bluuebunny/crossref_metadata_2025 huggingface dataset:
Untangling Dendrites with Quantitative Models
Authors: Segev Idan , London Michael
Published: July 2002

Our understanding of the function of dendrites has been greatly enriched by an inspiring dialogue between theory and experiments. Rather than functionally ignoring dendrites, representing neurons as single summing points, we have realized that dendrites are electrically and chemically distributed nonlinear units and that this has important consequences for interpreting experimental data and for the role of neurons in information processing. Here, we examine the route to unraveling some of the enigmas of dendrites and highlight the main insights that have been gained. Future directions are discussed that will enable theory and models to keep shedding light on dendrites, where the most fundamental input-output adaptive processes take place.
Observation of X-ray Lines from a Gamma-Ray Burst (GRB991216): Evidence of Moving Ejecta from the Progenitor
Authors: Piro L. , Garmire G. , Garcia M. , Stratta G. , Costa E. , Feroci M. , Mészáros P. , Vietri M. , Bradt H. , Frail D. , Frontera F. , Halpern J. , Heise J. , Hurley K. , Kawai N. , Kippen R. M. , Marshall F. , Murakami T. , Sokolov V. V. , Takeshima T. , Yoshida A.
Published: July 2002

We report on the discovery of two emission features observed in the x-ray spectrum of the afterglow of the gamma-ray burst (GRB) of 16 December 1999 by the Chandra X-ray Observatory. These features are identified with the Lyαline and the narrow recombination continuum by hydrogenic ions of iron at a redshiftz= 1.00 ± 0.02, providing an unambiguous measurement of the distance of a GRB. Line width and intensity imply that the progenitor of the GRB was a massive star system that ejected, before the GRB event, a quantity of iron ∼0.01 of the mass of the sun at a velocity ∼0.1 of the speed of light, probably by a supernova explosion.
The Evolutionary Fate and Consequences of Duplicate Genes
Authors: Lynch Michael , Conery John S.
Published: July 2002

Gene duplication has generally been viewed as a necessary source of material for the origin of evolutionary novelties, but it is unclear how often gene duplicates arise and how frequently they evolve new functions. Observations from the genomic databases for several eukaryotic species suggest that duplicate genes arise at a very high rate, on average 0.01 per gene per million years. Most duplicated genes experience a brief period of relaxed selection early in their history, with a moderate fraction of them evolving in an effectively neutral manner during this period. However, the vast majority of gene duplicates are silenced within a few million years, with the few survivors subsequently experiencing strong purifying selection. Although duplicate genes may only rarely evolve new functions, the stochastic silencing of such genes may play a significant role in the passive origin of new species.
Arabidopsis
Transcription Factors: Genome-Wide Comparative Analysis Among Eukaryotes
Authors: Riechmann J. L. , Heard J. , Martin G. , Reuber L. , Jiang C.-Z. , Keddie J. , Adam L. , Pineda O. , Ratcliffe O. J. , Samaha R. R. , Creelman R. , Pilgrim M. , Broun P. , Zhang J. Z. , Ghandehari D. , Sherman B. K. , -L. Yu G.
Published: July 2002

The completion of the
Arabidopsis thaliana
genome sequence allows a comparative analysis of transcriptional regulators across the three eukaryotic kingdoms.
Arabidopsis
dedicates over 5% of its genome to code for more than 1500 transcription factors, about 45% of which are from families specific to plants.
Arabidopsis
transcription factors that belong to families common to all eukaryotes do not share significant similarity with those of the other kingdoms beyond the conserved DNA binding domains, many of which have been arranged in combinations specific to each lineage. The genome-wide comparison reveals the evolutionary generation of diversity in the regulation of transcription.
Global Analysis of the Genetic Network Controlling a Bacterial Cell Cycle
Authors: Laub Michael T. , McAdams Harley H. , Feldblyum Tamara , Fraser Claire M. , Shapiro Lucy
Published: July 2002

This report presents full-genome evidence that bacterial cells use discrete transcription patterns to control cell cycle progression. Global transcription analysis of synchronized
Caulobacter crescentus
cells was used to identify 553 genes (19% of the genome) whose messenger RNA levels varied as a function of the cell cycle. We conclude that in bacteria, as in yeast, (i) genes involved in a given cell function are activated at the time of execution of that function, (ii) genes encoding proteins that function in complexes are coexpressed, and (iii) temporal cascades of gene expression control multiprotein structure biogenesis. A single regulatory factor, the CtrA member of the two-component signal transduction family, is directly or indirectly involved in the control of 26% of the cell cycle–regulated genes.
Directed Assembly of One-Dimensional Nanostructures into Functional Networks
Authors: Huang Yu , Duan Xiangfeng , Wei Qingqiao , Lieber Charles M.
Published: July 2002

One-dimensional nanostructures, such as nanowires and nanotubes, represent the smallest dimension for efficient transport of electrons and excitons and thus are ideal building blocks for hierarchical assembly of functional nanoscale electronic and photonic structures. We report an approach for the hierarchical assembly of one-dimensional nanostructures into well-defined functional networks. We show that nanowires can be assembled into parallel arrays with control of the average separation and, by combining fluidic alignment with surface-patterning techniques, that it is also possible to control periodicity. In addition, complex crossed nanowire arrays can be prepared with layer-by-layer assembly with different flow directions for sequential steps. Transport studies show that the crossed nanowire arrays form electrically conducting networks, with individually addressable device function at each cross point.
Scale Dependence in Plant Biodiversity
Authors: Crawley M. J. , Harral J. E.
Published: July 2002

