HIV isolates/strains. This observation has important implications for potential therapeutic uses of chemokines implying that disaggregated forms may be necessary for safe clinical investigation.

Site-directed mutagenesis of phosphate-contacting amino acids of bovine pancreatic deoxyribonuclease I

Bovine pancreatic deoxyribonuclease I (DNase I) is an endonuclease which cleaves double-stranded DNA. Cocrystal structures of DNase I with oligonucleotides have revealed interactions between the side chains of several amino acids (N74, R111, N170, S206, T207, and Y211) and the DNA phosphates. The effects these interactions have on enzyme catalysis and DNA hydrolysis selectivity have been investigated by site-directed mutagenesis. Mutations to R111, N170, T207, and Y211 severely compromised activity toward both DNA and a small chromophoric substrate. A hydrogen bond between R111 (which interacts with the phosphate immediately 5' to the cutting site) and the essential amino acid H134 is probably required to maintain this histidine in the correct orientation for efficient hydrolysis. Both T207 and Y211 bind to the phosphate immediately 3' to the cleavage site. Additionally, T207 is involved in binding an essential, structural, calcium ion, and Y211 is the nearest neighbor to D212, a critical catalytic residue. N170 interacts with the scissile phosphate and appears to play a direct role in the catalytic mechanism. The mutation N74D, which interacts with a phosphate twice removed from the scissile group, strongly reduced DNA hydrolysis. However, a comparison of DNase I variants from several species suggests that certain amino acids, which allow interaction with phosphates (positively charged or hydrogen bonding), are tolerated. S206, which binds to a DNA phosphate two positions away from the cleavage site, appears to play a relatively unimportant role. None of the enzyme variants, including a triple mutation in which N74, R111, and Y211 were altered, affected DNA hydrolysis selectivity. This suggests that phosphate binding residues play no role in the selection of DNA substrates.

A nodoventricular fiber associated with dual AV nodal conduction, AV nodal reentrant tachycardia, and anterior location of the slow AV nodal pathway

We present a case of a patient with a nodoventricular tract, associated with dual AV nodal conduction and AV nodal reentrant tachycardia, and an anteroseptal location of the slow AV nodal pathway. The remarkable feature of this case is the site of successful ablation, in the anteroseptum just anterior and superior to the His bundle, where both preexcitation and dual AV nodal physiology were abolished.

Ventricular fibrillation: one spiral or many?

Ventricular fibrillation is the major cause of sudden cardiac death, the leading cause of death in the industrialized world; however, the mechanisms for its onset are not well understood. To further understand the dynamics of fibrillation at and near its onset, we compared spatial and temporal variability of mean interactivation intervals in a stable canine model for ventricular fibrillation. Temporal variability was very small, suggesting that the relevant physiological parameters remained constant during our experiments. Spatial variability was usually significantly larger and appeared incompatible with the dynamics of a single, meandering spiral wave. This confirmed recent results that a single spiral wave cannot generate ventricular fibrillation. Thus the onset of fibrillation is a multistage process, with spiral-wave breakdown providing a crucial step in the quasi-periodic route to fibrillation.