bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrocreep and Cyclic Damage of Polymers
Authors: Vinogradov Aleksandra M.
Published: June 2008

The paper concerns the time-dependent response of polymer systems subjected to superimposed static and cyclic loads. An overview of recent experimental results regarding the cyclic creep response of two polymers, Nylon 6/6 and polyvinylidene fluoride (PVDF) is presented. It is shown that both materials have demonstrated accelerated creep rates due to cyclic loading effects. This phenomenon, defined as “vibrocreep”, is essentially nonlinear, since the material response under combined static and cyclic loads does not represent a simple superposition of the responses to static and fully reversed cyclic loads applied separately. Further, a nonlinear constitutive model, describing the interaction between creep and cyclic damage evolution in polymers is formulated. This constitutive model combines the concepts of linear viscoelastic theory of hereditary type with damage characterization using a damage function. It is shown that the damage function depends on the number of loading cycles and can be determined experimentally. In the paper, experimental results validating the developed constitutive model are presented.
Investigation of Fracture in Transparent Glass Fiber Reinforced Polymer Composites Using Photoelasticity
Authors: Khanna Sanjeev K. , Ellingsen Marius D. , Winter Robb M.
Published: June 2008

Composite materials are widely used in mechanical structures where a high ratio of strength or stiffness to weight is desired. Not only are composite materials widely used in building recreational equipment such as skis, snowboards or even sports cars, but also multiple types of military aircraft are built from composite materials. Airplane bodies are in principle cyclically loaded pressure vessels and are susceptible to the formation of fatigue cracks, and it is necessary to possess knowledge of how the material behaves with a crack present. In fact, all engineering structures have to be designed with the presence of crack like defects in mind. For traditional engineering materials such as steel and aluminum there exists a large body of knowledge regarding material behavior in the presence of a crack. Furthermore, their isotropic nature eases the process of mechanical analysis. Photoelasticity, an optical method, has been widely used to study fracture in isotropic transparent materials (Irwin, 1962, 1980; Dally, 1979; Daniel, 1984; Kobayashi, et al, 1973; Chona, 1987).
Low Temperature Effects on IM7/977-3 Cross-Ply Composite Material Properties at High Strain Rates
Authors: Song Shunjun , Vinson Jack R.
Published: June 2008

Composite materials are used in a wide variety of low temperature applications because of their unique and highly tailorable properties. These low temperature applications of composites include their use in Arctic environments and most of them involve dynamic loads, for example, spacecraft applications where they use cryogenic engines, hypervelocity impact situations at very high altitudes, civil engineering applications in extreme cold regions, and offshore structures in cold regions. The U.S. Navy stated that under certain conditions naval vessels might encounter strain rates up to 1200/sec. Because the dynamic properties of composite materials may vary widely with both strain rates and temperature, it is important to use the dynamic properties at the expected temperatures when the loading conditions involve high strain rates and extreme temperatures. Very few materials have been characterized at high strain rates even at room temperature. Still less effort has been spent in trying to model the high strain rate properties to develop a predictive capability at room temperature. It has been hoped that earlier modeling for metals, such as Johnson and Cook [1], and Zerilli and Armstrong [2] might be used for composite materials. The Johnson-Cook model was modified by Weeks and Sun [3] for composite materials. Other recent modeling research has been performed by Theruppukuzki and Sun [4], Hsiao, Daniel and Cordes [5] and Tsai and Sun [6]. Woldesenbet and Vinson [7] have characterized the high strain rate and fiber orientation effects on one typical graphite/epoxy composite. Most of these characterizations model ultimate strengths only.
Micro-Electromechanics of Sensor Patches of Free Paraboloidal Shell Structronic Systems
Authors: Ding J. H. , Tzou H. S.
Published: June 2008

Distributed sensing of structural states is essential to vibration control, health monitoring and shape control of precision structronic systems. Paraboloidal shells of revolution are widely used in aerospace, telecommunication, etc. structures. However, distributed sensing of paraboloidal shell structures is rarely investigated over the years. Micro-sensing characteristics, sensor segmentation, sensor placements, shell geometric parameters, etc. of deep/shallow paraboloidal shells are evaluated in this study. Signal generation of generic distributed sensors laminated on paraboloidal shells is defined; microscopic signal components of segmented sensor patches laminated on deep/shallow paraboloidal shells with free boundary conditions are analyzed. Parametric studies of microelectromechanics and microscopic signal generations of segmented sensor patches reveal detailed modal sensing signal generation and efficiency of segmented sensor patches laminated at various shell locations of three paraboloidal shells (i.e., a shallow, a standard, and a deep).
Standard Infant Crib Testing Enhanced With Live Children Shaking
Authors: Brickman Dennis B.
Published: June 2008

An infant asphyxiated when a machine screw detached from a crib, the headboard separated from the crib rod, and the infant’s head stuck in the opening. The evaluation of infant cribs by inanimate standard test protocols is enhanced by live child crib shake testing. This live testing provides data for quantifying the horizontal push and pull forces that children actually apply to the sides of a crib. Comparisons are made between the live child shake test results and the inanimate test requirements contained in crib safety standards. Although the inanimate standard test protocols are inconsistent, the machine screw did not fail from normal use because the inanimate test requirements far exceed the maximum live results.
Simulation of Stand-Up Lift Truck Accidents to Evaluate Their Design and Operator Training Implications
Authors: Zoghi-Moghadam Mohamad , Watkins Charles B. , Sadegh Ali , Dunlap Dan
Published: June 2008

