bluuebunny/crossref_metadata_2025 huggingface dataset:
Inflammatory Peeling Skin Syndrome Studied with Electron Microscopy
Authors: Tsai Katia , Valente Neusa Yuriko Sakae , Nico Marcello Menta Simonsen
Published: September 2006

Abstract:  Peeling skin syndrome is a rare autosomal recessive dermatosis characterized by lifelong continual skin shedding with underlying erythema. We present a 10‐year‐old boy with this disease. Easy peeling of the skin associated with keratotic areas was observed. Microscopic findings included psoriasiformis dermatitis. Cleavage was observed between corneocytes as well as between granular‐corneum cells and within the granular cell layer. Electron microscopic findings included intra‐ and intercellular cleavage of corneocytes and intracellular separation of granular cells. The molecular mechanisms of peeling skin syndrome are discussed.
Lichen Sclerosus of the Lip
Authors: Kelly Susan C. , Helm Klaus F. , Zaenglein Andrea L.
Published: September 2006

Abstract:  Lichen sclerosus is a chronic inflammatory mucocutaneous disorder predominately affecting prepubertal girls and postmenopausal women. Isolated lichen sclerosus affecting the oral mucosa is exceedingly rare. Only 13 patients with biopsy‐proved isolated oral disease have been reported in the literature. We report a 10‐year‐old Caucasian girl with a well‐demarcated 1.5 cm × 1.2 cm atrophic white plaque with a violaceous border and focal telangiectases on the right inferior vermillion lip, extending on to the labial mucosa. No other cutaneous surfaces, including genitalia, were involved. Incisional biopsy of the plaque on the lip revealed a patchy lichenoid infiltrate of lymphocytes associated with sclerosis of the papillary dermis and a thinned epidermis consistent with a diagnosis of lichen sclerosus. Treatment with a short course of high potency topical corticosteroids likely prevented the progression of this lesion.
Nonparametric Estimation of the Concordance Correlation Coefficient under Univariate Censoring
Authors: Guo Ying , Manatunga Amita K.
Published: September 2006

Summary Assessing agreement is often of interest in clinical studies to evaluate the similarity of measurements produced by different raters or methods on the same subjects. Lin's (1989, Biometrics45, 255–268) concordance correlation coefficient (CCC) has become a popular measure of agreement for correlated continuous outcomes. However, commonly used estimation methods for the CCC do not accommodate censored observations and are, therefore, not applicable for survival outcomes. In this article, we estimate the CCC nonparametrically through the bivariate survival function. The proposed estimator of the CCC is proven to be strongly consistent and asymptotically normal, with a consistent bootstrap variance estimator. Furthermore, we propose a time‐dependent agreement coefficient as an extension of Lin's (1989) CCC for measuring the agreement between survival times among subjects who survive beyond a specified time point. A nonparametric estimator is developed for the time‐dependent agreement coefficient as well. It has the same asymptotic properties as the estimator of the CCC. Simulation studies are conducted to evaluate the performance of the proposed estimators. A real data example from a prostate cancer study is used to illustrate the method.
Robustness of Prevalence Estimates Derived from Misclassified Data from Administrative Databases
Authors: Ladouceur Martin , Rahme Elham , Pineau Christian A. , Joseph Lawrence
Published: September 2006

SummaryBecause primary data collection can be expensive, researchers are increasingly using information collected in medical administrative databases for scientific purposes. This information, however, is typically collected for reasons other than research, and many such databases have been shown to contain substantial proportions of misclassification errors. For example, many administrative databases contain fields for patient diagnostic codes, but these are often missing or inaccurate, in part because physician reimbursement schemes depend on medical acts performed rather than any diagnosis. Errors in ascertaining which individuals have a given disease bias not only prevalence estimates, but also estimates of associations between the disease and other variables, such as medication use. We attempt to estimate the prevalence of osteoarthritis (OA) among elderly Quebeckers using a government administrative database. We compare a naive estimate relying solely on the physician diagnoses of OA listed in the database to estimates from several different Bayesian latent class models which adjust for misclassified physician diagnostic codes via use of other available diagnostic clues. We find that the prevalence estimates vary widely, depending on the model used and assumptions made. We conclude that any inferences from these databases need to be interpreted with great caution, until further work estimating the reliability of database items is carried out.
“Sticking One's Neck Out”: Reducing Mistrust in Sri Lanka's Peace Negotiations
Authors: Höglund Kristine , Svensson Isak
Published: September 2006

Lack of trust has been widely used as an explanation for the failure of peace negotiations. However, we know little about how mistrust can be reduced between belligerents involved in negotiating peace. Why are some confidence‐building strategies more successful than others? For theory‐building purposes, this article explores how a party can send conciliatory signals to the other party that increase trust by exposing itself to three different kinds of political risks. More specifically, it compares the variables that reduced mistrust — or failed to reduce mistrust — during two peace negotiations in Sri Lanka: in 1994–1995 and in 2002. Using a theoretical framework that combines social psychology and rational choice approaches, this article examines the communicative signaling process between the parties.

