bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomic and electronic structure of tetrahedrally coordinated compound semiconductor interfaces
Authors: Duke C. B. 
Published: July 2002

The most extensively specified atomic interface geometries for tetrahedrally coordinated compound semiconductors are those of the nonpolar (110) cleavage surfaces of zinc-blende structure semiconductors, specifically AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, and CdTe. These geometries have been determined experimentally by a variety of techniques, low-energy electron diffraction intensity analysis and ion scattering, in particular. They have been predicted by several quantum chemical methods, including extended tight-binding, pseudopotential, and ab initio models. All of the structures are known to be qualitatively identical: a bond-length-conserving rotation in the top layer followed by a relaxation of this layer toward the substrate and possibly small counter rotations in deeper layers. The atomic rotation in the top layer is driven by a rehybridization of the surface chemical bonds to redistribute the charge in the dangling bonds of the unrelaxed surface into the remaining surface and back bonds. The magnitudes of the surface atomic relaxations scale linearly with the bulk lattice constants. Atomic geometries also are available for a few overlayer structures on these surfaces, i.e., p(1×1) structures of Al on GaAs and of Sb on GaAs and InP. An area of current research is the extension of such studies to the cleavage faces, (101̄0) and (112̄0), of wurtzite-structure compound semiconductors. Theoretical predictions are available for ZnO, ZnS, ZnSe, CdS, and CdSe.
Experimental structure analyses have been reported only for the (101̄0) surfaces of ZnO and CdSe. The relaxed geometries of these surfaces are analogous to those of zinc-blende (110), and are driven by the same mechanism of dangling-bond charge redistribution. Another active research area is the study of the polar surfaces of zinc-blende structure materials. These surfaces exhibit complex reconstructions which depend both on the surface stoichiometry and on the sample preparation procedure. Structure analyses have been reported for GaAs(111)-(2×2), InSb(111)-(2×2), GaP(111)-(2×2), GaAs(1̄1̄1̄)-(2×2), InP(1̄1̄1̄)-(1×1), and GaAs (100)-(2×4), as well as for GaAs(311) surfaces. These reconstructions also are driven by rehybridization of the surface chemical bonds, but the precise nature of this rehybridization differs from one structure to another. The electronic structures of all three classes of interface have been studied by a combination of photoemission spectroscopy and quantum chemical calculations. The interface states are dominated by the surface-relaxation-induced rehybridization and/or consequences of interface chemical reactions. In those cases for which the atomic geometries are known independently, the qualitative features of the observed interface-state eigenvalue spectra are well reproduced by the model calculations, although the models disagree both among themselves and with the measurements on several details.
Characterization of Fluoroquinolone Resistance among Veterinary Isolates of Avian
Escherichia coli
Authors: White David G. , Piddock Laura J. V. , Maurer John J. , Zhao Shaohua , Ricci Vito , Thayer Stephan G. 
Published: July 2002

ABSTRACT

Fluoroquinolone-resistant avian
Escherichia coli
isolates from northern Georgia were investigated for
gyrA
and
parC
mutations. All isolates contained a mutation in GyrA replacing Ser83 with Leu; seven isolates also contained mutations replacing Asp87 with either Gly or Tyr. Random amplified polymorphic DNA analysis revealed that quinolone-resistant
E. coli
isolates were genetically diverse.
Characterization of an In Vitro-Selected Amoxicillin-Resistant Strain of
Helicobacter pylori
Authors: DeLoney Cindy R. , Schiller Neal L. 
Published: July 2002

