bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Strain Localization on Parameter Identification
Authors: Springmann Marcel , Kühhorn Arnold , Kuna Meinhard , Scherzer Matthias
Published: December 2008

In the present contribution, the parameter identification of ductile materials is reconceived in the frame of localization phenomena. To describe the damage process on a continuum mechanical basis, the Gurson–Tvergaard–Needleman damage model is implemented in the finite element system Scientific Parallel Computing-Program Module Hyperelastic Plastic (SPC-PMHP), which was developed for parallel computers to solve nonlinear initial boundary value problems within large strain formalism. The softening of the material is responsible for the loss of ellipticity of the differential equations and for the strain localization. A general localization criterion is given to determine when numerical solutions cease to show convergence. This criterion is based on an analysis of the determinant of the acoustic tensor, which includes the material tangent, the stresses, and the deformation gradient. On this account, the onset of localization is significantly affected by material parameters. The parameters are identified on the basis of locally measured displacement fields. As additional information, the strain localization criterion is included in the identification process. A numerical example shows the influence of the localization criterion on the parameter identification.
Measures of Bulk and Grain Strain in Deformation Processes
Authors: Hartley Craig S. , Spowart Jonathan E.
Published: December 2008

This study illustrates a method of measuring internal total strain based on the observation that networks of internal boundaries within a polycrystalline material deform locally in a manner congruent with the local metal flow. Appropriate measurements of the development of the spatial anisotropy of such networks with increasing deformation provide a basis for defining several measures of the local total strain. These quantities, called “grain strains” when the boundaries observed are grain boundaries, can serve as an experimental measure of the internal total strain at various locations in a specimen for comparison with computations based on finite element models using various constitutive relations or phase field simulations of grain growth or deformation. Experimental measurements of grain strains at the center of a ferritic steel sheet rolled in nominally 10% increments to 50% total reduction in thickness illustrate the method and correlate well with corresponding strains based on measures of the change in thickness of the sheet and the assumption of plane strain.
A Practical Method for Fatigue Crack Initiation Detection Using an Ion-Sputtered Film
Authors: Deng Gang , Sakanashi Yoshihiko , Nakanishi Tsutomu
Published: December 2008

The development of fatigue in a machine element can be divided into the fatigue crack initiation stage and the crack growth stage. The effects of the surface conditions, such as roughness and surface qualities, on the fatigue strength are considered to be restricted to the fatigue crack initiation stage. Thus, these effects can be evaluated exactly by the investigation on the fatigue crack initiation life. In this research a practical method is presented for detecting fatigue crack initiation during fatigue tests using an ion-sputtered film. Ion-sputtered films were formed on acrylic and steel test pieces having a specially designed round notch. Three-point bending fatigue tests were performed and the instants of fatigue crack initiation on the notched surface of both acrylic and steel test pieces during the tests were identified clearly; thus the fatigue crack initiation life can also be determined experimentally using the presented method. In addition, since the system used to measure the electric resistance of the film, which indicates the crack initiation, is extremely simple, that is, it consists of a variable resistor, a DC power source, and a data recorder, this method is considered very practical for monitoring crack initiation.
Some Analytical Solutions of the Kamal Equation for Isothermal Curing With Applications to Composite Patch Repair
Authors: Tsamasphyros G. J. , Papathanassiou Th. K. , Markolefas S. I.
Published: December 2008

In this paper, we derive some analytical solutions of the Kamal cure rate differential equation. The Kamal model is a first order quasilinear ordinary differential equation, describing the progress of the curing reaction of several thermosetting polymers. All the examined cases refer to isothermal curing processes. The solutions obtained in this paper are all of implicit form. The derived solutions are applied to a repair technique based on the adhesive bonding of polymer matrix composite patches onto damaged or corroded areas. Critical duration times of realistic cure cycles corresponding to composite patch repair are estimated. The practical importance of the proposed analytic solutions is demonstrated through the presented engineering application.
A Unified Phenomenological Model for Tensile and Compressive Response of Polymeric Foams
Authors: Walter Timothy R. , Richards Andrew W. , Subhash Ghatu
Published: December 2008

Tensile and compressive stress-strain responses were obtained for various densities of polymer foams. These experimental data were used to determine relevant engineering parameters (such as elastic moduli in tension and compression, ultimate tensile strength, etc.) as a function of foam density. A phenomenological model applicable for both compressive and tensile responses of polymeric foams is validated by comparing the model to the experimentally obtained compression and tensile responses. The model parameters were analyzed to determine the effect of each parameter on the mechanical response of the foam. The engineering parameters were later compared to the appropriate model parameters and a good correlation was obtained. It was shown that the model indeed captures the entire compressive and tensile response of polymeric foams effectively.
Stabilization of a Zirconia System and Evaluation of Its Electrolyte Characteristics for a Fuel Cell: Based on Electrical and Mechanical Considerations
Authors: Yamaji Akihiko , Koshikawa Takao , Araki Wakako , Adachi Tadaharu
Published: December 2008

