bluuebunny/crossref_metadata_2025 huggingface dataset:
Field emission properties of nanocrystalline chemically vapor deposited-diamond films
Authors: Gröning O. , Küttel O. M. , Gröning P. , Schlapbach L.
Published: July 2002

We have deposited nanocrystalline diamond films on p-type Si(100) substrates using plasma enhanced chemical vapor deposition (CVD). The diamond films were deposited at substrate temperatures between 950 and 980 °C using a high methane concentration of 5% in H2. The films obtained showed good field emission properties with threshold fields of around 5 V μm−1 (for 1 nA emission current). X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy showed that the nanocrystalline films still exhibit the basic electronic features of diamond with a band gap of 5.5 eV and a negative electron affinity when the surface is hydrogen plasma treated. The Fermi level position in these films is found to be 1±0.2 eV above the valence band maximum. The energy resolved field emission measurements show the typical asymmetric peak shape of Fowler-Nordheim (FN) tunneling through a surface potential barrier. The electrons emitted originate from a continuum of electronic states at the Fermi energy of the emitter. From a combined measurement of the field emitted electron energy distribution and the field emission I–V characteristic of an emitter we could independently determine the work function and the local electric field present at the emission site. In the case of nanocrystalline CVD diamond emitters we determined work function values around 5.7 eV and local fields in the range of 2000–3000 V μm−1 (for emission currents of 10–1000 pA). The corresponding field enhancement factors can range from 250 to 1700. Simultaneous field and photoelectron emission spectroscopy showed no indication of field penetration. Deviations from the FN law in the high current regime of the I–V plots may be related to an internal resistance of the emitter.
Independently contacted electron–hole gas heterostructures fabricated with focused ion beam doping during molecular beam epitaxial growth
Authors: Vijendran S. , Sazio P. J. A. , Beere H. E. , Jones G. A. C. , Ritchie D. A. , Norman C. E.
Published: July 2002

The successful combination of two mature technologies, molecular beam epitaxy (MBE) and focused ion beams into a single, versatile semiconductor growth system has recently been established. It has been shown that the focused ion MBE (FIMBE) system is able to produce spatially selected doping profiles of high quality material in both bulk-doped GaAs and modulation doped GaAs/AlGaAs heterostructures. With the versatility of a Au–Si–Be liquid metal ion source (LMIS), the range of devices that can be produced with three-dimensional topologies has been greatly increased. One such structure is the closely spaced, electron–hole gas heterostructure, which can be easily fabricated, and independently contacted using the FIMBE method. We have fabricated such structures with different barrier widths between the gases, and studied their low-temperature transport properties at various carrier densities.
Study of resolution limits due to intrinsic bias in chemically amplified photoresists
Authors: Postnikov Sergei V. , Stewart Michael D. , Tran Hoang Vi , Nierode Mark A. , Medeiros David R. , Cao T. , Byers Jeffrey , Webber Stephen E. , Wilson C. Grant
Published: July 2002

This article presents experimental results that suggest that classical Fickian diffusion cannot account for any significant fraction of the critical dimension bias observed in chemically amplified photoresists. A transport mechanism based on reaction front propagation is proposed as a possible explanation for the experimental observations.
Cluster formation during annealing of ultra-low-energy boron-implanted silicon
Authors: Collart E. J. H. , Murrell A. J. , Foad M. A. , van den Berg J. A. , Zhang S. , Armour D. , Goldberg R. D. , Wang T.-S. , Cullis A. G. , Clarysse T. , Vandervorst W.
Published: July 2002

The clustering of low-energy ion-implanted boron has been investigated. Two 1 keV boron implantations at doses of 1×1015 and 5×1015 cm−2 were annealed for 10 s between 700 and 1100 °C. The evolution of the boron concentration profiles was monitored using secondary ion mass spectrometry. Electrical activation was measured with four-point-probe measurements and spreading resistance profiling. The displaced Si concentration profiles were determined from medium-energy ion-scattering measurements.
High current density field emission from arrays of carbon nanotubes and diamond-clad Si tips
Authors: Tarntair F. G. , Chen L. C. , Wei S. L. , Hong W. K. , Chen K. H. , Cheng H. C.
Published: July 2002

Arrays of carbon nanotubes (CNT) and diamond-clad Si tips were grown by microwave plasma-enhanced chemical vapor deposition. The former ones were grown directly on prepatterned cobalt-coated silicon substrate, while the latter ones were grown on Si-tip arrays. Each array contains 50×50 emitting cells and each individual cell is 3 μm square. A maximum effective emission current density of about 17 A/cm2 (at a macroscopic field of 17.5 V/μm) has been demonstrated, while a macroscopic emission current density of 10 mA/cm2 with operating fields around 10 V/μm can be routinely achieved from an array of CNT emitters. In contrast, operating fields above 20 V/μm were needed to draw a comparable emission current density from all of the diamond-clad Si tips arrays. Emission stability test performed at 40 mA/cm2 for CNT arrays also showed little sign of degradation. Due to the high efficiency of electron emission, simple sample process, and large area growth capability, field emitter arrays based on CNT are attractive for flat panel display applications.
Properties of carbon-doped low-temperature GaAs and InP grown by solid-source molecular-beam epitaxy using CBr4
Authors: Liu W. K. , Lubyshev D. I. , Specht P. , Zhao R. , Weber E. R. , Gebauer J. , SpringThorpe A. J. , Streater R. W. , Vijarnwannaluk S. , Songprakob W. , Zallen R.
Published: July 2002

Carbon-doped GaAs and InP grown at low temperatures by molecular-beam epitaxy contain a high concentration of antisite defects which gives rise to ultrafast carrier trapping time and desirable radiation-hard properties. The use of CBr4 as the dopant source introduced significant bromine incorporation during low-temperature (LT) growth. Incomplete dissociation of the CBr4 molecules gives rise to the formation of C–Br complexes and results in a reduction of electrically active carbon concentration. In this work, we present our studies on the incorporation mechanism of C and Br in LT-GaAs and report on the effect of carbon and bromine incorporation on carrier lifetime and concentration of arsenic antisite defects. Preliminary results on LT-InP:C characterization are also presented.
Nota Bene: Why Did the Penguins Gasp?
Authors: Ash Caroline , Croft Samuel Ash
Published: July 2002

The Blue Planet
A Natural History of the Oceans. Andrew Byatt, Alastair Fothergill, and Martha Holmes. BBC One, Fall, 2001. Discovery Channel, January, 2002. Eight 50-minute episodes.