ABSTRACT

An amoxicillin-resistant (Amox
r
) strain of
Helicobacter pylori
was selected for by culturing an amoxicillin-sensitive (Amox
s
) strain in increasingly higher concentrations of amoxicillin, resulting in a 133-fold increase in MIC, from 0.03 to 0.06 μg/ml to 4 to 8 μg/ml. This resistance was stable upon freezing for at least 6 months and conferred cross-resistance to seven other β-lactam antibiotics. β-Lactamase activity was not detected in this Amox
r
strain; however, analysis of the penicillin-binding protein (PBP) profiles generated from isolated bacterial membranes of the Amox
s
parental strain and the Amox
r
strain revealed a significant decrease in labeling of PBP 1 by biotinylated amoxicillin (bio-Amox) in the Amox
r
strain. Comparative binding studies of PBP 1 for several β-lactams demonstrated that PBP 1 in the Amox
r
strain had decreased affinity for mezlocillin but not significantly decreased affinity for penicillin G. In addition, PBP profiles prepared from whole bacterial cells showed decreased labeling of PBP 1 and PBP 2 in the Amox
r
strain at all bio-Amox concentrations tested, suggesting a diffusional barrier to bio-Amox or a possible antibiotic efflux mechanism. Uptake analysis of
14
C-labeled penicillin G showed a significant decrease in uptake of the labeled antibiotic by the Amox
r
strain compared to the Amox
s
strain, which was not affected by pretreatment with carbonyl cyanide
m
-chlorophenylhydrazone, eliminating the possibility of an efflux mechanism in the resistant strain. These results demonstrate that alterations in PBP 1 and in the uptake of β-lactam antibiotics in
H. pylori
can be selected for by prolonged exposure to amoxicillin, resulting in increased resistance to this antibiotic.
Susceptibility to PNU-140690 (Tipranavir) of Human Immunodeficiency Virus Type 1 Isolates Derived from Patients with Multidrug Resistance to Other Protease Inhibitors
Authors: Rusconi Stefano , La Seta Catamancio Simona , Citterio Paola , Kurtagic Semir , Violin Michela , Balotta Claudia , Moroni Mauro , Galli Massimo , d'Arminio-Monforte Antonella 
Published: July 2002

ABSTRACT

In our study we examined the anti-human immunodeficiency virus type 1 (anti-HIV-1) activity of a novel HIV-1 protease inhibitor, PNU-140690 (tipranavir), against patient-derived isolates resistant to multiple other protease inhibitors (PIs). The aim of our experiments was to investigate the genotypes and the in vitro phenotypes of drug resistance of PNU-140690. We carried out drug susceptibility tests with peripheral blood mononuclear cells and a fixed amount of infectious virus (1,000 50% tissue culture infective doses) to determine the 50% inhibitory concentration (IC
50
) and IC
90
, PCR assays for the detection of drug resistance mutations in RNA in plasma, and direct sequencing of PCR products. Phenotypic resistance to PIs was invariably related to genotypic mutations. The substitutions among the amino acid residues of the protease included L10I, K20R, L24I, M36I, N37D, G48V, I54V, L63P, I64V, A71V, V77I, V82A, I84V, and L90M. Isolates from all of the patients had developed a maximal degree of resistance to indinavir, ritonavir, and nelfinavir (IC
50
s, >0.1 μM). We also compared these mutations with the amino acid changes previously described in association with in vivo tipranavir administration. The mutations included the following: I15V, E35D, N37D, R41K, D60E, and A71T. Infections with IIIB, 14aPre, and N70 were inhibited by an average drug IC
90
of 0.18 ± 0.02 μM in multiple experiments. The average mean ± standard error of mean IC
90
for the entire group of multidrug-resistant isolates derived from the mean values for two culture wells with p24 antigen supernatant appeared to be 0.619 ± 0.055 μM (range, 0.31 to 0.86 μM). Tipranavir retained a sustained antiviral activity against PI-MDR clinical isolates and might be useful in combination regimens with other antiretroviral agents for patients who have already failed other PI-containing therapies.
The
Legionella
(
Fluoribacter
)
gormanii
Metallo-β-Lactamase: a New Member of the Highly Divergent Lineage of Molecular-Subclass B3 β-Lactamases
Authors: Boschi Letizia , Mercuri Paola Sandra , Riccio Maria Letizia , Amicosante Gianfranco , Galleni Moreno , Frère Jean-Marie , Rossolini Gian Maria 
Published: July 2002