In addition, by drawing out the implications from this argument, we offer some insight into why the peace process in Sri Lanka became politically stalemated in 2003. We also use our comparison of Sri Lanka's peace processes to develop general propositions about the dynamics that can reduce mistrust. The main proposition that remains to be tested empirically is whether obstacles to peace can be transformed into important catalysts for the reduction of mistrust.
Have we detected the most luminous ULX so far?
Authors: Miniutti G. , Ponti G. , Dadina M. , Cappi M. , Malaguti G. , Fabian A. C. , Gandhi P.
Published: September 2006

abstract

We report the XMM–Newton detection of a moderately bright X-ray source (F0.5−7∼ 8.2 × 10−14 erg cm−2 s−1) superimposed on the outer arms of the inactive spiral galaxy MCG–03-34-63 (z= 0.0213). It is clearly offset from the nucleus (by about 19 arcsec) but well within the D25 ellipse of the galaxy, just along its bar axis. The field has also been observed with the Hubble Space Telescope (HST), enabling us to compute a lower limit of >94 on the X-ray-to-optical flux ratio which, together with the X-ray spectrum of the source, argues against a background active galactic nucleus. On the other hand, the detection of excess X-ray absorption and the lack of a bright optical counterpart argue against foreground contamination. Short time-scale variability is observed, ruling out the hypothesis of a particularly powerful supernova. If it is associated with the apparent host galaxy, the source is the most powerful ultraluminous X-ray source detected so far, with a peak luminosity of ∼1.35 × 1041 erg s−1 in the 0.5–7 keV band. If confirmed by future multi-wavelength observations, the inferred bolometric luminosity (∼3 × 1041 erg s−1) requires a rather extreme beaming factor (larger than 115) to accommodate accretion on to a stellar-mass black hole of 20 M⊙ and the source could instead represent one of the best intermediate-mass black hole candidate so far. If beaming is excluded, the Eddington limit implies a mass of >2300 M⊙ for the accreting compact object.
Aerodesign and Testing of an Aeromechanically Highly Loaded LP Turbine
Authors: Malzacher F. J. , Gier J. , Lippl F.
Published: September 2006

Future turbo systems for aircraft engines need very compact geometry, low weight, and high efficiency components. The geared turbofan enables the engine designer to decouple the speed of the fan and the LP turbine to combine a low speed fan with a high speed LP turbine. The low pressure turbine is a key component for this concept. The technological challenge is very much driven by the very high low-spool speed. Resulting as well from high inlet temperatures, the LP turbine needs cooling of the first stage. A new MTU LPT concept for such a high speed turbine has been developed and tested in a turbine rig. The concept consists of a two-stage turbine for extremely high speed and high stage pressure ratio (ER 2.3). This leads to extra high mechanical loading and an exotic combination of high Mach numbers (transonic) and very low Reynolds numbers. In this paper some design features are described. Some elements of the airfoil design were also tested in additional cascade tests. The two-stage turbine was tested at the Altitude Test Facility of the ILA, Stuttgart. The test setup is described including details of the instrumentation. Test data shows a good turbine performance. Measurements are also compared to 3D CFD, which is used to analyze local effects.
The Importance of Shroud Leakage Modeling in Multistage Turbine Flow Calculations
Authors: Rosic Budimir , Denton John D. , Pullan Graham
Published: September 2006

Three-dimensional steady multistage calculations, using the mixing plane approach, are compared with experimental measurement in a low-speed three-stage model turbine. The comparisons are made with two levels of shroud seal clearance, one representative of a real turbine and one with minimal seal clearance and almost no shroud leakage. Three different calculations are compared. The first computes the main blade path with no modeling of shroud leakage. The second includes a simple model of shroud leakage using sources and sinks on the end-walls, and the third is a multiblock calculation with all leakage paths and cavities computed. It is found that neglect of shroud leakage makes the computed velocity profiles and loss distributions significantly different to those measured. Simple modeling of shroud leakage gives some improvement but full calculation of the leakage flows and cavities is necessary to obtain good agreement between calculation and measurement.
Direct Numerical Simulations of Transitional Flow in Turbomachinery
Authors: Wissink J. G. , Rodi W.
Published: September 2006

An overview is provided of various direct numerical simulations (DNS) of transitional flows in turbine-related geometries. Two flow cases are considered: the first case concerns separating flow over a flat plate and the second case flows in turbine cascades. In the first case, in which Re=60,000, either an oscillating oncoming flow (1) or a uniform flow with and without oncoming turbulent free-stream fluctuations (2) is prescribed at the inlet. In both subcases (1) and (2), separation is induced by a contoured upper wall. In (1), the separated boundary layer is found to roll up due to a Kelvin-Helmholtz (KH) instability. This rolled-up shear layer is subject to spanwise instability and disintegrates rapidly into turbulent fluctuations. In (2), a massive separation bubble is obtained in the simulation without oncoming free-stream fluctuations. A KH instability is eventually triggered by numerical round-off error and is followed again by a rapid transition. With oncoming turbulent fluctuations, this KH instability is triggered much earlier and transition is enhanced, which leads to a drastic reduction in size of the separation bubble. The second case, concerning flow in turbine cascades, includes (1) flow in the T106 turbine cascade with periodically oncoming wakes at Re=51,800 and (2) flow and heat transfer in a MTU cascade with oncoming wakes and background turbulence at Re=72,000. In the simulation of flow in the T106 cascade with oncoming wakes, the boundary layer along the downstream half of the suction side is found to separate intermittently and subsequently rolls up due to a KH instability leading to separation-induced transition. At times when the wakes impinge separation is suppressed. In the simulations of flow around a MTU turbine blade, evidence of by-pass transition in the suction-side boundary-layer flow is observed while the pressure-side boundary layer remains laminar in spite of significant fluctuations present. In agreement with the experiments, the impinging wakes cause the heat transfer coefficient to increase significantly in the transitional suction-side region close to the trailing edge and by about 30% on the pressure side. The large increase in heat transfer in the pre-transitional suction-side region observed in the experiments could not be reproduced. The discrepancy is explained by differences in spectral contents of the turbulence in the oncoming wakes.
On the Momentum and Thermal Structures of Turbulent Spots in a Favorable Pressure Gradient
Authors: Chong T. P. , Zhong S.
Published: September 2006

