bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack Initiation and Growth in Solder Joints Under Cyclic Shear Deformation Using Piezomechanical Actuation
Authors: Shim Dong-Jin , Spearing S. Mark , Yang Qingda
Published: December 2006

Crack initiation and growth behavior in solder joints under cyclic shear deformation using piezomechanical actuation have been investigated. Experiments were conducted on specimens that consist of piezo–ceramic plates and eutectic Sn–Pb solder bonded in a double-lap shear configuration. Specimens were tested under various frequencies and ranges of applied electric field at room temperature, and a shear-lag model using elastic–perfectly plastic solder properties was developed to characterize the mechanical response of the solder joint. Nominal plastic shear strain ranges from 0.182% to 2.69% were considered. The applied shear strains measured using digital image correlation showed agreement with shear strains from analyses. The Coffin–Manson relationship was used to characterize crack initiation, and a power law was employed for crack growth. This work shows that the fatigue characteristics of solder joints using piezomechanical actuation exhibit reasonable agreement with those using other types of testing methods and provides the framework for a new accelerated testing methodology for solder joint reliability.
Using In Situ Atomic Force Microscopy to Investigate the Kinetics of Corrosion of WC–Co–Cr Cermet Coatings Applied by High-Velocity Oxy-Fuel
Authors: Souza V. A. D. , Neville A.
Published: December 2006

Most of the early applications of thermal spray coatings were focused toward providing a remedy to excessive wear degradation. However, as the introduction of such coatings into wider industrial sections increases there is also exposure to other potential degradation processes—aqueous corrosion is one such process. The complex microstructures in cermet coatings have been shown to translate to complex modes of corrosion attack. In this paper an electrochemical test methodology to probe the local/microaspects of corrosion initiation and propagation will be described. A new electrochemical cell has been devised in which the corrosion can be followed “live” and in “real-time.” The surface is subjected to in situ imaging by atomic force microscopy which shows that not only the binder (Co, Cr) corrodes in high-velocity oxy-fuel thermal spray coatings but also the hard phase, with oxidation and dissolution of WC∕W2C taking place. Also potentiostatic tests indicated that the corrosion of WC-based coatings follows an Arrhenius relationship enabling the determination of activation energy (Ea) for the corrosion of WC and demonstrating that the oxidation and dissolution of WC are temperature, particle size, potential, and pH related
Study of Bolt Load Loss in Bolted Aluminum Joints
Authors: Jaglinski T. , Nimityongskul A. , Schmitz R. , Lakes R. S.
Published: December 2006

Bolted joints are used widely in mechanical design and represent a weak link in a system where loss of joint clamping force can lead to degraded product performance or human injury. To meet current market demands, designers require reliable material data and analysis tools for their industry specific materials. The viscoelastic response of bolted aluminum joints used in the small die-cast engine industry at elevated temperatures was studied. Bolt load-loss tests were performed using strain gages in situ. It was found that after a week at temperature, most bolts lost 100% of their initial prestress. Nonlinear constitutive equations utilizing parameters obtained from uniaxial creep and relaxation tests were used in a simple one-dimensional model to predict the bolt load loss. The model cannot predict the detailed response and overpredicts retained bolt stress for bolt holes that are not preconditioned. For preconditioned holes, the behavior is intermediate between creep and relaxation.
Effect of Strain Gage Length When Determining Residual Stress by Slitting
Authors: Lee Matthew J. , Hill Michael R.
Published: December 2006

This paper investigates the effect of strain gage length on residual stress estimated by the slitting (or crack compliance) method. This effect is quantified for a range of gage length normalized by sample thickness, l∕t, between 0.005 and 0.100. For specific l∕t values, compliance matrix elements are determined by finite element methods for a range of crack depth and polynomial basis functions for residual stress. Resulting compliance matrices are shown and used to determine error in residual stress that may arise due to differences in l∕t assumed in data reduction and existing in the slitting experiment. Errors increase monotonically with increasing difference between assumed and actual l∕t and reach a root-mean-square error of 14% of peak stress. In order to avoid such errors, a scheme is presented that allows compliance matrices to be computed for 0.005⩽l∕t⩽0.100 from tabulated coefficients and limits root-mean-square error to <2% of peak stress. An example is provided to illustrate the application of the data reduction scheme to laboratory data.
Characterization of Polypropylene Nanocomposite Structures
Authors: Kanny K. , Moodley V. K.
Published: December 2006

This study describes the synthesis, mechanical properties, and morphology of nanophased polypropylene structures. The structures were manufactured by melt-blending low weight percentages of montmorillonite nanoclays and polypropylene thermoplastic. Both virgin and infused polypropylene structures were then subjected to quasi-static tensile, flexural, hardness and impact tests. Analysis of test data show that the mechanical properties increase with an increase in nanoclay loading up to a threshold of 2wt.%; thereafter, the material properties degrade. At low weight nanoclay loadings the enhancement of properties is attributed to the lower percolation points created by the high aspect ratio nanoclays. The increase in properties may also be attributed to the formation of intercalated and exfoliated nanocomposite structures formed at these loadings of clay. At higher weight loading, degradation in mechanical properties may be attributed to the formation of agglomerated clay tactoids. Results of transmission electron microscopy studies and scanning electron microscopy studies of the fractured surface of tensile specimens verify these hypotheses.
A Multiscale Analysis of Void Coalescence in Nickel
Authors: Jones M. K. , Horstemeyer M. F. , Belvin A. D.
Published: December 2006