The relationship between the number of species and the area sampled is one of the oldest and best-documented patterns in community ecology. Several theoretical models and field data from a wide range of plant and animal taxa suggest that the slope,
z
, of a graph of the logarithm of species richness against the logarithm of area is roughly constant, with
z
≈ 0.25. We collected replicated and randomized plant data at 11 spatial scales from 0.01 to 10
8
square meters in Great Britain which show that the slope of the log-log plot is not constant, but varies systematically with spatial scale, and from habitat to habitat at the same spatial scale. Values of
z
were low (0.1 to 0.2) at small scales (<100 square meters), high (0.4 to 0.5) at intermediate scales (1 hectare to 10 square kilometers), and low again (0.1 to 0.2) for the largest scale transitions (e.g., East Berks to all of Berkshire). Instead of one process determining changes in species richness across a wide range of scales, different processes might determine plant biodiversity at different spatial scales.
Improving the Health of the Global Poor
Authors: Jha Prabhat , Mills Anne , Hanson Kara , Kumaranayake Lilani , Conteh Lesong , Kurowski Christoph , Nguyen Son Nam , Cruz Valeria Oliveira , Ranson Kent , Vaz Lara M. E. , Yu Shengchao , Morton Oliver , Sachs Jeffrey D.
Published: July 2002

We analyzed the technical basis for a major global program to reduce disease among the poor. Effective interventions exist against the few diseases which most account for excess mortality among the poor. Achieving high coverage of effective interventions requires a well-functioning health system, as well as overcoming a set of financial and nonfinancial constraints. The annual incremental cost would be between $40 billion and $52 billion by 2015 in 83 low-income and sub-Saharan African countries. Such a program is feasible and would avoid millions of child, maternal, and adult deaths annually in poor countries.
An Efficient Two-Photon-Generated Photoacid Applied to Positive-Tone 3D Microfabrication
Authors: Zhou Wenhui , Kuebler Stephen M. , Braun Kevin L. , Yu Tianyue , Cammack J. Kevin , Ober Christopher K. , Perry Joseph W. , Marder Seth R.
Published: July 2002

A two-photon–activatable photoacid generator, based on a
bis
[(diarylamino) styryl]benzene core with covalently attached sulfonium moieties, has been synthesized. The photoacid generator has both a large two-photon absorption cross section (δ = 690 × 10
−50
centimeter
4
second per photon) and a high quantum yield for the photochemical generation of acid (φ
H
+
= 0.5). Under near-infrared laser irradiation, the molecule produces acid after two-photon excitation and initiates the polymerization of epoxides at an incident intensity that is one to two orders of magnitude lower than that needed for conventional ultraviolet-sensitive initiators. This photoacid generator was used in conjunction with a positive-tone chemically amplified resist for the fabrication of a three-dimensional (3D) microchannel structure.
Potent Enhancement of the Sensitivity of
Plasmodium falciparum
to Chloroquine by the Bisbenzylisoquinoline Alkaloid Cepharanthin
Authors: Haruki Kosuke , Bray Patrick G. , Ono Minoru , Ward Stephen A.
Published: July 2002

Cepharanthin is a proprietary extract of
Stephania cepharantha
, widely used in Japan for the treatment of inflammatory diseases. Cephranthin, its component alkaloids, and the standard resistance modulator verapamil were tested against
Plasmodium falciparum
for capacity to modulate sensitivity to chloroquine. Cepharanthin enhanced the activity of chloroquine against resistant clones by a factor of 15 at a concentration of only 200 nM (1.2 ng/ml). It is 50 times more potent than verapamil and 3 times more potent than the sum of its individual alkaloids. Combinations of component alkaloids acted synergistically to sensitize the parasite to chloroquine, possibly explaining the enhanced potency of Cepharanthin. Cepharanthin differed from verapamil in that it further sensitized clones that are considered to be fully susceptible, improving the baseline activity of chloroquine. Potent sensitization of parasites to chloroquine in vitro coupled with low toxicity suggests that coadministration of Cepharanthin might extend the clinical utility of chloroquine.
Valganciclovir Results in Improved Oral Absorption of Ganciclovir in Liver Transplant Recipients
Authors: Pescovitz Mark D. , Rabkin John , Merion Robert M. , Paya Carlos V. , Pirsch John , Freeman R. B. , O'Grady John , Robinson Charles , To Zung , Wren Kristina , Banken Ludger , Buhles William , Brown Frances
Published: July 2002

The pharmacokinetics of an orally administered valine ester of ganciclovir (GCV), valganciclovir (VGC), were studied. These were compared to the pharmacokinetics of oral and intravenous GCV. Twenty-eight liver transplant recipients received, in an open-label random order with a 3- to 7-day washout, each of the following: 1 g of oral GCV three times a day; 450 mg of VGC per os (p.o.) once a day (q.d.); 900 mg of VGC p.o. q.d.; and 5 mg of intravenous (i.v.) GCV per kg of body weight q.d., given over 1 h. GCV and VGC concentrations were measured in blood over 24 h. One-sided equivalence testing was performed to test for noninferiority of 450 mg of VGC relative to oral GCV (two-sided 90% confidence interval [CI] > 80%) and nonsuperiority of 900 mg of VGC relative to i.v. GCV (two-sided 90% CI < 125%). The exposure of 450 mg of VGC (20.56 μg · h/ml) was found to be noninferior to that of oral GCV (20.15 μg · h/ml; 90% CI for relative bioavailability of 95 to 109%), and the exposure of 900 mg of VGC (42.69 μg · h/ml) was found to be nonsuperior to that of i.v. GCV (47.61 μg · h/ml; 90% CI = 83 to 97%). Oral VGC delivers systemic GCV exposure equivalent to that of standard oral GCV (at 450 mg) or i.v. GCV (at 900 mg of VGC). VGC has promise for effective CMV prophylaxis or treatment with once-daily oral dosing in transplant recipients.
[1N,12N]Bis(Ethyl)-cis-6,7-Dehydrospermine: a New Drug for Treatment and Prevention ofCryptosporidium parvumInfection of Mice Deficient in T-Cell Receptor Alpha
Authors: Waters W. R. , Frydman B. , Marton L. J. , Valasinas A. , Reddy V. K. , Harp J. A. , Wannemuehler M. J. , Yarlett N.
Published: July 2002