This paper represents the results from an experimental investigation of the flow physics behind the difference in the transition zone length indicated by the momentum boundary layer and thermal boundary layer parameters observed on the suction surfaces of gas turbine blades. The experiments were carried out on turbulent spots created artificially in an otherwise laminar boundary layer developing over a heated flat plate in a zero pressure gradient and a favorable pressure gradient. A specially designed miniature triple wire probe was used to measure the streamwise velocity component U, transverse velocity component V and temperature T simultaneously during the passage of the spots. In this paper, the general characteristics of the ensemble-averaged velocity and temperature perturbations, rms fluctuations, and the second moment turbulent quantities are discussed and the influence of favorable pressure gradient on these parameters is examined. When a favorable pressure gradient is present, unlike in the velocity boundary layer where significant velocity fluctuations and Reynolds shear stress occur both on the plane of symmetry and the spanwise periphery, high temperature fluctuations (and turbulent heat fluxes) are confined in the plane of symmetry. The difference in the levels of velocity/temperature fluctuations at these two locations gives an indication of the effectiveness of momentum/heat transfer across the span of the spots. The results of this study indicate that the heat transfer within a spot is inhibited more than that of the momentum transfer at the presence of a favorable pressure gradient. This phenomenon is expected to slow down the development of a transitional thermal boundary layer, leading to a longer transitional zone length indicated by the heat transfer parameters as reported in the literature.
Combustion Control by Vortex Breakdown Stabilization
Authors: Paschereit Christian Oliver , Flohr Peter , Gutmark Ephraim J.
Published: September 2006

Flame anchoring in a swirl-stabilized combustor occurs in an aerodynamically generated recirculation region which is a result of vortex breakdown (VBD). The characteristics of the recirculating flow are dependent on the swirl number and on axial pressure gradients. Coupling with downstream pressure pulsations in the combustor affects the VBD process. The present paper describes combustion instability that is associated with vortex breakdown. The mechanism of the onset of this instability is discussed. Passive control of the instability was achieved by stabilizing the location of vortex breakdown using an extended lance. The reduction of pressure pulsations for different operating conditions and the effect on emissions in a laboratory scale model atmospheric combustor, in a high pressure combustor facility, and in a full scale land-based gas-turbine are described. The flashback safety, one of the most important features of a reliable gas turbine burner, was assessed by CFD, water tests, and combustion tests. In addition to the passive stabilization by the extended lance it enabled injection of secondary fuel directly into the recirculation zone where the flame is stabilized. Tests were conducted with and without secondary fuel injection. Measurements and computations optimized the location of the extended lance in the mixing chamber. The effect of variation of the amount of secondary fuel injection at different equivalence ratios and output powers was determined. Flow visualizations showed that stabilization of the recirculation zone was achieved. Following the present research, the VBD stabilization method has been successfully implemented in engines with sufficient stability margins and good operational flexibility. This paper shows the development process from lab scale tests to full scale engine tests until the implementation into field engines.
Dynamic Characteristics of the Diverging Taper Honeycomb-Stator Seal
Authors: Smalley Anthony J. , Camatti Massimo , Childs Dara W. , Hollingsworth Justin R. , Vannini Giuseppe , Carter Jeremy J.
Published: September 2006

This paper introduces a variant on the honeycomb-stator seal, which can extend the already strong stabilizing influence of this seal geometry for centrifugal compressors. The paper presents predicted and measured dynamic characteristics, demonstrating how a clearance, which diverges axially from inlet to outlet, increases the maximum effective damping of a honeycomb-stator seal, even though the average clearance is increased. The results also show a strong negative direct stiffness at zero and low frequency for this seal geometry (termed the “diverging taper honeycomb seal (DTHCS)”). The predictions are made with ISOTSEAL, software developed at The Texas A&M Turbomachinery Laboratory. (This code was developed within the Turbomachinery Laboratory and is not a commercial product (not for sale).) The test data, also obtained at the Turbomachinery Laboratory, confirm the nature and magnitude of both these dynamic characteristics with close fidelity. However, measured leakage falls significantly below predicted leakage. The frequency dependence of the seal dynamic characteristics and the strong negative static stiffness require careful attention in rotor dynamics analysis.
Modeling and Experimental Investigation of Micro-hydrostatic Gas Thrust Bearings for Micro-turbomachines
Authors: Teo C. J. , Spakovszky Z. S.
Published: September 2006