BBC Worldwide, London, 2001. 384 pp. £24.99. ISBN 0-563-38498-0. DK, New York, 2002. $40. ISBN 0-7894-8265-7.

This eight-part series from the BBC Natural History Unit is filled with breathtaking sequences that depict the ocean life and habitats from pole to pole and from high tide to the abyss.
History Explains Avian Patterns
Authors: Pruett-Jones Stephen
Published: July 2002

Evolutionary Ecology of Birds
Life Histories, Mating Systems and Extinction. Peter M. Bennett and Ian P. F. Owens. Oxford University Press, Oxford, 2002. 292 pp. $85, £49.50. ISBN 0-19-851088-8. Paper, $45, £24.95. ISBN 0-19-851089-6.

The authors use phylogenetic comparative methods to explore the evolutionary and ecological foundations of the diversity exhibited in avian life histories, reproductive behavior, and risks of extinction.
Putting a Human Face on a New Breed of Robot
Authors: Stone Richard
Published: July 2002

Tokyo--From the robot C-3PO of Star Wars fame to the android Data from the television series
Star Trek: The Next Generation,
people have dreamed of computers with human faces and feelings. Although getting machines to feel emotions is still out of reach, researchers at the Science University of Tokyo are developing a robot that can do the next best thing: recognize and display facial expressions. The robot looks much like a Japanese female mannequin, with a rubberized face and a shock of natural black hair. A computer hooked up to it can determine a displayed expression within 60 milliseconds by comparing the differences in position of facial features against stored templates for various expressions.
The Candidates Speak
Authors: Bischoff James R. , Kirn David H. , Williams Angelica , Heise Carla , Horn Sharon , Muna Mike , Ng Lelia , Nye Julie A. , Sampson-Johannes Adam , Fattaey Ali , McCormick Frank
Published: July 2002

An Adenovirus Mutant That Replicates Selectively in p53- Deficient Human Tumor Cells

The human adenovirus
E1B
gene encodes a 55-kilodalton protein that inactivates the cellular tumor suppressor protein p53. Here it is shown that a mutant adenovirus that does not express this viral protein can replicate in and lyse p53-deficient human tumor cells but not cells with functional p53. Ectopic expression of the 55-kilodalton EIB protein in the latter cells rendered them sensitive to infection with the mutant virus. Injection of the mutant virus into p53-deficient human cervical carcinomas grown in nude mice caused a significant reduction in tumor size and caused complete regression of 60 percent of the tumors. These data raise the possibility that mutant adenoviruses can be used to treat certain human tumors.
Cluster Mission to Rise From the Ashes
Authors: Hellemans Alexander
Published: July 2002

Paris—Europe's Cluster mission to study Earth's magnetosphere in unprecedented detail was blown up by a faulty launcher in June. But now a panel of scientific advisers has recommended to the European Space Agency that the four spacecraft be reconstructed and reflown around the turn of the century.
New Ideas Go With the Flow
Authors: Mervis Jeffrey
Published: July 2002

National Science Foundation director Neal Lane has taken on few new research initiatives during his 3 years at the agency's helm, but he is now trying to get three new research programs included in the president's budget request, to be released in February.
New Knockout Mice Point to Molecular Basis of Memory
Authors: Roush Wade
Published: July 2002

Neurobiologists have pinpointed the roots of memory in laboratory mice, by plucking out key proteins or adding an excess of them in particular clusters of brain cells. These feats at last offer direct confirmation of the reigning theory of how we remember and show how molecular changes affect the patterns of electrical activity that memories are made of.
A Mouse Model with Features of Familial Combined Hyperlipidemia
Authors: Masucci-Magoulas Lori , Goldberg Ira J. , Bisgaier Charles L. , Serajuddin Humaira , Francone Omar L. , Breslow Jan L. , Tall Alan R.
Published: July 2002

Familial combined hyperlipidemia (FCHL) is a common inherited lipid disorder, affecting 1 to 2 percent of the population in Westernized societies. Individuals with FCHL have large quantities of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) and develop premature coronary heart disease. A mouse model displaying some of the features of FCHL was created by crossing mice carrying the human apolipoprotein C-III (
APOC3
) transgene with mice deficient in the LDL receptor. A synergistic interaction between the apolipoprotein C-III and the LDL receptor defects produced large quantities of VLDL and LDL and enhanced the development of atherosclerosis. This mouse model may provide clues to the origin of human FCHL.
Thrust and Parry Over Nuclear Risks
Authors: Balter Michael
Published: July 2002

PARIS—
Claims about the health risks posed by nuclear-power installations are always controversial, but nowhere more so than in France, where some 75% of the nation's electricity is generated from nuclear energy. So, it was no surprise that publication of a study by two French epidemiologists earlier this month claiming to show a link between cases of childhood leukemia and the nuclear-waste reprocessing plant at La Hague on the Normandy coast sparked fireworks in the French press. Several French epidemiologists sharply criticized the study's methodology and conclusions. Their attacks have now drawn an unusual response from the
British Medical Journal
(
BMJ
), in which the paper appeared.
Deep-Sinking Slabs Stir the Mantle
Authors: Kerr Richard A.
Published: July 2002

