bluuebunny/crossref_metadata_2025 huggingface dataset:
Hepatic Akt expression correlates with advanced fibrosis in patients with chronic hepatitis C infection
Authors: Huang Jee‐Fu , Chuang Yen‐Hwang , Dai Chia‐Yen , Yu Ming‐Lung , Huang Chung‐Feng , Hsiao Pi‐Jung , Hsieh Ming‐Yen , Huang Ching‐I , Yeh Ming‐Lun , Yang Jeng‐Fu , Lin Zu‐Yau , Chen Shinn‐Chern , Chuang Wan‐Long
Published: April 2011

Aim:  Hepatitis C virus (HCV) proteins can activate the PI3K/Akt pathway which is involved in multiple cellular functions such as inflammatory cell activation and liver fibrosis. The aim of the present study was to elucidate the correlation between Akt expression and liver fibrosis staging in chronic hepatitis C (CHC) patients.

Methods:  Paraffin‐embedded liver sections from 133 consecutive treatment‐naïve CHC patients were recruited. The expression features of Akt were analyzed using immunohistochemical methods and the results were compared with histological, virological and biochemical profiles.

Results:  The 73 patients with high Akt expression carried higher histological activity index scores (6.52 ± 2.5 vs 5.62 ± 2.4, P = 0.04) and advanced fibrosis (72.7% vs 26.3%, P < 0.01) than other 60 patients with low Akt expression. The high Akt expression showed a significant incremental trend dependent on fibrosis stages, from 33.3% of F0 to 85.7% of F4 (P = 0.005). Akt expression was not correlated with degrees of steatosis and virological features of HCV infection, such as viral load and genotypes. Multivariate logistic regression analysis showed advanced fibrosis was the most significant factor associated with high Akt expression (odds ratio = 3.16).

Conclusion:  Hepatic Akt expression correlated with advanced liver fibrosis in CHC patients.
Evaluating the adaptive‐filter model of the cerebellum
Authors: Dean Paul , Porrill John
Published: April 2011

Abstract  The adaptive‐filter model of the cerebellar microcircuit is in widespread use, combining as it does an explanation of key microcircuit features with well‐specified computational power. Here we consider two methods for its evaluation. One is to test its predictions concerning relations between cerebellar inputs and outputs. Where the relevant experimental data are available, e.g. for the floccular role in image stabilization, the predictions appear to be upheld. However, for the majority of cerebellar microzones these data have yet to be obtained. The second method is to test model predictions about details of the microcircuit. We focus on features apparently incompatible with the model, in particular non‐linear patterns in Purkinje cell simple‐spike firing. Analysis of these patterns suggests the following three conclusions. (i) It is important to establish whether they can be observed during task‐related behaviour. (ii) Highly non‐linear models based on these patterns are unlikely to be universal, because they would be incompatible with the (approximately) linear nature of floccular function. (iii) The control tasks for which these models are computationally suited need to be identified. At present, therefore, the adaptive filter remains a candidate model of at least some cerebellar microzones, and its evaluation suggests promising lines for future enquiry.
Dorsal–ventral organization of theta‐like activity intrinsic to entorhinal stellate neurons is mediated by differences in stochastic current fluctuations
Authors: Dodson Paul D. , Pastoll Hugh , Nolan Matthew F.
Published: April 2011

Non‐technical summary  Navigation by mammals relies on neurons in the brain that encode location, but the mechanisms involved are not understood. Some theories propose critical roles for oscillations generated intrinsically by location‐encoding neurons. Correlations between the frequency of intrinsic activity and the resolution of location encoding support this idea. However, other evidence suggests that cellular mechanisms thought to set the frequency of intrinsic activity may instead primarily function to tune neuronal responses to synaptic input. This study provides evidence that activity intrinsic to location‐encoding neurons is explained by random opening and closing of neuronal ion channels and is not consistent with oscillator theories. The correlation between intrinsic frequency fluctuations and resolution of spatial encoding is explained by differences in the density of ion channels that account for tuning of synaptic responses. These results point towards the importance of synaptic response tuning for encoding of spatial location.
Cortical feedback regulation of input to visual cortex: role of intrageniculate interneurons
Authors: Augustinaite Sigita , Yanagawa Yuchio , Heggelund Paul
Published: April 2011

Non‐technical summary  Neurons in the dorsal lateral geniculate nucleus (dLGN) process and transmit signals from the retina to the visual cortex. Thalamocortical (TC) neurons and intrinsic interneurons receive input from the retina. TC neurons send output to the visual cortex, while interneurons inhibit TC neurons, forming an inhibitory feed‐forward loop. Thus, interneurons are involved in tuning of temporal and spatial resolution of the visual information transmitted through the TC neurons. This processing is regulated by cortical excitatory feedback. To gain insights into the dynamics of cortical regulation, we investigated short‐term synaptic plasticity at corticogeniculate synapses on both types of neurons in dLGN. We found depression at cortical synapses on interneurons in contrast to facilitation at cortical synapses on TC neurons. The depression and facilitation had distinctly different temporal characteristics. These differences in synaptic plasticity suggest that cortical feedback to dLGN might either attenuate or enhance thalamocortical transmission in a frequency‐dependent manner.
Striatal cellular properties conserved from lampreys to mammals
Authors: Ericsson Jesper , Silberberg Gilad , Robertson Brita , Wikström Martin A. , Grillner Sten
Published: April 2011

