Biomedical subjects

S G Williams

Publications and source records attributed to S G Williams.

At least 55 records · Page 3Linked to original sources

PubMed1998

A functional homolog of Escherichia coli NhaR in Vibrio cholerae.

Escherichia coli NhaR controls expression of a sodium/proton (Na+/H+) antiporter, NhaA. The Vibrio cholerae NhaR protein shows over 60% identity to those of Escherichia coli and Salmonella enteritidis. V. cholerae NhaR complements an E. coli nhaR mutant for growth in 100 mM LiCl-33 mM NaCl, pH 7.6, and enhances the Na+-dependent induction of an E. coli chromosomal nhaA::lacZ fusion. These findings indicate functional homology to E. coli NhaR. Two V. cholerae nhaR mutants were constructed by using kanamycin resistance cartridge insertion at different sites to disrupt the gene. Both mutants showed sensitivity to growth in 120 mM LiCl, pH 9.2, compared with the wild-type strain and could be complemented by the introduction of V. cholerae nhaR on a low-copy-number plasmid. An nhaR mutation had no detectable effect on the virulence of the V. cholerae strain in the infant mouse model, suggesting that the antiporter system involved is not required in vivo, at least in this animal model.

Amino Acid Sequence↗

PubMed1997

The management of high-grade hilar strictures by endoscopic insertion of self-expanding metal endoprostheses.

BACKGROUND AND STUDY AIMS: Treatment options for unresectable hepatic hilar strictures include percutaneous or endoscopic stent insertion, using either standard Teflon or self-expanding metal endoprostheses. The use of Teflon stents is complicated by stent migration and high occlusion rates. Published series of endoscopically placed metal stents have not concentrated on their use in the treatment of high-grade hilar strictures (Bismuth grades II and III). We therefore undertook a prospective and open pilot study to evaluate the efficacy of endoscopically placed metal endoprostheses in the palliation of jaundice due to high-grade hilar strictures. PATIENTS AND METHODS: Self-expanding metal stents were placed endoscopically in 17 patients (nine women, eight men; median age 64 years, range 33-77). Of the 17 malignancies 11 patients (65%) had a diagnosis of cholangiocarcinoma, and 12 (71%) had Bismuth grade III strictures. RESULTS: The stents were inserted successfully in all 1 patients. Adequate drainage, as demonstrated by a significant reduction in bilirubin, was achieved in 1: (88%); the two patients in whom drainage failed had extensive intrahepatic disease. Early complications (cholangitis) developed in one patients (6%), and there were seven late complications (41%) in five patients (four occluded stents and three cases of duodenal compression). The stent patency appeared to be prolonged (median stent patency 12 months, range 1.5-24 months, in patients surviving five months or more). The median survival was ten months (range 1-48 months) after stent insertion. All of the patients died during follow-up. CONCLUSIONS: These results suggest that endoscopically placed metal stents offer effective palliation for high grade hilar malignancies, although controlled trial comparing the use of metal and Teflon endoprostheses in this patient group are required.

Bile Duct Neoplasms↗

PubMed1997

Characterization of the Vibrio cholerae El Tor lipase operon lipAB and a protease gene downstream of the hly region.

