Biomedical subjects

Richard D Hayward

Publications and source records attributed to Richard D Hayward.

At least 19 recordsLinked to original sources

PubMed2007

Shunt infection: is there a near-miss scenario?

OBJECT: The aim of this study was to establish whether microbiological contamination at the time of shunt insertion can be detected and used to predict the likelihood of subsequent shunt infection. METHODS: A prospective study of pediatric patients undergoing primary shunt insertion was undertaken. Following the protocol devised for this study, three swab samples were collected from the surgical wounds during each procedure. These samples were incubated and subcultured, and the isolates were identified and stored. In patients who subsequently presented with clinical evidence of shunt infection, cerebrospinal fluid (CSF) was analyzed using microscopy, tissue cultures, and sensitivity testing. The organisms isolated at the time of shunt insertion and those responsible for subsequent shunt infection were then compared. The study population consisted of 107 pediatric patients. Because one patient underwent placement of an additional contralateral shunt system, there were 108 total shunt insertions yielding 325 swab samples. Organisms were identified in cultures of 50 swab samples (15%) obtained in 40 patients (37%). In seven of these 40 patients (17.5%) a CSF infection subsequently developed. In only one patient was the infectious organism the same as that isolated from the swab specimens. In an additional six patients (8.8%) a CSF infection occurred despite the lack of growth in the cultures from intraoperative swab samples. CONCLUSIONS: The organisms responsible for shunt infection were rarely detected in the operative wound at the time of shunt insertion, leading the authors to conclude that the vulnerable period for bacterial colonization of shunts may not be restricted to the operative procedure as is commonly believed, but may extend throughout the postoperative period of wound healing. These findings have implications not only for a better understanding of the cause of shunt infections but also for the development of strategies to prevent them.

Bacteriological Techniques↗

PubMed2006

Is there a role for magnetic resonance imaging in the evaluation of non-traumatic intraparenchymal haemorrhage in children?

BACKGROUND: In contrast to adults, intraparenchymal haemorrhage (IPH) is at least as common as ischaemic stroke in children. There is often uncertainty about the most appropriate modality for imaging in the acute stage. OBJECTIVE: To examine the diagnostic value of MRI and MR angiography (MRA) in the detection of underlying pathology in children with non-traumatic IPH. MATERIALS AND METHODS: A retrospective review was conducted of children with IPH from January 1997 to March 2003. After exclusion of patients with traumatic IPH or previously diagnosed vascular malformation, aneurysm, or brain tumour, 50 children were identified. Case notes and imaging studies were reviewed. RESULTS: An underlying lesion was demonstrated with MR in two-thirds of children (25/38) with IPH. A vascular lesion was the commonest cause, followed by tumour. Three children had false-negative MR scans. CONCLUSION: MR is a valuable non-invasive imaging modality for detection of both vascular and non-vascular causes of paediatric IPH. The high rate of the latter in childhood makes incorporation of MR into paediatric IPH imaging protocols especially important. Clinical guidelines regarding the optimum sequence of investigations in non-traumatic IPH would be helpful to standardize practice and enable critical appraisal.

Adolescent↗

PubMed2006

Pathogens reWritE Rho's rules.

Many bacterial pathogens use a specialized "type III" secretion system to deliver virulence effector proteins into host mammalian cells. In this issue of Cell, Alto et al. (2006) describe a new family of effectors that share a WxxxE sequence motif. These effectors directly stimulate host signaling pathways by mimicking activated Ras-like cellular GTPases.

Amino Acid Motifs↗

PubMed2006

Exploiting pathogenic Escherichia coli to model transmembrane receptor signalling.

Many microbial pathogens manipulate the actin cytoskeleton of eukaryotic target cells to promote their internalization, intracellular motility and dissemination. Enteropathogenic and enterohaemorrhagic Escherichia coli, which both cause severe diarrhoeal disease, can adhere to mammalian intestinal cells and induce reorganization of the actin cytoskeleton into 'pedestal-like' pseudopods beneath the extracellular bacteria. As pedestal assembly is triggered by E. coli virulence factors that mimic several host cell-signalling components, such as transmembrane receptors, their cognate ligands and cytoplasmic adaptor proteins, it can serve as a powerful model system to study eukaryotic transmembrane signalling. Here, we consider the impact of recent data on our understanding of both E. coli pathogenesis and cell biology, and the rich prospects for exploiting these bacterial factors as versatile tools to probe cellular signalling pathways.