An internal state variable void coalescence equation developed by Horstemeyer, Lathrop, Gokhale, and Dighe (2000, Theor. Appl. Fract. Mech., 33(1), pp. 31–47) that comprises void impingement and void sheet mechanisms is updated based on three-dimensional micromechanical simulations and novel experiments. This macroscale coalescence equation, developed originally from two-dimensional finite element simulations, was formulated to enhance void growth. In this study, three-dimensional micromechanical finite element simulations were employed using cylindrical and spherical void geometries in nickel that were validated by experiments. The number of voids, void orientation, and void spacing were all varied and tested and simulated under uniaxial loading conditions. The micromechanical results showed excellent agreement with experiments in terms of void volume fractions versus strain and local void geometry images. Perhaps more importantly, the macroscale internal state variable void coalescence equation did not require a functional form change but just a coefficient value modification.
Residual Elastic Strains in Autofrettaged Tubes: Elastic–Ideally Plastic Model Analysis
Authors: Korsunsky Alexander M.
Published: December 2006

Autofrettage is a treatment process that uses plastic deformation to create a state of permanent residual stress within thick-walled tubes by pressurizing them beyond the elastic limit. The present paper presents explicit analytical formulas for residual elastic strains within the tube wall derived on the basis of the classical elastic–ideally plastic solution. Then the problem is addressed of rational interpretation of the radial and hoop residual elastic strains measured at a fixed number of points. To this end, the mismatch between the experimental measurements and theoretical predictions of the residual elastic strains is represented in the form of quadratic functional, J, the minimum of which is sought in terms of the problem parameters, namely, the material yield stress, σY, and the radial position of the elastic-plastic boundary, c. It is shown that J shows an approximately parabolic variation in terms of either parameter when the other is fixed, and that therefore the global minimum of J can be readily found. This procedure is implemented and applied to a set of experimental data on neutron diffraction measurements (Venter, A.M., de Swardt, R.R., and Kyriacou, S., 2000, J. Strain Anal., 35, pp. 459–469). In conclusion, further applications of this family of interpretation approaches are discussed.
Prediction of Necking in Tubular Hydroforming Using an Extended Stress-Based Forming Limit Curve
Authors: Manoj Simha C. Hari , Gholipour Javad , Bardelcik Alexander , Worswick Michael J.
Published: December 2006

This paper presents an extended stress-based forming limit curve (XSFLC) that can be used to predict the onset of necking in sheet metal loaded under non-proportional load paths, as well as under three-dimensional stress states. The conventional strain-based ϵFLC is transformed into the stress-based FLC advanced by Stoughton (1999, Int. J. Mech. Sci., 42, pp. 1–27). This, in turn, is converted into the XSFLC, which is characterized by the two invariants, mean stress and equivalent stress. Assuming that the stress states at the onset of necking under plane stress loading are equivalent to those under three-dimensional loading, the XSFLC is used in conjunction with finite element computations to predict the onset of necking during tubular hydroforming. Hydroforming of straight and pre-bent tubes of EN-AW 5018 aluminum alloy and DP 600 steel are considered. Experiments carried out with these geometries and alloys are described and modeled using finite element computations. These computations, in conjunction with the XSFLC, allow quantitative predictions of necking pressures; and these predictions are found to agree to within 10% of the experimentally obtained necking pressures. The computations also provide a prediction of final failure location with remarkable accuracy. In some cases, the predictions using the XSFLC show some discrepancies when compared with the experimental results, and this paper addresses potential causes for these discrepancies. Potential improvements to the framework of the XSFLC are also discussed.
Effect of Atomization Method on the Morphology of Spray-Generated Particles
Authors: Eslamian Morteza , Ashgriz Nasser
Published: December 2006

Effect of various atomization methods and solute concentration on the morphology of spray dried magnesium sulphate particles is investigated. Four types of atomizers are characterized and tested including (i) a vibrating mesh nebulizer, (ii) a splash plate nozzle, (iii) an air mist atomizer, and (iv) a pressure atomizer. Several types of particle morphologies are identified in this research. Spray characteristics, such as droplet number density, droplet size, and velocity, and accompanying atomizing air have major influence on the drying and morphology of the particles. High initial solute concentrations result in the formation of thick-walled particles, and this prevents the particles to burst. It is found to be difficult to obtain fully filled magnesium sulphate particles, even for saturated solutions at room temperature because the solution equilibrium saturation changes substantially with temperature.
Development of Short Fiber-Reinforced NiTi∕Al6061 Composite
Authors: Xie C. L. , Hailat M. , Wu X. , Newaz G. , Taya M. , Raju B.
Published: December 2006

The aluminum matrix composite reinforced by short NiTi shape memory alloy fibers, NiTi∕Al6061 composite, was fabricated using pressure-assisted sintering process in ambient air. Surface preparation and thermal pretreatment of NiTi fibers essential for solid state bonding of TixAly intermetallic compound were carried out. Strong interface bonding between NiTi fiber and Al6061 matrix was obtained. The strengthening mechanism of shape memory effect associated with short fiber reinforcement was theoretically examined by extending Taya’s previous model. The stress–strain behavior of the short fiber-reinforced NiTi∕Al6061 composite was investigated at room and elevated temperature both experimentally and analytically. In order to activate the shape memory effect, the composite was prestrained at a temperature between martensite start temperature Ms and austenite start temperature As, then yield stresses as a function of the prestrain were tested and predicted at a temperature above the austenite finish temperature Af. It was found that: (1) the yield stress of the composite increased with increasing the amount of prestrain; (2) the prestrain value should not exceed 0.01, to make use of strengthening of the composite without loss of the ductility of the matrix; and (3) failure of the composite was caused by the strength mismatch between the NiTi fiber and aluminum matrix.
Experimental and Theoretical Analysis on Formability of Aluminum Tailor-Welded Blanks
Authors: Jie M. , Cheng C. H. , Chan L. C. , Chow C. L. , Tang C. Y.
Published: December 2006