We have cloned and sequenced a region encoding a lipase operon and a putative, previously uncharacterized metalloprotease of Vibrio cholerae O1. These lie downstream of hlyA and hlyB, which encode the El Tor hemolysin and methyl-accepting chemotactic factor, respectively. Previous reports identified the hlyC gene downstream of hlyAB, encoding an 18.3-kDa protein. However, we now show that this open reading frame (ORF) encodes a 33-kDa protein, and since the amino acid sequence is highly homologous to the triacylglyceride-specific lipase of Pseudomonas spp., hlyC has been renamed lipA. LipA contains the highly conserved pentapeptide and catalytic triad amino acid regions of the catalytic sites of other lipases. The region downstream of lipA has been sequenced and has revealed ORFs lipB and prtV. The amino acid sequence of lipB is homologous to those of the accessory lipase proteins (lipase-specific foldase) required by Pseudomonas and various other bacterial species for the production of mature active lipase, and in agreement with this, we show that both lipA and lipB are required to restore a lipase-deficient lipA null mutant of V. cholerae. The intergenic stop codon for lipA overlaps the ribosome-binding site for lipB, and a stem-loop resembling a rho-independent terminator is present immediately downstream from lipB, suggesting that lipA and lipB form a lipase operon in V. cholerae. prtV lies downstream of lipAB but is transcribed in the opposite direction and is predicted to share the same putative transcriptional terminator with lipAB. The zinc-binding and catalytic domains conserved among many metalloproteases are present in PrtV, which is highly homologous to the immune inhibitor A (InA) metalloprotease of Bacillus thuringiensis. PrtV was visualized as approximately 102 kDa, which is consistent with the coding capacity of the gene. The genetic organization of this region suggests that it is possibly part of a pathogenicity island, encoding products capable of damaging host cells and/or involved in nutrient acquisition by V. cholerae. However, neither lipA nor prtV null mutants were attenuated in the infant mouse model, nor did they exhibit reduced colonization potential compared with wild type in competition experiments.

Amino Acid Sequence↗

PubMed1997

A prognostic model for the prediction of survival in cystic fibrosis.

BACKGROUND: The treatment for endstage cystic fibrosis is, where appropriate, double-lung, heart-lung or, occasionally, heart-lung-liver transplantation. Optimising the timing of transplantation depends upon an accurate prediction of survival, but while current criteria give some guidance to this, they are not based upon statistically derived prognostic models. METHODS: Data collected prospectively on 403 patients with cystic fibrosis, recruited between 1969 and 1987 (cohort A), were analysed by log rank and univariate Cox regression analysis to determine variables that accurately predict survival. The significant variables were then subject to time dependent multivariate Cox regression analysis to generate a prognostic model. The model was validated, within the study population, using split sample testing, and was subsequently validated in a further cohort of patients recruited since October 1988 (cohort B). RESULTS: One hundred and eighty eight (50.4%) of the study cohort died within the study period. Percentage predicted forced expiratory volume in one second (FEV1), percentage predicted forced vital capacity (FVC), short stature, high white cell count (WBC), and chronic liver disease (as evidenced by the presence of hepatomegaly) were negatively correlated with survival. These variables, when combined into a prognostic index, accurately predicted one year survival in the study population and in the cohort recruited since 1988. CONCLUSION: This prognostic index may prove valuable in predicting prognosis in other cohorts with cystic fibrosis and thereby improve the timing of transplantation.

Adolescent↗

PubMed1997

Vascular tree structure affects lung blood flow heterogeneity simulated in three dimensions.

Pulmonary arterial tree structures related to blood flow heterogeneity were simulated by using a symmetrical, bifurcating model in three-dimensional space. The branch angle (Theta), daughter-parent length ratio (rL), branch rotation angle (phi), and branch fraction of parent flow (gamma) for a single bifurcation were defined and repeated sequentially through 11 generations. With phi fixed at 90 degrees , tree structures were generated with Theta between 60 and 90 degrees , rL between 0.65 and 0.85, and an initial segment length of 5.6 cm and sectioned into 1-cm3 samples for analysis. Blood flow relative dispersions (RD%) between 52 and 42% and fractal dimensions (Ds) between 1.20 and 1.15 in 1-cm3 samples were observed even with equal branch flows. When gamma not equal 0.5, RD% increased, but Ds either decreased with gravity bias of higher branch flows or increased with random assignment of higher flows. Blood flow gradients along gravity and centripetal vectors increased with biased flow assignment of higher flows, and blood flows correlated negatively with distance only when gamma not equal 0.5. Thus a recursive branching vascular tree structure simulated Ds and RD% values for blood flow heterogeneity similar to those observed experimentally in the pulmonary circulation due to differences in the number of terminal arterioles per 1-cm3 sample, but blood flow gradients and a negative correlation of flows with distance required unequal partitioning of blood flows at branch points.

Algorithms↗

PubMed1996

Randomised study of endoscopic biliary endoprosthesis versus duct clearance for bileduct stones in high-risk patients.

