bluuebunny/crossref_metadata_2025 huggingface dataset:
Classical and quasiclassical spectral analysis of CH5+ using an ab initio potential energy surface
Authors: Brown Alex , Braams Bastiaan J. , Christoffel Kurt , Jin Zhong , Bowman Joel M.
Published: October 2003

We report a potential energy surface and calculations of power spectra for CH5+. The potential surface is obtained by precise fitting of MP2/cc-pVTZ electronic energies and gradients, which are obtained in classical direct-dynamics calculations. The power spectra are obtained using standard microcanonical classical and novel quasiclassical calculations of the velocity autocorrelation function, from which the power spectrum is obtained in the usual way. Both calculations agree qualitatively that the overall spectrum is quite complex; however, the latter calculations indicate that some spectral features may be assignable.
Population inversion by resonant magnetic confinement in terahertz quantum-cascade lasers
Authors: Scalari Giacomo , Blaser Stéphane , Ajili Lassaad , Faist Jérôme , Beere Harvey , Linfield Edmund , Ritchie David , Davies Giles
Published: October 2003

Ultralow-threshold terahertz laser emission exploiting in-plane confinement arising from perpendicular magnetic field applied on a quantum-cascade structure is reported. A special design strategy has been adopted that takes advantage of the selective opening and closing of relaxation channels by elastic scattering between Landau levels. The key effect is a reduction of the lower state lifetime of the lasing transition that produces population inversion. The structure shows laser action only with applied magnetic field and yields threshold current densities as low as 19 A/cm2 at 4.2 K and 32 A/cm2 at 60 K at a frequency of 3.6 THz.
Ultrafast intraband spectroscopy of electron capture and relaxation in InAs/GaAs quantum dots
Authors: Müller T. , Schrey F. F. , Strasser G. , Unterrainer K.
Published: October 2003

The electron capture and relaxation dynamics in self-assembled InAs/GaAs quantum dots (QDs) is investigated by means of interband-pump–intraband-probe spectroscopy. By tuning femtosecond infrared pulses into resonance with intraband transitions between confined QD states and the wetting layer continuum, the electron population of the QD ground and first excited states is determined as a function of time delay after the interband pump. Our experiments indicate that the most efficient relaxation pathway into the QD ground state is the stepwise relaxation through the excited states of the dot. The capture time at room temperature decreases from 2.8 to 1.5 ps with increasing excitation density above a certain threshold, and changes only slightly at low excitation densities. At low temperature (T=5 K), we determine a longer capture time of 4.7 ps.
Thermal emission of electrons from selected s-shell configurations in InAs/GaAs quantum dots
Authors: Engström O. , Malmkvist M. , Fu Y. , Olafsson H. Ö. , Sveinbjörnsson E. Ö.
Published: October 2003

The thermal emission of electrons from self-assembled InAs/GaAs quantum dots, prepared by molecular-beam epitaxy, with an average base/height size of 20 nm/11 nm in Schottky diodes has been investigated using deep level transient spectroscopy (DLTS). By applying an appropriate set of voltage pulses across the Schottky diode, the two different s-electron configurations have been investigated separately. This avoids the problem of interference between overlapping peaks in DLTS data. We find that a difference in activation energy for the thermal electron emission between the two configurations agrees with expected variation in electron energy levels due to the size distribution of the quantum dots.
Characterization of 7-nm-thick strained Ge-on-insulator layer fabricated by Ge-condensation technique
Authors: Nakaharai Shu , Tezuka Tsutomu , Sugiyama Naoharu , Moriyama Yoshihiko , Takagi Shin-ichi
Published: October 2003

A strained Ge-on-insulator (GOI) structure with a 7-nm-thick Ge layer was fabricated for applications to high-speed transistors. The GOI layer was formed by thermal oxidation of a strained SiGe layer grown epitaxially on a silicon-on-insulator (SOI) wafer. In transmission electron microscopy measurements, the obtained GOI layer exhibited a single-crystal structure with the identical orientation to an original SOI substrate and a smooth Ge/SiO2 interface. The rms of the surface roughness of the GOI layer was evaluated to be 0.4 nm by atomic force microscopy. The residual Si fraction in the GOI layer was estimated to be lower than the detection limit of Raman spectroscopy of 0.5% and also than the electron energy loss spectroscope measurements of 3%. It was found that the obtained GOI layer was compressively strained with a strain of 1.1%, which was estimated by the Raman spectroscopy. Judging from the observed crystal quality and the strain value, this technique is promising for fabrication of high-mobility strained Ge channel of high-performance GOI metal–insulator–semiconductor (MIS) transistors.
Widening of optical bandgap of polycrystalline InN with a few percent incorporation of oxygen
Authors: Yoshimoto Masahiro , Yamamoto Hiroaki , Huang Wei , Harima Hiroshi , Saraie Junji , Chayahara Akiyoshi , Horino Yuji
Published: October 2003

The absolute concentration of oxygen in polycrystalline InN was measured using a combination of Rutherford backscattering and x-ray photoemission spectroscopy. Polycrystalline InN was grown on quartz and glassy carbon at 500 °C by molecular-beam epitaxy using In metal and activated nitrogen species generated in rf plasma. The optical bandgap of polycrystalline InN increased from 1.55 to 2.27 eV with increasing oxygen concentration from 1% to 6%. Polycrystalline InN with an optical bandgap of 1.9 eV, which has often been reported, contains oxygen of a molar fraction of 3%.
Complete characterization of the nonlinear spatial distribution induced in poled silica glass with a submicron resolution
Authors: Kudlinski A. , Quiquempois Y. , Lelek M. , Zeghlache H. , Martinelli G.
Published: October 2003