The purpose of this study is to clarify the relationship between ionic conductivity and phase transformation of zirconia system codoped with scandium oxide Sc2O3 and ytterbium oxide Yb2O3. Aiming to achieve high ionic conductivity as well as high mechanical strength, the authors have also investigated the relationship between phase transformation and mechanical strength. The results have been discussed with respect to both the conductivity and the mechanical strength. The Sc- and Yb-codoped zirconia (ZrO2) used as samples in this study were prepared by a standard solid-state reaction. X-ray powder diffraction (XRD) method was used to determine the crystal structures of the sintered samples. To detect any phase change between room temperature and 1273K, thermal mechanical analysis (TMA) was conducted. To determine oxygen-ion conductivity in a temperature range from 873to1273K in air, impedance measurements were performed with alternating current (ac). Single-cell performance was confirmed under the condition of 26.2Pa partial hydrogen pressure. Finally, to measure bending strength, three-point bending tests were performed with a universal testing machine. The results of XRD and TMA showed that codoping of Sc2O3 and Yb2O3 into ZrO2 successfully stabilized the cubic phase when the average radius ratio of these two dopants in total was close to the ideal one for the eight-coordinate. The ac impedance measurement demonstrated that the cubic-phase stabilization achieved a high conductivity. Adequate amounts of dopants produced oxygen vacancies for high conductivity without complex defects: ZrO2 system doped with 1mol% of Yb2O3 and 8mol% of Sc2O3 showed the highest conductivity at 1273K and 0.30S∕cm. The bending strength decreased with increasing the content of doped Sc2O3 from 7mol%to11mol%, depending on the amount of the tetragonal phase, which contributes to strengthen materials. In the performance test, the ZrO2 system stabilized with doping 1mol%Yb2O3 and 8mol%Sc2O3 with thickness of 2.16mm showed maximum power density at 1273K, that is, 210mW∕cm2. From all the above tests, we recommend that, based on electrical and mechanical considerations, 1Yb8ScSZ is the present best option for an electrolyte material for a solid oxide fuel cell.
Numerical Study of Impact Penetration Shearing Employing Finite Strain Viscoplasticity Model Incorporating Adiabatic Shear Banding
Authors: Longère Patrice , Dragon André , Deprince Xavier
Published: December 2008

This work brings forward a twofold contribution relevant to the adiabatic shear banding (ASB) process as a part of dynamic plasticity of high-strength metallic materials. The first contribution is a reassessment of a three-dimensional finite deformation model starting from a specific scale postulate and devoted to cover a wide range of dissipative phenomena, including ASB-related material instabilities (strong softening prefailure stage). The model, particularly destined to deal with impacted structures was first detailed by (Longère et al. 2003, “Modelling Adiabatic Shear Banding Via Damage Mechanics Approach,” Arch. Mech., 55, pp. 3–38; 2005, “Adiabatic Shear Banding Induced Degradation in a Thermo-Elastic/Viscoplastic Material Under Dynamic Loading,” Int. J. Impact Eng., 32, pp. 285–320). The second novel contribution concerns numerical solution of a genuine ballistic penetration problem employing the above model for a target plate material. The ASB trajectories are shown to follow a multistage history and complex distribution pattern leading finally to plugging failure mechanism. The corresponding analysis and related parametric study are intended to put to the test the pertinency of the model as an advanced predictive tool for complex shock related problems.
Microstructure Development During High Strain Torsion of NiAl
Authors: Klöden Burghardt , Oertel Carl-Georg , Skrotzki Werner , Rybacki Erik
Published: December 2008

The microstructure development was investigated in torsion deformed NiAl. High strain torsion of solid bars was done with a Paterson rock deformation machine at temperatures between 700 K and 1300 K under a confining pressure of 400 MPa. The maximum shear strains and shear strain rates applied were 19 and 2.2×10−4 s−1, respectively. The shear stress–shear strain curves are characterized by a peak at low shear strains, which is followed by softening and a steady state at high shear strains. Increasing shear strain leads to grain refinement, with the average grain size decreasing with temperature. Moreover, a steady state grain aspect ratio and inclination of the grain long axis with respect to the shear plane is observed. With increasing shear strain, the fraction of low angle grain boundaries goes over a maximum and approaches a steady state of about 20–40%. The development of the microstructure is characterized by two different temperature regimes. Up to 1000 K, continuous dynamic recrystallization characterized by limited grain growth takes place, leading to a transformation of low into high angle grain boundaries. At temperatures above 1000 K, discontinuous dynamic recrystallization occurs by massive grain growth. The results are qualitatively discussed on the basis of models dealing with dynamic recrystallization.
Texture Formation and Swift Effect in High Strain Torsion of NiAl
Authors: Klöden Burghardt , Oertel Carl-Georg , Skrotzki Werner , Rybacki Erik
Published: December 2008

Texture formation and Swift effect were investigated in torsion deformed NiAl. High-strain torsion of solid bars was done with a Paterson rock deformation machine at temperatures between 700 K and 1300 K under a confining pressure of 400 MPa. The maximum shear strains and shear strain rates applied were 19×10−4 s−1 and 2.2×10−4 s−1, respectively. Textures were measured by diffraction of neutrons, electrons, and synchrotron radiation. The textures consist of an oblique cube and Goss component, the intensity of which depends on the initial texture and deformation temperature. The axial lengthening and shortening observed are related to the Goss and the oblique cube components, respectively. There is qualitative agreement between experiment and simulation at low temperature and low shear strains. With increasing temperature, continuous and discontinuous dynamic recrystallization take place, strongly influencing the development of texture and Swift effect.
Analysis of Large Strain Hot Torsion Textures Associated With “Continuous” Dynamic Recrystallization
Authors: Lim S. M. , Desrayaud C. , Montheillet F.
Published: December 2008