OSHA regulations mandate that operators of stand-up rider lift trucks be trained to jump clear of the truck in overturn accidents. Operator compartment doors have been considered as a design modification to protect operators against lower leg injuries in some other types of stand-up rider accidents. However, they restrict the ability of operators to rapidly jump clear and must be evaluated against the injuries that operators can incur by remaining in the truck. This paper describes computer simulation by a newly developed biodynamic model and testing with anthropomorphic test devices and actual trucks to advance the state of knowledge concerning injury potential in tip-over and off-the-dock accidents. Implications of the results for design as well as for OSHA training regulations are discussed.
Determination of Nanomechanical Properties of Polyester Matrix Composite Using Nanoindentation
Authors: Yedla Samatha B. , Kalukanimuttam M. , Winter R. M. , Khanna Sanjeev K.
Published: June 2008

Fiber reinforced polymer composites are two component material systems in which fibers are embedded in a polymer matrix. Such a system inherently has an interface region where the two components meet. The interface region around the fiber is also referred to as the ‘interphase’. Properties at the fiber-matrix interphase change by changing the chemistry of the composite system. Study of property variations with changing chemistry will help in better understanding and tailoring of the composite properties. The present work concentrates on the investigation of nanomechanical properties at the fiber-matrix interphase of glass fibers embedded in a polyester matrix. The glass fibers were coated with two types of silanes to produce a strong and a weak bond at the fiber-matrix interphase. Nanoindentation techniques coupled with atomic force microscopy imaging capabilities have been used for this investigation. Two different tips were employed for indenting, one being a Berkovich diamond tip supplied by Hysitron, Inc., and another a parabolic tungsten tip, which was made in the laboratory. Indentations were performed in the fiber-matrix interphase region and also in the bulk matrix. Mechanical properties such as modulus, stiffness, hardness and penetration depth were obtained in the interphase and their variation on moving away from the fiber. Variations of the elastic modulus in the interphase region and its relation to the chemistry are presented. The results obtained using two different tip shapes have been compared.
Focusing of shock waves induced by optical breakdown in water
Authors: Sankin Georgy N. , Zhou Yufeng , Zhong Pei
Published: June 2008

The focusing of laser-generated shock waves by a truncated ellipsoidal reflector was experimentally and numerically investigated. Pressure waveform and distribution around the first (F1) and second foci (F2) of the ellipsoidal reflector were measured. A neodymium doped yttrium aluminum garnet laser of 1046nm wavelength and 5ns pulse duration was used to create an optical breakdown at F1, which generates a spherically diverging shock wave with a peak pressure of 2.1–5.9MPa at 1.1mm stand-off distance and a pulse width at half maximum of 36–65ns. Upon reflection, a converging shock wave is produced which, upon arriving at F2, has a leading compressive wave with a peak pressure of 26MPa and a zero-crossing pulse duration of 0.1μs, followed by a trailing tensile wave of −3.3MPa peak pressure and 0.2μs pulse duration. The −6dB beam size of the focused shock wave field is 1.6×0.2mm2 along and transverse to the shock wave propagation direction. Formation of elongated plasmas at high laser energy levels limits the increase in the peak pressure at F2. General features in the waveform profile of the converging shock wave are in qualitative agreement with numerical simulations based on the Hamilton model.
Introducing atmospheric attenuation within a diffusion model for room-acoustic predictions
Authors: Billon Alexis , Picaut Judicaël , Foy Cédric , Valeau Vincent , Sakout Anas
Published: June 2008

This paper presents an extension of a diffusion model for room acoustics to handle the atmospheric attenuation. This phenomenon is critical at high frequencies and in large rooms to obtain correct acoustic predictions. An additional term is introduced in the diffusion equation as well as in the diffusion constant, in order to take the atmospheric attenuation into account. The modified diffusion model is then compared with the statistical theory and a cone-tracing software. Three typical room-acoustic configurations are investigated: a proportionate room, a long room and a flat room. The modified diffusion model agrees well with the statistical theory (when applicable, as in proportionate rooms) and with the cone-tracing software, both in terms of sound pressure levels and reverberation times.
Modeling of piezoelectric transducers with combined pseudospectral and finite-difference methods
Authors: Filoux E. , Callé S. , Certon D. , Lethiecq M. , Levassort F.
Published: June 2008

A new hybrid finite-difference (FD) and pseudospectral (PS) method adapted to the modeling of piezoelectric transducers (PZTs) is presented. The time-dependent equations of propagation are solved using the PS method while the electric field induced in the piezoelectric material is determined through a FD representation. The purpose of this combination is to keep the advantages of both methods in one model: the adaptability of FD representation to model piezoelectric elements with various geometries and materials, and the low number of nodes per wavelength required by the PS method. This approach is implemented to obtain an accurate algorithm to simulate the propagation of acoustic waves over large distances, directly coupled to the calculation of the electric field created inside the piezoelectric material, which is difficult with classical algorithms. These operations are computed using variables located on spatially and temporally staggered grids, which attenuate Gibbs phenomenon and increase the algorithm’s accuracy. The two-dimensional modeling of a PZT plate excited by a 50MHz sinusoidal electrical signal is performed. The results are successfully compared to those obtained using the finite-element (FE) algorithm of ATILA™ software with configurations spatially and temporally adapted to the FE requirements. The cost efficiency of the FD-PS time-domain method is quantified and verified.
Evaluating the maximum playback sound levels from portable digital audio players
Authors: Keith Stephen E. , Michaud David S. , Chiu Vincent
Published: June 2008