This paper presents an investigation on forming limits of tailor-welded blanks (TWBs) made of 5754-O aluminum sheets using both experimental and numerical approaches. TWBs may be composed of two or more welded flat metal sheets of different thicknesses, shapes, or mechanical properties. Due to the existence of weldment and the individual configurations of base blanks, TWBs should be considered as heterogeneous in its structure. The mechanical properties of those base metals and weld metal required for the simulation were measured individually. With the aid of the acquired data, finite element simulations for analyzing the forming process of TWBs were carried out using a general purpose finite element package, LS-DYNA. A localized necking criterion based on the vertex theory was employed to predict forming limit strains and failure locations of the aluminum TWBs. The theoretical predictions were satisfactorily validated with those obtained from the experiments.
A Statistical Methodolgy for the Preparation of a Competing Modes Fatigue Design Curve
Authors: Cashman Gerald T.
Published: December 2006

A methodology is presented for the preparation of a competing modes fatigue design curve. Examples using extruded and isothermally forged powder metallurgy René 95 are presented. Monte Carlo simulation results are given to identify sample size requirements appropriate for the generation of reliable design curves.
The β-Defensin Gallinacin-6 Is Expressed in the Chicken Digestive Tract and Has Antimicrobial Activity against Food-Borne Pathogens
Authors: van Dijk Albert , Veldhuizen Edwin J. A. , Kalkhove Stefanie I. C. , Tjeerdsma-van Bokhoven Johanna L. M. , Romijn Roland A. , Haagsman Henk P.
Published: December 2006

Food-borne pathogens are responsible for most cases of food poisoning in developed countries and are often associated with poultry products, including chicken. Little is known about the role of β-defensins in the chicken digestive tract and their efficacy. In this study, the expression of chicken β-defensin gallinacin-6 (Gal-6) and its antimicrobial activity against food-borne pathogens were investigated. Reverse transcription-PCR analysis showed high expression of Gal-6 mRNA in the esophagus and crop, moderate expression in the glandular stomach, and low expression throughout the intestinal tract. Putative transcription factor binding sites for nuclear factor kappa beta, activator protein 1, and nuclear factor interleukin-6 were found in the Gal-6 gene upstream region, which suggests a possible inducible nature of the Gal-6 gene. In colony-counting assays, strong bactericidal and fungicidal activity was observed, including bactericidal activity against food-borne pathogens
Campylobacter jejuni
,
Salmonella enterica
serovar Typhimurium,
Clostridium perfringens
, and
Escherichia coli
. Treatment with 16 μg/ml synthetic Gal-6 resulted in a 3 log unit reduction in
Clostridium perfringens
survival within 60 min, indicating fast killing kinetics. Transmission electron microscopy examination of synthetic-Gal-6-treated
Clostridium perfringens
cells showed dose-dependent changes in morphology after 30 min, including intracellular granulation, cytoplasm retraction, irregular septum formation in dividing cells, and cell lysis. The high expression in the proximal digestive tract and broad antimicrobial activity suggest that chicken β-defensin gallinacin-6 plays an important role in chicken innate host defense.
Cumulative Effects of Several Nonenzymatic Mechanisms on the Resistance of
Pseudomonas aeruginosa
to Aminoglycosides
Authors: El'Garch Farid , Jeannot Katy , Hocquet Didier , Llanes-Barakat Catherine , Plésiat Patrick
Published: December 2006

Screening of a Tn
5-
Hg insertional library (12,000 clones) constructed in wild-type
Pseudomonas aeruginosa
strain PAO1 identified four genes (namely,
galU
,
nuoG
,
mexZ
, and
rplY
) whose disruption individually led to increased resistance to aminoglycosides (means of twofold). Inactivation of these genes was associated with (i) impaired outer membrane uptake, (ii) reduced active transport, (iii) increased MexXY-OprM-mediated active efflux, and (iv) alteration of target of aminoglycosides, respectively. In addition, suppression of the gene
rplY
, which codes for ribosomal protein L25, was found to result in both moderate upregulation of the efflux system MexXY-OprM and hypersusceptibility to β-lactam antibiotics. Construction of double, triple, and quadruple mutants demonstrated cumulative effects of the different mechanisms on aminoglycoside resistance, with MICs increasing from 16- to 64-fold in the quadruple mutant compared to the wild-type strain PAO1. Altogether, these results illustrate how
P. aeruginosa
may gradually develop high resistance to these antibiotics via intrinsic (i.e., nonenzymatic) mechanisms, as in cystic fibrosis patients.
Impact of Empiric Antibiotic Therapy on Outcomes in Patients with
Pseudomonas aeruginosa
Bacteremia
Authors: Osih Regina B. , McGregor Jessina C. , Rich Shayna E. , Moore Anita C. , Furuno Jon P. , Perencevich Eli N. , Harris Anthony D.
Published: December 2006