BACKGROUND: The value of an endoprosthesis for long-term management of bileduct stones has not been formally established. The main theoretical advantage of endoprosthesis insertion (BE) over conventional endoscopic duct clearance (DC) is the prevention of stone impaction, with obstruction and consequent cholangitis or pancreatitis. In a randomised study we compared the results of these two methods in patients with symptomatic bileduct stones who were at high risk because of old age (> 70 yr) or serious debilitating disease. METHODS: 43 high-risk patients were randomised to BE with a 7F double-pigtail endoprosthesis and < 0.75 cm sphincterotomy, and 43 to DC with standard 1.25-1.50 cm sphincterotomy and stone extraction by balloon or basket, with or without mechanical lithotripsy. The principal endpoint was the rate of biliary related complications. FINDINGS: In the BE group biliary drainage was achieved in the first session in all but one patient (who required 2 sessions). In the DC group, 24 patients had duct clearance at the first attempt and 35 (81%) after a median of 2 sessions (range 2-4); eight of this group had an endoprosthesis inserted to maintain long-term drainage. At 72 h the complication rates were 7% in the BE group and 16% in the DC group (p = 0.18). However, the long-term complication rate for BE was higher: by Kaplan-Meier analysis, at a median of 20 months the proportions free of biliary complications were 64% BE and 86% DC (p = 0.03, log-rank test). INTERPRETATION: For immediate bileduct drainage, endoprosthesis insertion proved a safe and effective alternative to duct clearance. Because of the risk of subsequent cholangitis, its use as a definitive treatment should be confined to highly selected cases.

Aged↗

PubMed1996

Molecular characterisation of formamidase from Methylophilus methylotrophus.

A 3.2-kbp PstI fragment of DNA encoding formamidase from the methylotrophic bacterium Methylophilus methylotrophus which had previously been cloned (pNW3) [Wyborn, N.R., Scherr, D.J. & Jones, C.W. (1994) Microbiology 140, 191-195], was subcloned as a 2.3 kbp HindIII fragment (pNW323). Nucleotide sequencing showed that the subclone contained two genes which encoded formamidase (fmdA) and a possible regulatory protein (fmdB). Predicted molecular masses for FmdA and FmdB were 44438 Da (compared with approximately 44500 Da by electrospray mass spectrometry and 51000 Da by SDS/PAGE of the purified enzyme) and 12306 Da, respectively. The derived amino acid sequence of formamidase was supported by N-terminal amino acid sequencing of the enzyme and of proteolytic fragments prepared from it using V8 endoproteinase and was 57% similar to that of the acetamidase from Mycobacterium smegmatis. The structural similarities between these two enzymes, and their existence as a separate class of bacterial amidase, were confirmed by immunological investigations.

Amidohydrolases↗

PubMed1996

Systemic haemodynamic changes in patients with cystic fibrosis with and without chronic liver disease.

BACKGROUND/AIMS: There are well-documented systemic haemodynamic changes associated with chronic liver disease. Patients with cystic fibrosis may develop chronic liver disease, but it is not known whether these systemic haemodynamic changes develop and, if they do, whether they are influenced by the associated chronic lung disease. We therefore undertook a study to document the circulatory status of cystic fibrosis patients with and without chronic liver disease. METHODS: Fifty-six subjects with cystic fibrosis were studied. Systemic haemodynamic and pulmonary parameters, in sub-groups both with (LD) and without (NLD) liver disease, were measured at rest and during measured exertion. Cystic fibrosis-related chronic liver disease was diagnosed using previously validated ultrasound criteria. Patients underwent assessment at rest and in the fourth minute of seated bicycle exercise at 25W. Heart rate (ECG), blood pressure (semiautomated sphygmomanometer), aortic blood velocity (pulsed Doppler suprasternal probe), arterial oxygen saturation (pulse oximeter) and respiratory variables (pneumotachometer with expired gas analysis by an automatic system) were measured. RESULTS: A complete data set was available for 45 patients (22 LD) at rest and 40 patients (19 LD) on exercise. The patients were well matched for age, sex, height, weight, and pulmonary function. Patients with chronic liver disease had a hyperkinetic circulation while ventilatory variables before and during exercise were similar for the two groups. There was evidence that the circulatory changes were exacerbated by both deteriorating hepatic and pulmonary function. CONCLUSIONS: Cystic fibrosis patients with chronic liver disease have a hyperdynamic circulation similar to that documented in other forms of chronic liver disease. These circulatory changes are exacerbated by deteriorating hepatic and pulmonary function.