Adaptation, Physiological↗

PubMed2006

Prevalence of abnormal pattern reversal visual evoked potentials in craniosynostosis.

BACKGROUND: The purpose of this study was to examine the prevalence and type of changes observed in the pattern reversal visual evoked potentials recorded at the first assessment of children with craniosynostosis. METHODS: Visual evoked potentials were recorded from 114 patients with craniosynostosis. Eighty-one patients were syndromic and 33 were nonsyndromic. No patient had received any craniofacial surgical intervention. At the time of the test, 22 of 40 patients were aged 6 months and younger, and 18 patients were between 6 months and 1 year of age. Pattern reversal visual evoked potentials were recorded from a midoccipital electrode positioned 3 cm above the inion. The pattern reversal visual evoked potentials elicited to 50' checks with three reversals per second viewed with both eyes were analyzed for n80-p100 amplitude, p100 latency, and breadth of waveform. RESULTS: Sixty percent of patients had abnormal pattern reversal visual evoked potentials to 50' checks. This did not show a significant association with age, or classification of craniosynostosis. CONCLUSIONS: The high prevalence of abnormal pattern reversal visual evoked potentials to a robust stimulus suggests that visual pathway dysfunction, as measured electrophysiologically, can affect a majority of patients with craniosynostosis. This study indicates that a baseline evaluation of all children with craniosynostosis at their first presentation is essential if subsequent electrophysiologic visual pathway monitoring is to take place.

Craniosynostoses↗

PubMed2005

Spontaneous regression of residual low-grade cerebellar pilocytic astrocytomas in children.

BACKGROUND: Cerebellar low-grade astrocytomas (CLGAs) of childhood are benign tumours and are usually curable by surgical resection alone or combined with adjuvant radiotherapy. OBJECTIVE: To undertake a retrospective study of our children with CLGA to determine the optimum schedule for surveillance imaging following initial surgery. In this report we describe the phenomenon of spontaneous regression of residual tumour and discuss its prognostic significance regarding future imaging. MATERIALS AND METHODS: A retrospective review was conducted of children treated for histologically proven CLGA at Great Ormond Street Hospital from 1988 to 1998. RESULTS: Of 83 children with CLGA identified, 13 (15.7%) had incomplete resections. Two children with large residual tumours associated with persistent symptoms underwent additional treatment. Eleven children were followed by surveillance imaging alone for a mean of 6.83 years (range 2-13.25 years). Spontaneous tumour regression was seen in 5 (45.5%) of the 11 children. There were no differences in age, gender, symptomatology, histological grade or Ki-67 fractions between those with spontaneous tumour regression and those with progression. There was a non-significant trend that larger volume residual tumours progressed. CONCLUSIONS: Residual tumour followed by surveillance imaging may either regress or progress. For children with residual disease we recommend surveillance imaging every 6 months for the first 2 years, every year for years 3, 4 and 5, then every second year if residual tumour is still present 5 years after initial surgery. This would detect not only progressive or recurrent disease, but also spontaneous regression which can occur later than disease progression.

Adolescent↗

PubMed2005

Cholesterol binding by the bacterial type III translocon is essential for virulence effector delivery into mammalian cells.

A ubiquitous early step in infection of man and animals by enteric bacterial pathogens like Salmonella, Shigella and enteropathogenic Escherichia coli (EPEC) is the translocation of virulence effector proteins into mammalian cells via specialized type III secretion systems (TTSSs). Translocated effectors subvert the host cytoskeleton and stimulate signalling to promote bacterial internalization or survival. Target cell plasma membrane cholesterol is central to pathogen-host cross-talk, but the precise nature of its critical contribution remains unknown. Using in vitro cholesterol-binding assays, we demonstrate that Salmonella (SipB) and Shigella (IpaB) TTSS translocon components bind cholesterol with high affinity. Direct visualization of cell-associated fluorescently labelled SipB and parallel immunogold transmission electron microscopy revealed that cholesterol levels limit both the amount and distribution of plasma membrane-integrated translocon. Correspondingly, cholesterol depletion blocked effector translocation into cultured mammalian cells by not only the related Salmonella and Shigella TTSSs, but also the more divergent EPEC system. The data reveal that cholesterol-dependent association of the bacterial TTSS translocon with the target cell plasma membrane is essential for translocon activation and effector delivery into mammalian cells.