To assess the maximum sound levels that may be experienced by young people in Canada from modern digital audio players, this study measured nine recent models of players and 20 earphones. Measurement methodology followed European standard BS EN 50332. Playback levels ranged from 101to107dBA at maximum volume level. Estimated listener sound levels could vary from 79to125dBA due to the following factors: (i) earphone seal against the ear, (ii) player output voltage, (iii) earphone sensitivity, and (iv) recorded music levels. There was a greater potential for high sound levels if intra-concha “earbud” earphones were used due to the effect of earphone seal. Simpler measurement techniques were explored as field test methods; the best results were obtained by sealing the microphone of a sound level meter to the earphone using a cupped hand and correcting for the free field response of the ear. Measurement of noise levels 0.25m from the earphone showed that a bystander is unlikely to accurately judge listener sound levels.
Spatial release from energetic and informational masking in a divided speech identification task
Authors: Ihlefeld Antje , Shinn-Cunningham Barbara
Published: June 2008

When listening selectively to one talker in a two-talker environment, performance generally improves with spatial separation of the sources. The current study explores the role of spatial separation in divided listening, when listeners reported both of two simultaneous messages processed to have little spectral overlap (limiting “energetic masking” between the messages). One message was presented at a fixed level, while the other message level varied from equal to 40dB less than that of the fixed-level message. Results demonstrate that spatial separation of the competing messages improved divided-listening performance. Most errors occurred because listeners failed to report the content of the less-intense talker. Moreover, performance generally improved as the broadband energy ratio of the variable-level to the fixed-level talker increased. The error patterns suggest that spatial separation improves the intelligibility of the less-intense talker by improving the ability to (1) hear portions of the signal that would otherwise be masked, (2) segregate the two talkers properly into separate perceptual streams, and (3) selectively focus attention on the less-intense talker. Spatial configuration did not noticeably affect the ability to report the more-intense talker, suggesting that it was processed differently than the less-intense talker, which was actively attended.
Binaural intelligibility prediction based on the speech transmission index
Authors: van Wijngaarden Sander J. , Drullman Rob
Published: June 2008

Although the speech transmission index (STI) is a well-accepted and standardized method for objective prediction of speech intelligibility in a wide range of environments and applications, it is essentially a monaural model. Advantages of binaural hearing in speech intelligibility are disregarded. In specific conditions, this leads to considerable mismatches between subjective intelligibility and the STI. A binaural version of the STI was developed based on interaural cross correlograms, which shows a considerably improved correspondence with subjective intelligibility in dichotic listening conditions. The new binaural STI is designed to be a relatively simple model, which adds only few parameters to the original standardized STI and changes none of the existing model parameters. For monaural conditions, the outcome is identical to the standardized STI. The new model was validated on a set of 39 dichotic listening conditions, featuring anechoic, classroom, listening room, and strongly echoic environments. For these 39 conditions, speech intelligibility [consonant-vowel-consonant (CVC) word score] and binaural STI were measured. On the basis of these conditions, the relation between binaural STI and CVC word scores closely matches the STI reference curve (standardized relation between STI and CVC word score) for monaural listening. A better-ear STI appears to perform quite well in relation to the binaural STI model; the monaural STI performs poorly in these cases.
Effects of frequency disparities on trading of an ambiguous tone between two competing auditory objects
Authors: Lee Adrian K. C. , Shinn-Cunningham Barbara G.
Published: June 2008

Listeners are relatively good at estimating the true content of each physical source in a sound mixture in most everyday situations. However, if there is a spectrotemporal element that logically could belong to more than one object, the correct way to group that element can be ambiguous. Many psychoacoustic experiments have implicitly assumed that when a sound mixture contains ambiguous sound elements, the ambiguous elements “trade” between competing sources, such that the elements contribute more to one object in conditions when they contribute less to others. However, few studies have directly tested whether such trading occurs. While some studies found trading, trading failed in some recent studies in which spatial cues were manipulated to alter the perceptual organization. The current study extended this work by exploring whether trading occurs for similar sound mixtures when frequency content, rather than spatial cues, was manipulated to alter grouping. Unlike when spatial cues were manipulated, results are roughly consistent with trading. Together, results suggest that the degree to which trading is obeyed depends on how stimuli are manipulated to affect object formation.
Infants use prosodically conditioned acoustic-phonetic cues to extract words from speech
Authors: Johnson Elizabeth K.
Published: June 2008

The Headturn Preference Paradigm was used to examine infants’ use of prosodically conditioned acoustic-phonetic cues to find words in speech. Twelve-month-olds were familiarized to one passage containing an intended target (e.g., toga from toga#lore) and one passage containing an unintended target (e.g., dogma from dog#maligns). Infants were tested on the familiarized intended word (e.g., toga), familiarized unintended word (e.g., dogma), and two unfamiliar words. Infants listened longer to familiar intended words than to familiar unintended or unfamiliar words, demonstrating their use of word-level prosodically conditioned cues to segment words from speech. Implications for models of developmental speech perception are discussed.
Estimation of the detection probability for Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) with a passive acoustic method
Authors: Akamatsu T. , Wang D. , Wang K. , Li S. , Dong S. , Zhao X. , Barlow J. , Stewart B. S. , Richlen M.
Published: June 2008