The development of ideal orientations within the steady-state region of hot torsion flow curves of fcc and bcc metals undergoing “continuous” dynamic recrystallization is analyzed. It is well known that in fcc metals, e.g., Al deformed at 400°C and above, the experimentally observed end texture consists of the twin-symmetric B(112¯)[11¯0]/B¯(1¯1¯2)[1¯10] component, whereby the (hkl)[uvw] indices correspond to the shear plane z and the shear direction θ, respectively. In bcc iron however, only one of the self-symmetric D1(112¯)[111] and D2(1¯1¯2)[111] components dominates (the former in the case of positive shear or clockwise rotation about the r-axis, and the latter during negative shear). The tendency toward a single end orientation imposes certain limitations on grain refinement, as this would ultimately imply the coalescence of subgrains of or close to this orientation, and therefore the disappearance of existing high angle boundaries (≥15 deg). It is believed that the preference of D1 over D2, or vice versa, could be related to phenomena other than glide-induced rotations, e.g., grain boundary migration resulting from differences in work hardening rates. In this paper, the standard Taylor model is first used to predict the texture evolution in simple shear under the full-constraint rate-sensitive scheme. This is then coupled with an approach that takes into account grain boundary migration resulting from differences in dislocation densities within grains of varying orientations. The preliminary results are in agreement with experimental findings, i.e., grains with initial orientations close to D2 grow at the expense of neighboring grains during negative shear and vice versa.
Identification of Simple Shear in Plane Strain Deformation
Authors: Damamme G. , Colin A. , Desrayaud C. , Montheillet F.
Published: December 2008

A theoretical analysis of plane strain incompressible velocity fields is first carried out. Two types of local fields are distinguished according to the sign of det(L), where L is the velocity gradient tensor, whereas det(L)=0 is associated with simple shear. A geometrical interpretation is used to illustrate the various decompositions of L. Finally, it is suggested that the condition det(L)=0 can be used to predict the occurrence of shear bands during metal forming processes.
Measurement and Assessment of Fatigue Life of Spot-Weld Joints
Authors: Ertas Ahmet H. , Vardar Oktem , Sonmez Fazil O. , Solim Zafer
Published: December 2008

Spot-weld joints are commonly used to fasten together metal sheets. Because fatigue fracture is the most critical failure mode for these joints under fluctuating loads, understanding their fatigue failure behavior and assessment of their fatigue lives are crucial from the viewpoint of failure prevention in design. In this study, a series of experiments was conducted to study the fatigue failure of spot-welded modified tensile-shear specimens made of a low carbon steel. Two different types of resistance spot welding were investigated (manual and automated). Tests were repeated under different load ranges, and the corresponding fatigue lives were determined. The specimens were also examined under an optical microscope. In the numerical part of this study, a finite element analysis was carried out using commercial software, ANSYS, to determine the stress and strain states within the specimens. The material nonlinearity, local plastic deformations around the welds during loading, and the residual stresses and strains developed after unloading as a result of plastic deformations were taken into account. Based on the predicted stress and strain states, fatigue analyses were performed using several models for life assessment. Then, the measured and predicted fatigue lives were compared, and the suitability of the models was discussed. Among the strain-based models, Coffin–Manson and Morrow’s means stress models yielded the best predictions.
Plastic Behavior of Metals at Large Strains: Experimental Studies Involving Simple Shear
Authors: Rauch E. F.
Published: December 2008

Two experimental devices that promote simple shear are used to investigate the plastic behavior of metals under very large strains. First, researches on the anisotropic behaviors of sheets of metals performed with the help of the planar simple shear test are reviewed. In particular, it is shown that, with this device, stage IV may be reached and analyzed on polycrystals as well as on single crystals. The second part is devoted to equal channel angular extrusion, which is known to promote grain refinement after several passes. A direct comparison of the crystallographic textures measured on sheared and on extruded samples confirms that the extrusion promotes massively simple shear. Besides, the grain refinement is measured with a dedicated transmission electron microscopy (TEM) attachment. It is shown that the grain size decreases regularly for a low carbon steel as well as for copper, down to around 1 μm. It is argued that the sustained hardening in stage IV is a mechanical signature of the grain size decrease. The trend is interpreted and reproduced quantitatively with the help of a simple modeling approach.
Modeling Effects of Compliant Coatings on HCF Resistance of Primary Inclusions in High Strength Steels
Authors: Prasannavenkatesan Rajesh , McDowell David L. , Olson Gregory B. , Jou Herng-Jeng
Published: December 2008

Nucleation of fatigue cracks at nonmetallic primary inclusions in high cycle fatigue of martensitic steel is computationally investigated. We explore the capabilities of an elastic interphase material adhered to the inclusion surface to alter the driving force for fatigue crack nucleation in the matrix. By varying the elastic stiffness of the encapsulating interphase, the stresses and cyclic plastic strains are examined in the matrix in the proximity of a partially debonded inclusion, a worst case scenario for nucleation. The matrix is modeled as elastic-plastic with pure kinematic hardening expressed in a hardening minus dynamic recovery format. The inclusion and interphase are modeled as isotropic linear elastic. An idealized spherical, homogeneous inclusion is considered to facilitate parametric study. A nonlocal average value of the maximum plastic shear strain amplitude was used in a modified form of the Fatemi–Socie parameter in the proximity of inclusions as a fatigue indicator parameter to facilitate comparative parametric study of potency for crack nucleation.
Pharmacokinetics of High-Dose Oseltamivir in Healthy Volunteers
Authors: Wattanagoon Y. , Stepniewska K. , Lindegårdh N. , Pukrittayakamee S. , Silachamroon U. , Piyaphanee W. , Singtoroj T. , Hanpithakpong W. , Davies G. , Tarning J. , Pongtavornpinyo W. , Fukuda C. , Singhasivanon P. , Day N. P. J. , White N. J.
Published: December 2008