3T3 Cells↗

PubMed2005

Surveillance imaging strategies following surgery and/or radiotherapy for childhood cerebellar low-grade astrocytoma.

OBJECT: The authors sought to evaluate surveillance strategies for the detection and monitoring of residual and recurrent disease in children with cerebellar low-grade astrocytomas (CLGAs) treated surgically or with radiotherapy. Patients were divided into three groups: (1) those in whom a "complete" resection was achieved; (2) those with residual disease with no immediate adjuvant therapy; and (3) those who received radiotherapy for residual/recurrent disease. METHODS: Magnetic resonance (MR) imaging studies and clinical data obtained in children with CLGA who presented between January 1988 and September 1998 were reviewed. Eighty-four children were followed for a mean period of 73 months (range 2-159 months). One child died. Of the 70 children in whom a complete resection was achieved, nine (13%) developed a recurrence detected by surveillance imaging at 6, 8, 9, 9, 13, 27, 39, 44, and 47 months, respectively. Following an incomplete resection, radiologically detected tumor progression leading to further treatment was detected at 7, 9, 12, 13, and 20 months, respectively, and an additional six tumors regressed or stablized. In 11 of 12 children treated with radiotherapy, stabilization/regression occurred radiologically at a mean of 14.9 months. CONCLUSIONS: The authors recommend surveillance MR imaging in children treated for CLGA at 6 months and 1, 2, 3.5, and 5 years following a complete resection and after radiotherapy performed either initially or following recurrence. For follow up of residual tumor, 6-month interval imaging for at least 3 years, yearly images for another 2 years, and subsequent 2-year imaging is recommended.

Adolescent↗

PubMed2004

Phosphorylation of the enteropathogenic E. coli receptor by the Src-family kinase c-Fyn triggers actin pedestal formation.

Enteropathogenic Escherichia coli (EPEC) causes diarrhoeal disease worldwide. Pathogen adherence to host cells induces reorganization of the actin cytoskeleton into 'pedestal-like' pseudopods beneath the extracellular bacteria. This requires two bacterial virulence factors that mimic a ligand-receptor interaction. EPEC delivers its own receptor, the translocated intimin receptor (Tir), into the target cell plasma membrane, which is phosphorylated on interaction with the bacterial surface protein intimin. Tir phosphorylated on Tyr 474 (ref. 4) binds the cellular adaptor Nck, triggering actin polymerization. Nevertheless, despite its critical role, the mechanism of Tir Tyr 474 phosphorylation remains unknown. Here, by artificially uncoupling Tir delivery and activity, we show that Tir phosphorylation and Nck-dependent pedestal formation require the Src-family kinase (SFK) c-Fyn. SFK inhibitors prevent Tyr 474 phosphorylation, and cells lacking c-fyn are resistant to pedestal formation. c-Fyn exclusively phosphorylates clustered Tir in vitro, and kinase knockdown suppresses Tir phosphorylation and pedestal formation in cultured cells. These results identify the transient interaction with host c-Fyn as a pivotal link between bacterial Tir and the cellular Nck-WASP-Arp2/3 cascade, illuminating a tractable experimental system in which to dissect tyrosine kinase signalling.

Actin Cytoskeleton↗

PubMed2004

Control of actin turnover by a salmonella invasion protein.