Cryptosporidium parvuminfection of T-cell receptor alpha (TCR-α)-deficient mice results in a persistent infection. In this study, treatment with a polyamine analogue (SL-11047) preventedC. parvuminfection in suckling TCR-α-deficient mice and cleared an existing infection in older mice. Treatment with putrescine, while capable of preventing infection, did not clearC. parvumfrom previously infected mice. These findings provide further evidence that polyamine metabolic pathways are targets for new anticryptosporidial chemotherapeutic agents.
Differential Effects of Antiretroviral Nucleoside Analogs on Mitochondrial Function in HepG2 Cells
Authors: Pan-Zhou Xin-Ru , Cui Lixin , Zhou Xiao-Jian , Sommadossi Jean-Pierre , Darley-Usmar Victor M.
Published: July 2002

Numerous studies have reported effects of antiviral nucleoside analogs on mitochondrial function, but they have not correlated well with the observed toxic side effects. By comparing the effects of the five Food and Drug Administration-approved anti-human immunodeficiency virus nucleoside analogs, zidovudine (3′-azido-3′-deoxythymidine) (AZT), 2′,3′-dideoxycytidine (ddC), 2′,3′-dideoxyinosine (ddI), 2′,3′-didehydro-2′,3′-deoxythymidine (d4T), and β-L-2′,3′-dideoxy-3′-thiacytidine (3TC), as well as the metabolite of AZT, 3′-amino-3′-deoxythymidine (AMT), on mitochondrial function in a human hepatoma cell line, this issue has been reexamined. Evidence for a number of mitochondrial defects with AZT, ddC, and ddI was found, but only AZT induced a marked rise in lactic acid levels. Only in mitochondria isolated from AZT (50 μM)-treated cells was significant inhibition of cytochrome
c
oxidase and citrate synthase found. Our investigations also demonstrated that AZT, d4T, and 3TC did not affect the synthesis of the 11 polypeptides encoded by mitochondrial DNA, while ddC caused 70% reduction of total polypeptide content and ddI reduced by 43% the total content of 8 polypeptides (including NADH dehydrogenase subunits 1, 2, 4, and 5, cytochrome
c
oxidase subunits I to III, and cytochrome
b
). We hypothesize that in hepatocytes the reserve capacity for mitochondrial respiration is such that inhibition of respiratory enzymes is unlikely to become critical. In contrast, the combined inhibition of the citric acid cycle and electron transport greatly enhances the dependence of the cell on glycolysis and may explain why apparent mitochondrial dysfunction is more prevalent with AZT treatment.
Comparative Activities of Ciprofloxacin and Levofloxacin against
Streptococcus pneumoniae
in an In Vitro Dynamic Model
Authors: Zinner Stephen H. , Simmons Kelly , Gilbert Deborah
Published: July 2002

The activities of levofloxacin (500 mg every 24 h) and ciprofloxacin (750 mg every 12 h) against six pneumococcal isolates in an in vitro dynamic model were compared. For one strain, levofloxacin reduced the inoculum by over 4 log CFU/ml and ciprofloxacin reduced the inoculum by over 2 log CFU/ml. For four isolates, both drugs reduced inocula by 4 log CFU/ml within 6 h, suggesting that this dose of ciprofloxacin should be as effective as levofloxacin against these pneumococci.
Multicenter Surveillance of Antimicrobial Resistance of
Streptococcus pneumoniae
,
Haemophilus influenzae
, and
Moraxella catarrhalis
in Taiwan during the 1998–1999 Respiratory Season
Authors: Hsueh Po-Ren , Liu Yung-Ching , Shyr Jainn-Ming , Wu Tsu-Lan , Yan Jing-Jou , Wu Jiunn-Jong , Leu Hsieh-Shong , Chuang Yin-Ching , Yeu-Jen Lau  , Luh Kwen-Tay
Published: July 2002

A susceptibility surveillance study of 276 isolates of
Streptococcus pneumoniae
, 301 of
Haemophilus influenzae
, and 110 of
Moraxella catarrhalis
was carried out from November 1998 to May 1999 in Taiwan. High rates of nonsusceptibility to penicillin (76%), extended-spectrum cephalosporins (56%), azithromycin (94%), clarithromycin (95%), and trimethoprim-sulfamethoxazole (TMP-SMX) (65%) for
S. pneumoniae
isolates and high rates of nonsusceptibility to amoxicillin (58%) and TMP-SMX (52%) for
H. influenzae
isolates were found. Higher percentages of
S. pneumoniae
isolates nonsusceptible to aminopenicillins, extended-spectrum cephalosporins, macrolides, and TMP-SMX were observed among penicillin-intermediate and -resistant isolates. All quinolones tested were active in vitro against these three organisms.
A Novel Complex Mutant β-Lactamase, TEM-68, Identified in a
Klebsiella pneumoniae
Isolate from an Outbreak of Extended-Spectrum β-Lactamase-Producing Klebsiellae
Authors: Fiett Janusz , Pałucha Andrzej , Mia˛czyńska Beata , Stankiewicz Maria , Przondo-Mordarska Hanna , Hryniewicz Waleria , Gniadkowski Marek
Published: July 2002