Yangtze finless porpoises were surveyed by using simultaneous visual and acoustical methods from 6 November to 13 December 2006. Two research vessels towed stereo acoustic data loggers, which were used to store the intensity and sound source direction of the high frequency sonar signals produced by finless porpoises at detection ranges up to 300m on each side of the vessel. Simple stereo beam forming allowed the separation of distinct biosonar sound source, which enabled us to count the number of vocalizing porpoises. Acoustically, 204 porpoises were detected from one vessel and 199 from the other vessel in the same section of the Yangtze River. Visually, 163 and 162 porpoises were detected from two vessels within 300m of the vessel track. The calculated detection probability using acoustic method was approximately twice that for visual detection for each vessel. The difference in detection probabilities between the two methods was caused by the large number of single individuals that were missed by visual observers. However, the sizes of large groups were underestimated by using the acoustic methods. Acoustic and visual observations complemented each other in the accurate detection of porpoises. The use of simple, relatively inexpensive acoustic monitoring systems should enhance population surveys of free-ranging, echolocating odontocetes.
Pharmacokinetics of Miltefosine in Old World Cutaneous Leishmaniasis Patients
Authors: Dorlo Thomas P. C. , van Thiel Pieter P. A. M. , Huitema Alwin D. R. , Keizer Ron J. , de Vries Henry J. C. , Beijnen Jos H. , de Vries Peter J.
Published: June 2008

The pharmacokinetics of miltefosine in leishmaniasis patients are, to a great extent, unknown. We examined and characterized the pharmacokinetics of miltefosine in a group of patients with Old World (
Leishmania major
) cutaneous leishmaniasis. Miltefosine plasma concentrations were determined in samples taken during and up to 5 months after the end of treatment from 31 Dutch military personnel who contracted cutaneous leishmaniasis in Afghanistan and were treated with 150 mg miltefosine/day for 28 days. Samples were analyzed with a validated liquid chromatography-tandem mass spectrometry assay with a lower limit of quantification (LLOQ) of 4 ng/ml. Population pharmacokinetic modeling was performed with nonlinear mixed-effect modeling, using NONMEM. The pharmacokinetics of miltefosine could best be described by an open two-compartment disposition model, with a first elimination half-life of 7.05 days and a terminal elimination half-life of 30.9 days. The median concentration in the last week of treatment (days 22 to 28) was 30,800 ng/ml. The maximum duration of follow-up was 202 days after the start of treatment. All analyzed samples contained a concentration above the LLOQ. Miltefosine is eliminated from the body much slower than previously thought and is therefore still detectable in human plasma samples taken 5 to 6 months after the end of treatment. The presence of subtherapeutic miltefosine concentrations in the blood beyond 5 months after treatment might contribute to the selection of resistant parasites, and moreover, the measures for preventing the teratogenic risks of miltefosine treatment should be reconsidered.
Restoration of Susceptibility of Intracellular Methicillin-ResistantStaphylococcus aureusto β-Lactams: Comparison of Strains, Cells, and Antibiotics
Authors: Lemaire Sandrine , Olivier Aurélie , Van Bambeke Françoise , Tulkens Paul M. , Appelbaum Peter C. , Glupczynski Youri
Published: June 2008

Staphylococcus aureusinvades eukaryotic cells. When methicillin-resistantS. aureus(MRSA) ATCC 33591 is phagocytized by human THP-1 macrophages, complete restoration of susceptibility to cloxacillin and meropenem is shown and the strain becomes indistinguishable from MSSA ATCC 25923 due to the acid pH prevailing in phagolysosomes (S. Lemaire et al., Antimicrob. Agents Chemother. 51:1627-1632, 2007). We examined whether this observation can be extended to (i) strains of current clinical and epidemiological interest (three hospital-acquired MRSA [HA-MRSA] strains, two community-acquired MRSA [CA-MRSA] strains, two HA-MRSA strains with the vancomycin-intermediate phenotype, one HA-MRSA strain with the vancomycin-resistant phenotype, and one animal [porcine] MRSA strain), (ii) activated THP-1 cells and nonprofessional phagocytes (keratinocytes, Calu-3 bronchial epithelial cells), and (iii) other β-lactams (imipenem, oxacillin, cefuroxime, cefepime). All strains showed (i) a marked reduction in MICs in broth at pH 5.5 compared with the MIC at pH 7.4 and (ii) sigmoidal dose-response curves with cloxacillin (0.01× to 100× MIC, 24 h of incubation) after phagocytosis by THP-1 macrophages that were indistinguishable from each other and from the dose-response curve for methicillin-susceptibleS. aureus(MSSA) ATCC 25923 (relative potency [50% effect], 6.09× MIC [95% confidence interval {CI}, 4.50 to 8.25]; relative efficacy [change in bacterial counts over the original inoculum for an infinitely large cloxacillin concentration, or maximal effect], −0.69 log CFU [95% CI, −0.79 to −0.58]). Similar dose-response curves for cloxacillin were also observed with MSSA ATCC 25923 and MRSA ATCC 33591 after phagocytosis by activated THP-1 macrophages, keratinocytes, and Calu-3 cells. By contrast, there was a lower level of restoration of susceptibility of MRSA ATCC 33591 to cefuroxime and cefepime after phagocytosis by THP-1 macrophages, even when the data were normalized for differences in MICs. We conclude that the restoration of MRSA susceptibility to β-lactams after phagocytosis is independent of the strain and the types of cells but varies between β-lactams.
Role of Global Regulators and Nucleotide Metabolism in Antibiotic Tolerance in
Escherichia coli
Authors: Hansen Sonja , Lewis Kim , Vulić Marin
Published: June 2008

