Authority in the analytic relationship.
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Humans↗
Biomedical subjects
Paul Williams
Publications and source records attributed to Paul Williams.
Quorum sensing: an emerging target for antibacterial chemotherapy?
The emergence of bacterial strains exhibiting resistance to multiple antibiotic classes poses a major threat to medicine and public health. This has been compounded over the last few decades by the failure of drug discovery programmes to provide new broad spectrum antibacterials with novel modes of action. As a consequence, there is renewed interest in antibacterial targets which disrupt the capacity of pathogenic bacteria to cause infection by attenuating virulence. In this respect, one crucial feature of almost all bacterial infections is that the pathogen must attain a critical cell population density sufficient to overwhelm the host defences. Many pathogens are now known to regulate diverse physiological processes, including virulence, in a cell density dependent manner through cell-cell communication. This phenomenon, which relies upon the interaction of a diffusible signal molecule with a sensor kinase or response regulator, has become known as 'quorum sensing'. This review considers the molecular basis of quorum sensing and whether it constitutes a potential therapeutic target for the design of small molecule antagonists capable of controlling infection by attenuating adaptation to the host environment.
4-Butyrolactone↗
The biocontrol strain Pseudomonas fluorescens F113 produces the Rhizobium small bacteriocin, N-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone, via HdtS, a putative novel N-acylhomoserine lactone synthase.
Several different species of Pseudomonas: produce N:-acylhomoserine lactones (AHLs), quorum-sensing signal molecules which are involved in the cell-density-dependent control of secondary metabolite and virulence gene expression. When Pseudomonas fluorescens F113 was cross-streaked against AHL biosensors capable of sensitively detecting either short (C(4)-C(8)) or long (C(10)-C(14)) acyl chain AHLs, no activity was detectable. However, by extracting cell-free stationary-phase culture supernatants with dichloromethane followed by reverse-phase HPLC, three distinct fractions were obtained capable of activating the AHL biosensors. Three AHLs were subsequently characterized using high-resolution MS and chemical synthesis. These were (i) N:-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone (3OH, C(14:1)-HSL), a molecule previously known as the Rhizobium leguminosarum small bacteriocin as a consequence of its growth inhibitory properties, (ii) N:-decanoylhomoserine lactone (C(10)-HSL) and (iii) N:-hexanoylhomoserine lactone (C(6)-HSL). A gene (hdtS) capable of directing synthesis of all three P. fluorescens AHLs in Escherichia coli was cloned and sequenced. In vitro transcription/translation of hdtS yielded a protein of approximately 33 kDa capable of directing the synthesis of 3OH, C(14:1)-HSL, C(10)-HSL and C(6)-HSL in E. coli. HdtS does not belong to either of the known AHL synthase families (LuxI or LuxM) and is related to the lysophosphatidic acid acyltransferase family. HdtS may therefore constitute a member of a third protein family capable of AHL biosynthesis.
4-Butyrolactone↗
RpoS-dependent stress tolerance in Pseudomonas aeruginosa.
Pseudomonas aeruginosa is able to persist during feast and famine in many different environments including soil, water, plants, animals and humans. The alternative sigma factor encoded by the rpoS gene is known to be important for survival under stressful conditions in several other bacterial species. To determine if the P. aeruginosa RpoS protein plays a similar role in stationary-phase-mediated resistance, an rpoS mutant was constructed and survival during exposure to hydrogen peroxide, high temperature, hyperosmolarity, low pH and ethanol was investigated. Disruption of the rpoS gene resulted in a two- to threefold increase in the rate of kill of stationary-phase cells. The rpoS mutant also survived less well than the parental strain during the initial phase of carbon or phosphate-carbon starvation. However, after 25 d starvation the remaining population of culturable cells was not significantly different. Stationary-phase cells of the RpoS-negative strain were much more stress resistant than exponentially growing RpoS-positive cells, suggesting that factors other than the RpoS protein must be associated with stationary-phase stress tolerance in P. aeruginosa. Comparison of two-dimensional PAGE of the rpoS mutant and the parental strain showed four major modifications of protein patterns associated with the rpoS mutation.
Bacterial Proteins↗
The Staphylococcus aureus and Staphylococcus epidermidis transferrin-binding proteins are expressed in vivo during infection.