Twenty-two
Klebsiella pneumoniae
and two
K. oxytoca
extended-spectrum β-lactamase (ESBL)-producing isolates were collected in 1996 from patients in two pediatric wards of the University Hospital in Wrocław, Poland. Molecular typing has revealed that the
K. pneumoniae
isolates represented four different epidemic strains. Three kinds of enzymes with ESBL activity (pI values of 5.7, 6.0, and 8.2) were identified. The pI 6.0 β-lactamases belonged to the TEM family, and sequencing of the
bla
TEM
genes amplified from representative isolates revealed that these enzymes were TEM-47, previously identified in
K. pneumoniae
isolates from pediatric hospitals in Łódź and Warsaw. One of the TEM-47-producing strains from Wrocław was very closely related to the isolates from the other cities, and this indicated countrywide spread of the epidemic strain. The pI 5.7 β-lactamase was produced by a single
K. pneumoniae
isolate for which, apart from oxyimino-β-lactams, the MICs of β-lactam–inhibitor combinations were also remarkably high. Sequencing revealed that this was a novel TEM β-lactamase variant, TEM-68, specified by the following combination of mutations: Gly238Ser, Glu240Lys, Thr265Met, and Arg275Leu. The new enzyme has most probably evolved from TEM-47 by acquiring the single substitution of Arg275, which before was identified only twice in enzymes with inhibitor resistance (IR) activity. TEM-68 was shown to be a novel complex mutant TEM β-lactamase (CMT-2) which combines strong ESBL activity with relatively weak IR activity and, when expressed in
K. pneumoniae
, is able to confer high-level resistance to a wide variety of β-lactams, including inhibitor combinations. This data confirms the role of the Arg275Leu mutation in determining IR activity and documents the first isolation of
K. pneumoniae
producing the complex mutant enzyme.
Comparison of Fluconazole and Itraconazole in a Rabbit Model of Coccidioidal Meningitis
Authors: Sorensen Kevin N. , Sobel Raymond A. , Clemons Karl V. , Pappagianis Demosthenes , Stevens David A. , Williams Paul L.
Published: July 2002

Coccidioidal meningitis is a devastating disease that requires long-term therapy with little hope of cure. A rabbit model of coccidioidal meningitis was used to compare the therapeutic efficacies of fluconazole (FCZ) and itraconazole (ITZ). Hydrocortisone-treated male New Zealand white rabbits were infected intracisternally with 5.0 × 10
4
to 5.4 × 10
4
arthroconidia of
Coccidioides immitis
. Oral treatment with polyethylene glycol 200 (PEG) (
n
= 9), FCZ (
n
= 8; 80 mg/kg of body weight/day), or ITZ (
n
= 8; 80 mg/kg/day) began 5 days after infection and continued for 28 consecutive days. Both FCZ and ITZ reduced the number of CFU of
C. immitis
organisms in the spinal cord and brain compared with the number in PEG-treated animals (
P
≤ 0.003), but the results for FCZ and ITZ were not different from each other. Histopathologic severity (semiquantitative scoring system by an observer blinded to treatment) was equally reduced in both FCZ and ITZ treatment groups compared with that in controls (
P
≤ 0.0004). Both treatments resulted in lower cerebrospinal fluid (CSF) protein concentrations and leukocyte counts and faster clearing of
C. immitis
from CSF compared with the results for PEG-treated controls. Neither drug affected CSF glucose levels. Both compounds were effective at reducing neurological and systemic signs and extending survival (
P
≤ 0.014). FCZ was more effective at reducing head and body shakes, posture changes, and incontinence; ITZ was more effective at reducing continuous fever. Mean levels of FCZ and ITZ in the serum and CSF were determined by bioassay; at 17 to 26 h postdosing, levels were 28.1 to 40.0 and 22.4 to 29.9 μg/ml, respectively, for FCZ and 0.77 to 2.51 and 0 μg/ml, respectively, for ITZ. The sera of most animals developed antibody to
C. immitis
, but azole treatment attenuated antibody development in CSF and its titer. In conclusion, both FCZ and ITZ were efficacious, but neither was curative in a rabbit model of coccidioidal meningitis.
Activities of Taurolidine In Vitro and in Experimental Enterococcal Endocarditis
Authors: Torres-Viera C. , Thauvin-Eliopoulos C. , Souli M. , DeGirolami P. , Farris M. G. , Wennersten C. B. , Sofia R. D. , Eliopoulos G. M.
Published: July 2002

In vitro, the antimicrobial agent taurolidine inhibited virtually all of the bacteria tested, including vancomycin-resistant enterococci, oxacillin-resistant staphylococci, andStenotrophomonas maltophilia, at concentrations between 250 and 2,000 μg/ml. Taurolidine was not effective in experimental endocarditis. While it appears unlikely that this antimicrobial would be useful for systemic therapy, its bactericidal activity and the resistance rates found (<10−9) are favorable indicators for its possible development for topical use.
Comparison of the Echinocandin Caspofungin with Amphotericin B for Treatment of Histoplasmosis following Pulmonary Challenge in a Murine Model
Authors: Kohler Steve , Wheat L. Joseph , Connolly Patricia , Schnizlein-Bick Carol , Durkin Michelle , Smedema Melinda , Goldberg Janet , Brizendine Edward
Published: July 2002

Twenty clinical isolates ofHistoplasma capsulatumwere tested for their in vitro susceptibilities to caspofungin in comparison to those to amphotericin B by following National Committee for Clinical Laboratory Standards guidelines for yeasts. The mean MICs were 16.6 μg/ml (range, 8 to 32 μg/ml) for caspofungin and 0.56 μg/ml (range, 0.5 to 1.0 μg/ml) for amphotericin B. Survival experiments used a 105dose in a pulmonary challenge model with B6C3F1mice. All mice that received amphotericin B at 2 mg/kg of body weight every other day (q.o.d.), 30% of mice that received caspofungin at 8 mg/kg/day, and 20% of mice that received caspofungin at 4 mg/kg/day survived to day 15, while mice that received caspofungin at 2 mg/kg/day and all control mice that received the vehicle died by day 14. Amphotericin B at 2 mg/kg q.o.d. markedly reduced the fungal burden in the lungs and spleens, as measured byHistoplasmaantigen detection techniques and quantitative cultures, for each comparison. Caspofungin at 10 mg/kg twice a day (b.i.d.) did not reduce the fungal burden, as measured by antigen detection techniques, but slightly reduced the levels of fungi in both the lungs and spleens, as determined by quantitative cultures. Caspofungin at 5 mg/kg b.i.d. did not affect fungal burden. Overall, caspofungin had only a slight effect on survival or fungal burden.
Mycobacterium aviumGrown inAcanthamoeba castellaniiIs Protected from the Effects of Antimicrobials
Authors: Miltner Elizabeth C. , Bermudez Luiz E.
Published: July 2002