The impact of appropriate empirical antimicrobial therapy for
Pseudomonas aeruginosa
bacteremia on patient outcomes has not been clearly established. We assessed the effect of appropriate empirical therapy on in-hospital mortality and length of stay (LOS) among patients with
P. aeruginosa
bacteremia. This was a retrospective cohort study of inpatients with a positive blood culture for
P. aeruginosa
between January 2001 and June 2005. Empirical therapy was defined as appropriate if the patient received an antibiotic the organism was susceptible to between 8 h before culture collection and the time the susceptibility results were available. The severity of the illness was measured 24 h before culture collection. The data were analyzed using logistic regression (in-hospital mortality) and linear regression (LOS). Overall, there were 167 episodes of
P. aeruginosa
bacteremia, 123 (86%) of which received appropriate empirical antibiotics. Sixty-one patients died (36.5%). The median time from culture collection to susceptibility results was 3.4 days. After we adjusted for age, severity of illness, and time at risk, we found that the appropriate empirical therapy was not significantly associated with mortality (odds ratio = 0.96; 95% confidence interval = 0.31 to 2.93). There was a 7% reduction in the mean LOS for patients who had received appropriate therapy at the time susceptibility results were available compared to those who did not (
P
= 0.74). These data suggest that the use of appropriate empirical therapy, i.e., before susceptibility results are known may not be as critical to patient outcomes as other studies have suggested.
Flavonoid Dimers as Bivalent Modulators for Pentamidine and Sodium StiboglucanateResistance in
Leishmania
Authors: Wong Iris L. K. , Chan Kin-Fai , Burkett Brendan A. , Zhao Yunzhe , Chai Yi , Sun Hongzhe , Chan Tak Hang , Chow Larry M. C.
Published: December 2006

Drug
resistance by overexpression of ATP-binding cassette (ABC) transporters
is an impediment in the treatment of leishmaniasis. Flavonoids are
known to reverse multidrug resistance (MDR) in
Leishmania
and
mammalian cancers by inhibiting ABC transporters. Here, we found that
synthetic flavonoid dimers with three (compound 9c) or four
(compound 9d) ethylene glycol units exhibited a significantly higher
reversing activity than other shorter or longer ethylene glycol-ligated
dimers, with ∼3-fold sensitization of pentamidine and sodium
stibogluconate (SSG) resistance in
Leishmania
, respectively.
This modulatory effect was dosage dependent and not observed in
apigenin monomers with the linker, suggesting that the modulatory
effect is due to its bivalent nature. The mechanism of reversal
activity was due to increased intracellular accumulation of pentamidine
and total antimony in
Leishmania
. Compared to other MDR
modulators such as verapamil, reserpine, quinine, quinacrine, and
quinidine, compounds 9c and 9d were the only agents that can reverse
SSG resistance. In terms of reversing pentamidine resistance, 9c and 9d
have activities comparable to those of reserpine and quinacrine.
Modulators 9c and 9d exhibited reversal activity on pentamidine
resistance among
LeMDR1
−/−
,
LeMDR1
+/+
, and
LeMDR1
-overexpressed mutants, suggesting that these modulators
are specific to a non-LeMDR1 pentamidine transporter. The
LeMDR1
copy number is inversely related to pentamidine
resistance, suggesting that it might be involved in importing
pentamidine into the mitochondria. In summary, bivalency could be a
useful strategy for the development of more potent ABC transporter
modulators and flavonoid dimers represent a promising reversal agent
for overcoming pentamidine and SSG resistance in parasite
Leishmania
.
Orally Administered Erythromycin in Rainbow Trout (
Oncorhynchus mykiss
): Residues in Edible Tissues and Withdrawal Time
Authors: Esposito Annarita , Fabrizi Laura , Lucchetti Dario , Marvasi Luigi , Coni Ettore , Guandalini Emilio
Published: December 2006

Aquaculture production has notably increased in the last decades, mainly thanks to intensive farming. Together with market globalization, this gives rise to the spreading of several fish diseases, thus increasing the demand for veterinary drugs for aquatic species. Nonetheless, very few chemicals are registered for use in aquaculture, and fish farmers are often forced to resort to off-label use of drugs authorized for other food-producing animal species. Rainbow trout is the major farmed fish species in Italy and the second one in Europe. Erythromycin is the antibiotic of choice against gram-positive cocci, the major concern for trout farming, but it is not yet registered for aquaculture use in most European countries. The aim of this study was to follow the depletion of erythromycin in rainbow trout (
Oncorhynchus mykiss
), after its administration at 100 mg kg
−1
trout body weight day
−1
for 21 days through medicated feed (water temperature, 11.5°C). Erythromycin residues in fish muscle plus skin in natural proportion were determined by a validated liquid chromatography-electrospray ionization-tandem mass spectrometry method. Interpolation of our data, following European Agency for the Evaluation of Medicinal Products guidelines, gives a withdrawal time of 255°C-days (°C-day = water temperature × days), thus showing that the general value (500°C-day) recommended by the Council Directive (EEC) no. 82/2001 for off-label drug use in aquaculture would be too conservative in this case, with excessive costs for the farmers. Our study provides preliminary data for a more prudent use of erythromycin in rainbow trout, suggesting a possible withdrawal time after treatment.
Efficacy of Orally Administered T-705 on Lethal Avian Influenza A (H5N1) Virus Infections in Mice
Authors: Sidwell Robert W. , Barnard Dale L. , Day Craig W. , Smee Donald F. , Bailey Kevin W. , Wong Min-Hui , Morrey John D. , Furuta Yousuke
Published: December 2006