ABSTRACT

A metallo-β-lactamase determinant was cloned from a genomic library of
Legionella
(
Fluoribacter
)
gormanii
ATCC 33297
T
constructed in the plasmid vector pACYC184 and transformed into
Escherichia coli
DH5α, by screening for clones showing a reduced susceptibility to imipenem. The product of the cloned determinant, named FEZ-1, contains a 30-kDa polypeptide and exhibits an isoelectric pH of 7.6. Sequencing revealed that FEZ-1 is a molecular-class B β-lactamase which shares the closest structural similarity (29.7% of identical residues) with the L1 enzyme of
Stenotrophomonas maltophilia
, being a new member of the highly divergent subclass B3 lineage. All the residues that in L1 are known to be directly or indirectly involved in coordination of the zinc ions were found to be conserved also in FEZ-1, suggesting that the geometry of zinc coordination in the active site of the latter enzyme is identical to that of L1. Unlike L1, however, FEZ-1 appeared to be monomeric in gel permeation chromatography experiments and exhibited a distinctive substrate specificity with a marked preference for cephalosporins and meropenem. The properties of FEZ-1 overall resembled those of a β-lactamase previously purified from the same strain of
L. gormanii
(T. Fujii, K. Sato, K. Miyata, M. Inoue, and S. Mitsuhashi, Antimicrob. Agents Chemother. 29:925–926, 1986) and are as yet unique among class B enzymes, reinforcing the notion that considerable functional heterogeneity can be encountered among members of this class. A system for overexpression of the
bla
FEZ-1
gene in
E. coli
, based on the T7 phage promoter, was also developed.
TEM-72, a New Extended-Spectrum β-Lactamase Detected in
Proteus mirabilis
and
Morganella morganii
in Italy
Authors: Perilli Mariagrazia , Segatore Bernardetta , Rosaria De Massis Maria , Riccio Maria Letizia , Bianchi Ciro , Zollo Alessandro , Rossolini Gian Maria , Amicosante Gianfranco 
Published: July 2002

ABSTRACT

A new natural TEM-2 derivative, named TEM-72, was identified in a
Proteus mirabilis
strain and in a
Morganella morganii
strain isolated in Italy in 1999. Compared to TEM-1, TEM-72 contains the following amino acid substitutions: Q39K, M182T, G238S, and E240K. Kinetic analysis showed that TEM-72 exhibits an extended-spectrum activity, including activity against oxyimino-cephalosporins and aztreonam. Expression of
bla
TEM-72
in
Escherichia coli
was capable of decreasing the host susceptibility to the above drugs.
Use of Saliva Specimens for Monitoring Indinavir Therapy in Human Immunodeficiency Virus-Infected Patients
Authors: Wintergerst Uwe , Kurowski M. , Rolinski B. , Müller M. , Wolf E. , Jaeger H. , Belohradsky B. H. 
Published: July 2002

ABSTRACT
Indinavir concentrations were determined in plasma and saliva over a random period of 4 h. On average, levels in saliva were 70% ± 38% of the corresponding levels in plasma. These findings suggest that saliva might serve as an appropriate specimen for monitoring of plasma indinavir levels in patients treated with indinavir.
Pharmacodynamics of Gemifloxacin against
Streptococcus pneumoniae
in an In Vitro Pharmacokinetic Model of Infection
Authors: MacGowan Alasdair P. , Rogers Chris A. , Holt H. Alan , Wootton Mandy , Bowker Karen E. 
Published: July 2002