Mycobacterium aviumis a common cause of systemic bacterial infection in patients with AIDS. Infection withM. aviumhas been linked to bacterial colonization of domestic water supplies and commonly occurs through the gastrointestinal tract.Acanthamoeba castellanii, a waterborne protozoan, may serve as an environmental host forM. avium. It has been shown that growth ofM. aviumin amoebae enhances invasion and intracellular replication of the bacteria in human macrophages and intestinal epithelial cell line HT-29 as well as in mice. We determined that growth ofM. aviumwithinA. castellaniiinfluenced susceptibility to rifabutin, azithromycin, and clarithromycin. No significant activity againstM. aviumwas seen with rifabutin, azithromycin, and clarithromycin when used to treat monolayers on both day 1 and day 4 after infection. When tested in a macrophage-like cell line (U937), all compounds showed significant anti-M. aviumactivity. Growth ofM. aviumin amoebae appears to reduce the effectiveness of the antimicrobials. These findings may have significant implications for prophylaxis ofM. aviuminfection in AIDS.
In Vitro Activities of Gemifloxacin versus Five Quinolones and Two Macrolides against 271 Spanish Isolates of
Legionella pneumophila
: Influence of Charcoal on Susceptibility Test Results
Authors: García M. T. , Pelaz C. , Giménez M. J. , Aguilar L.
Published: July 2002

The MICs at which 90% of isolates are inhibited for gemifloxacin, trovafloxacin, and grepafloxacin were low (≤0.01 μg/ml) for 271
Legionella
isolates when they were determined by the broth microdilution method but increased (≥6 dilutions) when they were determined by the agar dilution method. This was due to the charcoal in the agar dilution medium, as shown by the progressive decrease in the MICs when the charcoal concentrations decreased. As free drug is the active fraction, charcoal binding should be considered.
Impact of n-6 Polyunsaturated Fatty Acids on Growth of Multidrug-Resistant
Pseudomonas aeruginosa
: Interactions with Amikacin and Ceftazidime
Authors: Giamarellos-Bourboulis E. J. , Grecka P. , Dionyssiou-Asteriou A. , Giamarellou H.
Published: July 2002

Twenty-six multidrug-resistant
Pseudomonas aeruginosa
isolates were exposed over time to 300 μg of gamma-linolenic acid or arachidonic acid per ml or to the combination of both acids at 150 μg/ml each with ceftazidime and amikacin with or without albumin to observe the in vitro interactions of the antibiotics. Antibiotics and albumin were applied at their levels found in serum. Synergy between acids and antibiotics was found against 13 isolates, and it was expressed after 5 h of growth in the presence of albumin. The results indicate that further application in experimental infection models is merited.
Nonylphenolethoxylates as Malarial Chloroquine Resistance Reversal Agents
Authors: Crandall Ian , Charuk Jeffrey , Kain Kevin C.
Published: July 2002

Malaria-associated morbidity and mortality are increasing because of widespread resistance to one of the safest and least expensive antimalarials, chloroquine. The availability of an inexpensive agent that is capable of reversing chloroquine resistance would have a major impact on malaria treatment worldwide. The interaction of nonylphenolethoxylates (NPEs, commercially available synthetic surfactants) with drug-resistant
Plasmodium falciparum
was examined to determine if NPEs inhibited the growth of the parasites and if NPEs could sensitize resistant parasites to chloroquine. NPEs inhibited the development of the parasite when present in the low- to mid-micromolar range (5 to 90 μM), indicating that they possess antimalarial activity. Further, the presence of <10 μM concentrations of NPEs caused the 50% inhibitory concentrations for chloroquine-resistant lines to drop to levels (≤12 nM) observed for sensitive lines and generally considered to be achievable with treatment courses of chloroquine. Long-chain (>30 ethoxylate units) NPEs were found to be most active in
P. falciparum
, which contrasts with previously observed maximal activity of short-chain (∼9 ethoxylate units) NPEs in multidrug-resistant mammalian cell lines. NPEs may be attractive chloroquine resistance reversal agents since they are inexpensive and may be selectively directed against
P. falciparum
without inhibiting mammalian tissue P glycoproteins. Antimalarial preparations that include these agents may prolong the effective life span of chloroquine and other antimalarials.
Rifampin Reduces Concentrations of Trimethoprim and Sulfamethoxazole in Serum in Human Immunodeficiency Virus-Infected Patients
Authors: Ribera Esteban , Pou Leonor , Fernandez-Sola Antoni , Campos Francisco , Lopez Rosa M. , Ocaña Imma , Ruiz Isabel , Pahissa Albert
Published: July 2002

To determine whether rifampin reduces concentrations of trimethoprim (TMP) and sulfamethoxazole (SMX) in serum of human immunodeficiency virus (HIV)-infected persons, levels of these agents were determined by high-performance liquid chromatography before and after more than 12 days of standard antituberculosis treatment for 10 patients who had been taking one double-strength tablet of co-trimoxazole once daily for more than 1 month. Statistically significant, 47 and 23% decreases in TMP and SMX mean areas under the concentration-time curve from 0 to 24 h (AUC
0–24
), respectively, were observed after administration of rifampin.
N
-Acetyl-SMX profiles without and with rifampin were similar. The steady-state AUC
0–24
metabolite/parent drug ratio increased by 32% with rifampin administration. Our study shows that rifampin reduces profiles of TMP and SMX in serum of HIV-infected patients.
Synergy, Pharmacodynamics, and Time-Sequenced Ultrastructural Changes of the Interaction between Nikkomycin Z and the Echinocandin FK463 against
Aspergillus fumigatus
Authors: Chiou Christine C. , Mavrogiorgos Nikolaos , Tillem Elizabeth , Hector Richard , Walsh Thomas J.
Published: July 2002