Bacterial populations produce a small number of persister cells that exhibit multidrug tolerance. Persister cells are largely responsible for the antibiotic recalcitrance of biofilm infections. The mechanism of persister cell formation largely remains unknown due to the challenges in identifying persister genes. We screened an ordered comprehensive library of 3,985
Escherichia coli
knockout strains to identify mutants with altered antibiotic tolerance. Stationary-state cultures in 96-well plates were exposed to ofloxacin at a concentration which allows only tolerant persister cells to survive. The persister cell level of each culture was determined. A total of 150 mutants with decreased persistence were identified in the initial screen, and subsequent validation confirmed that neither the growth rate nor the ofloxacin MIC was affected for 10 of them. The genes affected in these strains were
dnaJ
and
dnaK
(chaperones),
apaH
(diadenosine tetraphosphatase),
surA
(peptidyl-prolyl
cis
-
trans
isomerase),
fis
and
hns
(global regulators),
hnr
(response regulator of RpoS),
dksA
(transcriptional regulator of rRNA transcription),
ygfA
(5-formyl-tetrahydrofolate cyclo-ligase), and
yigB
(flavin mononucleotide [FMN] phosphatase). The prominent presence of global regulators among these strains pointed to the likely redundancy of persister cell formation mechanisms: the elimination of a regulator controlling several redundant persister genes would be expected to produce a phenotype. This observation is consistent with previous findings for a possible role of redundant genes such as toxin/antitoxin modules in persister cell formation.
ygfA
and
yigB
were of special interest. The mammalian homolog of YgfA (methenyltetrahydrofolate synthetase) catalyzes the conversion of 5-formyl-tetrahydrofolate (THF) into the rapidly degraded 5,10-methenyl-THF, depleting the folate pool. The YigB protein is a phosphatase of FMN which would deplete the pool of this cofactor. Stochastic overexpression of these genes could lead to dormancy and, hence, tolerance by depleting the folate and FMN pools, respectively. Consistent with this scenario, the overexpression of both genes produced increased tolerance to ofloxacin.
Effect of Chemotherapy with Praziquantel on the Production of Cytokines and Morbidity Associated with Schistosomiasis Mansoni
Authors: Martins-Leite P. , Gazzinelli G. , Alves-Oliveira L. F. , Gazzinelli A. , Malaquias L. C. C. , Correa-Oliveira R. , Teixeira-Carvalho A. , Silveira A. M. S.
Published: June 2008

The objective of the present study was to test the hypothesis that treatment of schistosomiasis mansoni with praziquantel can alter significantly the immune response of patients and generate a reversal of the level of fibrosis. Peripheral blood mononuclear cell (PBMC) samples were collected from, and abdominal ultrasound examinations conducted on, volunteers infected withSchistosoma mansoniand living in an area where the disease is endemic, both prior to and one year after treatment with praziquantel. Subjects were classified into groups according to the level of pathology (i.e., absent, incipient, moderate, or severe fibrosis). PBMCs were stimulated with schistosome soluble egg antigens (SEA), and the levels of production of the cytokines gamma interferon (IFN-γ), tumor necrosis factor alpha, transforming growth factor β, and interleukin-4 (IL-4), IL-10, and IL-13 were determined. The chemotherapy was effective in reducing morbidity, particularly for individuals presenting with severe fibrosis. When levels of cytokine production in posttreatment PBMC cultures stimulated by SEA were categorized as low or high, significant differences in the distribution of IL-13 levels between groups presenting with or not presenting with fibrosis were established. Comparison of pre- and posttreatment SEA-induced cytokine levels in individuals who had experienced no change in the grade of fibrosis following chemotherapy revealed that the level of IFN-γ decreased in subjects with fibrosis whereas that of IL-10 decreased in individuals with and without fibrosis. The data suggest that chemotherapy is effective in reducing the morbidity of the disease and that the level of IL-13 may be a useful indicator of the persistence of fibrosis following treatment.
VIM-15 and VIM-16, Two New VIM-2-Like Metallo-β-Lactamases in
Pseudomonas aeruginosa
Isolates from Bulgaria and Germany
Authors: Schneider Ines , Keuleyan Emma , Rasshofer Rudolf , Markovska Rumyana , Queenan Anne Marie , Bauernfeind Adolf
Published: June 2008

Two
Pseudomonas aeruginosa
urine isolates from Bulgaria and Germany produced two new VIM-2 variants. VIM-15 had one amino acid substitution (Tyr218Phe) which caused a significant increase in hydrolytic efficiency. The substitution Ser54Leu, characterizing VIM-16, showed no influence on enzyme activity. Both genes were part of class I integrons located in the chromosome.
Activities of Ceftobiprole, Linezolid, Vancomycin, and Daptomycin against Community-Associated and Hospital-Associated Methicillin-Resistant
Staphylococcus aureus
Authors: Leonard Steven N. , Cheung Chrissy M. , Rybak Michael J.
Published: June 2008