The evolution of the second-harmonic signal is monitored as the poled sample is etched with hydrofluoric acid. The sample thickness is measured in real time using an interferometric method. The full set of data allows us to fully reconstruct the nonlinear spatial distribution created inside the glass, whatever the nonlinearities’ origin.
Transmission of high-power CO2 laser pulses through a plasma channel
Authors: Pogorelsky I. V. , Pavlishin I. V. , Ben-Zvi I. , Kumita T. , Kamiya Y. , Hirose T. , Greenberg B. , Kaganovich D. , Zigler A. , Andreev N. , Bobrova N. , Sasorov P.
Published: October 2003

A 5 J, 180 ps CO2 laser pulse is channeled by a 17 mm long capillary discharge. Plasma dynamic simulations confirm occurrence of optical guiding conditions along a plasma column of a quasiparabolic radial profile with the minimum axial free-electron density ∼1017 cm−3.
Growth of cubic InN on r-plane sapphire
Authors: Cimalla V. , Pezoldt J. , Ecke G. , Kosiba R. , Ambacher O. , Spieß L. , Teichert G. , Lu H. , Schaff W. J.
Published: October 2003

InN has been grown directly on r-plane sapphire substrates by plasma-enhanced molecular-beam epitaxy. X-ray diffraction investigations have shown that the InN layers consist of a predominant zinc blende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase which content increases with proceeding growth. The lattice constant for zinc blende InN was found to be a=4.986 Å. For this unusual growth of a metastable cubic phase on a noncubic substrate an epitaxial relationship was proposed where the metastable zinc blende phase grows directly on the r-plane sapphire while the wurtzite phase arises as the special case of twinning in the cubic structure.
Voltage-controlled spectral tuning of photoelectric signals in a conducting polymer-bacteriorhodopsin device
Authors: Manoj A. G. , Narayan K. S.
Published: October 2003

Bacteriorhodopsin (bR), a protein existing in the halobacterial purple membrane serves as a light-driven pump which sets up an electrochemical gradient and transports protons across the cell membrane. In this report, we explore the synergetic processes at a conducting polymer/bR interface due to photoexcitation in presence of a voltage bias. The possibility of changing the oxidation state of the polymer electrochemically is coupled to the optically activated proton gradient in the bR side. This approach of controlling the nature of the conducting polymer-bR interface demonstrates a facile route to stabilize the deprotonated, long-lived intermediate state present in the bR photocycle. These processes result in interesting solid-state device properties such as incident-wavelength-controlled rectification of the photoinduced current and voltage-controlled spectral responses.
Carbonate formation during post-deposition ambient exposure of high-k dielectrics
Authors: Gougousi Theodosia , Niu Dong , Ashcraft Robert W. , Parsons Gregory N.
Published: October 2003

When thick films of group-III (La, Y)- and group-IV (Hf, Zr)-based high-k dielectrics are exposed to ambient for several months, Fourier transform infrared spectroscopy shows formation of carbonate species in the film bulk, likely due to reaction with atmospheric CO2. Group-III-based films show signs of carbonate feature growth within 10 min of air exposure, especially in films processed at relatively low temperatures (<600 °C). Carbonate formation is verified also for group-IV-based films, but at a significantly reduced concentration. Post-exposure annealing can reduce the carbonate observed in the IR spectra. However, post-exposure annealing likely does not remove carbon contamination, and it results in interface silicon oxide growth. The observed reactions of high-k films with the ambient may impose significant constraints on the post-deposition handling of high-k films.
In situ spectroscopic measurement of transmitted light related to defect formation in SiO2 during femtosecond laser irradiation
Authors: Fukata N. , Yamamoto Y. , Murakami K. , Hase M. , Kitajima M.
Published: October 2003

We measured real-time spectra of light transmitted through SiO2 specimens during irradiation of amplified ultrashort laser with a fluence of 540 mJ/cm2. The real-time spectra exhibit a peak at around 400 nm, which significantly depends on the irradiation time. The observation and identification of defects were performed by measurements of electron spin resonance (ESR). Both dependences of the peak at around 400 nm on irradiation time and laser power are in good agreement with those of the ESR signal intensity of positively charged oxygen vacancies (E′ center). This strong correlation shows that self-trapped excitons are created followed by the formation of the E′ center and finally that of ESR inactive centers, namely, oxygen-deficiency centers.
Groove-binding unsymmetrical cyanine dyes for staining of DNA: syntheses and characterization of the DNA-binding
Authors: Karlsson H. Jonas , Eriksson Maja , Perzon Erik , Åkerman Björn , Lincoln Per , Westman Gunnar
Published: October 2003