T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) was inhibitory to four strains of avian H5N1 influenza virus in MDCK cells, with the 90% effective concentrations ranging from 1.3 to 7.7 μM, as determined by a virus yield reduction assay. The efficacy was less than that exerted by oseltamivir carboxylate or zanamivir but was greater than that exerted by ribavirin. Experiments with mice lethally infected with influenza A/Duck/MN/1525/81 (H5N1) virus showed that T-705 administered per os once, twice, or four times daily for 5 days beginning 1 h after virus exposure was highly inhibitory to the infection. Dosages from 30 to 300 mg/kg of body weight/day were well tolerated; each prevented death, lessened the decline of arterial oxygen saturation (SaO2), and inhibited lung consolidation and lung virus titers. Dosages from 30 to 300 mg/kg/day administered once or twice daily also significantly prevented the death of the mice. Oseltamivir (20 mg/kg/day), administered per os twice daily for 5 days, was tested in parallel in two experiments; it was only weakly effective against the infection. The four-times-daily T-705 treatments at 300 mg/kg/day could be delayed until 96 h after virus exposure and still significantly inhibit the infection. Single T-705 treatments administered up to 60 h after virus exposure also prevented death and the decline of SaO2. Characterization of the pathogenesis of the duck influenza H5N1 virus used in these studies was undertaken; although the virus was highly pathogenic to mice, it was less neurotropic than has been described for clinical isolates of the H5N1 virus. These data indicate that T-705 may be useful for the treatment of avian influenza virus infections.
Oral versus Intravenous Flucytosine in Patients with Human Immunodeficiency Virus-Associated Cryptococcal Meningitis
Authors: Brouwer Annemarie E. , van Kan Hendrikus J. M. , Johnson Elizabeth , Rajanuwong Adul , Teparrukkul Prapit , Wuthiekanun Vannaporn , Chierakul Wirongrong , Day Nick , Harrison Thomas S.
Published: December 2006

In a randomized controlled trial of amphotericin B-based therapy for human immunodeficiency virus (HIV)-associated cryptococcal meningitis in Thailand, we also compared the mycological efficacy, toxicity, and pharmacokinetics of oral versus intravenous flucytosine at 100 mg/kg of body weight/day for the initial 2 weeks. Half of 32 patients assigned to the two arms containing flucytosine were randomized to oral and half to intravenous flucytosine. Early fungicidal activity was determined from serial quantitative cultures of cerebrospinal fluid (CSF), and toxicity was assessed by clinical and laboratory monitoring. Flucytosine and fluorouracil concentrations in plasma and CSF were measured by high-performance liquid chromatography. No significant bone marrow or hepatotoxicity was seen, there was no detectable difference in bone marrow toxicity between patients on intravenous and those on oral formulation, and no patients discontinued treatment. In patients receiving intravenous flucytosine, the median 24-h area under the concentration-time curve was significantly higher than in the oral group. Despite this difference, there was no difference in early fungicidal activity between patients on intravenous compared with patients on oral flucytosine. The results suggest that either formulation can be used safely at this dosage in a developing country setting, without drug concentration monitoring. The bioavailability of the oral formulation may be reduced in late-stage HIV-infected patients in Thailand. Concentrations of flucytosine with intravenous formulation at 100 mg/kg/day may be in excess of those required for maximal fungicidal activity.
Reversible Inhibition of Mitochondrial Protein Synthesis during Linezolid-Related Hyperlactatemia
Authors: Garrabou Glòria , Soriano Alejandro , López Sònia , Guallar Jordi P. , Giralt Marta , Villarroya Francesc , Martínez Jose A. , Casademont Jordi , Cardellach Francesc , Mensa Josep , Miró Òscar
Published: December 2006

The objective of the present study was to determine the mitochondrial toxicity mechanisms of linezolid-related hyperlactatemia. Five patients on a long-term schedule of linezolid treatment were studied during the acute phase of hyperlactatemia and after clinical recovery and lactate normalization following linezolid withdrawal. Mitochondrial studies were performed with peripheral blood mononuclear cells and consisted of measurement of mitochondrial mass, mitochondrial protein synthesis homeostasis (cytochromecoxidase [COX] activity, COX-II subunit expression, COX-II mRNA abundance, and mitochondrial DNA [mtDNA] content), and overall mitochondrial function (mitochondrial membrane potential and intact-cell oxidative capacity). During linezolid-induced hyperlactatemia, we found extremely reduced protein expression (16% of the remaining content compared to control values [100%],P< 0.001) for the mitochondrially coded, transcribed, and translated COX-II subunit. Accordingly, COX activity was also found to be decreased (51% of the remaining activity,P< 0.05). These reductions were observed despite the numbers of COX-II mitochondrial RNA transcripts being abnormally increased (297%,P= 0.10 [not significant]) and the mitochondrial DNA content remaining stable. These abnormalities persisted even after the correction for mitochondrial mass, which was mildly decreased during the hyperlactatemic phase. Most of the mitochondrial abnormalities returned to control ranges after linezolid withdrawal, lactate normalization, and clinical recovery. Linezolid inhibits mitochondrial protein synthesis, leading to decreased mitochondrial enzymatic activity, which causes linezolid-related hyperlactatemia, which resolves upon discontinuation of linezolid treatment.
Can Alcohol-Based Hand-Rub Solutions Cause You To Lose Your Driver's License? Comparative Cutaneous Absorption of Various Alcohols
Authors: Brown T. L. , Gamon S. , Tester P. , Martin R. , Hosking K. , Bowkett G. C. , Gerostamoulos D. , Grayson M. L.
Published: December 2006