Non‐technical summary  The striatum is a structure in the forebrain that plays an important role in the control of movements. Diseases that affect this region lead to severe movement disorders, such as Parkinson's disease. We show here in the lamprey, the oldest vertebrate group to emerge, that the characteristic cellular properties of neurons in striatum in many respects are similar to those of mammals. Our results show how specific ion channels, including particular potassium channels (Kir) that are open at very negative membrane potentials help shape the way these cells respond to and transmit neuronal signals. These specific features are thus conserved throughout vertebrate evolution, and contribute thereby to our understanding of the mode of operation of striatum, at a cellular level, and how movements are controlled.
Impact of Nonuniform Leading Edge Coatings on the Aerodynamic Performance of Compressor Airfoils
Authors: Elmstrom Michael E. , Millsaps Knox T. , Hobson Garth V. , Patterson Jeffrey S.
Published: April 2011

A computational fluid dynamic (CFD) investigation is presented that provides predictions of the aerodynamic impact of uniform and nonuniform coatings applied to the leading edge of a compressor airfoil in a cascade. Using a NACA 65(12)10 airfoil, coating profiles of varying leading edge nonuniformity were added. A nonuniform coating is obtained when a liquid coating is applied to a surface with high curvature, such as an airfoil leading edge. The CFD code used, RVCQ3D, is a Reynolds averaged Navier–Stokes solver, with a k-omega turbulence model. The code predicted that these changes in leading edge shape can lead to alternating pressure gradients in the first few percent of chord that create small separation bubbles and possibly early transition to turbulence. The change in total pressure loss and trailing edge deviation are presented as a function of a coating nonuniformity parameter. Results are presented over a range of negative and positive incidences and inlet Mach numbers from 0.6 to 0.8. A map is provided that shows the allowable degree of coating nonuniformity as a function of incidence and inlet Mach number.
Gas Turbine Combustor Flow Structure Control Through Modification of the Chamber Geometry
Authors: Mohammad B. S. , Cai J. , Jeng San-Mou
Published: April 2011

As combustors are put in service, problems such as erosion, hot spots, and liner oxidation occur, and a solution based on lessons learned is essential to avoid similar problems in future combustor generations. In the present paper, a combustor flow structure control via combustor geometry alteration is investigated using laser Doppler velocimetry. Mainly, three configurations are studied. The first configuration is that of a swirl cup feeding a dump (rectangular cross section) combustor. The rectangular chamber is configured with a width to breadth (w/b) ratio of 85%. The second configuration is similar to the first one, but a combustion dome is installed. The dome is configured with a 9 deg difference in the expansion angle on both sides (asymmetric dome). The third configuration is that of a swirl cup and a combustion dome installed in a prototype combustor (single annular combustor (SAC) sector), with both primary and secondary dilution jets blocked. The SAC is configured with a cross sectional area that decreases toward the exit through the tilting of the inner combustor liner. The results show that the combustion dome eliminates the corner recirculation zone and the low velocity region close to the combustor walls. The combustion dome asymmetry results in a significant asymmetry in the velocity magnitude, as well as the turbulence activities and the tilting of the central recirculation zone (CRZ) toward the surface with the higher expansion angle. The liner tilting results in a 40% reduction in the length of the CRZ. However, once the primary jets are open, they define the termination point of the CRZ. The chamber w/b ratio results in a CRZ with the same diameter ratio (85%) in all configurations. Interestingly, the maximum reverse flow velocity is roughly constant in all measurement plans and configurations up to a downstream distance of 1R (R is the flare radius). However, with open primary jets, the CRZ strength increases appreciably. It appears that the confinement dictates both the flow field outside the CRZ and the size of the CRZ, while the swirl cup configuration mainly influences the strength of the CRZ. Regarding turbulence activities, the presence of the dome damps the fluctuations in the expanding swirling jet region. On the other hand, the primary jets increase the turbulence activities appreciably in the jet impingement region, as well as the upper portion of the CRZ (60% increase).
Friction Factor Behavior From Flat-Plate Tests of Smooth and Hole-Pattern Roughened Surfaces With Supply Pressures up to 84 bars
Authors: Childs Dara W. , Kheireddin Bassem , Phillips Stephen , Asirvatham Thanesh Deva
Published: April 2011

A flat-plate tester was used to measure the friction factor behavior for a hole-pattern roughened surface apposed to a smooth surface. The tests were executed to characterize the friction factor behavior of annular seals that use a roughened-surface stator and a smooth rotor. Friction factors were obtained from measurements of the mass flow rate and static pressure measurements along the smooth and roughened surfaces. In addition, dynamic pressure measurements were made at four axial locations at the bottom of individual holes and at facing locations in the smooth plate. The test facility is described, and a procedure for determining the friction factor is reviewed. Three clearances were investigated: 0.635 mm, 0.381 mm, and 0.254 mm. Tests were conducted with air at three different inlet pressures (84 bars, 70 bars, and 55 bars), producing a Reynolds numbers range from 50,000 to 700,000. Three surface configurations were tested, including smooth-on-smooth, smooth-on-hole, and hole-on-hole. The hole-pattern plates are identical with the exception of the hole depth. For the smooth-on-smooth and smooth-on-hole configurations, the friction factor remains largely constant or increases slightly with increasing Reynolds numbers. The friction factor increases as the clearance between the plates increases. The test program was initiated to investigate a friction-factor jump phenomenon cited by Ha et al. (1992, “Friction-Factor Characteristics for Narrow-Channels With Honeycomb Surfaces,” Trans. ASME, J. Tribol., 114, pp. 714–721) in test results from a flat-plate tester where, at elevated values of Reynolds numbers, the friction factor began to increase steadily with increasing Reynolds numbers. They tested apposed honeycomb surfaces. For the present tests, the phenomenon was also observed for tests of apposed roughened surfaces but was not observed for smooth-on-smooth or smooth-on-rough configurations. When the phenomenon was observed, dynamic pressure measurements showed a peak-pressure oscillation at the calculated Helmholtz frequency of the holes.
Overtip Shock Wave Structure and Its Impact on Turbine Blade Tip Heat Transfer
Authors: Zhang Q. , O’Dowd D. O. , He L. , Wheeler A. P. S. , Ligrani P. M. , Cheong B. C. Y.
Published: April 2011