Two new crescent-shaped unsymmetrical cyanine dyes have been synthesised and their interactions with DNA have been investigated by different spectroscopic methods. These dyes are analogues to a minor groove binding unsymmetrical cyanine dye, BEBO, recently reported by us. In this dye, the structure of the known intercalating cyanine dye BO was extended with a benzothiazole substituent. To investigate how the identity of the extending heterocycle affects the binding to DNA, the new dyes BETO and BOXTO have a benzothiazole group and a benzoxazole moiety, respectively. Whereas BEBO showed a heterogeneous binding to calf thymus DNA, linear and circular dichroism studies of BOXTO indicate a high preference for minor groove binding. BETO also binds in the minor groove to mixed sequence DNA but has a contribution of non-ordered and non-emissive species present. A non-intercalative binding mode of the new dyes, as well as for BEBO, is further supported by electrophoresis unwinding assays. These dyes, having comparable spectral properties as the intercalating cyanine dyes, but bind in the minor groove instead, might be useful complements for staining of DNA. In particular, the benzoxazole substituted dye BOXTO has attractive fluorescence properties with a quantum yield of 0.52 when bound to mixed sequence DNA and a 300-fold increase in fluorescence intensity upon binding.
Women and the Art of Peacemaking: Data from Israeli‐Palestinian Interactive Problem‐Solving Workshops
Authors: Pearson d'Estree Tamra , Babbitt Eileen F.
Published: October 2003

Are women “natural” peacemakers? If so, is this because of natural inclinations to avoid conflict or to engage in tough discussions? Are there particular skills in which women excel that make them more likely than their male counterparts to be able to build relational bridges, to facilitate negotiations, and to reduce tensions? After a review of the literature on gender differences in such skills, a systematic comparison of interaction quality is made between two Israeli‐Palestinian interactive problem‐solving workshops that differed only in gender composition. A third Israeli‐Palestinian workshop that involved female political elites is also examined for subsequent changes in the conflict relationship or for changes in political activity. The implications of different repertoires of skills for altering political processes are discussed.
Nozick, Prohibition, and No‐Fault Motor Insurance
Authors: Handfield Toby
Published: October 2003

ABSTRACT No‐fault insurance schemes involve prohibiting exercise of the natural rights of individuals to recover damages from those whose negligence causes them harm. Public debate about no‐fault emphasises consequentialist benefits, and takes little account of the putative rights of individuals to recovery. I argue, however, that even on a relatively extreme rights‐based conception of justice, such as Robert Nozick’s, it may be possible to justify a no‐fault scheme. The argument proceeds by: (1) elucidating what compensation the Nozickian must offer in return for prohibiting an activity such as the private recovery of damages; and consequently (2) arguing that there is no prima facie reason to think that the compensation afforded by participation in a no‐fault scheme would be any less adequate than that afforded by participation in a system of tort law
Cash Flow Immediacy and the Value of Investment Timing
Authors: Boyle Glenn W. , Guthrie Graeme A.
Published: October 2003

In a model with stochastic interest rates, irreversible investment, and two investment dates, the value of investment delay has two components: the expected gain from committing now to investment at a future date and the potential gain from the ability to reverse this commitment. Holding net present value constant, we show that the values of both these components are increasing in the proportion of project cash flows that accrue in the more distant future. Our results emphasize the importance of the interaction between cash flow immediacy and interest rate uncertainty for the optimal investment policy.
Effects of Questions about Word Meaning during L2 Spanish Lexical Learning
Authors: Barcroft Joe
Published: October 2003

This study concerned the effects of questions about word meaning during an immediate lexical learning task. English‐speaking learners of Spanish as a second language (L2) attempted to learn 24 new Spanish words while viewing word‐picture pairs. For 12 of the words, they thought about specific questions related to the meaning of each target word (e.g., In what ways can this object be used?). For the other 12 words, they were instructed only to do their best to learn the target words. After the learning phase, the participants completed three recall tasks: (a) free recall in Spanish, (b) free recall in English, and (c) cued recall in Spanish (when presented with pictures only). The results indicated significantly greater cued‐recall scores in the no questions condition than in the questions condition, a finding that provided evidence for a potentially inhibitory effect of semantic elaboration during L2 word learning.
The Role of Discourse Signaling Cues in Second Language Listening Comprehension
Authors: Jung Euen Hyuk (Sarah)
Published: October 2003

In contrast to the extensive research on reading, few studies have been conducted to investigate the role of discourse signaling cues in second language (L2) listening. Even the few existing studies provide inconsistent support for the beneficial effects of discourse signaling cues on L2 listening comprehension. Most of these studies also fail to show how these cues affect listeners' comprehension of different levels of information in the text. The current study examined the effects of discourse signaling cues on L2 learners' listening comprehension of high‐ and low‐level information in academic lectures. The study involved 80 Korean learners of English as a Foreign Language. Of the 80 learners, half listened to the lecture with discourse signaling cues (i.e., signaled group), and the other half listened to the lecture without such cues (i.e., nonsignaled group). Half the learners in each group performed summary tasks; the other half performed recall tasks. The findings showed that discourse signaling cues play an important role in L2 listening comprehension. Compared to the nonsignaled group, the signaled group recalled significantly more high‐ as well as low‐level information from the lecture in an accurate manner.
A Cellular Framework for Gut-Looping Morphogenesis in Zebrafish
Authors: Horne-Badovinac Sally , Rebagliati Michael , Stainier Didier Y. R.
Published: October 2003

Many vertebrate organs adopt asymmetric positions with respect to the midline, but little is known about the cellular changes and tissue movements that occur downstream of left-right gene expression to produce this asymmetry. Here, we provide evidence that the looping of the zebrafish gut results from the asymmetric migration of the neighboring lateral plate mesoderm (LPM). Mutations that disrupt the epithelial structure of the LPM perturb this asymmetric migration and inhibit gut looping. Asymmetric LPM migration still occurs when the endoderm is ablated from the gut-looping region, suggesting that the LPM can autonomously provide a motive force for gut displacement. Finally, reducing left-sided Nodal activity randomizes the pattern of LPM migration and gut looping. These results reveal a cellular framework for the regulation of organ laterality by asymmetrically expressed genes.
Immune Control of Tuberculosis by IFN-γ-Inducible LRG-47
Authors: MacMicking John D. , Taylor Gregory A. , McKinney John D.
Published: October 2003