We evaluated the activity of ceftobiprole against 100 community-associated methicillin-resistant
Staphylococcus aureus
(CA-MRSA) and 100 hospital-associated MRSA (HA-MRSA) isolates. Eight isolates were evaluated by time-kill studies for kill rate and potential for synergy with tobramycin. Ceftobiprole MIC
50
and MIC
90
values were 1 and 2 μg/ml, respectively, against CA-MRSA and HA-MRSA. In time-kill analysis, ceftobiprole was bactericidal at all concentrations tested.
IS
Ecp1
-Mediated Transposition of
qnrB
-Like Gene in
Escherichia coli
Authors: Cattoir Vincent , Nordmann Patrice , Silva-Sanchez Jesus , Espinal Paula , Poirel Laurent
Published: June 2008

A novel QnrB-like plasmid-mediated resistance determinant, QnrB19, was identified from an
Escherichia coli
clinical isolate from Colombia. Its gene was associated with an IS
Ecp1
-like insertion element that did not act as a promoter for its expression. Using an in vitro model of transposition, we showed that the IS
Ecp1
-like element was able to mobilize the
qnrB19
gene.
Potent In Vitro Activity of Tomopenem (CS-023) against Methicillin-Resistant
Staphylococcus aureus
and
Pseudomonas aeruginosa
Authors: Koga Tetsufumi , Masuda Nobuhisa , Kakuta Masayo , Namba Eiko , Sugihara Chika , Fukuoka Takashi
Published: June 2008

Tomopenem (formerly CS-023) is a novel 1β-methylcarbapenem with broad-spectrum coverage of gram-positive and gram-negative pathogens. Its antibacterial activity against European clinical isolates of methicillin-resistant
Staphylococcus aureus
(MRSA) and
Pseudomonas aeruginosa
was compared with those of imipenem and meropenem. The MICs of tomopenem against MRSA and
P. aeruginosa
at which 90% of the isolates tested were inhibited were 8 and 4 μg/ml, respectively, and were equal to or more than fourfold lower than those of imipenem and meropenem. The antibacterial activity of tomopenem against MRSA was correlated with a higher affinity for the penicillin-binding protein (PBP) 2a. Its activity against laboratory mutants of
P. aeruginosa
with (i) overproduction of chromosomally coded AmpC β-lactamase; (ii) overproduction of the multidrug efflux pumps MexAB-OprM, MexCD-OprJ, and MexEF-OprN; (iii) deficiency in OprD; and (iv) various combinations of AmpC overproduction, MexAB-OprM overproduction, and OprD deficiency were tested. The increases in the MIC of tomopenem against each single mutant compared with that against its parent strain were within a fourfold range. Tomopenem exhibited antibacterial activity against all mutants, with an observed MIC range of 0.5 to 8 μg/ml. These results suggest that the antibacterial activity of tomopenem against the clinical isolates of MRSA and
P. aeruginosa
should be ascribed to its high affinity for PBP 2a and its activity against the mutants of
P. aeruginosa
, respectively.
Cell-Penetrating Peptide TP10 Shows Broad-Spectrum Activity against both
Plasmodium falciparum
and
Trypanosoma brucei brucei
Authors: Arrighi Romanico B. G. , Ebikeme Charles , Jiang Yang , Ranford-Cartwright Lisa , Barrett Michael P. , Langel Ülo , Faye Ingrid
Published: June 2008

Malaria and trypanosomiasis are diseases which afflict millions and for which novel therapies are urgently required. We have tested two well-characterized cell-penetrating peptides (CPPs) for antiparasitic activity. One CPP, designated TP10, has broad-spectrum antiparasitic activity against
Plasmodium falciparum
, both blood and mosquito stages, and against blood-stage
Trypanosoma brucei brucei
.
In Vitro Activity of Tigecycline against Multidrug-Resistant
Acinetobacter baumannii
and Selection of Tigecycline-Amikacin Synergy
Authors: Moland Ellen S. , Craft David W. , Hong Seong-geun , Kim Soo-young , Hachmeister Lucas , Sayed Shimon D. , Thomson Kenneth S.
Published: June 2008

Polymyxin B, minocycline, and tigecycline were the most potent of 10 antibiotics against 170 isolates of multidrug-resistant
Acinetobacter baumannii
. In time-kill studies, the exposure of a highly tigecycline-resistant isolate to tigecycline resulted in enhanced susceptibility to amikacin and synergistic bactericidal activities of the two drugs.
Spread of OXA-48-Positive Carbapenem-Resistant
Klebsiella pneumoniae
Isolates in Istanbul, Turkey
Authors: Carrër Amélie , Poirel Laurent , Eraksoy Haluk , Cagatay A. Atahan , Badur Selim , Nordmann Patrice
Published: June 2008

The first outbreak of carbapenem-resistant
Klebsiella pneumoniae
isolates producing the plasmid-encoded carbapenem-hydrolyzing oxacillinase OXA-48 is reported. The 39 isolates belonged to two different clones and were collected at the University Hospital of Istanbul, Turkey, from May 2006 to February 2007, and they coproduced various β-lactamases (SHV-12, OXA-9, and TEM-1 for clone A and CTX-M-15, TEM-1, and OXA-1 for clone B).
Implication of an Outer Surface Lipoprotein in Adhesion of
Bifidobacterium bifidum
to Caco-2 Cells
Authors: Guglielmetti Simone , Tamagnini Isabella , Mora Diego , Minuzzo Mario , Scarafoni Alessio , Arioli Stefania , Hellman Jukka , Karp Matti , Parini Carlo
Published: June 2008