Salmonella force their way into nonphagocytic host intestinal cells to initiate infection. Uptake is triggered by delivery into the target cell of bacterial effector proteins that stimulate cytoskeletal rearrangements and membrane ruffling. The Salmonella invasion protein A (SipA) effector is an actin binding protein that enhances uptake efficiency by promoting actin polymerization. SipA-bound actin filaments (F-actin) are also resistant to artificial disassembly in vitro. Using biochemical assays of actin dynamics and actin-based motility models, we demonstrate that SipA directly arrests cellular mechanisms of actin turnover. SipA inhibits ADF/cofilin-directed depolymerization both by preventing binding of ADF and cofilin and by displacing them from F-actin. SipA also protects F-actin from gelsolin-directed severing and reanneals gelsolin-severed F-actin fragments. These data suggest that SipA focuses host cytoskeletal reorganization by locally inhibiting both ADF/cofilin- and gelsolin-directed actin disassembly, while simultaneously stimulating pathogen-induced actin polymerization.

Actin Depolymerizing Factors↗

PubMed2004

Self-association of EPEC intimin mediated by the beta-barrel-containing anchor domain: a role in clustering of the Tir receptor.

Outer membrane intimin directs attachment of enteropathogenic Escherichia coli (EPEC) via its Tir receptor in mammalian target cell membranes. Phosphorylation of Tir triggers local actin polymerization and the formation of 'pedestal-like' pseudopods. We demonstrate that the intimin protein contains three domains, a flexible N-terminus (residues 40-188), a central membrane-integrated beta-barrel (189-549), and a tightly folded Tir-binding domain (550-939). Intimin was shown by electron microscopy to form ring-like structures with an approximately 7 nm external diameter and an electron dense core, and to form channels of 50picoSiemens conductance in planar lipid bilayers. Gel filtration, multiangle light scattering and cross-linking showed that this central beta-barrel membrane-anchoring domain directs intimin dimerization. Isothermal titration calorimetry revealed a high affinity, single-binding site interaction of 2 : 1 stoichiometry between dimeric intimin and Tir, and modelling suggests that this interaction determines a reticular array-like superstructure underlying receptor clustering. In support of this model, actin rearrangement induced in Tir-primed cultured cells by intimin-containing proteoliposomes was dependent on the concentration of both intimin and Tir, and co-localized with clustered phosphorylated Tir.

3T3 Cells↗

PubMed2004

The target cell plasma membrane is a critical interface for Salmonella cell entry effector-host interplay.

Salmonella species trigger host membrane ruffling to force their internalization into non-phagocytic intestinal epithelial cells. This requires bacterial effector protein delivery into the target cell via a type III secretion system. Six translocated effectors manipulate cellular actin dynamics, but how their direct and indirect activities are spatially and temporally co-ordinated to promote productive cytoskeletal rearrangements remains essentially unexplored. To gain further insight into this process, we applied mechanical cell fractionation and immunofluorescence microscopy to systematically investigate the subcellular localization of epitope-tagged effectors in transiently transfected and Salmonella-infected cultured cells. Although five effectors contain no apparent membrane-targeting domains, all six localized exclusively in the target cell plasma membrane fraction and correspondingly were visualized at the cell periphery, from where they induced distinct effects on the actin cytoskeleton. Unexpectedly, no translocated effector pool was detectable in the cell cytosol. Using parallel in vitro assays, we demonstrate that the prenylated cellular GTPase Cdc42 is necessary and sufficient for membrane association of the Salmonella GTP exchange factor and GTPase-activating protein mimics SopE and SptP, which have no intrinsic lipid affinity. The data show that the host plasma membrane is a critical interface for effector-target interaction, and establish versatile systems to further dissect effector interplay.

Animals↗

PubMed2004

Recurrent atlantoaxial rotatory fixation in children: a rare complication of a rare condition. Report of four cases.

Atlantoaxial rotatory fixation (AARF) is an uncommon condition of childhood. Occasionally AARF may recur. The authors describe the cases of four patients with recurrent AARF (RAARF). The probable cause of the RAARF and operative procedure selected are discussed. In three cases, attempts were made to stabilize the atlantoaxial complex rather than to perform fusion to preserve the function of the joint complex. Joint stabilization is performed by incorporating a "check ligament" into the joint construct between the axial spinous process and the atlantal lateral mass. The authors believe this technique of joint stabilization augments the strength of the joint, allowing normal, but preventing excessive, rotation, until the joint reaches physiological maturity.