In this paper, the transonic flow pattern and its influence on heat transfer on a high-pressure turbine blade tip are investigated using experimental and computational methods. Spatially resolved heat transfer data are obtained at conditions representative of a single-stage high-pressure turbine blade (Mexit=1.0, Reexit=1.27×106, gap=1.5% chord) using the transient infrared thermography technique within the Oxford high speed linear cascade research facility. Computational fluid dynamics (CFD) predictions are conducted using the Rolls-Royce HYDRA/PADRAM suite. The CFD solver is able to capture most of the spatial heat flux variations and gives prediction results, which compare well with the experimental data. The results show that the majority of the blade tip experiences a supersonic flow with peak Mach number reaching 1.8. Unlike other low-speed data in the open literature, the turbine blade tip heat transfer is greatly influenced by the shock wave structure inside the tip gap. Oblique shock waves are initiated near the pressure-side edge of the tip, prior to being reflected multiple times between the casing and the tip. Supersonic flow within the tip gap is generally terminated by a normal shock near the exit of the gap. Both measured and calculated heat transfer spatial distributions illustrate very clear stripes as the signature of the multiple shock structure. Overall, the supersonic part of tip experiences noticeably lower heat transfer than that near the leading-edge where the flow inside the tip gap remains subsonic.
Computational Predictions of Heat Transfer and Film-Cooling for a Turbine Blade With Nonaxisymmetric Endwall Contouring
Authors: Lynch Stephen P. , Thole Karen A. , Kohli Atul , Lehane Christopher
Published: April 2011

Three-dimensional contouring of the compressor and turbine endwalls in a gas turbine engine has been shown to be an effective method of reducing aerodynamic losses by mitigating the strength of the complex vortical structures generated at the endwall. Reductions in endwall heat transfer in the turbine have been also previously measured and reported in literature. In this study, computational fluid dynamics simulations of a turbine blade with and without nonaxisymmetric endwall contouring were compared to experimental measurements of the exit flowfield, endwall heat transfer, and endwall film-cooling. Secondary kinetic energy at the cascade exit was closely predicted with a simulation using the SST k-ω turbulence model. Endwall heat transfer was overpredicted in the passage for both the SST k-ω and realizable k-ε turbulence models, but heat transfer augmentation for a nonaxisymmetric contour relative to a flat endwall showed fair agreement to the experiment. Measured and predicted film-cooling results indicated that the nonaxisymmetric contouring limits the spread of film-cooling flow over the endwall depending on the interaction of the film with the contour geometry.
Predictions of Enhanced Heat Transfer of an Internal Blade Tip-Wall With Hemispherical Dimples or Protrusions
Authors: Xie Gongnan , Sundén Bengt , Wang Qiuwang
Published: April 2011

The blade tip region encounters high thermal loads because of the hot gas leakage flows, and it must therefore be cooled to ensure a long durability and safe operation. A common way to cool a blade tip is to design serpentine passages with 180 deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip lifetime. Dimples and protrusions are well recognized as effective devices to augment heat transfer in various applications. In this paper, enhanced heat transfer of an internal blade tip-wall has been predicted numerically. The computational models consist of a two-pass channel with a 180 deg turn and arrays of hemispherical dimples or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are in the range of 100,000–600,000. The computations are three dimensional, steady, incompressible, and nonrotating. The overall performance of the two-pass channels is also evaluated. It is found that due to the combination of turning impingement and protrusion crossflow or dimple advection, the heat transfer coefficient of the augmented tip is a factor of 2.0 higher than that of a smooth tip. This augmentation is achieved at the cost of a penalty of pressure drop by around 5%. By comparing the present dimples’ or protrusions’ performance with others in previous works, it is found that the augmented tips show the best performance, and the dimpled or protruded tips are superior to those pin-finned tips when the active area enhancement is excluded. It is suggested that dimples and protrusions can be used to enhance blade tip heat transfer and hence improve blade tip cooling.
Properties of the Bennett Mechanism Derived From the RRRS Closure Ellipse
Authors: Milenkovic Paul , Brown Morgan V.
Published: April 2011

For many single-loop closed-chain mechanisms, mobility may be characterized by the closure of sets in the theory of Lie groups. The four-revolute (4R) Bennett mechanism remains a persistent exception, requiring the formulation and expression of solutions to the loop closure relations, either directly or indirectly through spatial geometric figures. The simpler loop closure relations of the revolute-revolute-revolute-spherical (RRRS) loop, however, place conditions on the mobility of the 4R mechanism. That loop closure in turn may be interpreted as the congruence of a pair of ellipses. This new result is applied to proving the uniqueness of the Bennett mechanism along with deriving conditions where it is free from singularities. Design parameters are also identified for overconstrained RRRS mechanisms with 1DOF that are neither plane nor line symmetric. Such mechanisms, however, place the S-joint along the revolute axis of an underlying Bennett mechanism.
Anomalous optical processes in photoluminescence from ultrasmall quantum dots of ZnO
Authors: Kukreja L. M. , Misra P. , Das A. K. , Sartor J. , Kalt H.
Published: April 2011