We found that the human intestinal isolate
Bifidobacterium bifidum
MIMBb75 strongly adhered to Caco-2 cells. Proteinase K and lithium chloride treatments showed that proteins play a key role in MIMBb75 adhesion to Caco-2 cells. By studying the cell wall-associated proteins, we identified a surface protein, which we labeled BopA. We purified the protein chromatographically and found that it functioned as an adhesion promoter on Caco-2 cells. In silico analysis of the gene coding for this protein and globomycin experiments showed that BopA is a cysteine-anchored lipoprotein expressed as a precursor polypeptide. A database search indicated that BopA appears to function biologically as an oligopeptide/tripeptide-solute-binding protein in the ABC transport system. We discovered a protein corresponding to BopA and its gene in eight other highly adherent
B. bifidum
strains. Finally, we found that
B. bifidum
MIMBb75 and BopA affected the production of interleukin-8 in Caco-2 epithelial cells. BopA is the first protein described to date to be directly involved in the adhesion of bifidobacteria to Caco-2 cells and to show immunomodulatory activity.
SEL, a Selective Enrichment Broth for Simultaneous Growth of
Salmonella enterica
,
Escherichia coli
O157:H7, and
Listeria monocytogenes
Authors: Kim Hyochin , Bhunia Arun K.
Published: June 2008

Multipathogen detection on a single-assay platform not only reduces the cost for testing but also provides data on the presence of pathogens in a single experiment. To achieve this detection, a multipathogen selective enrichment medium is essential to allow the concurrent growth of pathogens. SEL broth was formulated to allow the simultaneous growth of
Salmonella enterica
,
Escherichia coli
O157:H7, and
Listeria monocytogenes
. The results were compared to those obtained with the respective individual selective enrichment broths, Rappaport-Vassiliadis (RV) for
S. enterica
, modified
E. coli
broth with 20 mg of novobiocin/liter for
E. coli
O157:H7, and Fraser broth for
L. monocytogenes
, and a currently used universal preenrichment broth (UPB). The growth of each pathogen in SEL inoculated at 10
1
or 10
3
CFU/ml was superior to that in the respective individual enrichment broth, except in the case of RV, in which
Salmonella
cells inoculated at both concentrations grew equally well. In mixed-culture experiments with cells of the three species present in equal concentrations or at a 1:10:1,000 ratio, the overall growth was proportional to the initial inoculation levels; however, the growth of
L. monocytogenes
was markedly suppressed when cells of this species were present at lower concentrations than those of the other two species. Further, SEL was able to resuscitate acid- and cold-stressed cells, and recovery was comparable to that in nonselective tryptic soy broth containing 6% yeast extract but superior to that in the respective individual selective broths. SEL promoted the growth of all three pathogens in a mixture in ready-to-eat salami and in turkey meat samples. Moreover, each pathogen was readily detected by a pathogen-specific immunochromatographic lateral-flow or multiplex PCR assay. Even though the growth of each pathogen in SEL was comparable to that in UPB, SEL inhibited greater numbers of nontarget organisms than did UPB. In summary, SEL was demonstrated to be a promising new multiplex selective enrichment broth for the detection of the three most prominent food-borne pathogens by antibody- or nucleic acid-based methods.
Effector CD8+T Lymphocytes against Liver Stages ofPlasmodium yoeliiDo Not Require Gamma Interferon for Antiparasite Activity
Authors: Chakravarty Sumana , Baldeviano G. Christian , Overstreet Michael G. , Zavala Fidel
Published: June 2008

The protective immune response against liver stages of the malaria parasite critically requires CD8+T cells. Although the nature of the effector mechanism utilized by these cells to repress parasite development remains unclear, a critical role for gamma interferon (IFN-γ) has been widely assumed based on circumstantial evidence. However, the requirement for CD8+T-cell-mediated IFN-γ production in protective immunity to this pathogen has not been directly tested. In this report, we use an adoptive transfer strategy with circumsporozoite (CS) protein-specific transgenic T cells to examine the role of CD8+T-cell-derived IFN-γ production inPlasmodium yoelii-infected mice. We show that despite a marginal reduction in the expansion of naive IFN-γ-deficient CS-specific transgenic T cells, their antiparasite activity remains intact. Further, adoptively transferred IFN-γ-deficient CD8+T cells were as efficient as their wild-type counterparts in limiting parasite growth in naive mice. Taken together, these studies demonstrate that IFN-γ secretion by CS-specific CD8+T cells is not essential to protect mice against live sporozoite challenge.
Identification of the Origin of Transfer (oriT) and a New Gene Required for Mobilization of the SXT/R391 Family of Integrating Conjugative Elements
Authors: Ceccarelli Daniela , Daccord Aurélie , René Mélissa , Burrus Vincent
Published: June 2008