One major challenge for the successful operation of high-power-density micro-devices lies in the stable operation of the bearings supporting the high-speed rotating turbomachinery. Previous modeling efforts by Piekos (2000, “Numerical Simulation of Gas-Lubricated Journal Bearings for Microfabricated Machines,” Ph.D. thesis, Department of Aeronautics and Astronautics, MIT), Liu et al. (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbo Machinery,” ASME J. Vib. Acoust., 127, pp. 157–164), and Spakovszky and Liu (2005, “Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,” ASME J. Vib. Acoust. 127, pp. 254–261) have focused on the operation and stability of journal bearings. Thrust bearings play a vital role in providing axial support and stiffness, and there is a need to improve the understanding of their dynamic behavior. In this work, a rigorous theory is presented to analyze the effects of compressibility in micro-flows (characterized by low Reynolds numbers and high Mach numbers) through hydrostatic thrust bearings for application to micro-turbomachines. The analytical model, which combines a one-dimensional compressible flow model with finite-element analysis, serves as a useful tool for establishing operating protocols and assessing the stability characteristics of hydrostatic thrust bearings. The model is capable of predicting key steady-state performance indicators, such as bearing mass flow, axial stiffness, and natural frequency as a function of the hydrostatic supply pressure and thrust-bearing geometry. The model has been applied to investigate the static stability of hydrostatic thrust bearings in micro-turbine generators, where the electrostatic attraction between the stator and rotor gives rise to a negative axial stiffness contribution and may lead to device failure. Thrust-bearing operating protocols have been established for a micro-turbopump, where the bearings also serve as an annular seal preventing the leakage of pressurized liquid from the pump to the gaseous flow in the turbine. The dual role of the annular pad poses challenges in the operation of both the device and the thrust bearing. The operating protocols provide essential information on the required thrust-bearing supply pressures and axial gaps required to prevent the leakage of water into the thrust bearings. Good agreement is observed between the model predictions and experimental results. A dynamic stability analysis has been conducted, which indicates the occurrence of instabilities due to flow choking effects in both forward and aft thrust bearings. A simple criterion for the onset of axial rotor oscillations has been established and subsequently verified in a micro-turbocharger experiment. The predicted frequencies of the unstable axial oscillations compare well with the experimental measurements.
An Investigation of Wake-Shock Interactions in a Transonic Compressor With Digital Particle Image Velocimetry and Time-Accurate Computational Fluid Dynamics
Authors: Gorrell Steven E. , Car David , Puterbaugh Steven L. , Estevadeordal Jordi , Okiishi Theodore H.
Published: September 2006

The effects of varying axial gap on the unsteady flow field between the stator and rotor of a transonic compressor stage are important because they can result in significant changes in stage mass flow rate, pressure rise, and efficiency. Some of these effects are analyzed with measurements using digital particle image velocimetry (DPIV) and with time-accurate simulations using the 3D unsteady Navier-Stokes computational fluid dynamics solver TURBO. Generally there is excellent agreement between the measurements and simulations, instilling confidence in both. Strong vortices of the wake can break up the rotor bow shock and contribute to loss. At close spacing vortices are shed from the trailing edge of the upstream stationary blade row in response to the unsteady, discontinuous pressure field generated by the downstream rotor bow shock. Shed vortices increase in size and strength and generate more loss as spacing decreases, a consequence of the effective increase in rotor bow shock strength at the stationary blade row trailing edge. A relationship for the change in shed vorticity as a function of rotor bow shock strength is presented that predicts the difference between close and far spacing TURBO simulations.
Analysis of Some Improved Blade Tip Concepts
Authors: Prakash C. , Lee C. P. , Cherry D. G. , Doughty R. , Wadia A. R.
Published: September 2006

Over tip leakage in high-pressure turbines contributes to aerodynamic losses and migration of hot gasses towards the tip resulting in increased thermal distress. Consequently, turbine designers continue to search for improved blade tip concepts that offer the promise of reducing tip leakage. The present paper deals with the computational fluid dynamics analyses of some such tip configurations. The geometries, patented by GE, are variants of a conventional squealer tip and include (i) a pressure side tip shelf with vertical squealer tip wall and (ii) a pressure side tip shelf with an inclined squealer tip wall. It is found that the inclined shelf results in separation of flow leaking over the tip, resulting in reduced leakage and improved efficiency. The inclined shelf also shows a reduced efficiency derivative with clearance.
The Influence of
Variable Gas Properties on Turbomachinery Computational Fluid
Dynamics
Authors: Northall John
D.
Published: September 2006

This paper describes the inclusion of variable gas properties within a Reynolds average Navier-Stokes solver for turbomachinery and its application to multistage turbines. Most current turbomachinery computational fluid dynamics (CFD) models the gas as perfect with constant specific heats. However, the specific heat at constant pressure CP can vary significantly. This is most marked in the turbine where large variations of temperature are combined with variations in the fuel air ratio. In the current model CP is computed as a function of the local temperature and fuel air ratio using polynomial curve fits to represent the real gas behavior. The importance of variable gas properties is assessed by analyzing a multistage turbine typical of the core stages of a modern aeroengine. This calculation includes large temperature variations due to radial profiles at inlet, the addition of cooling air, and work extraction through the machine. The calculation also includes local variations in fuel air ratio resulting from the inlet profile and the dilution of the mixture by the addition of coolant air. A range of gas models is evaluated. The addition of variable gas properties is shown to have no significant effect on the convergence of the algorithm, and the extra computational costs are modest. The models are compared with emphasis on the parameters of importance in turbine design, such as capacity, work, and efficiency. Overall the effect on turbine performance prediction of including variable gas properties in three-dimensional CFD is found to be small.
A Study of Advanced High-Loaded Transonic Turbine Airfoils
Authors: Sonoda Toyotaka , Arima Toshiyuki , Olhofer Markus , Sendhoff Bernhard , Kost Friedrich , Giess P.-A.
Published: September 2006