We investigated the potential synergy between two cell wall-active agents, the echinocandin FK463 (FK) and the chitin synthase inhibitor nikkomycin Z (NZ), against 16 isolates of filamentous fungi. Susceptibility testing was performed with a broth macrodilution procedure by NCCLS methods. The median minimal effective concentration (MEC) of FK against all
Aspergillus
species was 0.25 μg/ml (range, 0.05 to 0.5 μg/ml). For
Fusarium solani
and
Rhizopus oryzae
, MECs of FK were >512 μg/ml. The median MEC of NZ against
Aspergillus fumigatus
was 32 μg/ml (range, 8 to 64 μg/ml), and that against
R. oryzae
was 0.5 μg/ml (range, 0.06 to 2 μg/ml); however, for the other
Aspergillus
species, as well as
F. solani
, MECs were >512 μg/ml. A checkerboard inhibitory assay demonstrated synergy against
A. fumigatus
(median fractional inhibitory concentration index = 0.312 [range, 0.15 to 0.475]). The effect was additive to indifferent against
R. oryzae
and indifferent against other
Aspergillus
spp. and
F. solani
. We further investigated the pharmacodynamics of hyphal damage by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and examined the time-sequenced changes in hyphal ultrastructure. Significant synergistic hyphal damage was demonstrated with the combination of NZ (2 to 32 μg/ml) and FK (0.03 to 0.5 μg/ml) over a wide range of concentrations (
P
< 0.001). The synergistic effect was most pronounced after 12 h of incubation and was sustained through 24 h. Time-sequenced light and electron microscopic studies demonstrated that structural alterations of hyphae were profound, with marked transformation of hyphae to blastospore-like structures, in the presence of FK plus NZ, while fungi treated with a single drug showed partial recovery at 24 h. The methods used in this study may be applicable to elucidating the activity and interaction of other cell wall-active agents. In summary, these two cell wall-targeted antifungal agents, FK and NZ, showed marked time-dependent in vitro synergistic activity against
A. fumigatus
.
Intrinsic Resistance of
Mycobacterium
smegmatis
to Fluoroquinolones May Be Influenced by New Pentapeptide Protein MfpA
Authors: Montero Clemente , Mateu Guaniri , Rodriguez Rosalva , Takiff Howard
Published: July 2002

The fluoroquinolones (FQ) are used in the treatment of
Mycobacterium
tuberculosis
, but the development of resistance could limit their effectiveness. FQ resistance (FQ
R
) is a multistep process involving alterations in the type II topoisomerases and perhaps in the regulation of efflux pumps, but several of the steps remain unidentified. Recombinant plasmid pGADIV was selected from a genomic library of wild-type (WT), FQ-sensitive
M.
smegmatis
by its ability to confer low-level resistance to sparfloxacin (SPX). In WT
M
.
smegmatis
, pGADIV increased the MICs of ciprofloxacin (CIP) by fourfold and of SPX by eightfold, and in
M
.
bovis
BCG it increased the MICs of both CIP and SPX by fourfold. It had no effect on the accumulation of
14
C-labeled CIP or SPX. The open reading frame responsible for the increase in FQ
R
,
mfpA
, encodes a putative protein belonging to the family of pentapeptides, in which almost every fifth amino acid is either leucine or phenylalanine. Very similar proteins are also present in
M
.
tuberculosis
and
M
.
avium
. The MICs of CIP and SPX were lower for an
M
.
smegmatis
mutant strain lacking an intact
mfpA
gene than for the WT strain, suggesting that, by some unknown mechanism, the gene product plays a role in determining the innate level of FQ
R
in
M
.
smegmatis
.
Structural and Functional Analysis of Horse Cathelicidin Peptides
Authors: Skerlavaj Barbara , Scocchi Marco , Gennaro Renato , Risso Angela , Zanetti Margherita
Published: July 2002

Cathelicidin-derived antimicrobial peptides are a component of the peptide-based host defense of neutrophils and epithelia, with a widespread distribution in mammals. We recently reported the cDNA sequences of three putative horse myeloid cathelicidins, named eCATH-1, -2, and -3. A Western analysis was performed to investigate their presence in neutrophils and processing to mature peptides. eCATH-2 and eCATH-3, but not eCATH-1, were found to be present in uncleaved forms in horse neutrophils. The corresponding mature peptides were detected in inflammatory sites, suggesting that processing of the propeptides takes place upon neutrophil activation. A functional characterization was then performed with synthetic eCATH peptides. Circular dichroism measurements indicated an amphipathic α-helical conformation of these peptides in an anisotropic environment, and in vitro assays revealed a potent activity and a broad spectrum of antimicrobial activity for eCATH-1 and a somewhat more restricted spectrum of activity for eCATH-2. Conversely, a strong dependence on salt concentration was observed when the activity of eCATH-3 was tested. This peptide efficiently killed bacteria and some fungal species, i.e.,Cryptococcus neoformansandRhodotorula rubra, in low-ionic-strength media, but the activity was inhibited in the presence of physiological salt medium. This behavior could be modified by modulating the amphipathicity of the molecule. In fact, the synthetic analogue LLK-eCATH-3, with a slightly modified sequence that increases the hydrophobic moment of the peptide, displayed a potent activity in physiological salt medium against the strains resistant to eCATH-3 under these conditions.
Pharmacokinetics of Ethionamide Administered under Fasting Conditions or with Orange Juice, Food, or Antacids
Authors: Auclair Barbara , Nix David E. , Adam Rodney D. , James Gordon T. , Peloquin Charles A.
Published: July 2002