The effects of loading doses and probenecid coadministration on oseltamivir pharmacokinetics at four increasing dose levels in groups of eight healthy adult Thai volunteers (125 individual series) were evaluated. Doses of up to 675 mg were well-tolerated. The pharmacokinetics were dose linear. Oseltamivir phosphate (OS) was rapidly and completely absorbed and converted (median conversion level, 93%) to the active carboxylate metabolite. Median elimination half-lives (and 95% confidence intervals [CI]) were 1.0 h (0.9 to 1.1 h) for OS and 5.1 h (4.7 to 5.7 h) for oseltamivir carboxylate (OC). One subject repeatedly showed markedly reduced OS-to-OC conversion, indicating constitutionally impaired carboxylesterase activity. The coadministration of probenecid resulted in a mean contraction in the apparent volume of distribution of OC of 40% (95% CI, 37 to 44%) and a reduction in the renal elimination of OC of 61% (95% CI, 58 to 62%), thereby increasing the median area under the concentration-time curve (AUC) for OC by 154% (range, 71 to 278%). The AUC increase for OC in saliva was approximately three times less than the AUC increase for OC in plasma. A loading dose 1.25 times the maintenance dose should be given for severe influenza pneumonia. Probenecid coadministration may allow considerable dose saving for oseltamivir, but more information on OC penetration into respiratory secretions is needed to devise appropriate dose regimens.
Multiple Peptides Homologous to Herpes Simplex Virus Type 1 Glycoprotein B Inhibit Viral Infection
Authors: Akkarawongsa Radeekorn , Pocaro Nina E. , Case Gary , Kolb Aaron W. , Brandt Curtis R.
Published: December 2008

The 773-residue ectodomain of the herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) has been resistant to the use of mutagenic strategies because the majority of the induced mutations result in defective proteins. As an alternative strategy for the identification of functionally important regions and novel inhibitors of infection, we prepared a library of overlapping peptides homologous to the ectodomain of gB and screened for the ability of the peptides to block infection. Seven of 138 15-mer peptides inhibited infection by more than 50% at a concentration of 100 μM. Three peptides (gB94, gB122, and gB131) with 50% effective concentrations (EC
50
s) below 20 μM were selected for further studies. The gB131 peptide (residues 681 to 695 in HSV-1 gB [gB-1]) was a specific entry inhibitor (EC
50
, ∼12 μM). The gB122 peptide (residues 636 to 650 in gB-1) blocked viral entry (EC
50
, ∼18 μM), protected cells from infection (EC
50
, ∼72 μM), and inactivated virions in solution (EC
50
, ∼138 μM). We were unable to discern the step or steps inhibited by the gB94 peptide, which is homologous to residues 496 to 510 in gB-1. Substitution of a tyrosine in the gB122 peptide (Y640 in full-length gB-1) reduced the antiviral activity eightfold, suggesting that this residue is critical for inhibition. This peptide-based strategy could lead to the identification of functionally important regions of gB or other membrane proteins and identify novel inhibitors of HSV-1 entry.
Association between Antimicrobial Consumption and Resistance in
Escherichia coli
Authors: Bergman Miika , Nyberg Solja T. , Huovinen Pentti , Paakkari Pirkko , Hakanen Antti J.
Published: December 2008

During a 9-year study period from 1997 through 2005, the association between antimicrobial resistance rates in
Escherichia coli
and outpatient antimicrobial consumption was investigated in 20 hospital districts in Finland. A total of 754,293
E. coli
isolates, mainly from urine samples, were tested for antimicrobial resistance in 26 clinical microbiology laboratories. The following antimicrobials were studied: ampicillin, amoxicillin-clavulanate, cephalosporins, fluoroquinolones, trimethoprim, trimethoprim-sulfamethoxazole, pivmecillinam, and nitrofurantoin. We applied a protocol used in earlier studies in which the level of antimicrobial consumption over 1 year was compared with the level of resistance in the next year. Statistically significant associations were found for nitrofurantoin use versus nitrofurantoin resistance (
P
< 0.0001), cephalosporin use versus nitrofurantoin resistance (
P
= 0.0293), amoxicillin use versus fluoroquinolone resistance (
P
= 0.0031), and fluoroquinolone use versus ampicillin resistance (
P
= 0.0046). Interestingly, we found only a few associations between resistance and antimicrobial consumption. The majority of the associations studied were not significant, including the association between fluoroquinolone use and fluoroquinolone resistance.
Population Pharmacokinetics of Emtricitabine in Human Immunodeficiency Virus Type 1-Infected Pregnant Women and Their Neonates
Authors: Hirt Déborah , Urien Saik , Rey Elisabeth , Arrivé Elise , Ekouévi Didier K. , Coffié Patrick , Leang Sim Kruy , Lalsab Sarita , Avit Divine , Nerrienet Eric , McIntyre James , Blanche Stéphane , Dabis François , Tréluyer Jean-Marc
Published: December 2008