ABSTRACT

The pharmacodynamics of gemifloxacin against
Streptococcus pneumoniae
were investigated in a dilutional pharmacodynamic model of infection. Dose fractionation was used to simulate concentrations of gemifloxacin in human serum associated with 640 mg every 48 h (one dose), 320 mg every 24 h (two doses), and 160 mg every 12 h (four doses). Five strains of
S. pneumoniae
for which MICs were 0.016, 0.06, 0.1, 0.16, and 0.24 mg/liter were used to assess the antibacterial effect of gemifloxacin. An inoculum of 10
7
to 10
8
CFU/ml was used, and each experiment was performed at least in triplicate. The pharmacodynamic parameters (area under the concentration-time curve [AUC]/MIC, maximum concentration of drug in serum [
C
max
]/MIC, and the time that the serum drug concentration remains higher than the MIC [
T
> MIC]) were related to antibacterial effect as measured by the area under the bacterial-kill curve from 0 to 48 h (AUBKC
48
) using an inhibitory sigmoid
E
max
model. Weighted least-squares regression was used to predict the effect of the pharmacodynamic parameters on AUBKC
48
, and Cox proportional-hazards regression was used to predict the effect of the three pharmacodynamic parameters on the time needed to kill 99.9% of the starting inoculum (
T
99.9). There was a clear relationship between strain susceptibility and clearance from the model. The simulations (160 mg every 12 h) were associated with slower initial clearance than were the other simulations; in contrast, bacterial regrowth occurred with the 640-mg simulation when MICs were ≥0.1 mg/liter. The percentage coefficient of variance was 19% for AUBKC
48
, and the inhibitory sigmoid
E
max
model best fit the relationship between AUBKC
48
and AUC/MIC.
C
max
/MIC and
T
> MIC fit less well. The maximum response occurred at an AUC/MIC of >300 to 400. In weighted least-squares regression analysis, there was no evidence that
C
max
/MIC was predictive of AUBKC
48
, but both AUC/MIC and
T
> MIC were. A repeat analysis using only data for which the
T
> MIC was >75% and for which hence regrowth was minimized indicated that AUC/MIC alone was predictive of AUBKC
48
. Initial univariate analysis indicated that all three pharmacodynamic parameters were predictive of
T
99.9, but in the multivariate model only
C
max
/MIC reached significance. These data indicate that gemifloxacin is an effective antipneumococcal agent and that AUC/MIC is the best predictor of antibacterial effect as measured by AUBKC
48
. However,
C
max
/MIC is the best predictor of speed of kill, as measured by
T
99.9.
T
> MIC also has a role in determining AUBKC
48
, especially when the dose spacing is considerable. Once-daily dosing seems most suitable for gemifloxacin.
Dosage-Dependent Antifungal Efficacy of V-Echinocandin (LY303366) against Experimental Fluconazole-Resistant Oropharyngeal and Esophageal Candidiasis
Authors: Petraitis Vidmantas , Petraitiene Ruta , Groll Andreas H. , Sein Tin , Schaufele Robert L. , Lyman Caron A. , Francesconi Andrea , Bacher John , Piscitelli Stephen C. , Walsh Thomas J. 
Published: July 2002

ABSTRACT

V-echinocandin (VER-002; LY303366) is a semisynthetic derivative of echinocandin B and a potent inhibitor of fungal (1, 3)-β-
d
-glucan synthase. We studied the antifungal efficacy, the concentrations in saliva and tissue, and the safety of VER-002 at escalating dosages against experimental oropharyngeal and esophageal candidiasis caused by fluconazole-resistant
Candida albicans
in immunocompromised rabbits. Study groups consisted of untreated controls, animals treated with VER-002 at 1, 2.5, and 5 mg/kg of body weight/day intravenously (i.v.), animals treated with fluconazole at 2 mg/kg/day i.v., or animals treated with amphotericin B at 0.3 mg/kg/day. VER-002-treated animals showed a significant dosage-dependent clearance of
C. albicans
from the tongue, oropharynx, esophagus, stomach, and duodenum in comparison to that for untreated controls. VER-002 also was superior to amphotericin B and fluconazole in clearing the organism from all sites studied. These in vivo findings are consistent with the results of in vitro time-kill assays, which demonstrated that VER-002 has concentration-dependent fungicidal activity. Esophageal tissue VER-002 concentrations were dosage proportional and exceeded the MIC at all dosages. Echinocandin concentrations in saliva were greater than or equal to the MICs at all dosages. There was no elevation of serum hepatic transaminase, alkaline phosphatase, bilirubin, potassium, or creatinine levels in VER-002-treated rabbits. In summary, the echinocandin VER-002 was well tolerated, penetrated the esophagus and salivary glands, and demonstrated dosage-dependent antifungal activity against fluconazole-resistant esophageal candidiasis in immunocompromised rabbits.
Pharmacokinetics and Inflammatory Fluid Penetration of Intravenous Daptomycin in Volunteers
Authors: Wise R. , Gee T. , Andrews J. M. , Dvorchik B. , Marshall G. 
Published: July 2002