The development of high-performance turbine airfoils has been investigated under the condition of a supersonic exit Mach number. In order to obtain a new aerodynamic design concept for a high-loaded turbine rotor blade, we employed an evolutionary algorithm for numerical optimization. The target of the optimization method, which is called evolutionary strategy (ES), was the minimization of the total pressure loss and the deviation angle. The optimization process includes the representation of the airfoil geometry, the generation of the grid for a blade-to-blade computational fluid dynamics analysis, and a two-dimensional Navier-Stokes solver with a low-Re k-ε turbulence model in order to evaluate the performance. Some interesting aspects, for example, a double shock system, an early transition, and a redistribution of aerodynamic loading on blade surface, observed in the optimized airfoil, are discussed. The increased performance of the optimized blade has been confirmed by detailed experimental investigation, using conventional probes, hotfilms, and L2F system.
Rotordynamic Force Coefficients of Pocket Damper Seals
Authors: Ertas B. , Gamal A. , Vance J.
Published: September 2006

This paper presents measured frequency dependent stiffness and damping coefficients for 12-bladed and 8-bladed pocket damper seals (PDS) subdivided into four different seal configurations. Rotating experimental tests are presented for inlet pressures at 69 bar (1000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the eight-bladed PDS. Results of the frequency dependent force coefficients for the four PDS designs are compared. The conclusions of the tests show that the eight-bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12-bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a destabilizing influence on rotor-bearing systems.
Mechanism of Active Renal Tubular Efflux of Tenofovir
Authors: Ray Adrian S. , Cihlar Tomas , Robinson Kelly L. , Tong Leah , Vela Jennifer E. , Fuller Michael D. , Wieman Lani M. , Eisenberg Eugene J. , Rhodes Gerry R.
Published: September 2006

Tenofovir (TFV) undergoes renal elimination by a combination of glomerular filtration and active tubular secretion. While transporter-mediated uptake of TFV from the blood into proximal-tubule cells has been well characterized, comparatively little is known about the efflux system responsible for transporting TFV into the lumen during active tubular secretion. Therefore, members of the ATP-binding cassette family of efflux pumps expressed at the apical side of proximal-tubule cells were studied for the ability to transport TFV. Studies in multiple independent in vitro systems show TFV not to be a substrate for P glycoprotein (Pgp) or multidrug resistance protein type 2 (MRP2). In contrast to Pgp and MRP2, TFV was observed to be a substrate for MRP4. TFV accumulated to fivefold lower levels in MRP4-overexpressing cells, and its accumulation could be increased by an MRP inhibitor. Furthermore, MRP4-overexpressing cells were found to be 2.0- to 2.5-fold less susceptible to cytotoxicity caused by TFV. ATP-dependent uptake of TFV was observed in membrane vesicles containing MRP4 but not in vesicles lacking the transporter. On the basis of these and previous results, the molecular transport pathway for the active tubular secretion of TFV through renal proximal-tubule cells involves uptake from the blood mediated by human organic anion transporters 1 and 3 and efflux into urine by MRP4. A detailed understanding of the molecular mechanism of TFV active tubular secretion will facilitate the assessment of potential renal drug-drug interactions with coadministered agents.
High-Level Carbapenem Resistance in a
Klebsiella pneumoniae
Clinical Isolate Is Due to the Combination of
bla
ACT-1
β-Lactamase Production, Porin OmpK35/36 Insertional Inactivation, and Down-Regulation of the Phosphate Transport Porin PhoE
Authors: Kaczmarek Frank M. , Dib-Hajj Fadia , Shang Wenchi , Gootz Thomas D.
Published: September 2006

Clinical isolates of
Klebsiella pneumoniae
resistant to carbapenems and essentially all other antibiotics (multidrug resistant) are being isolated from some hospitals in New York City with increasing frequency. A highly related pair of
K. pneumoniae
strains isolated on the same day from one patient in a hospital in New York City were studied for antibiotic resistance. One (KP-2) was resistant to imipenem, meropenem, and sulopenem (MICs of 16 to 32 μg/ml) while the other (KP-1) was susceptible (MIC of 0.5 μg/ml); both contained the
bla
ACT-1
,
bla
SHV-1
, and
bla
TEM-1
β-lactamases.
bla
ACT-1
in both strains was encoded on a large ∼150-kb plasmid. Both isolates contained an identical class 1 integron encoding resistance to aminoglycosides and chloramphenicol. They each had identical insertions in
ompK35
and
ompK36
, resulting in disruption of these key porin genes. The carbapenem-resistant and -susceptible isolates were extensively studied for differences in the structural and regulatory genes for the operons
acrRAB
,
marORAB
,
romA-ramA
,
soxRS
,
micF
,
micC
,
phoE
,
phoBR
,
rpoS
, and
hfq
. No changes were detected between the isolates except for a significant down-regulation of
ompK37
,
phoB
, and
phoE
in KP-2 as deduced from reverse transcription-PCR analysis of mRNA and polyacrylamide gel electrophoresis separation of outer membrane proteins. Backcross analysis was conducted using the wild-type
phoE
gene cloned into the vector pGEM under regulation of its native promoter as well as the
lacZ
promoter following transformation into the resistant KP-2 isolate. The wild-type gene reversed carbapenem resistance only when under control of the heterologous
lacZ
promoter. In the background of
ompK35-ompK36
gene disruption, the up-regulation of
phoE
in KP-1 apparently compensated for porin loss and conferred carbapenem susceptibility. Down-regulation of
phoE
in KP-2 may represent the normal state of this gene, or it may have been selected from KP-1 in vivo under antibiotic pressure, generating the carbapenem-resistant clone. This is the first study in the
Enterobacteriaceae
where expression of the phosphate-regulated PhoE porin has been associated with resistance to antimicrobials. Our results with this pair of
Klebsiella
clinical isolates highlight the complex and evolving nature of multiple drug resistance in this species.
Role of VraSR in Antibiotic Resistance and Antibiotic-Induced Stress Response in
Staphylococcus aureus
Authors: Gardete S. , Wu S. W. , Gill S. , Tomasz A.
Published: September 2006