Ensembles of alumina capped ZnO quantum dots (ZQDs) were grown using pulsed laser deposition. The ZQDs of mean radii comparable to and smaller than the pertinent excitonic Bohr radius (∼2.34 nm), called ultrasmall quantum dots, show size dependent optical absorption edges, which follow the strong confinement model. In this model the confinement energy and Coulombic interaction energy of the localized electron-hole pairs are significantly higher than their correlation energy and the optical transitions are perceived to be nonexcitonic in nature. In photoluminescence (PL) spectra of such ZQDs of mean radius of ∼2.3 nm at temperatures of 6 K and above, the primary recombinations are found to be due to the surface bound and Al donor bound electron-hole pairs. The band-edge recombination peak of the PL spectra appeared at about 70 K and above, which was found to be about 166 meV Stoke and/or thermally redshifted with respect to the experimentally observed absorption edge. Almost all of the PL spectra at different temperatures conspicuously showed the LO and 2LO phonon replicas of the primary transitions, suggesting strong coupling between the recombining charge carriers and the LO phonon, which is rather unusual for nonexcitonic recombinations. The temperature dependent PL peak positions followed the well known Varshni’s relation with fitting parameters close to that of the bulk ZnO. The peak intensity of the observed PL transitions followed the normal law of thermal quenching which could be fitted with the Arrhenius equation having activation energy of about 10 meV. Temperature dependence of full width at half maximum of the PL peaks when fitted with the Hellmann and O’Neill models did not result in a close match. However, from this fit one could estimate a value of the carrier-LO phonon coupling coefficient of ∼980 meV, which is higher than that reported earlier for the ZQDs. These observations are hitherto unfamiliar and expected to provide further insight into the basic optical processes in alumina capped ultrasmall ZQDs.
Transparent quantum waveguide
Authors: Dandoloff Rossen , Jensen Bjørn , Saxena Avadh
Published: April 2011

We present an alternative approach to the teaching of introductory quantum mechanics by considering the interaction between a particle and a waveguide. We focus on the accumulated phase when the particle travels across a waveguide composed of an arbitrary number of rectangular sections and show that the condition for resonant transmission can be deduced to leading order by simple algebra.
ERKs Induce Expression of the Transcriptional Repressor Blimp-1 and Subsequent Plasma Cell Differentiation
Authors: Yasuda Tomoharu , Kometani Kohei , Takahashi Noriko , Imai Yuuki , Aiba Yuichi , Kurosaki Tomohiro
Published: April 2011

The differentiation of B cells into antibody-producing plasma cells requires extracellular signal–regulated kinases.
Relevance of Timing for Determination of Posaconazole Plasma Concentrations
Authors: Heinz Werner J. , Zirkel Janina , Kuhn Anna , Schirmer Diana , Lenker Ulrike , Keller Daniela , Klinker Hartwig
Published: April 2011

For posaconazole, drug monitoring is suggested, but the relevance of timing for the determination of posaconazole concentration (PC) remains unclear. We investigated the variation of PC before and 4 and 8 h after the administration of 400 mg of posaconazole. Mean concentrations were 645, 678, and 616 ng/ml. The differences between trough and maximum concentrations were below 20% in 17 and below 30% in 20 of 25 patients. Hence, untimed posaconazole plasma concentrations give reliable information for most patients.
Randomized Pharmacokinetic and Pharmacodynamic Comparison of Fluoroquinolones for Tuberculous Meningitis
Authors: Thwaites Guy E. , Bhavnani Sujata M. , Chau Tran Thi Hong , Hammel Jeffrey P. , Török M. Estée , Van Wart Scott A. , Mai Pham Phuong , Reynolds Daniel K. , Caws Maxine , Dung Nguyen Thi , Hien Tran Tinh , Kulawy Robert , Farrar Jeremy , Ambrose Paul G.
Published: April 2011

Tuberculous meningitis (TBM) is the most lethal form of tuberculosis, and new treatments that improve outcomes are required. We randomly assigned adults with TBM to treatment with standard antituberculosis treatment alone or in combination with ciprofloxacin (750 mg/12 h), levofloxacin (500 mg/12 h), or gatifloxacin (400 mg/24 h) for the first 60 days of therapy. Fluoroquinolone concentrations were measured with plasma and cerebrospinal fluid (CSF) specimens taken at predetermined, randomly assigned times throughout treatment. We aimed to describe the pharmacokinetics of each fluoroquinolone during TBM treatment and evaluate the relationship between drug exposure and clinical response over 270 days of therapy (Controlled Trials number ISRCTN07062956). Sixty-one patients with TBM were randomly assigned to treatment with no fluoroquinolone (
n
= 15), ciprofloxacin (
n
= 16), levofloxacin (
n
= 15), or gatifloxacin (
n
= 15). Cerebrospinal fluid penetration, measured by the ratio of the plasma area under the concentration-time curve from 0 to 24 h (AUC
0–24
) to the cerebrospinal fluid AUC
0–24
, was greater for levofloxacin (median, 0.74; range, 0.58 to 1.03) than for gatifloxacin (median, 0.48; range, 0.47 to 0.50) or ciprofloxacin (median, 0.26; range, 0.11 to 0.77). Univariable and multivariable analyses of fluoroquinolone exposure against a range of different treatment responses revealed worse outcomes among patients with lower and higher plasma and CSF exposures than for patients with intermediate exposures (a U-shaped exposure-response). TBM patients most likely to benefit from fluoroquinolone therapy were identified, along with exposure-response relationships associated with improved outcomes. Fluoroquinolones add antituberculosis activity to the standard treatment regimen, but to improve outcomes of TBM, they must be started early, before the onset of coma.
Clinical and Molecular Characteristics of Extended-Spectrum- β-Lactamase-Producing Escherichia coli Causing Bacteremia in the Rotterdam Area, Netherlands
Authors: van der Bij Akke K. , Peirano Gisele , Goessens Wil H. F. , van der Vorm Eric R. , van Westreenen M. , Pitout Johann D. D.
Published: April 2011