Interferon-γ (IFN-γ) provides an essential component of immunity to tuberculosis by activating infected host macrophages to directly inhibit the replication of
Mycobacterium tuberculosis
(
Mtb
). IFN-γ–inducible nitric oxide synthase 2 (NOS2) is considered a principal effector mechanism, although other pathways may also exist. Here, we identify one member of a newly emerging 47-kilodalton (p47) guanosine triphosphatase family, LRG-47, that acts independently of NOS2 to protect against disease. Mice lacking LRG-47 failed to control
Mtb
replication, unlike those missing the related p47 guanosine triphosphatases IRG-47 or IGTP. Defective bacterial killing in IFN-γ–activated LRG-47
–/–
macrophages was associated with impaired maturation of
Mtb
-containing phagosomes, vesicles that otherwise recruited LRG-47 in wild-type cells. Thus, LRG-47 may serve as a critical vacuolar trafficking component used to dispose of intracellular pathogens like
Mtb
.
Breast and Ovarian Cancer Risks Due to Inherited Mutations in
BRCA1
and
BRCA2
Authors: King Mary-Claire , Marks Joan H. , Mandell Jessica B.
Published: October 2003

Risks of breast and ovarian cancer were determined for Ashkenazi Jewish women with inherited mutations in the tumor suppressor genes
BRCA1
and
BRCA2
. We selected 1008 index cases, regardless of family history of cancer, and carried out molecular analysis across entire families. The lifetime risk of breast cancer among female mutation carriers was 82%, similar to risks in families with many cases. Risks appear to be increasing with time: Breast cancer risk by age 50 among mutation carriers born before 1940 was 24%, but among those born after 1940 it was 67%. Lifetime risks of ovarian cancer were 54% for
BRCA1
and 23% for
BRCA2
mutation carriers. Physical exercise and lack of obesity in adolescence were associated with significantly delayed breast cancer onset.
HCV Persistence and Immune Evasion in the Absence of Memory T Cell Help
Authors: Grakoui Arash , Shoukry Naglaa H. , Woollard David J. , Han Jin-Hwan , Hanson Holly L. , Ghrayeb John , Murthy Krishna K. , Rice Charles M. , Walker Christopher M.
Published: October 2003

Spontaneous resolution of hepatitis C virus (HCV) infection in humans usually affords long-term immunity to persistent viremia and associated liver diseases. Here, we report that memory CD4
+
Tcells are essential for this protection. Antibody-mediated depletion of CD4
+
Tcells before reinfection of two immune chimpanzees resulted in persistent, low-level viremia despite functional intra-hepatic memory CD8
+
Tcell responses. Incomplete control of HCV replication by memory CD8
+
Tcells in the absence of adequate CD4
+
Tcell help was associated with emergence of viral escape mutations in class I major histocompatibility complex–restricted epitopes and failure to resolve HCV infection.
Genomics and Global Health: Time for a Reappraisal
Authors: Weatherall David J.
Published: October 2003

Although currently there are only a limited number of genomic technologies that are applicable to health care in the developing countries, this is unlikely to be the case in the near future. If, however, the full potential of genomics for health care is to be fulfilled, there will have to be a complete change of emphasis in education and research in the richer countries toward a more global view of disease and its consequences.
Generating Diverse Skeletons of Small Molecules Combinatorially
Authors: Burke Martin D. , Berger Eric M. , Schreiber Stuart L.
Published: October 2003

Lack of efficient access to collections of synthetic compounds that have skeletal diversity is a key bottleneck in the small-molecule discovery process. We report a synthesis strategy that involves transforming substrates with different appendages that pre-encode skeletal information, named σ elements, into products that have different skeletons with the use of common reaction conditions. With this approach, split-pool synthesis can be used to pre-encode skeletal diversity combinatorially and thereby generate such small molecules very efficiently. A split-pool synthesis of more than 1000 compounds produced overlapping, combinatorial matrices of molecular skeletons and appended building blocks in both enantiomeric and diastereomeric forms.
Mitochondrial and Metabolic Effects of Nucleoside Reverse Transcriptase Inhibitors (NRTIs) in Mice Receiving One of Five Single- and Three Dual-NRTI Treatments
Authors: Note Reine , Maisonneuve Caroline , Lettéron Philippe , Peytavin Gilles , Djouadi Fatima , Igoudjil Anissa , Guimont Marie-Christine , Biour Michel , Pessayre Dominique , Fromenty Bernard
Published: October 2003