Atlanto-Axial Joint↗

PubMed2003

The purified Shigella IpaB and Salmonella SipB translocators share biochemical properties and membrane topology.

An essential early event in Shigella and Salmonella pathogenesis is invasion of non-phagocytic intestinal epithelial cells. Pathogen entry is triggered by the delivery of multiple bacterial effector proteins into target mammalian cells. The Shigella invasion plasmid antigen B (IpaB), which inserts into the host plasma membrane, is required for effector delivery and invasion. To investigate the biochemical properties and membrane topology of IpaB, we purified the native full-length protein following expression in laboratory Escherichia coli. Purified IpaB assembled into trimers via an N-terminal domain predicted to form a trimeric coiled-coil, and is predominantly alpha-helical. Upon lipid interaction, two transmembrane domains (residues 313-333 and 399-419) penetrate the bilayer, allowing the intervening hydrophilic region (334-398) to cross the membrane. Purified IpaB integrated into model, erythrocyte and mammalian cell membranes without disrupting bilayer integrity, and induced liposome fusion in vitro. An IpaB-derived 162 residue alpha-helical polypeptide (IpaB(418-580)) is a potent inhibitor of IpaB-directed liposome fusion in vitro and blocked Shigella entry into cultured mammalian cells at 10(-8) M. It is also a heterologous inhibitor of Salmonella invasion protein B (SipB) activity and Salmonella entry. In contrast, IpaB(418-580) failed to prevent the contact-dependent haemolytic activity of Shigella. These findings question the proposed direct link between contact-dependent haemolysis and Shigella entry, and demonstrate that IpaB and SipB share biochemical properties and membrane topology, consistent with a conserved mode of action during cell entry.

Amino Acid Sequence↗

PubMed2003

Surveillance neuroimaging of intracranial medulloblastoma in children: how effective, how often, and for how long?

OBJECT: The goal of this paper was to review brain and spine images obtained in children with medulloblastomas to determine the risk factors for tumor recurrence and to assess the impact of surveillance imaging on patient outcomes among patients who remain alive 1 month postsurgery. METHODS: Imaging studies and clinical data obtained in children with medulloblastomas, who presented between January 1987 and August 1998, were retrospectively reviewed. Images were termed surveillance if they were follow-up studies and symptom prompted if they were obtained to investigate new symptoms. One hundred seven patients (mean age 6 years and 3 months, range 2 months-15 years and 6 months) were entered into the study. Fifty-three children experienced tumor recurrence; 41 had one recurrence, nine had two, and three had three recurrences. Surveillance imaging revealed 10 of the first 53 recurrences and 15 of all 68 recurrences. When the first recurrence was identified by the emergence of symptoms (42 patients), the children tended to survive for a shorter time (hazard ratio 3.72, 95% confidence interval 1.42-9.76, p = 0.008) than children in whom the first recurrence was detected before symptoms occurred (10 patients). The median survival time following symptomatic tumor recurrence was 4 months and that after surveillance-detected tumor recurrence was 17 months. The median increased survival time among patients whose recurrence was asymptomatic and identified by imaging studies was 13 months, more than half the mean time between surveillance imaging sessions. Incomplete tumor resection was associated with a significantly reduced time to recurrence (p = 0.048) and to death (p = 0.002). The number of recurrences that were experienced was associated with a reduced time to death (p < 0.001). CONCLUSIONS: Surveillance imaging is associated with an increase in survival in children with medulloblastomas. More frequent surveillance imaging in children with incomplete tumor excision and recurrent disease may further improve the length of survival.

Adolescent↗

PubMed2003

The jugular foramen in complex and syndromic craniosynostosis and its relationship to raised intracranial pressure.