This study was conducted in order to (i) determine the effect of food, orange juice, or antacids on the absorption of a single oral 500-mg dose of ethionamide (ETA) in healthy volunteers, including an assessment of bioequivalence, and (ii) determine ETA population pharmacokinetic (PK) parameters. The pharmacokinetics of ETA in serum was determined for 12 healthy males and females in a randomized, four-period crossover study. Volunteers received single 500-mg doses of ETA either on an empty stomach (reference) or with food, orange juice, or antacids. Serum samples were collected for 48 h and assayed by high-performance liquid chromatography. Data were analyzed by noncompartmental and population methods. Mean test/reference ratios and 90% confidence intervals were determined. No statistically significant differences were seen in the maximum concentration of ETA (Cmax), time to maximum concentration (Tmax), or area under the concentration-time curve from 0 h to infinity (AUC0–∞) between the four treatments (P> 0.05 by analysis of variance). The least-squares mean ratios (with confidence intervals in parentheses) forCmaxwere 105% (81.2 to 135%) after orange juice, 94% (72.8 to 121%) after food, and 88% (68.4 to 114%) after antacids. The least-squares mean ratios (with confidence intervals is in parentheses) for AUC0–∞were 91% (72.7 to 115%) after orange juice, 96% (76.4 to 121%) after food, and 95% (75.5 to 120%) after antacids. The meanTmaxwas slightly prolonged following antacid or food administration (2.3 to 2.6 h) compared to administration on an empty stomach or with juice (1.7 to 1.9 h). The median population PK parameters were as follows:Ka= 0.37 to 0.48 h−1,V/F= 2.0 to 2.8 liters/kg, CL/F= 56.5 to 72.2 liters/h, and terminal half-life = 1.7 to 2.1 h, whereKais the absorption rate constant,Vis the volume of distribution, and CL is clearance. The PK behavior of ETA was not significantly modified by the different conditions studied. Mean ratios for AUC ranged from 0.91 to 0.96 for the orange juice, food, and antacid treatments, indicating a minimal effect on relative bioavailability. ETA can, therefore, be administered with food if tolerance is an issue.
Variant Human Immunodeficiency Virus Type 1 Proteases and Response to Combination Therapy Including a Protease Inhibitor
Authors: Servais Jean , Lambert Christine , Fontaine Elodie , Plesséria Jean-Marc , Robert Isabelle , Arendt Vic , Staub Thérèse , Schneider François , Hemmer Robert , Burtonboy Guy , Schmit Jean-Claude
Published: July 2002

The objective of this observational study was to assess the genetic variability in the human immunodeficiency virus (HIV) protease gene from HIV type 1 (HIV-1)-positive (clade B), protease inhibitor-naı̈ve patients and to evaluate its association with the subsequent effectiveness of a protease inhibitor-containing triple-drug regimen. The protease gene was sequenced from plasma-derived virus from 116 protease inhibitor-naı̈ve patients. The virological response to a triple-drug regimen containing indinavir, ritonavir, or saquinavir was evaluated every 3 months for as long as 2 years (n= 40). A total of 36 different amino acid substitutions compared to the reference sequence (HIV-1 HXB2) were detected. No substitutions at the active site similar to the primary resistance mutations were found. The most frequent substitutions (prevalence, >10%) at baseline were located at codons 15, 13, 12, 62, 36, 64, 41, 35, 3, 93, 77, 63, and 37 (in ascending order of frequency). The mean number of polymorphisms was 4.2. A relatively poorer response to therapy was associated with a high number of baseline polymorphisms and, to a lesser extent, with the presence of I93L at baseline in comparison with the wild-type virus. A71V/T was slightly associated with a poorer response to first-line ritonavir-based therapy. In summary, within clade B viruses, protease gene natural polymorphisms are common. There is evidence suggesting that treatment response is associated with this genetic background, but most of the specific contributors could not be firmly identified. I93L, occurring in about 30% of untreated patients, may play a role, as A71V/T possibly does in ritonavir-treated patients.
Penicillin-Binding Protein 5 and Expression of Ampicillin Resistance in
Enterococcus faecium
Authors: Rice Louis B. , Carias Lenore L. , Hutton-Thomas Rebecca , Sifaoui Farid , Gutmann Laurent , Rudin Susan D.
Published: July 2002

We report a structural and transcriptional analysis of the
pbp5
region of
Enterococcus faecium
C68.
pbp5
exists within a larger operon that includes upstream open reading frames (ORFs) corresponding to previously reported
psr
(penicillin-binding protein synthesis repressor) and
ftsW
(whose product is a transmembrane protein that interacts with PBP3 in
Escherichia coli
septum formation) genes. Hybridization of mRNA from C68, CV133, and four ampicillin-resistant CV133 mutants revealed four distinct transcripts from this region, consisting of (i)
E. faecium ftsW
(

ftsW
Efm

) alone; (ii)
psr
and
pbp5
; (iii)
pbp5
alone; and (iv)

ftsW
Efm

,
psr
, and
pbp5
. Quantities of the different transcripts varied between strains and did not always correlate with quantities of PBP5 or levels of ampicillin resistance. Since the
psr
of C68 is presumably nonfunctional due to an insertion of an extra nucleotide in the codon for the 44th amino acid, the region extending from the

ftsW
Efm

promoter through the
pbp5
gene of C68 was cloned in
E. coli
to facilitate mutagenesis. The
psr
ORF was regenerated using site-directed mutagenesis and introduced into
E. faecium
D344-SRF on conjugative shuttle vector pTCV-lac (pCWR558 [
psr
ORF interrupted]; pCWR583 [
psr
ORF intact]). Ampicillin MICs for both D344-SRF(pCWR558) and D344-SRF(pCWR583) were 64 μg/ml. Quantities of
pbp5
transcript and protein were similar in strains containing either construct regardless of whether they were grown in the presence or absence of ampicillin, arguing against a role for PSR as a repressor of
pbp5
transcription. However, quantities of
psr
transcript were increased in D344-SRF(pCWR583) compared to D344-SRF(pCWR558), especially after growth in ampicillin; suggesting that PSR acts in some manner to activate its own transcription.
Cross-Resistance Testing of Antihepadnaviral Compounds Using Novel Recombinant Baculoviruses Which Encode Drug-Resistant Strains of Hepatitis B Virus
Authors: Delaney William E. , Edwards Ros , Colledge Danni , Shaw Tim , Torresi Joseph , Miller Thomas G. , Isom Harriet C. , Bock C. Thomas , Manns Michael P. , Trautwein Christian , Locarnini Stephen
Published: July 2002