We assessed cutaneous ethanol (ETOH) and isopropanol (ISOP) absorption after intensive (30 times per h) use of alcohol-based hand-rub solutions by healthcare workers (HCWs). ETOH was detectable in the breath of 6/20 HCWs (0.001 to 0.0025%) at 1 to 2 min postexposure and in the serum of 2/20 HCWs at 5 to 7 min postexposure. Serum ISOP levels were unrecordable at all time points.
Once-Weekly Micafungin Therapy Is as Effective as Daily Therapy for Disseminated Candidiasis in Mice with Persistent Neutropenia
Authors: Gumbo Tawanda , Drusano George L. , Liu Weiguo , Kulawy Robert W. , Fregeau Christine , Hsu Vasha , Louie Arnold
Published: December 2006

The effect of micafungin dose scheduling on the treatment of candidemia is unknown. Neutropenic mice with disseminated
Candida glabrata
infection were treated with single intraperitoneal micafungin doses of 0 to 100 mg/kg of body weight and sacrificed 7 days later. The maximal decline in kidney fungal burden was 5.8 log
10
CFU/g. A 1-week pharmacokinetic-pharmacodynamic study revealed a micafungin serum half-life of 6.13 h. In mice treated with ≥50 mg/kg, there was maximal fungal decline without regrowth during the 1-week dosing interval. Next, doses associated with 34% (34% effective dose [ED
34
]) and 50% (ED
50
) of maximal kill were administered at one of three dose schedules: a single dose at
t
= 0, two equal doses at
t
= 0 and
t
= 3.5 days, and 7 equal doses daily. Some mice received a single dose of 100 mg/kg. Fungal burden was examined on days 1, 5, and 7. In mice treated with the ED
34
, microbial kill with the daily therapy initially lagged behind the intermittent doses but exceeded it by day 7. In mice treated with the ED
50
, daily and intermittent doses had equivalent day 7 effects. In mice treated with 100 mg/kg, there was no regrowth. The relative likelihoods that the area under the concentration-time curve/MIC ratio was linked to microbial kill versus peak concentration/MIC ratio or time above the MIC was 10.3 and 10,161.2, respectively. In all the experiments, no paradoxical increase in fungal burden was observed with high micafungin doses. However, only a single
Candida
isolate was tested. Regimens that simulated micafungin concentration-time profiles in patients treated with a single micafungin dose of 1,400 mg once a week demonstrated maximal fungal decline. Once-weekly micafungin therapy is as efficacious as daily therapy in a murine model of disseminated candidiasis.
Evaluation of the In Vivo Activity of Tribendimidine against
Schistosoma mansoni
,
Fasciola hepatica
,
Clonorchis sinensis
, and
Opisthorchis viverrini
Authors: Keiser Jennifer , Shu-Hua Xiao , Chollet Jacques , Tanner Marcel , Utzinger Jürg
Published: December 2006

We examined the in vivo activity of tribendimidine against selected trematodes. A single 150-mg/kg dose of tribendimidine achieved a 99.1% reduction of
Clonorchis sinensis
in rats. A 400-mg/kg dose of tribendimidine reduced
Opisthorchis viverrini
in hamsters by 95.7%. High doses of tribendimidine showed no activity against
Schistosoma mansoni
and
Fasciola hepatica
.
In Vitro Activities of Amphotericin B, Caspofungin, Itraconazole, Posaconazole, and Voriconazole against 45 Clinical Isolates of Zygomycetes: Comparison of CLSI M38-A, Sensititre YeastOne, and the Etest
Authors: Torres-Narbona Marta , Guinea Jesús , Martínez-Alarcón José , Peláez Teresa , Bouza Emilio
Published: December 2006

We evaluated the activities of amphotericin B, itraconazole, voriconazole, caspofungin, and posaconazole against zygomycetes by CLSI M38-A, Etest and Sensititre. The most active drug was posaconazole, followed by amphotericin B and itraconazole. The correlation of the Etest and Sensititre with CLSI M38-A was moderate for posaconazole but poor for the others.
Impact of Antimicrobial Usage on Antimicrobial Resistance in Commensal
Escherichia coli
Strains Colonizing Broiler Chickens
Authors: Smith J. L. , Drum D. J. V. , Dai Y. , Kim J. M. , Sanchez S. , Maurer J. J. , Hofacre C. L. , Lee M. D.
Published: December 2006

Escherichia coli
strains isolated from commercial broilers and an experimental flock of chickens were screened to determine phenotypic expression of antimicrobial resistance and carriage of drug resistance determinants. The goal of this study was to investigate the influence of oxytetracycline, sarafloxacin, and enrofloxacin administration on the distribution of resistance determinants and strain types among intestinal commensal
E. coli
strains isolated from broiler chickens. We detected a high prevalence of resistance to drugs such as tetracycline (36 to 97%), sulfonamides (50 to 100%), and streptomycin (53 to 100%) in
E. coli
isolates from treated and untreated flocks. These isolates also had a high prevalence of class 1 integron carriage, and most of them possessed the streptomycin resistance cassette,
aadA1
. In order to investigate the contribution of
E. coli
strain distribution to the prevalence of antimicrobial resistance and the resistance determinants, isolates from each flock were DNA fingerprinted by enterobacterial repetitive intergenic consensus sequence (ERIC) PCR. Although very diverse
E. coli
strain types were detected, four ERIC strain types were present on all of the commercial broiler farms, and two of the strains were also found in the experimental flocks. Each
E. coli
strain consisted of both susceptible and antimicrobial agent-resistant isolates. In some instances, isolates of the same
E. coli
strain expressed the same drug resistance patterns although they harbored different
tet
determinants or streptomycin resistance genes. Therefore, drug resistance patterns could not be explained solely by strain prevalence, indicating that mobile elements contributed significantly to the prevalence of resistance.
Characterization of Environmental Sources of the Human and Animal Pathogen
Cryptococcus gattii
in British Columbia, Canada, and the Pacific Northwest of the United States
Authors: Kidd Sarah E. , Chow Yat , Mak Sunny , Bach Paxton J. , Chen Huiming , Hingston Adrian O. , Kronstad James W. , Bartlett Karen H.
Published: December 2006