Although treatments with nucleoside reverse transcriptase inhibitors (NRTIs) can modify fat metabolism and fat distribution in humans, the mechanisms of these modifications and the roles of diverse NRTIs are unknown. We studied the mitochondrial and metabolic effects of stavudine (d4T), zidovudine (AZT), didanosine (ddI), lamivudine (3TC), zalcitabine (ddC), and three combinations (AZT-3TC, d4T-3TC, and d4T-ddI) in mice treated for 2 weeks with daily doses equivalent to the human dose per body area. Concentrations of AZT and d4T in plasma were lower when these drugs were administered with 3TC or ddI. Whatever the treatment, mitochondrial DNA was not significantly decreased in muscle, heart, brain, or white adipose tissue but was moderately decreased in liver tissue after the administration of AZT, 3TC, or d4T alone. Blood lactate was unchanged, even when NRTIs were administered at supratherapeutic doses. In contrast, the level of plasma ketone bodies increased with the administration of AZT or high doses of d4T but not with ddC, 3TC, or ddI, suggesting that the thymine moiety could be involved. Indeed, the levels of plasma ketone bodies increased in mice treated with β-aminoisobutyric acid, a thymine catabolite. Treatment with AZT, d4T, or β-aminoisobutyric acid increased hepatic carnitine palmitoyltransferase I (CPT-I) mRNA expression and the mitochondrial generation of ketone bodies from palmitate. In conclusion, therapeutic doses of NRTIs have no or moderate effects on mitochondrial DNA and no effects on plasma lactate in mice. However, AZT and high doses of d4T increase the levels of hepatic CPT-I, mitochondrial fatty acid β-oxidation, and ketone bodies, and these catabolic effects are reproduced by β-aminoisobutyric acid, a thymine metabolite.
CesRK, a Two-Component Signal Transduction System in
Listeria monocytogenes
, Responds to the Presence of Cell Wall-Acting Antibiotics and Affects β-Lactam Resistance
Authors: Kallipolitis Birgitte H. , Ingmer Hanne , Gahan Cormac G. , Hill Colin , Søgaard-Andersen Lotte
Published: October 2003

Listeria monocytogenes
is a food-borne pathogen that can cause a variety of illnesses ranging from gastroenteritis to life-threatening septicemia. The β-lactam antibiotic ampicillin remains the drug of choice for the treatment of listeriosis. We have previously identified a response regulator of a putative two-component signal transduction system that plays a role in the virulence and ethanol tolerance of
L. monocytogenes
. Here we present evidence that the response regulator, CesR, and a histidine protein kinase, CesK, which is encoded by the gene downstream from
cesR
, are involved in the ability of
L. monocytogenes
to tolerate ethanol and cell wall-acting antibiotics of the β-lactam family. Furthermore, CesRK controls the expression of a putative extracellular peptide encoded by the
orf2420
gene, located immediately downstream from
cesRK.
Inactivation of
orf2420
revealed that it contributes to ethanol tolerance and pathogenesis in mice. Interestingly, we found that transcription of
orf2420
was strongly induced by subinhibitory concentrations of various cell wall-acting antibiotics, ethanol, and lysozyme. The induction of
orf2420
expression was abolished in the absence of CesRK. Our data suggest that CesRK is involved in regulating aspects of the cell envelope architecture and that changes in cell wall integrity provide a potent stimulus for CesRK-mediated regulation. These results further our understanding of how
L. monocytogenes
senses and responds to antibiotics that are used therapeutically in the treatment of infectious diseases.
Synthesis, Degradation, and Antimicrobial Properties of Targeted Macromolecular Prodrugs of Norfloxacin
Authors: Roseeuw Eveline , Coessens Veerle , Balazuc Anne-Marie , Lagranderie Micheline , Chavarot Pierre , Pessina Augusto , Neri Maria Grazia , Schacht Etienne , Marchal Gilles , Domurado Dominique
Published: October 2003

Long-term antibiotic treatment is required to cure tuberculosis. Targeted antibiotics should improve the efficacy of treatment by concentrating the drugs close to the bacteria. The aim of the present study was to synthesize targeted conjugates. For this purpose, we used mannose as a homing device to direct norfloxacin into macrophages. Dextran was used as the polymer bearing both mannose and norfloxacin. Using different peptide spacer arms to link norfloxacin to dextran, we demonstrated that norfloxacin acts as an antibiotic only when it is released in its native form. Also, targeting by using mannose as a homing device is required to achieve antimycobacterial activity in vivo. Thus, norfloxacin, which is inactive against mycobacteria in its native form in vivo, can be transformed into an active drug by targeting.
pfcrt
Allelic Types with Two Novel Amino Acid Mutations in Chloroquine-Resistant
Plasmodium falciparum
Isolates from the Philippines
Authors: Chen Nanhua , Kyle Dennis E. , Pasay Cielo , Fowler Elizabeth V. , Baker Joanne , Peters Jennifer M. , Cheng Qin
Published: October 2003

Mutations in the
pfcrt
and
pfmdr1
genes have been associated with chloroquine resistance in
Plasmodium falciparum
. Ten and five mutations, respectively, have been identified in these genes from chloroquine-resistant parasites worldwide. Mutation patterns in
pfcrt
revealed that chloroquine resistance evolved independently in southeast Asia, South America, and Papua New Guinea. However, the evolution of chloroquine resistance in the rest of the Pacific region is unclear. In this study, we examined sequence polymorphisms in these genes in isolates from Morong, Philippines, and compared them to known chloroquine resistance sequences. Two novel mutations, A144T and L160Y, were identified outside of the 10 known mutations in
pfcrt
in Morong isolates. These novel mutations were identified only in parasites with K76T and N326D but without the common A220S mutation found in most chloroquine-resistant isolates. This represents a unique chloroquine resistance allelic type (K76T/A144T/L160Y/N326D) not previously found elsewhere in the world. One Morong isolate also had an additional C72S mutation, whereas only one isolate possessed an allelic type typical of chloroquine resistance in Asia. Parasites with the novel
pfcrt
allelic types were resistant to chloroquine in vitro and were unresponsive to verapamil (0.9 μM) chemosensitization, similar to chloroquine-resistant parasites from South America and Papua New Guinea. These results suggest that chloroquine resistance evolved independently in the Philippines and represents a second chloroquine resistance founder event in the South Pacific.
Extended-Spectrum β-Lactamase-Producing
Enterobacteriaceae
in Community and Private Health Care Centers
Authors: Arpin Corinne , Dubois Véronique , Coulange Laure , André Catherine , Fischer Isabelle , Noury Patrick , Grobost Frédéric , Brochet Jean-Philippe , Jullin Jacqueline , Dutilh Brigitte , Larribet Gilberte , Lagrange Isabelle , Quentin Claudine
Published: October 2003