Integrating conjugative elements (ICEs) are self-transmissible, mobile elements that are widespread among bacteria. Following their excision from the chromosome, ICEs transfer by conjugation, a process initiated by a single-stranded DNA break at a specific locus called the origin of transfer (oriT). The SXT/R391 family of ICEs includes SXTMO10, R391, and more than 25 related ICEs found in gammaproteobacteria. A previous study mapped theoriTlocus of SXTMO10to a 550-bp intergenic region betweentraDand s043. We suspected that this was not the correctoriTlocus, because the identicaltraD-s043 region in R391 and other SXT/R391 family ICEs was annotated as a gene of an unknown function. Here, we investigated the location and structure of theoriTlocus in the ICEs of the SXT/R391 family and demonstrated thatoriTSXTcorresponds to a 299-bp sequence that contains multiple imperfect direct and inverted repeats and is located in the intergenic region between s003 andrumB′. TheoriTSXTlocus is well conserved among SXT/R391 ICEs, like R391, R997, and pMERPH, and cross-recognition oforiTSXTandoriTR391by R391 and SXTMO10was demonstrated. Furthermore, we identified a previously unannotated gene,mobI, located immediately downstream fromoriTSXT, which proved to be essential for SXTMO10transfer and SXTMO10-mediated chromosomal DNA mobilization. Deletion ofmobIdid not impair the SXTMO10-dependent transfer of the mobilizable plasmid CloDF13, suggesting thatmobIhas no role in the assembly of the SXTMO10mating pair apparatus. Instead,mobIappears to be involved in the recognition oforiTSXT.
Glutathione and Transition-Metal Homeostasis inEscherichia coli
Authors: Helbig Kerstin , Bleuel Corinna , Krauss Gerd J. , Nies Dietrich H.
Published: June 2008

Glutathione (GSH) and its derivative phytochelatin are important binding factors in transition-metal homeostasis in many eukaryotes. Here, we demonstrate that GSH is also involved in chromate, Zn(II), Cd(II), and Cu(II) homeostasis and resistance inEscherichia coli. While the loss of the ability to synthesize GSH influenced metal tolerance in wild-type cells only slightly, GSH was important for residual metal resistance in cells without metal efflux systems. In mutant cells without the P-type ATPase ZntA, the additional deletion of the GSH biosynthesis system led to a strong decrease in resistance to Cd(II) and Zn(II). Likewise, in mutant cells without the P-type ATPase CopA, the removal of GSH led to a strong decrease of Cu(II) resistance. The precursor of GSH, γ-glutamylcysteine (γEC), was not able to compensate for a lack of GSH. On the contrary, γEC-containing cells were less copper and cadmium tolerant than cells that contained neither γEC nor GSH. Thus, GSH may play an important role in trace-element metabolism not only in higher organisms but also in bacteria.
ATPase Activity and Oligomeric State of TrwK, the VirB4 Homologue of the Plasmid R388 Type IV Secretion System
Authors: Arechaga Ignacio , Peña Alejandro , Zunzunegui Sandra , del Carmen Fernández-Alonso María , Rivas Germán , de la Cruz Fernando
Published: June 2008

Type IV secretion systems (T4SS) mediate the transfer of DNA and protein substrates to target cells. TrwK, encoded by the conjugative plasmid R388, is a member of the VirB4 family, comprising the largest and most conserved proteins of T4SS. VirB4 was suggested to be an ATPase involved in energizing pilus assembly and substrate transport. However, conflicting experimental evidence concerning VirB4 ATP hydrolase activity was reported. Here, we demonstrate that TrwK is able to hydrolyze ATP in vitro in the absence of its potential macromolecular substrates and other T4SS components. The kinetic parameters of its ATPase activity have been characterized. The TrwK oligomerization state was investigated by analytical ultracentrifugation and electron microscopy, and its effects on ATPase activity were analyzed. The results suggest that the hexameric form of TrwK is the catalytically active state, much like the structurally related protein TrwB, the conjugative coupling protein.
Effect of a 5-min cold-water immersion recovery on exercise performance in the heat
Authors: Peiffer J J , Abbiss C R , Watson G , Nosaka K , Laursen P B
Published: June 2008

Background

This study examined the effect of a 5-min cold-water immersion (14°C) recovery intervention on repeated cycling performance in the heat.

Methods

10 male cyclists performed two bouts of a 25-min constant-paced (254 (22) W) cycling session followed by a 4-km time trial in hot conditions (35°C, 40% relative humidity). The two bouts were separated by either 15 min of seated recovery in the heat (control) or the same condition with 5-min cold-water immersion (5th—10th minute), using a counterbalanced cross-over design (CP1TT1→ CWI or CON → CP2TT2). Rectal temperature was measured immediately before and after both the constant-paced sessions and 4-km timed trials. Cycling economy and Vo2were measured during the constant-paced sessions, and the average power output and completion times were recorded for each time trial.

Results

Compared with control, rectal temperature was significantly lower (0.5 (0.4)°C) in cold-water immersion before CP2until the end of the second 4-km timed trial. However, the increase in rectal temperature (0.5 (0.2)°C) during CP2was not significantly different between conditions. During the second 4-km timed trial, power output was significantly greater in cold-water immersion (327.9 (55.7) W) compared with control (288.0 (58.8) W), leading to a faster completion time in cold-water immersion (6.1 (0.3) min) compared with control (6.4 (0.5) min). Economy and Vo2were not influenced by the cold-water immersion recovery intervention.

Conclusion

5-min cold-water immersion recovery significantly lowered rectal temperature and maintained endurance performance during subsequent high-intensity exercise. These data indicate that repeated exercise performance in heat may be improved when a short period of cold-water immersion is applied during the recovery period.