BACKGROUND AND PURPOSE: Complex and syndromic craniosynostosis can be complicated by raised intracranial pressure (ICP), which in the absence of other identifiable origins, is probably caused by venous hypertension. Children with these conditions have been shown to have narrowing of the sigmoid sinus-jugular vein complex. Evidence of bony narrowing of the jugular foramina in children with complex or syndromic craniosynostosis and raised ICP compared with that in children with craniosynostosis without raised ICP would provide support for the theory that venous hypertension occurs in the former children. METHODS: Measurements of the jugular foramina were obtained from reformatted helical CT scans obtained in 12 children with complex or syndromic craniosynostosis and raised ICP (group 1) and in two control groups of children with normal ICP. The first control group comprised 10 children with simple nonsyndromic synostosis of one or two sutures (group 2), and the second control group included nine children with complex or syndromic craniosynostosis (group 3). RESULTS: Children with raised ICP had narrower jugular foramina than did the age-matched control subjects. For group 1, the mean diameter of jugular foramina was 6.5 mm; group 2, 11.5 mm (P <.01); and group 3, 10 mm (P <.05). No significant difference existed between the two control groups. CONCLUSION: Significantly narrower jugular foramina in children with raised ICP is further evidence of the role of venous outflow obstruction and intracranial venous hypertension in the development of raised ICP in complex and syndromic craniosynostosis.

Child↗

PubMed2002

Congenital lumbosacral lipomas: pitfalls in analysing the results of prophylactic surgery.

OBJECTIVES: Our objectives were to examine the assumption that the natural history of congenital lumbosacral lipomas in children presenting early and those presenting late is the same, and to determine whether there are factors that might predict the post-operative outcome of surgery among the presenting features of children with lumbosacral lipomas. METHODS: The authors present a clinical series of 50 consecutive cases of congenital lumbosacral lipoma that had been treated surgically. All patients underwent both pre- and post-operative urological assessment and pre-operative imaging with MRI. The case notes, urology assessments and MRI films were studied to provide data on the clinical presentation, follow-up history and urological outcome of the children, as well as on the anatomical features of their lipomas. RESULTS: Analysis of the data revealed a predominance in girls and a bimodal distribution of age at presentation with peaks at 0-2 and 7-8 years. Skin stigmata were more frequent in children below 6 years of age than in older children (P=0.035). The MRI scans demonstrated that the conus lay within the sacral canal more often in girls than boys (P=0.025). Severe bladder dysfunction was significantly more frequent in those presenting at =3 years of age (P=0.017) and there were more normal outcomes in patients operated upon before the age of 3 than in those operated upon at or after this age ( P<0.0001). Eight patients who had been operated upon had severe urological problems at the time of their last assessment (median age of 8 years and 2 months). They were predominantly girls with major pre-operative urological dysfunction. CONCLUSIONS: Formal pre-operative urological assessment proved to be the strongest determinant of final urological outcome. Other predictors of poor urological outcome were large lipoma size and sacral position for the lipoma. This series demonstrates how early and late presenting children may represent different patient groups, follow different natural histories and may therefore not be reliable for comparison purposes. Future studies of prophylactic untethering need to follow cohorts beyond the age of deterioration found in untreated cases (8 years) and must report the salient MRI features that we suggest are predictive of poor outcome.

Adolescent↗

PubMed2002

Processing of viable Salmonella typhimurium for presentation of a CD4 T cell epitope from the Salmonella invasion protein C (SipC).

We have identified Salmonella invasion protein C (SipC) as a target antigen for CD4 T cell recognition in mice infected with Salmonella typhimurium. SipC is a product of the type III secretion system encoded by S. typhimurium pathogenicity island 1. A SipC-specific T cell response was induced by infection with either the C5 wild type or attenuated SL3261 vaccine strain of S. typhimurium. We localized the response of T cell lines from infected mice to an epitope near the carboxyl terminus of SipC (SipC(381-394)) and studied the way it was processed from viable S. typhimurium. We demonstrated that CD4 T cell recognition of this epitope required actin-dependent uptake of S. typhimurium. Presentation also occurred when transport of newly synthesized MHC class II from the endoplasmic reticulum was disrupted and when the pH of intracellular compartments was raised, suggesting presentation by mature MHC class II recycled from the macrophage surface into neutral intracellular compartments. Salmonellae are known to colonize macrophages by localizing to compartments that do not make contact with the bactericidal environment of late endosomes or lysosomes, and thus might avoid lysosomal antigen processing. However, we demonstrate that a CD4 T cell response to S. typhimurium-secreted proteins may be induced by an alternative pathway capable of antigen presentation in conditions similar to those in the compartments where Salmonella localize.

Animals↗