SAN FRANCISCO
—For eons, pieces of Earth's ocean floor have vanished like the lost continent of Atlantis, sinking below the surface as part of the plate-tectonic cycle. Now, seismic images reveal that these slabs plummet deep into the Earth; the new work may end a long-running debate by showing that the slabs mix the Earth's mantle from top to bottom.
A New Recipe for Atom Condensates
Authors: Taubes Gary
Published: July 2002

A group at the University of Colorado and the National Institute of Standards and Technology in Boulder has serendipitously created two Bose-Einstein condensates—each one a crowd of atoms in a single quantum state—in a supercooled magnetic trap. Their cooling technique worked directly on only one of the condensates, but the other one cooled “sympathetically,” which suggests that the strategy could be used to condense
Japanese Mission Stretches Limits of Interferometry
Authors: Normile Dennis
Published: July 2002

TOKYO
—A new Japanese satellite, scheduled for launch on 7 February, should give radio astronomers a much better look at black holes and other extremely energetic objects in the universe. A successful mission is also expected to boost the fortunes of one of the country's premier research institutes as it seeks a larger role in Japan's exploration of space.
Assailing the Seasons
Authors: Forman Paul
Published: July 2002

The Flight from Science and Reason
. PAUL R. GROSS, NORMAN LEVITT, and MARTIN W. LEWIS, Eds. xii, 593 pp. New York Academy of Sciences, New York, 1996; $95, ISBN 1-57331-002-6. Paperback edition, Johns Hopkins University Press, Baltimore, MD, 1997; paper, $19.95, ISBN 0-8018-5676-0. Annals of the New York Academy of Sciences, vol. 775. From a conference, New York, May-June 1995.
A Cosmological Postulate
Authors: Wilczek Frank
Published: July 2002

The Inflationary Universe.
The Quest for a New Theory of Cosmic Origins. ALAN H. GUTH. Helix (Addison-Wesley), Reading, MA, 1997. xviii, 358 pp., illus. $25 or C$33.95. ISBN 0-201-14942-7.
Assessing Assessments
Authors: Bailar John C.
Published: July 2002

How Science Takes Stock.
A History of Meta-Analysis. MORTON HUNT. Russell Sage Foundation, New York, 1997. xii, 210 pp., illus. $29.95 or £24. ISBN 0-87154-389-3.
Ste5 RING-H2 Domain: Role in Ste4-Promoted Oligomerization for Yeast Pheromone Signaling
Authors: Inouye Carla , Dhillon Namrita , Thorner Jeremy
Published: July 2002

Ste5 is a scaffold for the mitogen-activated protein kinase (MAPK) cascade components in a yeast pheromone response pathway. Ste5 also associates with Ste4, the β subunit of a heterotrimeric guanine nucleotide–binding protein, potentially linking receptor activation to stimulation of the MAPK cascade. A RING-H2 motif at the Ste5 amino terminus is apparently essential for function because Ste5(C177S) and Ste5(C177A C180A) mutants did not rescue the mating defect of a
ste5Δ
cell. In vitro Ste5(C177A C180A) bound each component of the MAPK cascade, but not Ste4. Unlike wild-type Ste5, the mutant did not appear to oligomerize; however, when fused to a heterologous dimerization domain (glutathione S-transferase), the chimeric protein restored mating in an
ste5Δ
cell and an
ste4Δ ste5Δ
double mutant. Thus, the RING-H2 domain mediates Ste4-Ste5 interaction, which is a prerequisite for Ste5-Ste5 self-association and signaling.
A Modern Visionary
Authors: Porter Glenn
Published: July 2002

The One Best Way.
Frederick Winslow Taylor and the Enigma of Efficiency. ROBERT KANIGEL. Viking, New York, 1997. xii, 676 pp., illus. $34.95 or C$45. ISBN 0-670-86402-1. Sloan Technology Series.
Test of General Relativity and Measurement of the Lense-Thirring Effect with Two Earth Satellites
Authors: Ciufolini Ignazio , Pavlis Erricos , Chieppa Federico , Fernandes-Vieira Eduardo , Pérez-Mercader Juan
Published: July 2002

The Lense-Thirring effect, a tiny perturbation of the orbit of a particle caused by the spin of the attracting body, was accurately measured with the use of the data of two laser-ranged satellites, LAGEOS and LAGEOS II, and the Earth gravitational model EGM-96. The parameter μ, which measures the strength of the Lense-Thirring effect, was found to be 1.1 ± 0.2; general relativity predicts μ ≡ 1. This result represents an accurate test and measurement of one of the fundamental predictions of general relativity, that the spin of a body changes the geometry of the universe by generating space-time curvature.
Tree Species Diversity in Commercially Logged Bornean Rainforest
Authors: Cannon Charles H. , Peart David R. , Leighton Mark
Published: July 2002

The effects of commercial logging on tree diversity in tropical rainforest are largely unknown. In this study, selectively logged tropical rainforest in Indonesian Borneo is shown to contain high tree species richness, despite severe structural damage. Plots logged 8 years before sampling contained fewer species of trees greater than 20 centimeters in diameter than did similar-sized unlogged plots. However, in samples of the same numbers of trees (requiring a 50 percent larger area), logged forest contained as many tree species as unlogged forest. These findings warrant reassessment of the conservation potential of large tracts of commercially logged tropical rainforest.
Molecular Assembly and Encapsulation Directed by Hydrogen-Bonding Preferences and the Filling of Space
Authors: Martı́n Tomás , Obst Ulrike , Rebek Julius
Published: July 2002

Multiple copies of a molecule, held together in finite aggregates, give rise to properties and functions that are unique to their assembled states. Because these aggregates are held together by weak forces operating over short distances, a premium is placed on complementarity: The molecular surfaces must facilitate specific interactions that direct the assembly to one aggregate rather than another. Hydrogen-bonding preferences can be combined with molecular curvature to favor the assembly of four self-complementary subunits into a pseudo-spherical capsule. Filling the capsule with smaller, complementary molecules provides the final instruction for the assembly process.
Model Metaorganism
Authors: Bell Graham
Published: July 2002

Volvox

Molecular-Genetic Origins of Multicellularity and Cellular Differentiation. David L. Kirk. Cambridge University Press, Cambridge, 1998. 397 pp. $85. ISBN 0-521-45207-4.