We investigated the clinical and molecular characteristics of bacteremia caused by extended-spectrum-β-lactamase (ESBL)-producing
Escherichia coli
over a 2-year period (2008 to 2009) in the Rotterdam region (including 1 teaching hospital and 2 community hospitals) of Netherlands. The majority of patients presented with community onset urinary and intra-abdominal infections, with an increase in prevalence during 2009. The majority of
E. coli
isolates produced CTX-M-15, and 4 sequence types (ST38, ST131, ST405, and ST648) predominated. There were significant differences in clinical and molecular characteristics between the 2 community hospitals.
Selection, Optimization, and Pharmacokinetic Properties of a Novel, Potent Antiviral Locked Nucleic Acid-Based Antisense Oligomer Targeting Hepatitis C Virus Internal Ribosome Entry Site
Authors: Laxton Carl , Brady Kevin , Moschos Sterghios , Turnpenny Paul , Rawal Jaiessh , Pryde David C. , Sidders Ben , Corbau Romu , Pickford Chris , Murray E. J.
Published: April 2011

We have screened 47 locked nucleic acid (LNA) antisense oligonucleotides (ASOs) targeting conserved (>95% homology) sequences in the hepatitis C virus (HCV) genome using the subgenomic HCV replicon assay and generated both antiviral (50% effective concentration [EC50]) and cytotoxic (50% cytotoxic concentration [CC50]) dose-response curves to allow measurement of the selectivity index (SI). This comprehensive approach has identified an LNA ASO with potent antiviral activity (EC50= 4 nM) and low cytotoxicity (CC50>880 nM) targeting the 25- to 40-nucleotide region (nt) of the HCV internal ribosome entry site (IRES) containing the distal and proximal miR-122 binding sites. LNA ASOs targeting previously known accessible regions of the IRES, namely, loop III and the initiation codon in loop IV, had poor SI values. We optimized the LNA ASO sequence by performing a 1-nucleotide walk through the 25- to 40-nt region and show that the boundaries for antiviral efficacy are extremely precise. Furthermore, we have optimized the format for the LNA ASO using different gapmer and mixomer patterns and show that RNase H is required for antiviral activity. We demonstrate that RNase H-refractory ASOs targeting the 25- to 40-nt region have no antiviral effect, revealing important regulatory features of the 25- to 40-nt region and suggesting that RNase H-refractory LNA ASOs can act as potential surrogates for proviral functions of miR-122. We confirm the antisense mechanism of action using mismatched LNA ASOs. Finally, we have performed pharmacokinetic experiments to demonstrate that the LNA ASOs have a very long half-life (>5 days) and attain hepatic maximum concentrations >100 times the concentration required forin vitroantiviral activity.
In Vivo
Efficacy of Glycopeptide-Colistin Combination Therapies in a
Galleria mellonella
Model of
Acinetobacter baumannii
Infection
Authors: Hornsey M. , Wareham D. W.
Published: April 2011

The treatment of
Acinetobacter baumannii
infections poses a significant clinical challenge, with isolates resistant to all commonly used agents increasingly being reported. With few new agents in the pipeline, clinicians are increasingly turning to combinations of antimicrobials in the hope that they may act synergistically together. In this study we assessed the activities of two glycopeptide-colistin combinations both
in vitro
and using a
Galleria mellonella
caterpillar model of
A. baumannii
infection. In checkerboard assays both vancomycin and teicoplanin were highly active against susceptible and multidrug-resistant strains of
A. baumannii
when combined with colistin (fractional inhibitory concentration [FIC] of <0.25). Treatment of
G. mellonella
caterpillars infected with lethal doses of
A. baumannii
resulted in significantly enhanced survival rates when either vancomycin or teicoplanin was given with colistin compared to colistin treatment alone (
P
< 0.05). This effect was most marked when vancomycin was the glycopeptide administered, although this agent was also highly effective as monotherapy, possibly through an immunomodulatory action on the
G. mellonella
response to
A. baumannii
infection. This work suggests that glycopeptide-colistin combinations are highly active against
A. baumannii
both
in vitro
and in a simple animal model of infection. They should be considered further as potential treatments for difficult-to-treat
A. baumannii
infections.
Dose Range Evaluation of Mycograb C28Y Variant, a Human Recombinant Antibody Fragment to Heat Shock Protein 90, in Combination with Amphotericin B-Desoxycholate for Treatment of Murine Systemic Candidiasis
Authors: Louie Arnold , Stein Daniel S. , Zack Julia Z. , Liu Weiguo , Conde Haley , Fregeau Christine , VanScoy Brian D. , Drusano George L.
Published: April 2011