Adult↗

PubMed1996

Vibrio cholerae Hcp, a secreted protein coregulated with HlyA.

Hcp is a 28-kDa secreted protein of Vibrio cholerae regulated coordinately with the hemolysin, HlyA. Both proteins show a dependence on HlyU for expression, suggesting that Hcp may be secreted by V. cholerae in vivo. We have identified and sequenced two genes for Hcp, designated hcpA and hcpB (hemolysin-coregulated protein). The genes encode identical amino acid sequences. Both express a 28-kDa protein, despite open reading frames with only a 19-kDa capacity, suggesting that the Hcp protein runs aberrantly on polyacrylamide gel electrophoresis. There is no cleavage involved in secretion of Hcp from the cell, suggesting a novel mechanism of secretion. An hcp null mutant was constructed, and this strain displayed no deficiency in virulence or colonization in the infant mouse cholera model. From sequence data and primer extension analysis, we predict that the hcp promoter is the sigma 54 type, with a candidate integration host factor binding site upstream. Although hcp and hlyA are coregulated by HlyU, there are no obvious similarities between their promoters. We predict that an intermediate regulator may be involved in the activation of hcp by HlyU. This raises the possibility that HlyU is part of a regulatory cascade.

Amino Acid Sequence↗

PubMed1995

Regulation of tcp genes in classical and El Tor strains of Vibrio cholerae O1.

Expression of genes encoding the toxin-co-regulated pilus (TCP) varies between the two biotypes of Vibrio cholerae O1. Sequence analysis of the tcp locus from the classical and El Tor strains has revealed differences in the intergenic regions between tcpI and tcpP, and tcpH and tcpA, which may be involved in regulation. To investigate this possibility, transcription of tcpA, and the predicted upstream promoters for tcpI and tcpP, has been analysed in the classical and El Tor strains using promoter-cat (chloramphenicol acetyltransferase) fusions. Together with primer extension analyses, these studies indicate that the tcpA and tcpP promoters are toxR-dependent and suggest that TcpP may be involved in activation of both the tcpI and tcpP promoters. We conclude that differences in the level of tcpA expression in a classical and an El Tor strain are likely to be due to the effect of sequence variation on the ability of control factors to act on these regulatory regions.

Bacterial Outer Membrane Proteins↗

PubMed1995

An ultrasound scoring system for the diagnosis of liver disease in cystic fibrosis.

Advances in the management of the pulmonary complications of cystic fibrosis may result in an increasing prevalence of patients with chronic liver disease which may, therefore, become more important in the long-term management of cystic fibrosis patients. However, no simple and reliable test is available for the diagnosis of liver disease in cystic fibrosis. In particular percutaneous liver biopsy is highly inaccurate and potentially dangerous. Imaging techniques, including real-time ultrasound scanning, have been used to evaluate the hepato-biliary system in cystic fibrosis and may represent the best available techniques for documenting hepatic involvement. The purposes of this study were to construct an ultrasound scoring system using three cardinal features of hepatic ultrasound in cystic fibrosis: coarseness of the parenchyma, nodularity of the liver edge and increased periportal echogenicity, to enable the accurate, early diagnosis of liver involvement in cystic fibrosis. The scoring system was validated by correlating the results against ultrasound markers of portal hypertension, clinical and haematological data. The scoring system proved to be reproducible and to correlate well with the markers of hepatic disease detailed above. The results also suggest that the scoring system may allow the identification of patients with pre-cirrhotic chronic liver disease and so may prove of value in selecting a sub-group of patients more likely to respond to therapy.

Adult↗

PubMed1995

Agrobacterium radiobacter and related organisms take up fructose via a binding-protein-dependent active-transport system.