This synthesis of genetic, evolutionary, and ecological analyses of
Volvox
and its unicellular and colonial relatives provides an excellent progress report on a model system for investigating the origins of multicellularity.
How Do Communities Come Together?
Authors: Gotelli Nicholas J.
Published: July 2002

Ecological Assembly Rules
Perspectives, advances, retreats. Evan Weiher and Paul Keddy, Eds. Cambridge University Press, Cambridge, 1999. 430 pp. $90, £55. ISBN 0-521-65235-9.

Although it fails to present any major breakthroughs or new syntheses, this collection of articles does a good job demonstrating the increasingly sophisticated use of null models to test assembly patterns of community ecology.
The Heavens in a Jewel Box
Authors: Pasachoff Jay M.
Published: July 2002

Rose Center for Earth and Space
. American Museum of Natural History. Central Park West at 81st Street, New York, NY 10024.
www.amnh.org/rose/

Through shows that use state-of-the-art projections systems and a variety of exhibits, the American Museum of Natural History's Rose Center for Earth and Space (the successor to the old Hayden Planetarium) offers visitors a multidimensional tour of the universe.
A Framework for Melittology
Authors: Roubik David W.
Published: July 2002

The Bees of the World
. Charles D. Michener. Johns Hopkins University Press, Baltimore, MD, 2000. 929 pp. $135, £93. ISBN 0-8018-6133-0.

As the capstone of his research over more than a half century, Michener offers a comprehensive taxonomic and phylogenetic framework for bee biology.
Television: Fade to Black?
Authors: Sugden Andrew
Published: July 2002

State of the Planet
. David Attenborough Director. BBC1, November, 2000. See:
www.bbc.co.uk/nature/earth/state_planet/

In a three-part series on BBC1, Attenborough offers a personal perspective on the impact humans are having on Earth and its biota through pollution, habitat loss and fragmentation, species introductions, and over harvesting. He also discusses steps that we might take to ensure future generations inhabit a healthy, diverse world.
Transmembrane Molecular Pump Activity of Niemann-Pick C1 Protein
Authors: Davies Joanna P. , Chen Fannie W. , Ioannou Yiannis A.
Published: July 2002

Niemann-Pick C1 (NPC1) disease is characterized by cholesterol accumulation in lysosomes and aberrant feedback regulation of cellular cholesterol homeostasis. We provide evidence that the NPC1 protein has homology with the resistance-nodulation-division (RND) family of prokaryotic permeases and may normally function as a transmembrane efflux pump. Studies of acriflavine loading in normal and NPC1 fibroblasts indicated that NPC1 uses a proton motive force to remove accumulated acriflavine from the endosomal/lysosomal system. Expression of NPC1 in
Escherichia coli
(i) facilitated the transport of acriflavine across the plasma membrane, causing cytosolic accumulation, and (ii) resulted in transport of oleic acid but not cholesterol or cholesterol-oleate across the plasma membrane. These studies establish NPC1 as a eukaryotic member of the RND permease family.
Two Efflux Systems Expressed Simultaneously in Multidrug-Resistant
Pseudomonas aeruginosa
Authors: Pumbwe Lilian , Piddock Laura J. V.
Published: July 2002

Simultaneous overexpression of MexAB-OprM and MexEF-OprN was demonstrated for a multiply antibiotic-resistant clinical isolate of
Pseudomonas aeruginosa
(G49). G49 also had decreased expression of OprF. No mutations in
mexR
or its upstream promoter region,
mexT
,
oprM
,
oprF
, or
sigX
were revealed, suggesting regulation by a hitherto undescribed locus.
In Vitro Synergistic Effects of Double and Triple Combinations of β-Lactams, Vancomycin, and Netilmicin against Methicillin-Resistant
Staphylococcus aureus
Strains
Authors: Rochon-Edouard Stéphanie , Pestel-Caron Martine , Lemeland Jean-François , Caron François
Published: July 2002

Several studies have previously reported synergistic effects between vancomycin and a given β-lactam or a given aminoglycoside against methicillin-resistant
Staphylococcus aureus
(MRSA) strains. The aim of our study was to exhaustively compare the effects of different combinations of a β-lactam, vancomycin, and/or an aminoglycoside against 32 clinical MRSA strains with different aminoglycoside susceptibility patterns. The effects of 26 different β-lactam–vancomycin and 8 different aminoglycoside-vancomycin combinations were first studied using a disk diffusion screening method. The best interactions with vancomycin were observed with either imipenem, cefazolin, or netilmicin. By checkerboard studies, imipenem-vancomycin and cefazolin-vancomycin each provided a synergistic bacteriostatic effect against 22 strains; the mean fractional inhibitory concentration (FIC) indexes were 0.35 and 0.46 for imipenem-vancomycin and cefazolin-vancomycin, respectively. The vancomycin-netilmicin combination provided an indifferent effect against all of the 32 strains tested; the mean of FIC index was 1.096. The mean concentrations of imipenem, cefazolin, netilmicin, and vancomycin at which FIC indexes were calculated were clinically achievable. Killing experiments were then performed using imipenem, cefazolin, netilmicin, and vancomycin at one-half of the MIC, alone and in different combinations, against 10 strains. The vancomycin-netilmicin regimen was rarely bactericidal, even against strains susceptible to netilmicin. The imipenem-vancomycin and cefazolin-vancomycin combinations were strongly bactericidal against six and five strains, respectively. The addition of netilmicin markedly enhanced the killing activity of the combination of cefazolin or imipenem plus vancomycin, but only for the MRSA strains against which the β-lactam–vancomycin combinations had no bactericidal effect. It is noteworthy that the latter strains were both susceptible to netilmicin and heterogeneously resistant to methicillin.
High-Level Fluoroquinolone-Resistant Clinical Isolates of
Escherichia coli
Overproduce Multidrug Efflux Protein AcrA
Authors: Mazzariol Annarita , Tokue Yutaka , Kanegawa Tiffany M. , Cornaglia Giuseppe , Nikaido Hiroshi
Published: July 2002