Long-term nucleoside analog therapy for hepatitis B virus (HBV)-related disease frequently results in the selection of mutant HBV strains that are resistant to therapy. Molecular studies of such drug-resistant variants are clearly warranted but have been difficult to do because of the lack of convenient and reliable in vitro culture systems for HBV. We previously developed a novel in vitro system for studying HBV replication that relies on the use of recombinant baculoviruses to deliver greater than unit length copies of the HBV genome to HepG2 cells. High levels of HBV replication can be achieved in this system, which has recently been used to assess the effects of lamivudine on HBV replication and covalently closed circular DNA accumulation. The further development of this novel system and its application to determine the cross-resistance profiles of drug-resistant HBV strains are described here. For these studies, novel recombinant HBV baculoviruses which encoded the L526M, M550I, and L526M M550V drug resistance mutations were generated and used to examine the effects of these substitutions on viral sensitivity to lamivudine, penciclovir (the active form of famciclovir), and adefovir, three compounds of clinical importance. The following observations were made: (i) the L526M mutation confers resistance to penciclovir and partial resistance to lamivudine, (ii) the YMDD mutations M550I and L526M M550V confer high levels of resistance to lamivudine and penciclovir, and (iii) adefovir is active against each of these mutants. These findings are supported by the limited amount of clinical data currently available and confirm the utility of the HBV-baculovirus system as an in vitro tool for the molecular characterization of clinically significant HBV strains.
In Vitro Activities of Linezolid, Meropenem, and Quinupristin-Dalfopristin against Group C and G Streptococci, Including Vancomycin-Tolerant Isolates
Authors: Zaoutis Theoklis , Moore Lynn Steele , Furness Kathleen , Klein Joel D.
Published: July 2002

The in vitro activities of meropenem, linezolid, quinupristin-dalfopristin, vancomycin, and penicillin against 130 clinical isolates of group C and G streptococci, including vancomycin-tolerant isolates, were evaluated. Meropenem, linezolid, quinupristin-dalfopristin, vancomycin, and penicillin MICs at which 90% of the isolates were inhibited were 0.06, 2.0, 0.25, 0.5, and ≤0.016 μg/ml, respectively. Meropenem, linezolid, quinupristin-dalfopristin, and penicillin were active against group C and G streptococci, including vancomycin-resistant strains.
Efficacy of Linezolid in Treatment of Experimental Endocarditis Caused by Methicillin-Resistant
Staphylococcus aureus
Authors: Dailey Charlene F. , Dileto-Fang Christine L. , Buchanan Lewis V. , Oramas-Shirey Martha P. , Batts Donald H. , Ford Charles W. , Gibson John K.
Published: July 2002

The efficacies of orally (p.o.) dosed linezolid and intravenously (i.v.) dosed vancomycin against methicillin-resistant
Staphylococcus aureus
(MRSA) in rabbits with experimental aortic-valve endocarditis were investigated. After endocarditis was established with a recent clinical MRSA isolate, rabbits were dosed for 5 days with linezolid (p.o., three times a day) at either 25, 50, or 75 mg/kg of body weight or vancomycin (i.v., twice a day) at 25 mg/kg. The 25-mg/kg linezolid group had a high mortality rate and bacterial counts in the valve vegetations that were not different from those of the controls. Linezolid dosed p.o. at 50 and 75 mg/kg and i.v. vancomycin produced statistically significant reductions in bacterial counts compared to those of the untreated controls. The reduced bacterial counts and culture-negative valve rates for the animals treated with linezolid at 75 mg/kg were similar to those for the vancomycin-treated animals. Concentrations of linezolid in plasma were determined at several points in the dosing regimen. These results suggest that the efficacy of linezolid in this infection model is related to trough levels in plasma that remain above the MIC for this microorganism. At the ineffective dose of linezolid (25 mg/kg) the concentration at sacrifice was 0.045 times the MIC, whereas the concentrations of linezolid in plasma in the 50- and 75-mg/kg groups were 2 and 5 times the MIC at sacrifice, respectively. The results from this experimental model suggest that the oxazolidinone linezolid may be effective for the treatment of serious staphylococcal infections when resistance to other antimicrobials is present.
Mycobacterium smegmatis
d
-Alanine Racemase Mutants Are Not Dependent on
d
-Alanine for Growth
Authors: Chacon Ofelia , Feng Zhengyu , Harris N. Beth , Cáceres Nancy E. , Adams L. Garry , Barletta Raúl G.
Published: July 2002

Mycobacterium smegmatis
is a fast-growing nonpathogenic species particularly useful in studying basic cellular processes of relevance to pathogenic mycobacteria. This study focused on the
d
-alanine racemase gene (
alrA
), which is involved in the synthesis of
d
-alanine, a basic component of peptidoglycan that forms the backbone of the cell wall.
M. smegmatis alrA
null mutants were generated by homologous recombination using a kanamycin resistance marker for insertional inactivation. Mutants were selected on Middlebrook medium supplemented with 50 mM
d
-alanine and 20 μg of kanamycin per ml. These mutants were also able to grow in standard and minimal media without
d
-alanine, giving rise to colonies with a drier appearance and more-raised borders than the wild-type strain. The viability of the mutants and independence of
d
-alanine for growth indicate that inactivation of
alrA
does not impose an auxotrophic requirement for
d
-alanine, suggesting the existence of a new pathway of
d
-alanine biosynthesis in
M. smegmatis
. Biochemical analysis demonstrated the absence of any detectable
d
-alanine racemase activity in the mutant strains. In addition, the
alrA
mutants displayed hypersusceptibility to the antimycobacterial agent
d
-cycloserine. The MIC of
d
-cycloserine for the mutant strain was 2.56 μg/ml, 30-fold less than that for the wild-type strain. Furthermore, this hypersusceptibility was confirmed by the bactericidal action of
d
-cycloserine on broth cultures. The kinetic of killing for the mutant strain followed the same pattern as that for the wild-type strain, but at a 30-fold-lower drug concentration. This effect does not involve a change in the permeability of the cell wall by this drug and is consistent with the identification of
d
-alanine racemase as a target of
d
-cycloserine. This outcome is of importance for the design of novel antituberculosis drugs targeting peptidoglycan biosynthesis in mycobacteria.