The objectives of this study were to evaluate emtricitabine (FTC) pharmacokinetics in pregnant women and their neonates and to determine the optimal prophylactic dose for neonates after birth to prevent mother-to-child transmission of human immunodeficiency virus (HIV). A total of 38 HIV-infected pregnant women were administered tenofovir disoproxyl fumarate (300 mg)-FTC (200 mg) tablets—two tablets at the initiation of labor and one daily for 7 days postpartum. By pair, 11 maternal, one cord blood, and two neonatal FTC concentrations were measured using a high-performance liquid chromatography-tandem mass spectrometry validated method and analyzed by a population approach. Model and mean estimates (interpatient variability) were a two-compartment model for mothers, with an absorption rate constant of 0.54 h−1(61%), apparent elimination and intercompartmental clearances of 23.2 (17%) and 6.04 liters·h−1, and apparent central and peripheral volumes of 127 and 237 liters, respectively; an effect compartment linked to maternal circulation for cord blood and a neonatal compartment disconnected, after delivery, with a 10.6-h half-life (30%). After the 400-mg FTC administration, the median population area under the concentration-time curve and the minimal and maximal plasma FTC concentrations in pregnant women were 14.3 mg·liter−1·h and 1.68 and 0.076 mg/liter, respectively. At delivery, median (range) predicted maternal and cord blood FTC concentrations were, respectively, 1.16 (0.14 to 1.99) and 0.72 (0.05 to 1.19) mg·liter−1. We concluded that the 400-mg FTC administration in pregnant women produces higher exposition than does the 200-mg administration in other adults, at steady state. FTC was shown to have good placental transfer (80%). Administering 1 mg FTC/kg as soon as possible after birth or 2 mg/kg 12 h after birth should produce neonatal concentrations comparable to the concentrations observed in adults.
Preclinical Evaluation of GS-9160, a Novel Inhibitor of Human Immunodeficiency Virus Type 1 Integrase
Authors: Jones Gregg S. , Yu Fang , Zeynalzadegan Ameneh , Hesselgesser Joseph , Chen Xiaowu , Chen James , Jin Haolun , Kim Choung U. , Wright Matthew , Geleziunas Romas , Tsiang Manuel
Published: December 2008

GS-9160 is a novel and potent inhibitor of human immunodeficiency virus type 1 (HIV-1) integrase (IN) that specifically targets the process of strand transfer. It is an authentic inhibitor of HIV-1 integration, since treatment of infected cells results in an elevation of two-long terminal repeat circles and a decrease of integration junctions. GS-9160 has potent and selective antiviral activity in primary human T lymphocytes producing a 50% effective concentration (EC50) of ∼2 nM, with a selectivity index (50% cytotoxic concentration/EC50) of ∼2,000. The antiviral potency of GS-9160 decreased by 6- to 10-fold in the presence of human serum. The antiviral activity of GS-9160 is synergistic in combination with representatives from three different classes of antiviral drugs, namely HIV-1 protease inhibitors, nonnucleoside reverse transcriptase inhibitors, and nucleotide reverse transcriptase inhibitors. Viral resistance selections performed with GS-9160 yielded a novel pattern of mutations within the catalytic core domain of IN; E92V emerged initially, followed by L74M. While E92V as a single mutant conferred 12-fold resistance against GS-9160, L74M had no effect as a single mutant. Together, these mutations conferred 67-fold resistance to GS-9160, indicating that L74M may potentiate the resistance caused by E92V. The pharmacokinetic profile of GS-9160 in healthy human volunteers revealed that once-daily dosing was not likely to achieve antiviral efficacy; hence, the clinical development of this compound was discontinued.
Multiple Regulatory Pathways Associated with High-Level Ciprofloxacin and Multidrug Resistance in
Salmonella enterica
Serovar Enteritidis: Involvement of
ramA
and Other Global Regulators
Authors: O'Regan Edel , Quinn Teresa , Pagès Jean-Marie , McCusker Matthew , Piddock Laura , Fanning Séamus
Published: December 2008

Mechanisms of antibiotic resistance were examined in nalidixic acid-resistant
Salmonella enterica
serovar Enteritidis field isolates displaying decreased susceptibility to ciprofloxacin and in in vitro-derived ciprofloxacin-resistant mutants (104-cip and 5408-cip). All field isolates harbored a single
gyrA
mutation (D87Y). Deletion of
acrB
and complementation with wild-type
gyrA
increased quinolone susceptibility. Selection for ciprofloxacin resistance was associated with the development of an additional
gyrA
(S83F) mutation in 104-cip, novel
gyrB
(E466D) and
parE
(V461G) mutations in 5408-cip, overexpression of
acrB
and decreased susceptibility to nonquinolone antibiotics in both mutants, and decreased OmpF production and altered lipopolysaccharide in 104-cip. Complementation of mutated
gyrA
and
gyrB
with wild-type alleles restored susceptibility to quinolones in 104-cip and significantly decreased the ciprofloxacin MIC in 5408-cip. Complementation of
parE
had no effect on quinolone MICs. Deletion of
acrB
restored susceptibility to ciprofloxacin and other antibiotics tested. Both
soxS
and
marA
were overexpressed in 104-cip, and
ramA
was overexpressed in 5408-cip. Inactivation of each of these global regulators lowered ciprofloxacin MICs, decreased expression of
acrB
, and restored susceptibility to other antibiotics. Mutations were found in
soxR
(R20H) and in
soxS
(E52K) in 104-cip and in
ramR
(G25A) in 5408-cip. In conclusion, both efflux activity and a single
gyrA
mutation contribute to nalidixic acid resistance and reduced ciprofloxacin sensitivity. Ciprofloxacin resistance and decreased susceptibility to multiple antibiotics can result from different genetic events leading to development of target gene mutations, increased efflux activity resulting from differential expression of global regulators associated with mutations in their regulatory genes, and possible altered membrane permeability.
Effects of Zidovudine and Stavudine on Mitochondrial DNA of Differentiating 3T3-F442a Cells Are Not Associated with Imbalanced Deoxynucleotide Pools
Authors: Lynx Matthew D. , LaClair Darcy D. , McKee Edward E.
Published: December 2008