Systemic candidiasis causes significant mortality in patients despite amphotericin B (AMB) therapy. Mycograb C28Y variant, a human recombinant antibody fragment to heat shock protein 90, is closely related to Mycograb, which showed a survival advantage in combination with AMB in a phase III human trial. The Mycograb C28Y variant could potentially increase the antifungal effect of AMB. In our study, the interaction between AMB-desoxycholate (DAMB) and the Mycograb C28Y variant was characterized
in vitro
by using a checkerboard method. Quantitative cultures of kidneys, livers, and spleens of neutropenic mice with systemic
Candida albicans
infections were used to assess the
in vivo
interaction between 1.4 mg/kg of body weight/day of DAMB and 0.15, 1.5, and 15 mg/kg/day of the Mycograb C28Y variant after 1, 3, and 5 days of therapy. DAMB and Mycograb C28Y variant monotherapies, vehicle, and a no-treatment arm served as controls. Also, single- and multidose pharmacokinetics for the Mycograb C28Y variant were determined. Indifference or synergy between DAMB and the Mycograb C28Y variant was seen in two trials by the checkerboard method. The pharmacokinetics of the Mycograb C28Y variant was best described by a 2-compartment model with a median serum
t
1/2
α
of ∼0.198 h and a
t
1/2
β
of ∼1.77 h. In mice, DAMB together with the Mycograb C28Y variant was no more effective than AMB alone (
P
> 0.05 by analysis of variance). The Mycograb C28Y variant alone had no antifungal activity. We therefore conclude that the Mycograb C28Y variant in combination with DAMB offered no benefit over DAMB monotherapy in a neutropenic murine model of systemic candidiasis.
Posaconazole in Human Serum: a Greater Pharmacodynamic Effect than Predicted by the Non-Protein-Bound Serum Concentration
Authors: Lignell Anders , Löwdin Elisabeth , Cars Otto , Chryssanthou Erja , Sjölin Jan
Published: April 2011

It is generally accepted that only the unbound fraction of a drug is pharmacologically active. Posaconazole is an antifungal agent with a protein binding of 98 to 99%. Taking into account the degree of protein binding, plasma levels in patients, and MIC levels of susceptible strains, it can be assumed that the free concentration of posaconazole sometimes will be too low to exert the expected antifungal effect. The aim was therefore to test the activity of posaconazole in serum in comparison with that of the calculated unbound concentrations in protein-free media. Significant differences (
P
< 0.05) from the serum control were found at serum concentrations of posaconazole of 1.0 and 0.10 mg/liter, with calculated free concentrations corresponding to 1× MIC and 0.1× MIC, respectively, against one
Candida lusitaniae
strain selected for proof of principle. In RPMI 1640, the corresponding calculated unbound concentration of 0.015 mg/liter resulted in a significant effect, whereas that of 0.0015 mg/liter did not. Also, against seven additional
Candida
strains tested, there was an effect of the low posaconazole concentration in serum, in contrast to the results in RPMI 1640. Fluconazole, a low-grade-protein-bound antifungal, was used for comparison at corresponding concentrations in serum and RPMI 1640. No effect was observed at the serum concentration, resulting in a calculated unbound concentration of 0.1× MIC. In summary, there was a substantially greater pharmacodynamic effect of posaconazole in human serum than could be predicted by the non-protein-bound serum concentration. A flux from serum protein-bound to fungal lanosterol 14α-demethylase-bound posaconazole is suggested.
Genetic Resistance Elements Carrying
mef
Subclasses Other than
mef
(A) in Streptococcus pyogenes
Authors: Del Grosso Maria , Camilli Romina , Barbabella Giada , Blackman Northwood John , Farrell David J. , Pantosti Annalisa
Published: April 2011

In
Streptococcus pyogenes
, efflux-mediated erythromycin resistance is associated with the
mef
gene, represented mostly by
mef
(A), although a small portion of strains carry different
mef
subclasses. We characterized the composite genetic elements, including
mef
subclasses other than
mef
(A), associated with other resistance genes in
S. pyogenes
isolates. Determination of the genetic elements was performed by PCR mapping. The strains carrying mosaic
mef
(A/E), in which the 5′ region was identical to
mef
(A) and the 3′ region was identical to
mef
(E), also carried
tet
(O). The two genes were found enclosed in an element similar to
S. pyogenes
prophage Φm46.1, designated the Φm46.1-like element. In
S. pyogenes
strains carrying
mef
(E) and
tet
(M),
mef
(E) was included in a typical mega element, and in some strains, it was physically associated with
tet
(M) in the composite element Tn
2009
.
S. pyogenes
strains carrying
mef
(I) also carried
catQ
; the two genes were linked in a fragment representing a portion of the 5216IQ complex of
Streptococcus pneumoniae
, designated the defective IQ element. In the only isolate carrying a novel
mef
gene, this was associated with
catQ
and
tet
(M) in a genetic element similar to the 5216IQ complex of
S. pneumoniae
(5216IQ-like complex), suggesting that the novel
mef
is in fact a variant of
mef
(I). This study demonstrates that the composite elements containing
mef
are shared between
S. pyogenes
and
S. pneumoniae
and suggests that it is important to distinguish the
mef
subclass on the basis of the genetic element containing it.
Significant Natural Product Biosynthetic Potential of Actinorhizal Symbionts of the Genus Frankia, as Revealed by Comparative Genomic and Proteomic Analyses
Authors: Udwary Daniel W. , Gontang Erin A. , Jones Adam C. , Jones Carla S. , Schultz Andrew W. , Winter Jaclyn M. , Yang Jane Y. , Beauchemin Nicholas , Capson Todd L. , Clark Benjamin R. , Esquenazi Eduardo , Eustáquio Alessandra S. , Freel Kelle , Gerwick Lena , Gerwick William H. , Gonzalez David , Liu Wei-Ting , Malloy Karla L. , Maloney Katherine N. , Nett Markus , Nunnery Joshawna K. , Penn Kevin , Prieto-Davo Alejandra , Simmons Thomas L. , Weitz Sara , Wilson Micheal C. , Tisa Louis S. , Dorrestein Pieter C. , Moore Bradley S.
Published: April 2011