Exposure of
Staphylococcus aureus
to cell wall inhibitors induces massive overexpression of a number of genes, provided that the VraSR two-component sensory regulatory system is intact. Inactivation of
vraS
blocks this transcriptional response and also causes a drastic reduction in the levels of resistance to beta-lactam antibiotics and vancomycin. We used an experimental system in which the essential cell wall synthesis gene of
S. aureus
,
pbpB
, was put under the control of an isopropyl-β-
d
-thiogalactopyranoside-inducible promoter in order to induce reversible perturbations in cell wall synthesis without the use of any cell wall-active inhibitor. Changes in the level of transcription of
pbpB
were rapidly followed by parallel changes in the
vraSR
signal, and the abundance of the
pbpB
transcript was precisely mirrored by the abundance of the transcripts of
vraSR
and some additional genes that belong to the VraSR regulon. Beta-lactam resistance in
S. aureus
appears to involve a complex stress response in which VraSR performs the critical role of a sentinel system capable of sensing the perturbation of cell wall synthesis and allowing mobilization of genes that are essential for the generation of a highly resistant phenotype. One of the sites in cell wall synthesis “sensed” by the VraSR system appears to be a step catalyzed by PBP 2.
SME-3, a Novel Member of the
Serratia marcescens
SME Family of Carbapenem-Hydrolyzing β-Lactamases
Authors: Queenan Anne Marie , Shang Wenchi , Schreckenberger Paul , Lolans Karen , Bush Karen , Quinn John
Published: September 2006

Imipenem-resistant
Serratia marcescens
isolates were cultured from a lung transplant patient given multiple antibiotics over several months. The strains expressed SME-3, a β-lactamase of the rare SME carbapenem-hydrolyzing family. SME-3 differed from SME-1 by a single amino acid substitution of tyrosine for histidine at position 105, but the two β-lactamases displayed similar hydrolytic profiles.
Ribavirin Antagonizes the In Vitro Anti-Hepatitis C Virus Activity of 2′-
C
-Methylcytidine, the Active Component of Valopicitabine
Authors: Coelmont Lotte , Paeshuyse Jan , Windisch Marc P. , De Clercq Erik , Bartenschlager Ralf , Neyts Johan
Published: September 2006

Ribavirin antagonizes the in vitro anti-hepatitis C virus (HCV) activity of the pyrimidine nucleoside analogue 2′-
C
-methylcytidine, the active component of the experimental anti-HCV drug valopicitabine. In contrast, the combination of ribavirin with either the purine nucleoside analogue 2′-
C
-methyladenosine or the HCV protease inhibitor VX-950 resulted in an additive antiviral activity. These findings may have implications when planning clinical studies with valopicitabine.
Effect of Tigecycline on Normal Oropharyngeal and Intestinal Microflora
Authors: Nord Carl Erik , Sillerström Eva , Wahlund Elisabeth
Published: September 2006

Antibacterial agents disrupt the ecological balance of the normal human microflora. Tigecycline, a member of a new class of antibiotics (glycylcyclines), has been shown to have a potent broad-spectrum activity against most gram-positive and gram-negative aerobic and anaerobic bacteria. The aim of the study was to investigate the ecological effects of tigecycline on the normal oropharyngeal and intestinal microflora of healthy subjects. Thirteen healthy white subjects (six females and seven males) between 20 and 31 years of age received 100 mg of tigecycline in the morning on day 1 as a 30-min intravenous infusion followed by a 50-mg dose of tigecycline every 12 h as a 30-minute infusion for 10 days. One subject was withdrawn on day 2 because of an adverse event (urticaria). Serum, saliva, and fecal samples were collected before, during, and after administration for microbiological cultivation and for assays of tigecycline. All new colonizing bacteria were tested for susceptibility (resistance of ≥8 mg/liter) during the investigation period. The fecal concentrations on day 8 were from 3.0 to 14.1 mg/kg, with a mean value of 6.0 mg/kg and a median value of 5.6 mg/kg. The saliva concentrations were generally low (0 to 0.12 mg/liter). A minor effect on the oropharyngeal microflora was observed. The numbers of enterococci and
Escherichia coli
cells in the intestinal microflora were reduced at day 8 (
P
< 0.05), while those of other enterobacteria and yeasts increased. There was a marked reduction of lactobacilli and bifidobacteria (
P
< 0.05) but no impact on bacteroides. No
Clostridium difficile
strains were isolated. Two
Klebsiella pneumoniae
strains and five
Enterobacter cloacae
strains resistant to tigecycline were found on day 8.
Novel Robust Hepatitis C Virus Mouse Efficacy Model
Authors: Zhu Qing , Oei Yoko , Mendel Dirk B. , Garrett Evelyn N. , Patawaran Montesa B. , Hollenbach Paul W. , Aukerman Sharon L. , Weiner Amy J.
Published: September 2006