In 1999, 39 of 2,599 isolates of the family
Enterobacteriaceae
(1.5%) collected by eight private laboratories in the Aquitaine region in France produced an extended-spectrum β-lactamase (ESBL). Among these were 19
Enterobacter aerogenes
isolates; 8
Klebsiella pneumoniae
isolates; 6
Escherichia coli
isolates; 3
Proteus mirabilis
isolates; and 1 isolate each of
Serratia marcescens
,
Morganella morganii
, and
Providencia stuartii
. ESBL producers were isolated from 38 patients, including 33 residents of 11 clinics or nursing homes and 5 ambulatory patients. Seven different ESBLs were characterized. These mainly consisted of TEM-24 (25 isolates) and TEM-21 (9 isolates), but TEM-15 (2 isolates) and TEM-3, TEM-19, SHV-4, and CTX-M-1 (1 isolate each) were also characterized. Seven strains showed the coexistence of different TEM- and/or SHV-encoding genes, including a new SHV-1 variant, SHV-44, defined by the substitution R205L previously reported for SHV-3 in association with S238G. The epidemiology of the ESBL producers was investigated by random amplification of polymorphic DNA, typing by enterobacterial repetitive intergenic consensus PCR, analysis of resistance cotransferred with the ESBL, and analysis of the restriction profiles of the ESBL-encoding plasmids. Of the TEM-24-expressing strains, 18 were
E. aerogenes
isolates, including 9 from the same clinic, that were representatives of the epidemic clone disseminating in France. Of the TEM-21-producing strains that belonged to different species of the family
Enterobacteriaceae
(
E. coli
,
K. pneumoniae
, and
P. mirabilis
), 8 were isolated in the same nursing home. Outbreaks due to strain and/or plasmid dissemination in these clinic and nursing home were demonstrated. The presence of ESBL producers in five ambulatory patients probably resulted from nosocomial acquisition. Our data highlight the serious need to monitor patients for ESBL-producing
Enterobacteriaceae
in general practice.
Effects of Triclosan-Containing Rinse on the Dynamics and Antimicrobial Susceptibility of In Vitro Plaque Ecosystems
Authors: McBain Andrew J. , Bartolo Robert G. , Catrenich Carl E. , Charbonneau Duane , Ledder Ruth G. , Gilbert Peter
Published: October 2003

Dental plaque microcosms were established under a feast-famine regimen within constant-depth film fermentors and exposed four times daily postfeeding to a triclosan (TR)-containing rinse (dentifrice) (TRD). This was diluted so that the antimicrobial content was 0.6 mg/ml. Microcosms were characterized by heterotrophic plate counts and PCR-denaturing gradient gel electrophoresis (DGGE) with primers specific for the V2-V3 region of the eubacterial 16S rRNA gene (rDNA). Dominant isolates and PCR amplicons were identified by partial sequencing of 16S rDNA. TRD caused considerable decreases in the counts of both gram-negative organisms and total anaerobic cells, transiently lowered the numbers of streptococci and actinomycetes, and markedly increased the proportion of lactobacilli. DGGE indicated the presence of putatively unculturable bacteria and showed that aPorphyromonassp. andSelenomonas infelixhad been inhibited by TRD. Pure culture studies of 10 oral bacteria (eight genera) showed thatNeisseria subflava,Prevotella nigrescens, andPorphyromonas gingivaliswere highly susceptible to TR, while the lactobacilli and streptococci were the least susceptible. Clonal expansion of the lactobacilli in the pulsed microcosm could be explained on the basis of TR activity. The mean MICs of TR, chlorhexidine, erythromycin, penicillin V, and vancomycin for the population before and after 5 days of exposure to TRD showed few significant changes. In conclusion, changes in plaque microcosm populations following repeated exposure to TRD showed inhibition of the most susceptible flora and clonal expansion of less susceptible species.
Relevance of Soft-Tissue Penetration by Levofloxacin for Target Site Bacterial Killing in Patients with Sepsis
Authors: Zeitlinger M. A. , Dehghanyar P. , Mayer B. X. , Schenk B. S. , Neckel U. , Heinz G. , Georgopoulos A. , Müller M. , Joukhadar C.
Published: October 2003