Bacteria of the genus
Frankia
are mycelium-forming actinomycetes that are found as nitrogen-fixing facultative symbionts of actinorhizal plants. Although soil-dwelling actinomycetes are well-known producers of bioactive compounds, the genus
Frankia
has largely gone uninvestigated for this potential. Bioinformatic analysis of the genome sequences of
Frankia
strains ACN14a, CcI3, and EAN1pec revealed an unexpected number of secondary metabolic biosynthesis gene clusters. Our analysis led to the identification of at least 65 biosynthetic gene clusters, the vast majority of which appear to be unique and for which products have not been observed or characterized. More than 25 secondary metabolite structures or structure fragments were predicted, and these are expected to include cyclic peptides, siderophores, pigments, signaling molecules, and specialized lipids. Outside the hopanoid gene locus, no cluster could be convincingly demonstrated to be responsible for the few secondary metabolites previously isolated from other
Frankia
strains. Few clusters were shared among the three species, demonstrating species-specific biosynthetic diversity. Proteomic analysis of
Frankia
sp. strains CcI3 and EAN1pec showed that significant and diverse secondary metabolic activity was expressed in laboratory cultures. In addition, several prominent signals in the mass range of peptide natural products were observed in
Frankia
sp. CcI3 by intact-cell matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS). This work supports the value of bioinformatic investigation in natural products biosynthesis using genomic information and presents a clear roadmap for natural products discovery in the
Frankia
genus.
Distribution of Bacillus thuringiensis subsp. israelensis in Soil of a Swiss Wetland Reserve after 22 Years of Mosquito Control
Authors: Guidi Valeria , Patocchi Nicola , Lüthy Peter , Tonolla Mauro
Published: April 2011

Recurrent treatments with
Bacillus thuringiensis
subsp.
israelensis
are required to control the floodwater mosquito
Aedes vexans
that breeds in large numbers in the wetlands of the Bolle di Magadino Reserve in Canton Ticino, Switzerland. Interventions have been carried out since 1988. In the present study, the spatial distribution of resting
B. thuringiensis
subsp.
israelensis
spores in the soil was measured. The
B. thuringiensis
subsp.
israelensis
concentration was determined in soil samples collected along six transects covering different elevations within the periodically flooded zones. A total of 258 samples were processed and analyzed by quantitative PCR that targeted an identical fragment of 159 bp for the
B. thuringiensis
subsp.
israelensis cry4Aa
and
cry4Ba
genes.
B. thuringiensis
subsp.
israelensis
spores were found to persist in soils of the wetland reserve at concentrations of up to 6.8 log per gram of soil. Continuous accumulation due to regular treatments could be excluded, as the decrease in spores amounted to 95.8% (95% confidence interval, 93.9 to 97.7%). The distribution of spores was correlated to the number of
B. thuringiensis
subsp.
israelensis
treatments, the elevation of the sampling point, and the duration of the flooding periods. The number of
B. thuringiensis
subsp.
israelensis
treatments was the major factor influencing the distribution of spores in the different topographic zones (
P
< 0.0001). These findings indicated that
B. thuringiensis
subsp.
israelensis
spores are rather immobile after their introduction into the environment.
Extracellular Reduction of Hexavalent Chromium by Cytochromes MtrC and OmcA of Shewanella oneidensis MR-1
Authors: Belchik Sara M. , Kennedy David W. , Dohnalkova Alice C. , Wang Yuanmin , Sevinc Papatya C. , Wu Hong , Lin Yuehe , Lu H. Peter , Fredrickson James K. , Shi Liang
Published: April 2011

To characterize the roles of cytochromes MtrC and OmcA ofShewanella oneidensisMR-1 in Cr(VI) reduction, the effects of deleting themtrCand/oromcAgene on Cr(VI) reduction and the cellular locations of reduced Cr(III) precipitates were investigated. Compared to the rate of reduction of Cr(VI) by the wild type (wt), the deletion ofmtrCdecreased the initial rate of Cr(VI) reduction by 43.5%, while the deletion ofomcAor bothmtrCandomcAlowered the rate by 53.4% and 68.9%, respectively. In wt cells, Cr(III) precipitates were detected by transmission electron microscopy in the extracellular matrix between the cells, in association with the outer membrane, and inside the cytoplasm. No extracellular matrix-associated Cr(III) precipitates, however, were found in the cytochrome mutant cell suspension. In mutant cells without either MtrC or OmcA, most Cr(III) precipitates were found in association with the outer membrane, while in mutant cells lacking both MtrC and OmcA, most Cr(III) precipitates were found inside the cytoplasm. Cr(III) precipitates were also detected by scanning election microscopy on the surfaces of the wt and mutants without MtrC or OmcA but not on the mutant cells lacking both MtrC and OmcA, demonstrating that the deletion ofmtrCandomcAdiminishes the extracellular formation of Cr(III) precipitates. Furthermore, purified MtrC and OmcA reduced Cr(VI) with apparentkcatvalues of 1.2 ± 0.2 (mean ± standard deviation) and 10.2 ± 1 s−1andKmvalues of 34.1 ± 4.5 and 41.3 ± 7.9 μM, respectively. Together, these results consistently demonstrate that MtrC and OmcA are the terminal reductases used byS. oneidensisMR-1 for extracellular Cr(VI) reduction where OmcA is a predominant Cr(VI) reductase.
Dynamics of Flagellum- and Pilus-Mediated Association of Pseudomonas aeruginosa with Contact Lens Surfaces
Authors: Tran Victoria B. , Fleiszig Suzanne M. J. , Evans David J. , Radke Clayton J.
Published: April 2011