The lack of a robust small-animal model for hepatitis C virus (HCV) has hindered the discovery and development of novel drug treatments for HCV infections. We developed a reproducible and easily accessible xenograft mouse efficacy model in which HCV RNA replication is accurately monitored in vivo by real-time, noninvasive whole-body imaging of gamma-irradiated SCID mice implanted with a mouse-adapted luciferase replicon-containing Huh-7 cell line (T7-11). The model was validated by demonstrating that both a small-molecule NS3/4A protease inhibitor (BILN 2061) and human alpha interferon (IFN-α) decreased HCV RNA replication and that treatment withdrawal resulted in a rebound in replication, which paralleled clinical outcomes in humans. We further showed that protease inhibitor and IFN-α combination therapy was more effective in reducing HCV RNA replication than treatment with each compound alone and supports testing in humans. This robust mouse efficacy model provides a powerful tool for rapid evaluation of potential anti-HCV compounds in vivo as part of aggressive drug discovery efforts.
Method for Regulated Expression of Single-Copy Efflux Pump Genes in a Surrogate
Pseudomonas aeruginosa
Strain: Identification of the BpeEF-OprC Chloramphenicol and Trimethoprim Efflux Pump of
Burkholderia pseudomallei
1026b
Authors: Kumar Ayush , Chua Kim-Lee , Schweizer Herbert P.
Published: September 2006

Construction and integration of recombinant mini-Tn
7
expression vectors into the chromosome of a surrogate, efflux-sensitized, and biosafe
Pseudomonas aeruginosa
host was validated as a generally applicable method for studies of uncharacterized bacterial efflux pumps. Using this method, the
Burkholderia pseudomallei bpeEF-oprC
operon was shown to encode a chloramphenicol and trimethoprim efflux pump.
Effect of Rifampin on Steady-State Pharmacokinetics of Atazanavir with Ritonavir in Healthy Volunteers
Authors: Burger D. M. , Agarwala S. , Child M. , Been-Tiktak A. , Wang Y. , Bertz R.
Published: September 2006

Mycobacterium tuberculosisis a concern in patients with human immunodeficiency virus (HIV) infection. Rifampin (RIF), an agent used againstM. tuberculosis, is contraindicated with most HIV protease inhibitors. Atazanavir (ATV) has clinical efficacy comparable to a standard of care regimen in naive patients and, when dosed with low-dose ritonavir (RTV), also in treatment-experienced patients. We evaluated here the safety and pharmacokinetics of ATV, resulting from three regimens of ATV, RTV, and RIF in 71 healthy subjects. The pharmacokinetics for ATV and RTV were assessed after 6 and 10 days of dosing with ATV 400 mg (n= 53) and with ATV-RTV at 300 and 100 mg (ATV/RTV 300/100;n= 52), respectively. Steady-state pharmacokinetics for ATV, RTV, RIF, and desacetyl-rifampin (des-RIF) were measured after 10 days of dosing of ATV/RTV/RIF 300/100/600 (n= 17), ATV/RTV/RIF 300/200/600 (n= 17), or ATV/RTV/RIF 400/200/600 (n= 14). An RIF 600-alone arm was enrolled as a control group (n= 18). With ATV/RTV/RIF 400/200/600, ATV area under the concentration-time curve values were comparable, but theCminvalues were lower relative to ATV 400 alone. ATV exposures were substantially reduced for the other RIF-containing regimens relative to ATV 400 alone and for all regimens relative to ATV/RTV 300/100 alone. RIF and des-RIF exposures were 1.6- to 2.5-fold higher than with RIF 600 alone. The incidence of grade 3/4 alanine aminotransferase/aspartate aminotransferase values was limited to 1 subject each in both the ATV/RTV/RIF 300/200/600 and the ATV/RTV/RIF 400/200/600 treatments. Coadministration of ATV with RIF was safe and generally well tolerated. Since ATV exposures were reduced in all regimens, ATV and RIF should not be coadministered at the dosing regimens studied.
Mycobacterium leprae
Is Naturally Resistant to PA-824
Authors: Manjunatha Ujjini H. , Lahiri Ramanuj , Randhawa Baljit , Dowd Cynthia S. , Krahenbuhl James L. , Barry Clifton E.
Published: September 2006

Leprosy responds very slowly to the current multidrug therapy, and hence there is a need for novel drugs with potent bactericidal activity. PA-824 is a 4-nitroimidazo-oxazine that is currently undergoing phase I clinical trials for the treatment of tuberculosis. The activity of PA-824 against
Mycobacterium leprae
was tested and compared with that of rifampin in axenic cultures, macrophages, and two different animal models. Our results conclusively demonstrate that PA-824 has no effect on the viability of
M. leprae
in all three models, consistent with the lack of the nitroimidazo-oxazine-specific nitroreductase, encoded by Rv3547 in the
M. leprae
genome, which is essential for activation of this molecule.
Engineered VaginalLactobacillusStrain for Mucosal Delivery of the Human Immunodeficiency Virus Inhibitor Cyanovirin-N
Authors: Liu Xiaowen , Lagenaur Laurel A. , Simpson David A. , Essenmacher Kirsten P. , Frazier-Parker Courtney L. , Liu Yang , Tsai Daniel , Rao Srinivas S. , Hamer Dean H. , Parks Thomas P. , Lee Peter P. , Xu Qiang
Published: September 2006