ABSTRACT
The lipopeptide antimicrobial daptomycin was administered intravenously at a dose of 4 mg/kg of body weight to seven healthy male volunteers. The concentrations of daptomycin in plasma, cantharidin-induced inflammatory fluid, and urine were measured by a microbiological assay. The mean ± standard deviation peak concentrations in plasma and inflammatory fluid were 77.5 ± 8.3 and 27.6 ± 9.5 μg/ml, respectively; the mean terminal elimination half-lives were 7.74 and 13.2 h, respectively. The overall penetration of total drug into the inflammatory fluid (measured by ratio of the area under the concentration-time curve from 0 to 24 h for inflammatory fluid compared with that for plasma) was 68.4%. The mean urinary recovery over 24 h was 59.7%.
International Interlaboratory Quality Control Program for Measurement of Antiretroviral Drugs in Plasma
Authors: Aarnoutse Rob E. , Verweij-van Wissen Corrien P. W. G. M. , van Ewijk-Beneken Kolmer Eleonora W. J. , Wuis Eveline W. , Koopmans Peter P. , Hekster Yechiel A. , Burger David M. 
Published: July 2002

ABSTRACT
An international interlaboratory quality control program for measurement of antiretroviral drugs was initiated. The first round was confined to protease inhibitors and showed large variability in the performance of participating laboratories. The results demonstrate the need for and utility of an ongoing quality control program in this area of bioanalysis.
In Vitro Activities of Tigecycline (GAR-936) against Recently Isolated Clinical Bacteria in Spain
Authors: Betriu Carmen , Rodríguez-Avial Iciar , Sánchez Blas Ali , Gómez María , Álvarez Juan , Picazo Juan J. 
Published: July 2002

ABSTRACT

The antimicrobial activities of tigecycline (GAR-936) were compared with those of other agents against 1,087 strains recently isolated in 12 Spanish medical centers. Tigecycline showed activity against a wide spectrum of aerobic and anaerobic bacteria, including strains such as methicillin-resistant
Staphylococcus aureus
, coagulase-negative staphylococci, penicillin-resistant
Streptococcus pneumoniae
,
Enterococcus faecium
,
Acinetobacter baumannii
, and
Stenotrophomonas maltophilia.
Activities of New Fluoroquinolones, Ketolides, and Other Antimicrobials against Blood Culture Isolates of Viridans Group Streptococci from across Canada, 2000
Authors: Gershon Andrea S. , de Azavedo Joyce C. S. , McGeer Allison , Ostrowska Krystyna I. , Church Deirdre , Hoban Daryl J. , Harding Godfrey K. M. , Weiss Karl , Abbott Lewis , Smaill Fiona , Gourdeau Marie , Murray Gilles , Low Donald E. 
Published: July 2002

ABSTRACT
The rates of nonsusceptibility to penicillin, erythromycin, and clindamycin of 191 blood culture isolates of viridans group streptococci collected from across Canada in 2000 were 36, 42, and 10%, respectively. Although 8% of the strains were resistant to ciprofloxacin (MIC ⩾ 4 μg/ml), the MICs of gemifloxacin, BMS 284756, telithromycin, and ABT 773 at which 90% of the strains were inhibited were 0.06, 0.06, 0.12, and 0.03 μg/ml, respectively.
Pharmacodynamics of Moxifloxacin against
Streptococcus pyogenes
in an In Vitro Kinetic Model
Authors: Odenholt Inga , Löwdin Elisabeth , Gustafsson Ingegerd , Cars Otto 
Published: July 2002