To test whether zidovudine (3′-azido-3′-deoxythymidine) (AZT) inhibition of thymidine phosphorylation causes depletion of the TTP pool resulting in mitochondrial DNA depletion, 3T3-F442a cells were differentiated in the presence of AZT and analyzed to determine mitochondrial DNA content and deoxynucleotide levels. These results suggest that AZT toxicity may not be related to deoxynucleotide pool alterations.
Antifungal Therapy of
Aspergillus
Invasive Otitis Externa: Efficacy of Voriconazole and Review
Authors: Parize Perrine , Chandesris Marie-Olivia , Lanternier Fanny , Poirée Sylvain , Viard Jean-Paul , Bienvenu Boris , Mimoun Michaël , Méchai Frédéric , Mamzer Marie-France , Herman Philippe , Bougnoux Marie-Elisabeth , Lecuit Marc , Lortholary Olivier
Published: December 2008

Invasive otitis externa (IOE) due to
Aspergillus
is a rare, potentially life-threatening, invasive fungal infection affecting immunocompromised patients. The invasive process may lead to skull base osteomyelitis with progressive cranial nerve palsies and can result in irreversible hearing and neurological impairment. We report two cases of
Aspergillus
IOE treated with voriconazole alone and a literature review of antifungal therapy of
Aspergillus
IOE. Twenty-five patients, including the two described in the present report, were analyzed. Eighteen patients were treated with amphotericin B, and nine of them received itraconazole as an additional agent. Three patients received initial therapy with itraconazole, and one patient was treated with both voriconazole and caspofungin therapy. The two patients in the present report received voriconazole therapy alone with good clinical and biological tolerance despite prolonged treatment. The last patient did not receive antifungal therapy, as the diagnosis was made postmortem. Eighteen patients underwent an initial extensive surgical debridement. The majority of the patients had a favorable outcome, 17 patients experienced a complete recovery, and 6 showed a partial improvement. Both of the patients reported on here had favorable outcomes, and no aggressive surgical debridement was required. Although voriconazole has been shown to be effective for the treatment of invasive aspergillosis, its precise role in the management of
Aspergillus
IOE had not been documented. These observations demonstrate that voriconazole could be an effective and well-tolerated therapeutic option for the management of
Aspergillus
IOE.
Immobilization Reduces the Activity of Surface-Bound Cationic Antimicrobial Peptides with No Influence upon the Activity Spectrum
Authors: Bagheri Mojtaba , Beyermann Michael , Dathe Margitta
Published: December 2008

Early studies of immobilized peptides mainly focused upon the relationship between structural properties and the activity of soluble and surface-tethered sequences. The intention of this study was to analyze the influence of immobilization parameters upon the activity profile of peptides. Resin beads (TentaGel S NH2, HypoGel 400 NH2, and HypoGel 200 NH2) with polyethylene glycol spacers of different lengths were rendered antimicrobial by linkage of an amphipathic model KLAL peptide and magainin-derived MK5E. Standard solid-phase peptide synthesis, thioalkylation, and ligation strategies were used to immobilize the peptides at the C and N termini and via different side-chain positions. Depending upon the resin capacity and the coupling strategies, peptide loading ranged between 0.1 and 0.25 μmol/mg for C-terminally and around 0.03 μmol/mg for N-terminally and side-chain-immobilized peptides. Tethering conserved the activity spectra of the soluble peptides at reduced concentrations. The resin-bound peptides were antimicrobial towardEscherichia coliandBacillus subtilisin the millimolar range compared to the results seen with micromolar concentrations of the free peptides.B. subtiliswas more susceptible thanE. coli. The antimicrobial activity distinctly decreased with reduction of the spacer length. Slight differences in the antimicrobial effect of KLAL and MK5E bound at different chain positions on TentaGel S NH2suggest that the activity is less dependent upon the position of immobilization. Soluble KLAL was active toward red blood cells, whereas MK5E was nonhemolytic at up to about 400 μM. Resin-induced hemolysis hampered the determination of the hemolytic effect of the immobilized peptides. TentaGel S NH2-bound peptides enhanced the permeability of the POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-choline) and mixed POPC/1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPC/POPG) bilayers used to model the charge properties of the biological targets. The results suggest that surface immobilization of the cationic amphipathic antimicrobial peptides does not influence the membrane-permeabilizing mode of action. Peptide insertion into the target membrane and likely the exchange of membrane-stabilizing bivalent cations contribute to the antimicrobial effect. In conclusion, reasonable antimicrobial activity of surface-bound peptides requires the optimization of the coupling parameters, with the length of the spacer and the amount of target-accessible peptide being the most important factors.
CMY-31 and CMY-36 Cephalosporinases Encoded by ColE1-Like Plasmids
Authors: Zioga A. , Whichard J. M. , Kotsakis S. D. , Tzouvelekis L. S. , Tzelepi E. , Miriagou V.
Published: December 2008

Two CMY-2 derivatives, CMY-31 (Gln
215
→Arg) from
Salmonella enterica
serotype Newport and CMY-36 (Ala
77
→Cys and Gln
193
→Glu) from
Klebsiella pneumoniae
, were characterized. Both cephalosporinases functionally resembled CMY-2.
bla
CMY
alleles occurred as parts of a putative transposon comprising IS
Ecp1B
and a
Citrobacter freundii
-derived sequence carried by ColE1-like plasmids similar to CMY-5-encoding pTKH11 from
Klebsiella oxytoca
.
Identification by Genomic and Genetic Analysis of Two New Genes Playing a Key Role in Intermediate Glycopeptide Resistance in
Staphylococcus aureus
Authors: Renzoni Adriana , Kelley William L. , Barras Christine , Monod Antoinette , Huggler Elzbieta , François Patrice , Schrenzel Jacques , Studer René , Vaudaux Pierre , Lew Daniel P.
Published: December 2008