Women are at significant risk of human immunodeficiency virus (HIV) infection, with the cervicovaginal mucosa serving as a major portal for virus entry. Female-initiated preventatives, including topical microbicides, are urgently needed to help curtail the HIV/AIDS pandemic. Here we report on the development of a novel, live microbicide that employs a natural vaginal strain ofLactobacillus jenseniiengineered to deliver the potent HIV inhibitor cyanovirin-N (CV-N). To facilitate efficient expression of CV-N by this bacterium, theL. jensenii1153 genome was sequenced, allowing identification of native regulatory elements and sites for the chromosomal integration of heterologous genes. A CV-N expression cassette was optimized and shown to produce high levels of structurally intact CV-N when expressed inL. jensenii. Lactobacillus-derived CV-N was capable of inhibiting CCR5-tropic HIVBaLinfectivity in vitro with a 50% inhibitory concentration of 0.3 nM. The CV-N expression cassette was stably integrated as a single copy into the bacterial chromosome and resolved from extraneous plasmid DNA without adversely affecting the bacterial phenotype. This bacterial strain was capable of colonizing the vagina and producing full-length CV-N when administered intravaginally to mice during estrus phase. The CV-N-producingLactobacilluswas genetically stable when propagated in vitro and in vivo. This work represents a major step towards the development of an inexpensive yet durable protein-based microbicide to block the heterosexual transmission of HIV in women.
Ciprofloxacin-Resistant Gram-Negative Bacilli in the Fecal Microflora of Children
Authors: Qin Xuan , Razia Yasmin , Johnson James R. , Stapp Jennifer R. , Boster Daniel R. , Tsosie Treva , Smith Donna L. , Braden Christopher R. , Gay Kathryn , Angulo Frederick J. , Tarr Phillip I.
Published: September 2006

The extent to which antibiotic-resistant bacteria are excreted by humans who have not been exposed to antibiotics is not known. Children, who rarely receive fluoroquinolones, provide opportunities to assess the frequency of fecal excretion by fluoroquinolone-naïve hosts of fluoroquinolone-resistant gram-negative bacilli. Fresh nondiarrheal stools from children were processed by screening them on agar containing ciprofloxacin to recover ciprofloxacin-resistant gram-negative bacilli. Resistant isolates were identified, and ciprofloxacin MICs were determined. Resistant
Escherichia coli
isolates were also analyzed for urovirulence-associated loci. Thirteen (2.9%) of 455 stools yielded ciprofloxacin-resistant
E. coli
(seven children),
Stenotrophomonas maltophilia
(four children), and
Achromobacter xylosoxidans
and
Enterobacter aerogenes
(one child each). Neither the subjects themselves nor members of their households used fluoroquinolones in the 4 weeks preceding collection. Six of the seven resistant
E. coli
isolates belonged to phylogenetic groups B2 and D, in which extraintestinal pathogenic
E. coli
bacteria are frequently found. All resistant
E. coli
isolates contained at least three putative
E. coli
virulence loci. Most ciprofloxacin-resistant bacteria were resistant to additional antibiotics. Potentially pathogenic bacteria that are resistant to therapeutically important antimicrobial agents are excreted by some humans, despite these persons' lack of exposure to the particular drugs. The sources of these resistant organisms are unknown. This underrecognized reservoir of drug-resistant potential pathogens poses public health challenges.
Efficacy of Ambruticin Analogs in a Murine Model of Invasive Pulmonary Aspergillosis
Authors: Chiang Lisa Y. , Ejzykowicz Daniele E. , Tian Zong-Qiang , Katz Leonard , Filler Scott G.
Published: September 2006

Ambruticins are a family of polyketides. The antifungal activity of an ambruticin, KOSN-2079, was tested in the mouse model of invasive aspergillosis. KOSN-2079 significantly reduced pulmonary fungal burdens and improved survival over that with the vehicle control. These results support the continued development of ambruticins as antifungal agents.
Protein
O-
Mannosyltransferase Isoforms Regulate Biofilm Formation in
Candida albicans
Authors: Peltroche-Llacsahuanga Heidrun , Goyard Sophie , d′Enfert Christophe , Prill Stephan K.-H. , Ernst Joachim F.
Published: September 2006

Five isoforms of protein mannosyltransferase (Pmt)
O
-mannosylate secretory proteins in
Candida albicans. pmt
mutants were differentially defective for biofilm formation on plastic in static and flow-through systems, and a Pmt inhibitor blocked early stages of biofilm formation. Conceptually, Pmt inhibition may prevent surface anchoring and biofilm-dependent resistance of fungal pathogens.
Redefining a Structural Variant of Staphylococcal Cassette Chromosome
mec
, SCC
mec
Type VI
Authors: Oliveira Duarte C. , Milheiriço Catarina , de Lencastre Hermínia
Published: September 2006

Previously we identified a SCC
mec
variant similar in size to type IV but with a new
ccrAB
allotype, allotype 4. We addressed the epidemiological relevance of this variant and found it among several strains belonging to the same clone. We propose to rename this structural variant SCC
mec
type VI.