Immunoblotting with antibody against AcrA, an obligatory component of the AcrAB multidrug efflux system, showed that this protein was overexpressed by ≥170% in 9 of 10 clinical isolates of
Esherichia coli
with high-level ciprofloxacin resistance (MICs, ≥32 μg/ml) but not in any of the 15 isolates for which the MIC was ≤1 μg/ml.
OXA-24, a Novel Class D β-Lactamase with Carbapenemase Activity in an
Acinetobacter baumannii
Clinical Strain
Authors: Bou Germán , Oliver Antonio , Martínez-Beltrán Jesús
Published: July 2002

Acinetobacter baumannii
RYC 52763/97, a clinical isolate involved in a prolonged nosocomial outbreak at our hospital, was resistant to all β-lactams tested, including imipenem and meropenem, which had MICs of 128 and 256 μg/ml, respectively. This strain synthesized three β-lactamases: a plasmid-mediated TEM-1 β-lactamase (pI 5.4), an AmpC-type chromosomal cephalosporinase (pI 9.4), and a novel, presumptively chromosomally mediated OXA-related enzyme (pI 9.0) named OXA-24. After cloning and sequencing, the deduced amino acid sequence of the OXA-24 β-lactamase showed 40% homology with the OXA-10 (PSE-2) and OXA-7 β-lactamases, 39% homology with the OXA-11 and OXA-5 enzymes, and 33% homology with the LCR-1 β-lactamase. The amino acid sequence of the OXA-24 β-lactamase contained the STFK motif found in serine β-lactamases, but the typical class D triad KTG was replaced by KSG and the motif YGN was replaced by FGN. The OXA-24 β-lactamase hydrolyzed benzylpenicillin and cephaloridine but lacked activity against oxacillin, cloxacillin, and methicillin. The enzymatic activity was inhibited by chloride ions and by tazobactam (50% inhibitory concentration [IC
50
], 0.5 μM), sulbactam (IC
50
, 40 μM), and clavulanic acid (IC
50
, 50 μM). Carbapenem MICs for an
Escherichia coli
transformant (pBMB-1) expressing the cloned OXA-24 enzyme had a fourfold increase. Relative
V
max
/

K
m

values of 13 and 6 were obtained with imipenem and meropenem, respectively, and a positive microbiological assay result with imipenem was obtained with a purified enzymatic extract of this transformant strain. Therefore, we consider this new β-lactamase to be involved in the carbapenem resistance of
A. baumannii
RYC 52763/97.
Pharmacokinetics of Zidovudine Phosphorylation in Human Immunodeficiency Virus-Positive Thai Patients and Healthy Volunteers
Authors: Wattanagoon Yupaporn , Na Bangchang Kesara , Hoggard Patrick G. , Khoo Saye H. , Gibbons Sara E. , Phiboonbhanakit Danabhand , Karbwang Juntra , Back David J.
Published: July 2002

We assessed the pharmacokinetics of zidovudine (ZDV) in plasma and intracellular ZDV phosphate anabolites in peripheral blood mononuclear cells in Thai human immunodeficiency virus (HIV) type 1-infected patients and healthy volunteers. The plasma ZDV area under the concentration-time curve from 0 to 6 h (AUC
0–6
) was similar in patients and healthy volunteers (32.77 and 22.77 μmol/liter · h, respectively; confidence interval, −3.37 to 19.92). Although the concentration of ZDV triphosphate (ZDVTP) was similar in the two groups, the ZDV monophosphate (ZDVMP) AUC
0–6
was significantly greater in HIV patients (1.12 pmol/10
6
cells) than in healthy volunteers (0.15 pmol/10
6
cells). In agreement with previously published data obtained with Caucasians, the significant difference in intracellular phosphorylation in Thai volunteers and HIV patients is primarily due to ZDVMP. Comparing the data from this study with the data obtained with Caucasians suggests no marked ethnic differences in ZDV phosphorylation.
Activity of Moxifloxacin by Itself and in Combination with Ethambutol, Rifabutin, and Azithromycin In Vitro and In Vivo against
Mycobacterium avium
Authors: Bermudez Luiz E. , Inderlied Clark B. , Kolonoski Peter , Petrofsky Mary , Aralar Priscilla , Wu Martin , Young Lowell S.
Published: July 2002