Cryptococcus gattii
has recently emerged as a primary pathogen of humans and wild and domesticated animals in British Columbia, particularly on Vancouver Island.
C. gattii
infections are typically infections of the pulmonary and/or the central nervous system, and the incidence of infection in British Columbia is currently the highest reported globally. Prior to this emergence, the environmental distribution of and the extent of colonization by
C. gattii
in British Columbia were unknown. We characterized the environmental sources and potential determinants of colonization in British Columbia.
C. gattii
was isolated from tree surfaces, soil, air, freshwater, and seawater, and no seasonal prevalence was observed. The
C. gattii
concentrations in air samples were significantly higher during the warm, dry summer months, although potentially infectious propagules (<3.3 μm in diameter) were present throughout the year. Positive samples were obtained from many different areas of British Columbia, and some locations were colonization “hot spots.”
C. gattii
was generally isolated from acidic soil, and geographic differences in soil pH may influence the extent of colonization.
C. gattii
soil colonization also was associated with low moisture and low organic carbon contents. Most of the
C. gattii
isolates recovered belonged to the VGIIa genetic subtype; however, sympatric colonization by the VGIIb strain was observed at most locations. At one sampling site, VGIIa, VGIIb, VGI, and the
Cryptococcus neoformans
serotype AD hybrid all were coisolated. Our findings indicate extensive colonization by
C. gattii
within British Columbia and highlight an expansion of the ecological niche of this pathogen.
Persistence, Transmission, and Virulence Characteristics ofAeromonasStrains in a Duckweed Aquaculture-Based Hospital Sewage Water Recycling Plant in Bangladesh
Authors: Rahman Mokhlasur , Huys Geert , Rahman Motiur , Albert M. John , Kühn Inger , Möllby Roland
Published: December 2006

The persistence and transmission ofAeromonasin a duckweed aquaculture-based hospital sewage water treatment plant in Bangladesh was studied. A total of 670 samples from different sites of the hospital sewage water treatment plant, from feces of hospitalized children suffering from diarrhea, from environmental control ponds, and from feces of healthy humans were collected over a period of three years. In total, 1,315 presumptiveAeromonasisolates were biochemically typed by the PhenePlate rapid screening system (PhP-AE). A selection of 90 representative isolates was further analyzed with PhenePlate (PhP) extended typing (PhP-48), fatty acid methyl ester analysis, and amplified fragment length polymorphism (AFLP) fingerprinting. In addition, the prevalence of the putative virulence factors hemolysin and cytotoxin and the presence of the cytolytic enterotoxin gene (AHCYTOEN) were analyzed.Aeromonaswas found at all sites of the treatment plant, in 40% of the samples from environmental control ponds, in 8.5% of the samples from hospitalized children suffering from diarrhea, and in 3.5% of samples from healthy humans. A significantly high number ofAeromonasbacteria was found in duckweed, which indicates that duckweed may serve as a reservoir for these bacteria. PhP-AE typing allowed identification of more than 192 distinct PhP types, of which 18 major PhP types (MTs) were found in multiple sites and during several occasions. AFLP fingerprinting revealed the prevalence of genotypically indistinguishableAeromonasisolates among certain PhP MTs recovered from different sampling occasions and/or at multiple sites. Hemolytic and cytotoxic activities were observed in 43% of the tested strains, whereas 29% possessed the cytolytic enterotoxin gene AHCYTOEN. Collectively, two specific MTs associated with diarrhea were shown to exhibit high cytotoxicity. Furthermore, all tested isolates of these major types were positive for the cytolytic enterotoxin gene. In conclusion, our data indicate that certain phenotypically and genotypically stable clonal lineages ofAeromonashave persisted in the treatment system for a prolonged period and might spread from the hospitalized children suffering from diarrhea to fish produced for human consumption through the sewage water treatment system.
PCR-Based Detection ofAngiostrongylus cantonensisin Tissue and Mucus Secretions from Molluscan Hosts
Authors: Qvarnstrom Yvonne , Sullivan James J. , Bishop Henry S. , Hollingsworth Robert , da Silva Alexandre J.
Published: December 2006