Staphylococci express a 42 kDa cell-wall-associated protein which functions as a receptor for the mammalian iron-binding glycoprotein transferrin. To determine whether this transferrin-binding protein (TBP) is expressed during infection, Staphylococcus aureus and Staphylococcus epidermidis were grown in vivo in chambers implanted intraperitoneally in rats. SDS-PAGE and Western blotting of cell wall proteins prepared from staphylococci recovered directly from the chambers revealed the presence of both the TBP and bacterial-surface-associated rat transferrin. To obtain evidence for the in vivo expression of the staphylococcal TBPs in humans, sera and human peritoneal dialysate (HPD) from non-infected patients undergoing continuous ambulatory peritoneal dialysis (CAPD) and sera from healthy human volunteers were screened for anti-TBP antibodies. Western immunoblots revealed that three out of ten samples from the latter group, seven out of ten HPD samples and ten of ten CAPD patient serum samples contained antibodies to the TBP of both S. aureus and S. epidermidis. To gain further insights into the appearance of TBP antibodies, HPD samples were collected over time from CAPD patients whose HPD samples taken immediately after catheter insertion lacked anti-TBP antibodies. In two of these patients, each of whom experienced an episode of peritonitis due to S. epidermidis or Staphylococcus hominis, antibodies to the TBP appeared in the HPD collected immediately post-infection. To determine whether such TBP antibodies were capable of blocking interactions between transferrin and its staphylococcal receptor, HPD immunoglobulin fractions were purified using protein A-Sepharose beads. In competition assays, these immunoglobulins blocked the binding of 125I-labelled transferrin both to whole bacteria and to the isolated 42 kDa TBPs of S. aureus and S. epidermidis. These provide evidence to show that staphylococcal TBPs are expressed in vivo during infection.
Animals↗
Cryptic carbapenem antibiotic production genes are widespread in Erwinia carotovora: facile trans activation by the carR transcriptional regulator.
Few strains of Erwinia carotovora subsp. carotovora (Ecc) make carbapenem antibiotics. Strain GS101 makes the basic carbapenem molecule, 1-carbapen-2-em-3-carboxylic acid (Car). The production of this antibiotic has been shown to be cell density dependent, requiring the accumulation of the small diffusible molecule N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) in the growth medium. When the concentration of this inducer rises above a threshold level, OHHL is proposed to interact with the transcriptional activator of the carbapenem cluster (CarR) and induce carbapenem biosynthesis. The introduction of the GS101 carR gene into an Ecc strain (SCRI 193) which is naturally carbapenem-negative resulted in the production of Car. This suggested that strain SCRI 193 contained functional cryptic carbapenem biosynthetic genes, but lacked a functional carR homologue. The distribution of trans-activatable antibiotic genes was assayed in Erwinia strains from a culture collection and was found to be common in a large proportion of Ecc strains. Significantly, amongst the Ecc strains identified, a larger proportion contained trans-activatable cryptic genes than produced antibiotics constitutively. Southern hybridization of the chromosomal DNA of cryptic Ecc strains confirmed the presence of both the car biosynthetic cluster and the regulatory genes. Identification of homologues of the transcriptional activator carR suggests that the cause of the silencing of the carbapenem biosynthetic cluster in these strains is not the deletion of carR. In an attempt to identify the cause of the silencing in the Ecc strain SCRI 193 the carR homologue from this strain was cloned and sequenced. The SCRI 193 CarR homologue was 94% identical to the GS101 CarR and contained 14 amino acid substitutions. Both homologues could be expressed from their native promoters and ribosome-binding sites using an in vitro prokaryotic transcription and translation assay, and when the SCRI 193 carR homologue was cloned in multicopy plasmids and reintroduced into SCRI 193, antibiotic production was observed. This suggested that the mutation causing the silencing of the biosynthetic cluster in SCRI 193 was leaky and the cryptic Car phenotype could be suppressed by multiple copies of the apparently mutant transcriptional activator.
Base Sequence↗
Quorum sensing and Chromobacterium violaceum: exploitation of violacein production and inhibition for the detection of N-acylhomoserine lactones.