Moxifloxacin activity against
Mycobacterium avium
complex (MAC) was evaluated in vitro against 25 strains. The MIC was determined to range from 0.125 to 2.0 μg/ml. In addition, U937 macrophage monolayers infected with MAC strain 101 (serovar 1) were treated with moxifloxacin (0.25 to 8 μg/ml) daily, and the number of intracellular bacteria was quantitated after 4 days. Moxifloxacin showed inhibitory activity at 0.5 μg/ml and higher. To assess the activity of moxifloxacin containing regimens in vivo, we infected C57BL
bg
+
/
bg
+
mice with 3 × 10
7
MAC strain 101 bacteria intravenously. One week later treatment was begun with the following: (i) moxifloxacin (50 mg/kg/day or 100 mg/kg/day), ethambutol (100 mg/kg/day), or a combination of moxifloxacin and ethambutol; or (ii) moxifloxacin (100 mg/kg/day), azithromycin (200 mg/kg/day), or rifabutin (40 mg/kg/day) as oral monotherapy; or (iii) all permutations of two-drug therapy or all three drugs in combination. All groups contained at least 14 animals, and the control group received the drug vehicle. After 4 weeks, quantitative blood cultures were obtained and the number of bacteria in liver and spleen was quantitated. Moxifloxacin, ethambutol, and azithromycin were active as single agents in liver, spleen, and blood. Rifabutin showed inhibitory activity only in the blood. Two-drug combinations containing azithromycin were no more active than azithromycin alone. Similarly, the three-drug combination was not more active than azithromycin alone in the spleen. Rifabutin did not add to the activity of any other single agent or two-drug combination. Moxifloxacin at both concentrations in combination with ethambutol was significantly more active than each drug alone.
Antimalarial Drugs Clear Resistant Parasites from Partially Immune Hosts
Authors: Cravo Pedro , Culleton Richard , Hunt Paul , Walliker David , Mackinnon Margaret J.
Published: July 2002

Circumstantial evidence in human malaria suggests that elimination of parasites by drug treatment meets higher success rates in individuals having some background immunity. In this study, using the rodent malaria model
Plasmodium chabaudi
, we show that drug-resistant parasites can be cleared by drugs when the host is partially immune.
Streptococcus pneumoniae
Isolates with Reduced Susceptibility to Ciprofloxacin in Spain: Clonal Diversity and Appearance of Ciprofloxacin-Resistant Epidemic Clones
Authors: Alou Luis , Ramirez Mario , Garcı́a-Rey César , Prieto José , de Lencastre Hermı́nia
Published: July 2002

Analysis of the pulsed-field gel electrophoretic profiles of 82 pneumococcal isolates with reduced susceptibility to ciprofloxacin (RSC) and of 90 co-occurring susceptible isolates indicates a considerable genetic diversity among isolates with RCS and points to a close relation between the two groups. This finding suggests that pneumococci with RCS emerge through independent mutational events.
Circulating Metabolites of the Human Immunodeficiency Virus Protease Inhibitor Nelfinavir in Humans: Structural Identification, Levels in Plasma, and Antiviral Activities
Authors: Zhang Kanyin E. , Wu Ellen , Patick Amy K. , Kerr Bradley , Zorbas Mark , Lankford Angela , Kobayashi Takuo , Maeda Yuki , Shetty Bhasker , Webber Stephanie
Published: July 2002

Nelfinavir mesylate (Viracept, formally AG1343) is a potent and orally bioavailable human immunodeficiency virus (HIV) type 1 (HIV-1) protease inhibitor (
K

i

= 2 nM) and is being widely prescribed in combination with HIV reverse transcriptase inhibitors for the treatment of HIV infection. The current studies evaluated the presence of metabolites circulating in plasma following the oral administration of nelfinavir to healthy volunteers and HIV-infected patients, as well as the levels in plasma and antiviral activities of these metabolites. The results showed that the parent drug was the major circulating chemical species, followed in decreasing abundance by its hydroxy-
t
-butylamide metabolite (M8) and 3′-methoxy-4′-hydroxynelfinavir (M1). Antiviral assays with HIV-1 strain RF-infected CEM-SS cells showed that the 50% effective concentrations (EC
50
) of nelfinavir, M8, and M1 were 30, 34, and 151 nM, respectively, and that the corresponding EC
50
against another HIV-1 strain, IIIB, in MT-2 cells were 60, 86, and 653 nM. Therefore, apparently similar in vitro antiviral activities were demonstrated for nelfinavir and M8, whereas an approximately 5- to 11-fold-lower level of antiviral activity was observed for M1. The active metabolite, M8, showed a degree of binding to human plasma proteins similar to that of nelfinavir (ca
.
98%). Concentrations in plasma of nelfinavir and its metabolites in 10 HIV-positive patients receiving nelfinavir therapy (750 mg three times per day) were determined by a liquid chromatography tandem mass spectrometry assay. At steady state (day 28), the mean plasma nelfinavir concentrations ranged from 1.73 to 4.96 μM and the M8 concentrations ranged from 0.55 to 1.96 μM, whereas the M1 concentrations were low and ranged from 0.09 to 0.19 μM. In conclusion, the findings from the current studies suggest that, in humans, nelfinavir forms an active metabolite circulating at appreciable levels in plasma. The active metabolite M8 may account for some of the antiviral activity associated with nelfinavir in the treatment of HIV disease.
In Vitro Activity of Clarithromycin against Intracellular
Helicobacter pylori
Authors: Piccolomini Raffaele , Di Bonaventura Giovanni , Picciani Carla , Laterza Francesco , Vecchiet Jacopo , Neri Matteo
Published: July 2002

The in vitro intracellular effect of clarithromycin, amoxicillin, metronidazole, lansoprazole, and rifabutin, tested at concentrations corresponding to one times the MIC, two times the MIC, and four times the MIC, was evaluated against an invasive
Helicobacter pylori
strain. At four times the MIC, clarithromycin showed an early bactericidal effect within 4 h of incubation and, in determining the complete killing within a 16 h-incubation period, lansoprazole and rifabutin showed comparable activity, yielding bactericidal activities within 4 and 8 h of incubation, respectively. Amoxicillin and metronidazole showed bacteriostatic activity only.
PCR Assays That Identify the Grapevine Dieback FungusEutypa lata
Authors: Lecomte Pascal , Péros Jean-Pierre , Blancard Dominique , Bastien Nicolas , Délye Christophe
Published: July 2002