Washed cells of Agrobacterium radiobacter prepared from a fructose-limited continuous culture (D 0.045 h-1) transported D(-)[U-14C]fructose in a linear manner for up to 4 min at a rate several-fold higher than the rate of fructose utilization by the growing culture. D(-)[U-14C]Fructose transport exhibited a high affinity for fructose (KT < 1 microM) and was inhibited to varying extents by osmotic shock, by the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, and by unlabelled sugars (D-fructose/D-mannose > D-ribose > D-sorbose > D-glucose/D-galactose/D-xylose; no inhibition by D-arabinose). Prolonged growth of A. radiobacter in fructose-limited continuous culture led to the selection of a novel strain (AR100) which overproduced a fructose-binding protein (FBP) and showed an increased rate of fructose transport. FBP was purified from osmotic-shock fluid using anion-exchange fast protein liquid chromatography (FPLC). The monomeric protein (M(r) 34,200 by SDS-PAGE and 37,700 by gel-filtration FPLC) bound D-[U-14C]-fructose stoichiometrically (1.17 nmol nmol FBP-1) and with high affinity (KD 0.49 microM) as shown by equilibrium dialysis. Binding of D-[U-14C]fructose by FBP was variably inhibited by unlabelled sugars (D-fructose/D-mannose > D-ribose > D-sorbose; no inhibition by D-glucose, D-galactose or D-arabinose). The N-terminal amino acid sequence of FBP (ADTSVCLI-) was similar to that of several sugar-binding proteins from other species of bacteria. Fructose transport and FBP were variably induced in batch cultures of A. radiobacter by growth on different carbon sources (D-fructose > D-ribose/D-mannose > D-glucose; no induction by succinate). An immunologically similar protein to FBP was produced by Agrobacterium tumefaciens and various species of Rhizobium following growth on fructose. It is concluded that fructose is transported into A. radiobacter and related organisms via a periplasmic fructose/mannose-binding-protein-dependent active-transport system, in contrast to the phosphotransferase system used by many other species of bacteria.

Amino Acid Sequence↗

PubMed1995

Recent advances in the endoscopic management of variceal bleeding.

For the first time the endoscopist has more than one option for the management of gastro-oesophageal varices. It is now feasible to select the appropriate therapy on the basis of the clinical setting. Acute injection sclerotherapy remains a quick and simple technique for the control of active bleeding from oesophageal varices, and could be followed two or three days later by banding ligation. Earlier obliteration of varices with this technique may offer the prospect of only two or three sessions of therapy. The availability of the tissue adhesives and thrombin as injectates for fundal gastric varices provide the option of an initial attempt at endoscopic therapy in this high risk group.

Esophageal and Gastric Varices↗

PubMed1995

Hypokalaemic rhabdomyolysis: an unusual presentation of coeliac disease.

OBJECTIVE: To describe the clinical presentation and management of a patient with hypokalaemic rhabdomyolysis secondary to coeliac disease. DESIGN: Retrospective study. SETTING: Hospital based. PATIENT: A 60-year-old Caucasian man presenting with weakness caused by hypokalaemic rhabdomyolysis secondary to coeliac disease. INTERVENTIONS: Following the diagnosis by jejunal biopsy, the patient was treated with both intravenous and oral potassium supplements, and a gluten-free diet. OUTCOME MEASURES: Resolution of weakness and restitution of normal villous architecture following treatment. RESULTS: The patient's myopathy responded to the potassium supplements, his diarrhoea and histological changes resolved while on the gluten-free diet. CONCLUSION: Patients with coeliac disease may present with hypokalaemia in association with steatorrhoea. If potassium loss is rapid, rhabdomyolysis may occur. Coeliac disease should be considered a cause of malabsorption-induced hypokalaemic rhabdomyolysis.

Adult↗

PubMed1994

Management of variceal haemorrhage.

Fig 2 gives an algorithm for the treatment of bleeding oesophageal varices. Initial resuscitation of the patient is of paramount importance, ideally followed by early interventional endoscopy. Recent advances in available endoscopic techniques enable the endoscopist to suit the therapeutic approach to the clinical situation. Injection sclerotherapy remains the initial treatment of choice in bleeding patients. Endoscopic banding ligation is an alternative, best used in patients who have spontaneously stopped bleeding or as a complementary treatment a few days after the initial session of injection sclerotherapy. The tissue adhesives and thrombin can be used to treat bleeding gastric varices. [table: see text] Should the endoscopic expertise not be available, drug treatment (with somatostatin or octreotide) or balloon tamponade are the treatments of choice. Transjugular intrahepatic portal-systemic stent shunt is a new effective technique, not yet widely available, which has a documented complication rate that has yet to be fully defined. It is a good alternative to surgery as a "rescue" procedure for patients who continue to bleed despite two sessions of endoscopic intervention.