Antimicrobial therapy of soft tissue infections in patients with sepsis sometimes lacks efficiency, despite the documented susceptibility of the causative pathogen to the administered antibiotic. In this context, impaired equilibration between the antibiotic concentrations in plasma and those in tissues in critically ill patients has been discussed. To characterize the impact of tissue penetration of anti-infective agents on antimicrobial killing, we used microdialysis to measure the concentration-versus-time profiles of levofloxacin in the interstitial space fluid of skeletal muscle in patients with sepsis. Subsequently, we applied an established dynamic in vivo pharmacokinetic-in vitro pharmacodynamic approach to simulate bacterial killing at the site of infection. The population mean areas under the concentration-time curves (AUCs) for levofloxacin showed that levofloxacin excellently penetrates soft tissues, as indicated by the ratio of the AUC from time zero to 8 h (AUC
0-8
) for muscle tissue (AUC
0-8 muscle
) to the AUC
0-8
for free drug in plasma (AUC
0-8 plasma free
) (AUC
0-8 muscle
/AUC
0-8 plasma free
ratio) of 0.85. The individual values of tissue penetration and maximum concentration (
C
max
) in muscle tissue were highly variable. No difference in bacterial killing of a select
Staphylococcus aureus
strain for which the MIC was 0.5 μg/ml was found between individuals after exposure to dynamically changing concentrations of levofloxacin in plasma and tissue in vitro. In contrast, the decrease in the bacterial counts of
Pseudomonas aeruginosa
(MIC = 2 μg/ml) varied extensively when the bacteria were exposed to levofloxacin at the concentrations determined from the individual concentration-versus-time profiles obtained in skeletal muscle. The extent of bacterial killing could be predicted by calculating individual
C
max
/MIC and AUC
0-8 muscle
/AUC
0-8 plasma free
ratios (
R
= 0.96 and 0.93, respectively). We have therefore shown in the present study that individual differences in the tissue penetration of levofloxacin may markedly affect target site killing of bacteria for which MICs are close to 2 μg/ml.
In Vitro Activities of a New Des-Fluoro(6) Quinolone, Garenoxacin, against Clinical Anaerobic Bacteria
Authors: Liebetrau A. , Rodloff A. C. , Behra-Miellet J. , Dubreuil L.
Published: October 2003

The antimicrobial activities of garenoxacin and eight other antibiotics against 641 anaerobic isolates were evaluated with the NCCLS agar dilution method. Overall, the MICs of garenoxacin for 50 and 90% of the strains tested (in micrograms per milliliter) were as follows:
Bacteroides fragilis
group, 0.5 and 2;
Prevotella
spp., 0.25 and 2;
Fusobacterium
spp., 0.25 and 0.5;
Porphyromonas
spp., 0.125 and 0.25;
Bilophila wadsworthia
, 0.5 and 1;
Veillonella
spp., 0.25 and 0.5;
Clostridium
spp., 0.25 and 1;
Clostridium difficile
, 2 and >64;
Bifidobacterium
spp., 1 and 2;
Eggerthella lenta
, 0.25 and 1;
Propionibacterium
spp., 0.5 and 0.5; gram-positive cocci, 0.125 and 0.25.
One of Two Human Lactoferrin Variants Exhibits Increased Antibacterial and Transcriptional Activation Activities and Is Associated with Localized Juvenile Periodontitis
Authors: Velliyagounder Kabilan , Kaplan Jeffrey B. , Furgang David , Legarda Diana , Diamond Gill , Parkin Ruth E. , Fine Daniel H.
Published: October 2003

The iron-binding protein lactoferrin is a ubiquitous and abundant constituent of human exocrine secretions. Lactoferrin inhibits bacterial growth by sequestering essential iron and also exhibits non-iron-dependent antibacterial, antifungal, antiviral, antitumor, anti-inflammatory, and immunoregulatory activities. All of these non-iron-dependent activities are mediated by the highly charged N terminus of lactoferrin. In this study we characterized a Lys/Arg polymorphism at position 29 in the N-terminal region of human lactoferrin that results from a single nucleotide polymorphism in exon 1 of the human lactoferrin gene. We expressed cDNAs encoding both lactoferrin variants in insect cells and purified the two proteins by ion exchange chromatography. The two lactoferrin variants exhibited nearly identical iron-binding and iron-releasing activities and equivalent bactericidal activities against a strain of the gram-negative bacteriumActinobacillus actinomycetemcomitans. When tested against the gram-positive speciesStreptococcus mutansandStreptococcus mitis, however, lactoferrin containing Lys at position 29 exhibited significantly greater bactericidal activity than did lactoferrin containing Arg. In addition, the Lys-containing lactoferrin stimulated bovine tracheal epithelial cells to synthesize much higher levels of tracheal antimicrobial peptide mRNA than did the Arg-containing variant. A genotyping assay that distinguished between the two alleles based on a polymorphicEarI restriction site showed that the Lys and Arg alleles had frequencies of 24% and 76%, respectively, among 17 healthy human subjects, and 72% and 28%, respectively, among nine patients with localized juvenile periodontitis. Our findings suggest that these two lactoferrin variants are functionally different and that these differences may contribute to the pathogenesis of localized juvenile periodontitis.
Induction of Capsule Growth inCryptococcus neoformansby Mammalian Serum and CO2
Authors: Zaragoza Oscar , Fries Bettina C. , Casadevall Arturo
Published: October 2003

The pathogenic fungusCryptococcus neoformanshas a polysaccharide capsule that is essential for virulence in vivo. Capsule size is known to increase during animal infection, and this phenomenon was recently associated with virulence. Although various conditions have been implicated in promoting capsule growth, including CO2concentration, osmolarity, and phenotypic switching, it is difficult to reproduce the capsule enlargement effect in the laboratory. In this study, we report that serum can induce capsule growth, and we describe the conditions that induce this effect, not only by serum but also by CO2. Capsule enlargement was dependent on the medium used, and this determined whether the strain responded to serum or CO2efficiently. Serum was most effective in inducing capsule growth under nutrient-limited conditions. There was considerable variability between strains in their response to either serum or CO2, with some strains requiring both stimuli. Sera from several animal sources were each highly efficient in inducing capsule growth. The cyclic AMP (cAMP) pathway and Ras1 were both necessary for serum-induced capsule growth. The lack of induction in theras1mutant was not complemented by exogenous cAMP, indicating that these pathways act in parallel. However, both cAMP and Ras1 were dispensable for inducing a partial capsule growth by CO2, suggesting that multiple pathways participate in this process. The ability of serum to induce capsule growth suggests a mechanism for the capsular enlargement observed during animal infection.
Therapeutic Activity of an Engineered Synthetic Killer Antiidiotypic Antibody Fragment against Experimental Mucosal and Systemic Candidiasis
Authors: Polonelli Luciano , Magliani Walter , Conti Stefania , Bracci Luisa , Lozzi Luisa , Neri Paolo , Adriani Daniela , De Bernardis Flavia , Cassone Antonio
Published: October 2003