Flagella and pili are appendages that modulate attachment of
Pseudomonas aeruginosa
to solid surfaces. However, previous studies have mostly reported absolute attachment. Neither the dynamic roles of these appendages in surface association nor those of attachment phenotypes have been quantified. We used video microscopy to address this issue. Unworn, sterile, soft contact lenses were placed in a laminar-flow optical chamber. Initial lens association kinetics for
P. aeruginosa
strain PAK were assessed in addition to lens-surface association phenotypes. Comparisons were made to strains with mutations in flagellin (
fliC
) or pilin (
pilA
) or those in flagellum (
motAB
) or pilus (
pilU
) function. PAK and its mutants associated with the contact lens surface at a constant rate according to first-order kinetics. Nonswimming mutants associated ∼30 to 40 times slower than the wild type. PAK and its
pilA
mutant associated at similar rates, but each ∼4 times faster than the
pilU
mutant. Lens attachment by wild-type PAK induced multiple phenotypes (static, lateral, and rotational surface movement), each showing only minor detachment. Flagellin (
fliC
) and flagellar-motility (
motAB
) mutants did not exhibit surface rotation. Conversely, strains with mutations in pilin (
pilA
) and pilus retraction (
pilU
) lacked lateral-surface movement but displayed enhanced surface rotation. Slower surface association of swimming-incapable
P. aeruginosa
mutants was ascribed to lower convective-diffusion-arrival rates, not to an inability to adhere. Flagellum function (swimming) enhanced lens association, attachment, and rotation; hyperpiliation hindered lens association.
P. aeruginosa
bound through three different adhesion sites: flagellum, pili, and body. Reduction of bacterial attachment to contact lenses thus requires blockage of multiple adhesion phenotypes.
Determining Thermal Inactivation of Escherichia coli O157:H7 in Fresh Compost by Simulating Early Phases of the Composting Process
Authors: Singh Randhir , Kim Jinkyung , Shepherd Marion W. , Luo Feng , Jiang Xiuping
Published: April 2011

A three-strain mixture of
Escherichia coli
O157:H7 was inoculated into fresh dairy compost (ca. 10
7
CFU/g) with 40 or 50% moisture and was placed in an environmental chamber (ca. 70% humidity) that was programmed to ramp from room temperature to selected composting temperatures in 2 and 5 days to simulate the early composting phase. The surviving
E. coli
O157:H7 population was analyzed by direct plating and enrichment. Optimal and suboptimal compost mixes, with carbon/nitrogen (C/N) ratios of 25:1 and 16:1, respectively, were compared in this study. In the optimal compost mix,
E. coli
O157:H7 survived for 72, 48, and 24 h in compost with 40% moisture and for 72, 24, and 24 h with 50% moisture at 50, 55, and 60°C, respectively, following 2 days of come-up time (rate of heating up). However, in the suboptimal compost mix, the pathogen survived for 288, 72, and 48 h in compost with 40% moisture and for 240, 72, 24 h in compost with 50% moisture at the same temperatures, respectively. Pathogen survival was longer, with 5 days of come-up time compared with 2 days of come-up. Overall,
E. coli
O157:H7 was inactivated faster in the compost with 50% moisture than in the compost with 40% at 55 and 60°C. Both moisture and come-up time were significant factors affecting Weibull model parameters. Our results suggest that slow come-up time at the beginning of composting can extend pathogen survival during composting. Additionally, both the C/N ratio and the initial moisture level in the compost mix affect the rate of pathogen inactivation as well.
Antimicrobial Effect of Chitosan Nanoparticles on Streptococcus mutans Biofilms
Authors: Chávez de Paz Luis E. , Resin Anton , Howard Kenneth A. , Sutherland Duncan S. , Wejse Peter L.
Published: April 2011

Nanoparticle complexes were prepared from chitosans of various molecular weights (MW) and degrees of deacetylation (DD). The antimicrobial effect was assessed by the Live/Dead BacLight technique in conjunction with confocal scanning laser microscopy (CSLM) and image analysis. Nanocomplexes prepared from chitosans with high MW showed a low antimicrobial effect (20 to 25% of cells damaged), whereas those prepared from low-MW chitosans showed high antimicrobial effect (>95% of cells damaged).
Protein Targeting to the Parasitophorous Vacuole Membrane of Plasmodium falciparum
Authors: Eksi Saliha , Williamson Kim C.
Published: April 2011

Red blood cell (RBC) invasion and parasitophorous vacuole (PV) formation byPlasmodium falciparumare critical for the development and pathogenesis of malaria, a continuing global health problem. Expansion of the PV membrane (PVM) during growth is orchestrated by the parasite. This is particularly important in mature RBCs, which lack internal organelles and no longer actively synthesize membranes. Pfs16, a 16-kDa integral PVM protein expressed by gametocytes, was chosen as a model for studying the trafficking of material from the parasite across the PV space to the PVM. The locations of Pfs16-green fluorescent protein (GFP) reporter proteins containing distinct regions of Pfs16 were tracked from RBC invasion to emergence. Inclusion of the 53 C-terminal amino acids (aa) of Pfs16 to a GFP reporter construct already containing the N-terminal secretory signal sequence was sufficient for targeting to and retention on the PVM. An amino acid motif identified in this region was also found in seven other known PVM proteins. Removal of the 11 C-terminal aa did not affect PVM targeting, but membrane retention was decreased. Additionally, during emergence from the PVM and RBC, native Pfs16 and the full-length Pfs16-GFP reporter protein were found to concentrate on the ends of the gametocyte. Capping was not observed in constructs lacking the amino acids between the N-terminal secretory signal sequence and the transmembrane domain, suggesting that this region, which is not required for PVM targeting, is involved in capping. This is the first report to define the amino acid domains required for targeting to theP. falciparumPVM.