Quorum sensing relies upon the interaction of a diffusible signal molecule with a transcriptional activator protein to couple gene expression with cell population density. In Gram-negative bacteria, such signal molecules are usually N-acylhomoserine lactones (AHLs) which differ in the structure of their N-acyl side chains. Chromobacterium violaceum, a Gram-negative bacterium commonly found in soil and water, produces the characteristic purple pigment violacein. Previously the authors described a violacein-negative, mini-Tn5 mutant of C. violaceum (CV026) in which pigment production can be restored by incubation with supernatants from the wild-type strain. To develop this mutant as a general biosensor for AHLs, the natural C. violaceum AHL molecule was first chemically characterized. By using solvent extraction, HPLC and mass spectrometry, a single AHL, N-hexanoyl-L-homoserine lactone (HHL), was identified in wild-type C. violaceum culture supernatants which was absent from CV026. Since the production of violacein constitutes a simple assay for the detection of AHLs, we explored the ability of CV026 to respond to a series of synthetic AHL and N-acylhomocysteine thiolactone (AHT) analogues. In CV026, violacein is inducible by all the AHL and AHT compounds evaluated with N-acyl side chains from C4 to C8 in length, with varying degrees of sensitivity. Although AHL compounds with N-acyl side chains from C10 to C14 are unable to induce violacein production, if an activating AHL (e.g. HHL) is incorporated into the agar, these long-chain AHLs can be detected by their ability to inhibit violacein production. The versatility of CV026 in facilitating detection of AHL mixtures extracted from culture supernatants and separated by thin-layer chromatography is also demonstrated. These simple bioassays employing CV026 thus greatly extend the ability to detect a wide spectrum of AHL signal molecules.
Chromobacterium↗
Reiterative justice?
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Alcoholic Intoxication↗
A comparison of the cost-effectiveness of almotriptan and sumatriptan in the treatment of acute migraine using a composite efficacy/tolerability end point.
OBJECTIVE: To use a composite efficacy/tolerability end point to compare the cost-effectiveness, from the perspective of a U.S. health care payer, of almotriptan and sumatriptan in the treatment of an acute migraine attack. METHODS: The composite end point. Sustained pain free and No Adverse Events. (SNAE) was created from the sustained pain free and adverse event rates obtained in a meta-analysis of 53 placebo-controlled trials of oral triptans. The total direct cost of treating a single migraine attack was calculated from published sources. RESULTS: In the base-case analysis, the average cost-effectiveness ratios (CERs) were 82 US dollars , 133 US dollars , and 138 US dollars (per attack at which SNAE is achieved, 2004 prices) for almotriptan 12.5 mg, sumatriptan 50 mg, and sumatriptan 100 mg, respectively; the incremental CERs for almotriptan 12.5 mg were 12 US dollars and 16 US dollars (compared with sumatriptan 50 mg and sumatriptan 100 mg, respectively) per incremental attack at which SNAE is achieved. Sensitivity analyses were conducted to explore the impact of (1) relaxing the base-case assumptions (independence of efficacy and tolerability, uniform apportionment of health service use costs across attacks, number of tablets used to treat 1 attack); (2) varying input costs; and (3) uncertainty in the efficacy and tolerability estimates from the meta-analysis. In all of these sensitivity analyses, almotriptan 12.5 mg remained cost effective compared with sumatriptan 50 mg and 100 mg. CONCLUSION: Almotriptan was economically superior to sumatriptan in the treatment of a migraine attack.
Acute Disease↗
Timely initiation of dialysis--single-exchange experience in 39 patients starting peritoneal dialysis.
OBJECTIVE: To establish the effectiveness and patient acceptability of initiating peritoneal dialysis (PD) according to published guidelines. SETTING: A university teaching hospital and a neighboring district general hospital. DESIGN: Nonrandomized prospective pilot study. PATIENTS: 39 patients with a Kt/V > 2.0 attending predialysis clinics at both hospitals agreed to participate in this study. METHODS: Patients were started on a single exchange of dialysate overnight. Dialysis adequacy was monitored at least every 2 months and incremental increases in dialysis were used to maintain combined urinary and dialysis Kt/V above 2.0. Routine laboratory parameters and complications of dialysis were monitored during the follow-up period. RESULTS: The mean weekly Kt/V at initiation of dialysis was 2.09. Median actuarial survival on a single exchange before requiring incremental dialysis was 297 days. At the end of the study period, all patients were still alive: 8 remained on 1 exchange, 18 were on more than 1 exchange, 8 had switched to hemodialysis, and 5 had received renal transplants. During the 12,665 patient-days on single-exchange dialysis, there were 14 hospital admissions of 12 patients. This resulted in a mean of 1.64 hospital days per patient-year for the whole group. During the follow-up period there were 2 episodes of bacterial peritonitis, 3 pleural leaks, 1 patent processus vaginalis, and 1 inguinal hernia that required surgical intervention. The use single daily icodextrin exchanges was associated with a 46% incidence of culture-negative peritonitis. CONCLUSIONS: This pilot study has shown that a timely start of dialysis with a single overnight PD exchange is acceptable to patients. Incremental dialysis as residual renal function falls is easily managed and patients also find this acceptable. Complication and hospitalization rates were low. The presence of residual renal function often allows complications to be managed without the need for hemodialysis. The use of icodextrin as a single-exchange dialysate is associated with sterile peritonitis in a significant proportion of cases.
Adult↗