Eutypa latais the causal fungal agent ofEutypadieback, a serious grapevine necrotic disease. The erratic and delayed (1 to 2 months) appearance of characteristic conidia on culture media and the presence of numerous microorganisms in decaying wood make it difficult either to identify or to detectE. latain grapevine wood samples. We designed six pairs of PCR primers for diagnosis ofE. lata. Three primer pairs were derived from ribosomal DNA internal transcribed spacer sequences, and three pairs were derived from randomly amplified polymorphic DNA fragments. The six primer pairs could be used to amplify DNAs extracted from all of theE. lataisolates tested. They did not amplify DNAs from fungi and bacteria representing more than 50 different species of microorganisms associated with grapevine. We developed a simple protocol, leading to a rapid release of DNA, that enabled us to identifyE. latafrom pure or mixed cultures as well as from grapevine wood samples. Identification ofE. latain wood was achieved within a few hours, instead of the several weeks required for classical cultures on agar medium. We believe that the procedure described here can be adapted to detect other microorganisms involved in woody plant diseases.
Expression of the
Staphylococcus hyicus
Lipase in
Lactococcus lactis
Authors: Drouault Sophie , Corthier Gerard , Ehrlich S. Dusko , Renault Pierre
Published: July 2002

The extracellular
Staphylococcus hyicus
lipase was expressed under the control of different promoters in
Lactococcus lactis
and
Bacillus subtilis
. Its expression at high and moderate levels is toxic for the former and the latter hosts, respectively. In
L. lactis
, the lipase was expressed at a high level, up to 30% of the total cellular proteins, under the control of the inducible promoter P
nisA
. About 80% of the lipase remained associated with the cells. Close to half of this amount remained associated with the inner side of the cytoplasmic membrane as unprocessed pre-pro-lipase. The other half was trapped by the cell wall and partially degraded at the N-terminal end. This result suggests that extracellular proteases degrade the lipase. Surprisingly, the kinetics and the pattern of lipase degradation were different in the two
L. lactis
subspecies,
L. lactis
subsp.
cremoris
and
L. lactis
subsp.
lactis
. The extracellular proteolytic systems that degrade lipase are thus different in these closely related subspecies. The incorrect export of the lipase is not due to an inappropriate leader peptide but may be due to an inefficiency of several steps of lipase secretion. We propose that (i) the
S. hyicus
lipase may require a special accessory system to be correctly exported or (ii) the kinetics of lipase synthesis may be a critical factor for proper folding.
Quantification of
Hyphomicrobium
Populations in Activated Sludge from an Industrial Wastewater Treatment System as Determined by 16S rRNA Analysis
Authors: Layton A. C. , Karanth P. N. , Lajoie C. A. , Meyers A. J. , Gregory I. R. , Stapleton R. D. , Taylor D. E. , Sayler G. S.
Published: July 2002

The bacterial community structure of the activated sludge from a 25 million-gal-per-day industrial wastewater treatment plant was investigated using rRNA analysis. 16S ribosomal DNA (rDNA) libraries were created from three sludge samples taken on different dates. Partial rRNA gene sequences were obtained for 46 rDNA clones, and nearly complete 16S rRNA sequences were obtained for 18 clones. Seventeen of these clones were members of the beta subdivision, and their sequences showed high homology to sequences of known bacterial species as well as published 16S rDNA sequences from other activated sludge sources. Sixteen clones belonged to the alpha subdivision, 7 of which showed similarity to
Hyphomicrobium
species. This cluster was chosen for further studies due to earlier work on
Hyphomicrobium
sp. strain M3 isolated from this treatment plant. A nearly full-length 16S rDNA sequence was obtained from
Hyphomicrobium
sp. strain M3. Phylogenetic analysis revealed that
Hyphomicrobium
sp. strain M3 was 99% similar to
Hyphomicrobium denitrificans
DSM 1869
T
in
Hyphomicrobium
cluster II. Three of the cloned sequences from the activated sludge samples also grouped with those of
Hyphomicrobium
cluster II, with a 96% sequence similarity to that of
Hyphomicrobium
sp. strain M3. The other four cloned sequences from the activated sludge sample were more closely related to those of the
Hyphomicrobium
cluster I organisms (95 to 97% similarity). Whole-cell fluorescence hybridization of microorganisms in the activated sludge with genus-specific
Hyphomicrobium
probe S-G-Hypho-1241-a-A-19 enhanced the visualization of
Hyphomicrobium
and revealed that
Hyphomicrobium
appears to be abundant both on the outside of flocs and within the floc structure. Dot blot hybridization of activated sludge samples from 1995 with probes designed for
Hyphomicrobium
cluster I and
Hyphomicrobium
cluster II indicated that
Hyphomicrobium
cluster II-positive 16S rRNA dominated over
Hyphomicrobium
cluster I-positive 16S rRNA by 3- to 12-fold.
Hyphomicrobium
16S rRNA comprised approximately 5% of the 16S rRNA in the activated sludge.
Comparison of
Cryptosporidium parvum
Viability and Infectivity Assays following Ozone Treatment of Oocysts
Authors: Bukhari Z. , Marshall M. M. , Korich D. G. , Fricker C. R. , Smith H. V. , Rosen J. , Clancy J. L.
Published: July 2002