Balloon Occlusion↗

PubMed1994

The effect of nutrient limitation on glycerol uptake and metabolism in continuous cultures of Pseudomonas aeruginosa.

Pseudomonas aeruginosa NM48, a non-mucoid derivative of an alginate-producing strain isolated from a cystic fibrosis patient, was grown in batch culture with glycerol, glucose or succinate as carbon source, and in continuous culture (D 0.05 h-1) under glycerol or glucose limitation. Glycerol uptake, glycerol kinase and glycerol-3-phosphate dehydrogenase were induced by glycerol, but not by glucose or succinate. Linear uptake of [14C]glycerol by washed cells (Km < or = 2 microM) was inhibited by unlabelled glycerol and glyceraldehyde, but not by cyanide or the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), and was accompanied by substantial intracellular accumulation of glycerol-3-phosphate and/or dihydroxyacetone phosphate but not glycerol. Prolonged growth under glycerol limitation led to substantial increases in the activities and/or concentrations of the enzymes catalysing glycerol uptake and metabolism, together with a 48,000 M(r) outer-membrane protein which was also over-expressed following prolonged growth under glucose limitation. The N-terminal amino acid sequence (AEAFSPN-) and electrophoretic properties of this protein were the same as those of the previously characterized glucose porin (OprB) from P. aeruginosa, indicating that this porin is active with both glucose and glycerol. It is concluded that during growth under glycerol limitation, glycerol is transported into P. aeruginosa NM48 via OprB and a high-affinity, binding-protein-independent facilitated-diffusion system.

Adaptation, Biological↗

PubMed1994

DNA replication studies with coliphage 186: the involvement of the Escherichia coli DnaA protein in 186 replication is indirect.

The inability of coliphage 186 to infect productively a dnaA(Ts) mutant at a restrictive temperature was confirmed. However, the requirement by 186 for DnaA is indirect, since 186 can successfully infect suppressed dnaA (null) strains. The block to 186 infection of a dnaA(Ts) strain at a restrictive temperature is at the level of replication but incompletely so, since some 20% of the phage specific replication seen with infection of a dnaA+ host does occur. A mutant screen, to isolate host mutants blocked in 186-specific replication but not in the replication of the close relative coliphage P2, which has no DnaA requirement, yielded a mutant whose locus we mapped to the rep gene. A 186 mutant able to infect this rep mutant was isolated, and the mutation was located in the phage replication initiation endonuclease gene A, suggesting direct interaction between the Rep helicase and phage endonuclease during replication. DNA sequencing indicated a glutamic acid-to-valine change at residue 155 of the 694-residue product of gene A. In the discussion, we speculate that the indirect need of DnaA function is at the level of lagging-strand synthesis in the rolling circle replication of 186.

Bacterial Proteins↗

PubMed1994

Thrombin--an effective treatment for gastric variceal haemorrhage.

The optimum treatment of gastric varices has still to be defined. Lesser curve gastric varices may be treated by injection sclerotherapy, but this has a limited role in the treatment of fundal gastric varices. Surgical intervention is commonly needed but carries a high mortality in patients with advanced liver disease. This study evaluated the use of thrombin for the treatment of gastric varices in 11 consecutive patients (nine with fundal, two with high lesser curve varices), identified as having bled from this site. Bovine thrombin (1000 U/ml) was injected intravariceally (mean volume 5.5 ml, range 2-10 ml) producing initial haemostasis in all 11 cases. Varices were considered thrombosed or obliterated in all patients after a median of two injection episodes (range 1-3). After a median follow up of nine months only one patient had rebled from a gastric varix. Thrombin may represent a valuable alternative injectate for the treatment of gastric varices.

Acute Disease↗