Angiostrongylus cantonensisis a common cause of human eosinophilic meningitis. Recent outbreaks of this infection have shown that there is a need to determine the distribution of this nematode in the environment in order to control transmission.A. cantonensisis generally identified morphologically in the molluscan intermediate host by microscopic examination, which can be labor-intensive. The aim of this study was to develop a PCR-based method to detectA. cantonensisdirectly from molluscan tissue. A total of 34Parmarioncf.martensi(Simroth) semislugs, 25 of which were naturally infected withA. cantonensis, were used to develop this assay. Tissue pieces (approximately 25 mg) were digested with pepsin-HCl to recover third-stage larvae for morphological identification or were used for DNA extraction. PCR primers were designed to amplify 1,134 bp from theAngiostrongylus18S rRNA gene, and the amplicons produced were sequenced for identification at the species level. Both microscopy and the PCR-DNA sequencing analysis indicated that the same 25 semislugs were positive forA. cantonensis, showing that the two methods were equally sensitive and specific for this application. However, morphological detection requires access to living mollusks, whereas molecular analysis can also be performed with frozen tissue. The PCR-DNA sequencing method was further evaluated using tissue fromVeronicella cubensis(Pfeiffer) slugs and mucus secretions from infectedP. martensi. To our knowledge, this is the first use of a PCR-based method to confirm the presence ofA. cantonensisin mollusks collected in the environment.
Circumventing the Effect of Product Toxicity: Development of a Novel Two-Stage Production Process for the Lantibiotic Gallidermin
Authors: Valsesia G. , Medaglia G. , Held M. , Minas W. , Panke S.
Published: December 2006

Lantibiotics such as gallidermin are lanthionine-containing polypeptide antibiotics produced by gram-positive bacteria that might become relevant for the treatment of various infectious diseases. So far, self-toxicity has prevented the isolation of efficient overproducing strains, thus hampering their thorough investigation and preventing their exploitation in fields other than the food area. We wanted to investigate the effect of lantibiotic precursor peptides on the producing strains in order to evaluate novel strategies for the overproduction of these promising peptides. In this study, gallidermin was chosen as a representative example of the type A lantibiotics. A
Staphylococcus gallinarum
Tü3928 mutant, whose gene for the extracellular pregallidermin protease GdmP was replaced by a kanamycin-resistance gene, was constructed. Mass spectrometry (MS) analysis indicated that this mutant produced fully posttranslationally modified gallidermin precursors with truncated versions of the leader peptide, but not the entire leader as predicted from the
gdmA
sequence. In filter-on-plate assays, these truncated pregallidermins showed no toxicity against
Staphylococcus gallinarum
Tü3928 up to a concentration of 8 g/liter (corresponding to approximately 2.35 mM), while gallidermin produced clear inhibitory zones at concentrations as low as 0.25 g/liter (0.12 mM). We showed that the lack of toxicity is due entirely to the presence of the truncated leader, since MS as well as bioassay analysis showed that the peptides resulting from tryptic cleavage of pregallidermins and gallidermin produced by
S. gallinarum
Tü3928 had identical masses and approximately the same specific activity. This demonstrates that even a shortened leader sequence is sufficient to prevent the toxicity of mature gallidermin. In nonoptimized fermentations, the
gdmP
mutant produced pregallidermin to a 50%-higher molar titer, suggesting that the absence of self-toxicity has a beneficial effect on gallidermin production and giving a first confirmation of the suitability of the overproduction strategy.
Metabolic Engineering of Carotenoid Biosynthesis in
Escherichia coli
by Ordered Gene Assembly in
Bacillus subtilis
Authors: Nishizaki Tomoko , Tsuge Kenji , Itaya Mitsuhiro , Doi Nobuhide , Yanagawa Hiroshi
Published: December 2006

We attempted to optimize the production of zeaxanthin in
Escherichia coli
by reordering five biosynthetic genes in the natural carotenoid cluster of
Pantoea ananatis
. Newly designed operons for zeaxanthin production were constructed by the ordered gene assembly in
Bacillus subtilis
(OGAB) method, which can assemble multiple genes in one step using an intrinsic
B. subtilis
plasmid transformation system. The highest level of production of zeaxanthin in
E. coli
(820 μg/g [dry weight]) was observed in the transformant with a plasmid in which the gene order corresponds to the order of the zeaxanthin metabolic pathway (
crtE-crtB-crtI-crtY-crtZ
), among a series of plasmids with circularly permuted gene orders. Although two of five operons using intrinsic zeaxanthin promoters failed to assemble in
B. subtilis
, the full set of operons was obtained by repressing operon expression during OGAB assembly with a
p
R
promoter-
c
I repressor system. This result suggests that repressing the expression of foreign genes in
B. subtilis
is important for their assembly by the OGAB method. For all tested operons, the abundance of mRNA decreased monotonically with the increasing distance of the gene from the promoter in
E. coli
, and this may influence the yield of zeaxanthin. Our results suggest that rearrangement of biosynthetic genes in the order of the metabolic pathway by the OGAB method could be a useful approach for metabolic engineering.
Integrated Real-Time PCR for Detection and Monitoring of
Legionella pneumophila
in Water Systems
Authors: Yaradou Diaraf Farba , Hallier-Soulier Sylvie , Moreau Sophie , Poty Florence , Hillion Yves , Reyrolle Monique , André Janine , Festoc Gabriel , Delabre Karine , Vandenesch François , Etienne Jerome , Jarraud Sophie
Published: December 2006

We evaluated a ready-to-use real-time quantitative
Legionella pneumophila
PCR assay system by testing 136 hot-water-system samples collected from 55 sites as well as 49 cooling tower samples collected from 20 different sites, in parallel with the standard culture method. The PCR assay was reproducible and suitable for routine quantification of
L. pneumophila
. An acceptable correlation between PCR and culture results was obtained for sanitary hot-water samples but not for cooling tower samples. We also monitored the same
L. pneumophila
-contaminated cooling tower for 13 months by analyzing 104 serial samples. The culture and PCR results were extremely variable over time, but the curves were similar. The differences between the PCR and culture results did not change over time and were not affected by regular biocide treatment. This ready-to-use PCR assay for
L. pneumophila
quantification could permit more timely disinfection of cooling towers.