Endogenous, low-level glycopeptide resistance in
Staphylococcus aureus
results from multifactorial genetic changes. Comparative genomic hybridization analysis revealed the specific deletion of a 1.8-kb segment encompassing two adjacent open reading frames (ORFs) of unknown function in a teicoplanin-susceptible revertant (strain 14-4rev) compared to the sequence of its isogenic, teicoplanin-resistant parental strain, strain 14-4. This provocative finding prompted us to perform a detailed genetic analysis of the contribution of this genomic segment to glycopeptide resistance. Despite repeated efforts in our laboratory, 14-4 and 14-4rev have proven refractory to most genetic manipulations. To circumvent this difficulty, we evaluated the contribution of both putative ORFs (designated teicoplanin resistance factors
trfA
and
trfB
) on teicoplanin resistance in a different, genetically tractable background. Genetic analysis showed that single or double
trfA
and/or
trfB
mutations abolished teicoplanin resistance in two independent teicoplanin-resistant derivatives of NCTC8325 strain ISP794 generated by two-step passages with the drug. The frequency of teicoplanin-resistant mutants was markedly decreased by the absence of
trfAB
in the teicoplanin-susceptible ISP794 background. Nevertheless, a low rate of teicoplanin-resistant mutants was selected from ISP794
trfAB
, thus indicating an additional contribution of
trfAB
-independent pathways in the emergence of low-level glycopeptide resistance. Further experiments performed with clinical glycopeptide-intermediate
S. aureus
isolate NRS3 indicated that the
trfAB
mutation could affect not only teicoplanin resistance but also vancomycin and oxacillin resistance. In conclusion, our study demonstrates the key role of two novel loci in endogenous, low-level glycopeptide resistance in
S. aureus
whose precise molecular functions warrant further investigation.
Breakthrough
Aspergillus fumigatus
and
Candida albicans
Double Infection during Caspofungin Treatment: Laboratory Characteristics and Implication for Susceptibility Testing
Authors: Arendrup Maiken Cavling , Garcia-Effron Guillermo , Buzina Walter , Mortensen Klaus Leth , Reiter Nanna , Lundin Christian , Jensen Henrik Elvang , Lass-Flörl Cornelia , Perlin David S. , Bruun Brita
Published: December 2008

Caspofungin is used for the treatment of acute invasive candidiasis and as salvage treatment for invasive aspergillosis. We report characteristics of isolates of
Candida albicans
and
Aspergillus fumigatus
detected in a patient with breakthrough infection complicating severe gastrointestinal surgery and evaluate the capability of susceptibility methods to identify candin resistance. The susceptibility of
C. albicans
to caspofungin and anidulafungin was investigated by Etest, microdilution (European Committee on Antibiotic Susceptibility Testing [EUCAST] and CLSI), disk diffusion, agar dilution, and
FKS1
sequencing and in a mouse model. Tissue was examined by immunohistochemistry, PCR, and sequencing for the presence of
A. fumigatus
and resistance mutations. The MICs for the
C. albicans
isolate were as follows: >32 μg/ml caspofungin and 0.5 μg/ml anidulafungin by Etest, 2 μg/ml caspofungin and 0.125 μg/ml anidulafungin by EUCAST methods, and 1 μg/ml caspofungin and 0.5 μg/ml anidulafungin by CLSI methods. Sequencing of the
FKS1
gene revealed a mutation leading to an S645P substitution. Caspofungin and anidulafungin failed to reduce kidney CFU counts in animals inoculated with this isolate (
P
> 0.05 compared to untreated control animals), while both candins completely sterilized the kidneys in animals infected with a control isolate. Disk diffusion and agar dilution methods clearly separated the two isolates. Immunohistochemistry and sequencing confirmed the presence of
A. fumigatus
without
FSK1
resistance mutations in liver and lung tissues. Breakthrough disseminated aspergillosis and candidiasis developed despite an absence of characteristic
FKS1
resistance mutations in the
Aspergillus
isolates. EUCAST and CLSI methodology did not separate the candin-resistant clinical isolate from the sensitive control isolate as well as did the Etest and agar methods.
Changes in
aac(6
′
)-Ib-cr
Prevalence and Fluoroquinolone Resistance in Nosocomial Isolates of
Escherichia coli
Collected from 1991 through 2005
Authors: Warburg Gabriela , Korem Maya , Robicsek Ari , Engelstein Dalia , Moses Allon E. , Block Colin , Strahilevitz Jacob
Published: December 2008

Clinical isolates of
Escherichia coli
collected from 1991 through 2005 at a tertiary-care center were studied for
qnr
and
aac(6
′
)-Ib-cr
genes. Isolates bearing
aac(6
′
)-Ib-cr
emerged in 1998, coinciding with an increase in ciprofloxacin resistance. The presence of
aac(6
′
)-Ib-cr
was multiclonal and was associated with the presence of extended-spectrum β-lactamases.
Mutations at
embB
Codon 306 Are an Important Molecular Indicator of Ethambutol Resistance in
Mycobacterium tuberculosis
Authors: Starks Angela M. , Gumusboga Aysel , Plikaytis Bonnie B. , Shinnick Thomas M. , Posey James E.
Published: December 2008