Several in vitro surrogates have been developed as convenient, user-friendly alternatives to mouse infectivity assays for determining the viability of
Cryptosporidium parvum
oocysts. Such viability assays have been used increasingly to determine oocyst inactivation following treatment with chemical, physical, or environmental stresses. Defining the relationship between in vitro viability assays and oocyst infectivity in susceptible hosts is critical for determining the significance of existing oocyst inactivation data for these in vitro assays and their suitability in future studies. In this study, four viability assays were compared with mouse infectivity assays, using neonatal CD-1 mice. Studies were conducted in the United States and United Kingdom using fresh (<1 month) or environmentally aged (3 months at 4°C) oocysts, which were partially inactivated by ozonation before viability and/or infectivity analyses. High levels of variability were noted within and between the viability and infectivity assays in the U.S. and United Kingdom studies despite rigorous control over oocyst conditions and disinfection experiments. Based on the viability analysis of oocyst subsamples from each ozonation experiment, SYTO-59 assays demonstrated minimal change in oocyst viability, whereas 4′,6′-diamidino-2-phenylindole–propidium iodide assays, in vitro excystation, and SYTO-9 assays showed a marginal reduction in oocyst viability. In contrast, the neonatal mouse infectivity assay demonstrated significantly higher levels of oocyst inactivation in the U.S. and United Kingdom experiments. These comparisons illustrate that four in vitro viability assays cannot be used to reliably predict oocyst inactivation following treatment with low levels of ozone. Neonatal mouse infectivity assays should continue to be regarded as a “gold standard” until suitable alternative viability surrogates are identified for disinfection studies.
Glucose Uptake in
Clostridium beijerinckii
NCIMB 8052 and the Solvent-Hyperproducing Mutant BA101
Authors: Lee Jieun , Blaschek H. P.
Published: July 2002

Glucose uptake and accumulation by
Clostridium beijerinckii
BA101, a butanol hyperproducing mutant, were examined during various stages of growth. Glucose uptake in
C. beijerinckii
BA101 was repressed 20% by 2-deoxyglucose and 25% by mannose, while glucose uptake in
C. beijerinckii
8052 was repressed 52 and 28% by these sugars, respectively. We confirmed the presence of a phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) associated with cell extracts of
C. beijerinckii
BA101 by glucose phosphorylation by PEP. The PTS activity associated with
C. beijerinckii
BA101 was 50% of that observed for
C. beijerinckii
8052.
C. beijerinckii
BA101 also demonstrated lower PTS activity for fructose and glucitol. Glucose phosphorylation by cell extracts derived from both
C. beijerinckii
BA101 and 8052 was also dependent on the presence of ATP, a finding consistent with the presence of glucokinase activity in
C. beijerinckii
extracts. ATP-dependent glucose phosphorylation was predominant during the solventogenic stage, when PEP-dependent glucose phosphorylation was dramatically repressed. A nearly twofold-greater ATP-dependent phosphorylation rate was observed for solventogenic stage
C. beijerinckii
BA101 than for solventogenic stage
C. beijerinckii
8052. These results suggest that
C. beijerinckii
BA101 is defective in PTS activity and that
C. beijerinckii
BA101 compensates for this defect with enhanced glucokinase activity, resulting in an ability to transport and utilize glucose during the solventogenic stage.
Oxidative Transformation of Aminodinitrotoluene Isomers by Multicomponent Dioxygenases
Authors: Johnson Glenn R. , Smets Barth F. , Spain Jim C.
Published: July 2002

The electron-withdrawing nitro substituents of 2,4,6-trinitrotoluene (TNT) make the aromatic ring highly resistant to oxidative transformation. The typical biological transformation of TNT involves reduction of one or more of the nitro groups of the ring to produce the corresponding amine. Reduction of a single nitro substituent of TNT to an amino substituent increases the electron density of the aromatic nucleus considerably. The comparatively electron-dense nuclei of the aminodinitrotoluene (ADNT) isomers would be expected to be more susceptible to oxygenase attack than TNT. The hypothesis was tested by evaluating three nitroarene dioxygenases for the ability to hydroxylate the ADNT isomers. The predominant reaction was dioxygenation of the ring to yield nitrite and the corresponding aminomethylnitrocatechol. A secondary reaction was benzylic monooxygenation to form aminodinitrobenzyl alcohol. The substrate preferences and catalytic specificities of the three enzymes differed considerably. The discovery that the ADNT isomers are substrates for the nitroarene dioxygenases reveals the potential for extensive bacterial transformation of TNT under aerobic conditions.
Combined Molecular and Biochemical Approach Identifies
Aspergillus japonicus
and
Aspergillus aculeatus
as Two Species
Authors: Pařenicová Lucie , Skouboe Pernille , Frisvad Jens , Samson Robert A. , Rossen Lone , ten Hoor-Suykerbuyk Marjon , Visser Jaap
Published: July 2002

We examined nine
Aspergillus japonicus
isolates and 10
Aspergillus aculeatus
isolates by using molecular and biochemical markers, including DNA sequences of the ITS1-5.8S rRNA gene-ITS2 region, restriction fragment length polymorphisms (RFLP), and secondary-metabolite profiles. The DNA sequence of the internal transcribed spacers (ITS1 and ITS2) and the 5.8S rRNA gene could not be used to distinguish between
A. japonicus
and
A. aculeatus
but did show that these two taxa are more closely related to each other than to other species of black aspergilli.
Aspergillus niger
pyruvate kinase (
pki
A) and pectin lyase A (
pel
A) and
Agaricus bisporus
28S rRNA genes, which were used as probes in the RFLP analysis, revealed clear polymorphism between these two taxa. The
A. niger pki
A and
pel
A probes placed six strains in an
A. japonicus
group and 12 isolates in an
A. aculeatus
group, which exhibited intraspecific variation when they were probed with the
pel
A gene. The secondary-metabolite profiles supported division of the isolates into the two species and differed from those of other black aspergilli. The strains classified as
A. japonicus
produced indole alkaloids and a polar metabolite, while the
A. aculeatus
isolates produced neoxaline, okaramins, paraherquamidelike compounds, and secalonic acid.
A. aculeatus
CBS 114.80 showed specific RFLP patterns for all loci examined. The secondary-metabolite profile of strain CBS 114.80 also differed from those of
A. japonicus
and
A. aculeatus
. Therefore, this strain probably represents a third taxon. This study provides unambiguous criteria for establishing the taxonomic positions of isolates of black aspergilli, which are important in relation to industrial use and legal protection of these organisms.