ABSTRACT

The aim of the present study was to investigate the pharmacodynamics of moxifloxacin against strains of
Streptococcus pyogenes
with different susceptibilities to erythromycin by using an in vitro kinetic model simulating human pharmacokinetics of moxifloxacin at oral doses of 400 and 200 mg, respectively. When the different strains of
S. pyogenes
were exposed to the higher dose, the number of bacteria was reduced below the detection limit after 12 h and no regrowth was noted during the following 12 h. At the lower dose there was regrowth of the strains with constitutive and inducible erythromycin resistance of the MLS
B
phenotype. Replication assays of the regrowing bacteria indicated that the failure of moxifloxacin to kill the MLS
B
strains at the lower dose was likely caused by the emergence of preexisting resistant subpopulations. Thus, the present study indicates that the presently used 400-mg dose seems to have an advantage over the lower dose in that the risk for selection of resistant subpopulations is minimized.
Simultaneous Direct Counting of Total and Specific Microbial Cells in Seawater, Using a Deep-Sea Microbe as Target
Authors: Maruyama Akihiko , Sunamura Michinari 
Published: July 2002

ABSTRACT

To rapidly and accurately enumerate total and specific microbes in aquatic samples, fluorescent in situ hybridization was combined with direct counting via direct immobilization of cells on a polymer-coated Nuclepore filter. The technique, named FISH-DC, achieved almost complete recovery of total cells and reproducibility of
Psychrobacter pacificensis
cells of deep-sea origin (error, ≤3%) in a mixed culture and in natural seawater. Target cells immobilized on the filter were also successfully enumerated after stringent 3-cycle hybridization and even after a 16-month preservation at −30°C.
Rhizobitoxine Production by
Bradyrhizobium elkanii
Enhances Nodulation and Competitiveness on
Macroptilium atropurpureum
Authors: Yuhashi Ken-Ichi , Ichikawa Norikazu , Ezura Hiroshi , Akao Shoichiro , Minakawa Yasuo , Nukui Noriyuki , Yasuta Tsuyoshi , Minamisawa Kiwamu 
Published: July 2002

ABSTRACT

Application of 1-aminoocyclopropane-1-carboxylic acid, an ethylene precursor, decreased nodulation of
Macroptilium atropurpureum
by
Bradyrhizobium elkanii. B. elkanii
produces rhizobitoxine, an ethylene synthesis inhibitor. Elimination of rhizobitoxine production in
B. elkanii
increased ethylene evolution and decreased nodulation and competitiveness on
M. atropurpureum
. These results suggest that rhizobitoxine enhances nodulation and competitiveness of
B. elkanii
on
M. atropurpureum
.
Production and Consumption of Nitric Oxide by Three Methanotrophic Bacteria
Authors: Ren Tie , Roy Réal , Knowles Roger 
Published: July 2002

ABSTRACT

We studied nitrogen oxide production and consumption by methanotrophs
Methylobacter luteus
(group I),
Methylosinus trichosporium
OB3b (group II), and an isolate from a hardwood swamp soil, here identified by 16S ribosomal DNA sequencing as
Methylobacter
sp. strain T20 (group I). All could consume nitric oxide (nitrogen monoxide, NO), and produce small amounts of nitrous oxide (N
2
O). Only
Methylobacter
strain T20 produced large amounts of NO (>250 parts per million by volume [ppmv] in the headspace) at specific activities of up to 2.0 × 10
−17
mol of NO cell
−1
day
−1
, mostly after a culture became O
2
limited. Production of NO by strain T20 occurred mostly in nitrate-containing medium under anaerobic or nearly anaerobic conditions, was inhibited by chlorate, tungstate, and O
2
, and required CH
4
. Denitrification (methanol-supported N
2
O production from nitrate in the presence of acetylene) could not be detected and thus did not appear to be involved in the production of NO. Furthermore,

cd
1

and Cu nitrite reductases, NO reductase, and N
2
O reductase could not be detected by PCR amplification of the
nirS
,
nirK
,
norB
, and
nosZ
genes, respectively.
M. luteus
and
M. trichosporium
produced some NO in ammonium-containing medium under aerobic conditions, likely as a result of methanotrophic nitrification and chemical decomposition of nitrite. For
Methylobacter
strain T20, arginine did not stimulate NO production under aerobiosis, suggesting that NO synthase was not involved. We conclude that strain T20 causes assimilatory reduction of nitrate to nitrite, which then decomposes chemically to NO. The production of NO by methanotrophs such as
Methylobacter
strain T20 could be of ecological significance in habitats near aerobic-anaerobic interfaces where fluctuating O
2
and nitrate availability occur.