Ethambutol resistance in clinical
Mycobacterium tuberculosis
isolates is associated primarily with missense mutations in the
embB
gene. However, recent reports have described the presence of
embB
mutations, especially those at
embB
codon 306, in isolates susceptible to ethambutol. To clarify the role of
embB
mutations in ethambutol resistance, we sequenced the ethambutol resistance-determining region in spontaneous ethambutol-resistant mutants. In our study, 66% of spontaneous mutants contained a single point mutation in
embB
, with 55% of these occurring at
embB
306. The MIC of ethambutol for spontaneous mutants was increased two- to eightfold relative to the pansusceptible
M. tuberculosis
strains from which the mutants were generated. To further characterize the role of
embB
306 mutations, we directly introduced mutant alleles,
embB
(
M306V
) or
embB
(
M306I
), into pansusceptible
M. tuberculosis
strains and conversely reverted mutant alleles in spontaneous ethambutol-resistant mutants back to those of the wild type via allelic exchange using specialized linkage transduction. We determined that the MIC of ethambutol was reduced fourfold for three of the four spontaneous ethambutol-resistant
embB
306 mutants when the mutant allele was replaced with the wild-type
embB
allele. The MIC for one of the spontaneous mutants genetically reverted to wild-type
embB
was reduced by only twofold. When the wild-type
embB
allele was converted to the mutant allele
embB
(
M306V
), the ethambutol MIC was increased fourfold, and when the allele was changed to M306I, the ethambutol MIC increased twofold. Our data indicate that
embB
306 mutations are sufficient to confer ethambutol resistance, and detection of these mutations should be considered in the development of rapid molecular tests.
Affinity of Tomopenem (CS-023) for Penicillin-Binding Proteins in
Staphylococcus aureus
,
Escherichia coli
, and
Pseudomonas aeruginosa
Authors: Koga Tetsufumi , Sugihara Chika , Kakuta Masayo , Masuda Nobuhisa , Namba Eiko , Fukuoka Takashi
Published: December 2008

Tomopenem (formerly CS-023), a novel 1β-methylcarbapenem, exhibited high affinity for penicillin-binding protein (PBP) 2 in
Staphylococcus aureus
, PBP 2 in
Escherichia coli
, and PBPs 2 and 3 in
Pseudomonas aeruginosa
, which are considered major lethal targets. Morphologically, tomopenem induced spherical forms in
E. coli
and short filamentation with bulges in
P. aeruginosa
, which correlated with the drug's PBP profiles. The potential of resistance of these bacteria to tomopenem was comparable to that to imipenem.
In Vivo and In Vitro Efficacy of Amodiaquine Monotherapy for Treatment of Infection by Chloroquine-Resistant
Plasmodium vivax
Authors: Hasugian A. R. , Tjitra E. , Ratcliff A. , Siswantoro H. , Kenangalem E. , Wuwung R. M. , Purba H. L. E. , Piera K. A. , Chalfien F. , Marfurt J. , Penttinen P. M. , Russell B. , Anstey N. M. , Price R. N.
Published: December 2008

Amodiaquine retains efficacy against infection by chloroquine-resistant
Plasmodium falciparum
; however, little information is available on its efficacy against infection by chloroquine-resistant
Plasmodium vivax
. Patients presenting to a rural clinic with a pure
P. vivax
infection that recurred after recent antimalarial treatment were retreated, this time with amodiaquine monotherapy, and the risk of further recurrence within 4 weeks was assessed. Of the 87 patients with pure
P. vivax
infection, 15 patients did not complete a full course of treatment, 4 of whom were intolerant to treatment. In the 72 patients completing treatment, 91% (63 of 69) had cleared their parasitemia within 48 h with no early treatment failure. Follow-up to day 28 or recurrent parasitemia was achieved for 56 patients (78%). The cumulative incidence of treatment failure by day 28 was 22.8% (95% confidence interval, 7.3 to 38%). The in vitro sensitivity profile was determined for a separate set of isolates from outpatients with pure
P. vivax
infection. The median 50% inhibitory concentration of amodiaquine was 11.3 nM (range, 0.37 to 95.8) and was correlated significantly with that of chloroquine (Spearman rank correlation coefficient, 0.602;
P
< 0.001) Although amodiaquine results in a rapid clinical response, the risk of recurrence by day 28 is unacceptably high, reducing its suitability as an alternative treatment of infection by chloroquine-resistant
P. vivax
in this region.
Salmonella entericaSerovar Typhimurium Strains with Regulated Delayed Attenuation In Vivo
Authors: Curtiss Roy , Wanda Soo-Young , Gunn Bronwyn M. , Zhang Xin , Tinge Steven A. , Ananthnarayan Vidya , Mo Hua , Wang Shifeng , Kong Wei
Published: December 2008

Recombinant bacterial vaccines must be fully attenuated for animal or human hosts to avoid inducing disease symptoms while exhibiting a high degree of immunogenicity. Unfortunately, many well-studied means for attenuatingSalmonellarender strains more susceptible to host defense stresses encountered following oral vaccination than wild-type virulent strains and/or impair their ability to effectively colonize the gut-associated and internal lymphoid tissues. This thus impairs the ability of recombinant vaccines to serve as factories to produce recombinant antigens to induce the desired protective immunity. To address these problems, we designed strains that display features of wild-type virulent strains ofSalmonellaat the time of immunization to enable strains first to effectively colonize lymphoid tissues and then to exhibit a regulated delayed attenuation in vivo to preclude inducing disease symptoms. We recently described one means to achieve this based on a reversible smooth-rough synthesis of lipopolysaccharide O antigen. We report here a second means to achieve regulated delayed attenuation in vivo that is based on the substitution of a tightly regulatedaraCPBADcassette for the promoters of thefur,crp,phoPQ, andrpoSgenes such that expression of these genes is dependent on arabinose provided during growth. Thus, following colonization of lymphoid tissues, the Fur, Crp, PhoPQ, and/or RpoS proteins cease to be synthesized due to the absence of arabinose such that attenuation is gradually manifest in vivo to preclude induction of diseases symptoms. Means for achieving regulated delayed attenuation can be combined with other mutations, which together may yield safe efficacious recombinant attenuatedSalmonellavaccines.