Peptides derived from the sequence of a single-chain, recombinant, antiidiotypic antibody (IdAb; KT-scFv) acting as a functional internal image of a microbicidal, wide-spectrum yeast killer toxin (KT) were synthesized and studied for their antimicrobial activity by using the KT-susceptibleCandida albicansas model organism. A decapeptide containing the first three amino acids (SAS) of the light chain CDR1 was selected and optimized by alanine replacement of a single residue. This peptide exerted a strong candidacidal activity in vitro, with a 50% inhibitory concentration of 0.056 μM, and was therefore designated killer peptide (KP). Its activity was neutralized by laminarin, a β1-3 glucan molecule, but not by pustulan, a β1-6 glucan molecule. KP also competed with the binding of a KT-like monoclonal IdAb to germinating cells of the fungus. In a rat model of vaginal candidiasis, local, postchallenge administration of KP was efficacious in rapidly abating infections caused by fluconazole-susceptible or -resistantC. albicansstrains. In systemic infection of BALB/c or SCID mice preinfected intravenously with a lethal fungal load, KP caused a highly significant prolongation of the median survival time, with >80% of the animals still surviving after >60 days, whereas >90% of control mice died within 3 to 5 days. KP is therefore the first engineered peptide derived from a recombinant IdAb retaining KT microbicidal activity, probably through the interaction with the β-glucan KT receptor on target microbial cells.
Antibodies to
Plasmodium falciparum
Rifin Proteins Are Associated with Rapid Parasite Clearance and Asymptomatic Infections
Authors: Abdel-Latif Mohamed S. , Dietz Klaus , Issifou Saadou , Kremsner Peter G. , Klinkert Mo-Quen
Published: October 2003

Plasmodium falciparum
rifin proteins, belonging to the largest known family of variable infected-erythrocyte surface-expressed proteins encoded by
rif
genes, were recently shown to be capable of inducing a strong immune response in
P. falciparum
-infected adults living in an area in Gabon where malaria is endemic. In the present study, the levels of antirifin antibodies were analyzed in serum obtained from 60 children from the same area who were admitted to hospital and diagnosed with severe malaria. High antirifin antibody concentrations in these individuals correlated significantly with their capacity to rapidly clear their parasites from the circulation after the start of chemotherapy. A doubling of antirifin antibody concentrations reduced the clearance time by 5 h (95% confidence interval, 4.1 to 6.9 h). In the same group of children, who were followed up for 2 years, antirifin antibody levels did not correlate with a reduced rate of reinfection or with a delay in the time to the first reinfection. However, the initial antirifin antibody levels were sustained over the study period. The likelihood that these antibodies could confer a certain degree of protection against malaria is supported by our findings of statistically higher levels of antirifin antibodies to all four rifin proteins in a group of 42 asymptomatic parasitemic children.
PPE Antigen Rv2430c of
Mycobacterium tuberculosis
Induces a Strong B-Cell Response
Authors: Choudhary Rakesh Kumar , Mukhopadhyay Sangita , Chakhaiyar Prachee , Sharma Naresh , Murthy K. J. R. , Katoch V. M. , Hasnain Seyed E.
Published: October 2003

The variation in sequence and length in the C-terminal region among members of the unique PE (Pro-Glu) and PPE (Pro-Pro-Glu) protein families of
Mycobacterium tuberculosis
is a likely source of antigenic variation, giving rise to the speculation that these protein families could be immunologically important. Based on in silico analysis, we selected a hypothetical open reading frame (ORF) encoding a protein belonging to the PPE family and having epitopes with predictably higher antigenic indexes. Reverse transcriptase PCR using total RNA extracted from in vitro-cultured
M. tuberculosis
H37Rv generated an mRNA product corresponding to this gene, indicating the expression of this ORF (Rv2430c) at the mRNA level. Recombinant protein expressed in
Escherichia coli
was used to screen the sera of
M. tuberculosis
-infected patients, as well as those of clinically healthy controls (
n
= 10), by enzyme-linked immunosorbent assay. The panel of patient sera comprised sera from fresh infection cases (category 1;
n
= 32), patients with relapsed tuberculosis (category 2;
n
= 30), and extrapulmonary cases (category 3;
n
= 30). Category 2 and 3 sera had strong antibody responses to the PPE antigen, equal to or higher than those to other well-known antigens, such as Hsp10 or purified protein derivative (PPD). However, a higher percentage of patients belonging to category 1, as opposed to clinically healthy controls, showed stronger antibody response against the PPE protein when probed with anti-immunoglobulin M (IgM) (71 versus 37.5%) or anti-IgG (62.5 versus 28.12%). Our results reveal that this PPE ORF induces a strong B-cell response compared to that generated by
M. tuberculosis
Hsp10 or PPD, pointing to the immunodominant nature of the protein.