bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin of the Cytoplasmic pH Changes during Anaerobic Stress in Higher Plant Cells. Carbon-13 and Phosphorous-31 Nuclear Magnetic Resonance Studies
Authors: Gout Elisabeth , Boisson Anne-Marie , Aubert Serge , Douce Roland , Bligny Richard 
Published: July 2002

AbstractWe tested the contribution of nucleoside triphosphate (NTP) hydrolysis, ethanol, and organic acid syntheses, and H+-pump ATPases activity in the acidosis of anoxic sycamore (Acer pseudoplatanus) plant cells. Culture cells were chosen to alter NTP pools and fermentation with specific nutrient media (phosphate [Pi]-deprived and adenine- or glycerol-supplied). In vivo 31P- and 13C-nuclear magnetic resonance (NMR) spectroscopy was utilized to noninvasively measure intracellular pHs, Pi, phosphomonoesters, nucleotides, lactate, and ethanol. Following the onset of anoxia, cytoplasmic (cyt) pH (7.5) decreased to 6.8 within 4 to 5 min, whereas vacuolar pH (5.7) and external pH (6.5) remained stable. The NTP pool simultaneously decreased from 210 to &lt;20 nmol g−1 cell wet weight, whereas nuceloside diphosphate, nucleoside monophosphate, and cyt pH increased correspondingly. The initial cytoplasmic acidification was at a minimum in Pi-deprived cells containing little NTP, and at a maximum in adenine-incubated cells showing the highest NTP concentration. Our data show that the release of H+ ions accompanying the Pi-liberating hydrolysis of NTP was the principal cause of the initial cyt pH drop and that this cytoplasmic acidosis was not overcome by H+ extrusion. After 15 min of anoxia, a partial cyt-pH recovery observed in cells supplied with Glc, but not with glycerol, was attributed to the H+-consuming ATP synthesis accompanying ethanolic fermentation. Following re-oxygenation, the cyt pH recovered its initial value (7.5) within 2 to 3 min, whereas external pH decreased abruptly. We suggest that the H+-pumping ATPase located in the plasma membrane was blocked in anoxia and quickly reactivated after re-oxygenation.
Synchrotron radiation topographic observation of KTiOPO4crystals under an electric field
Authors: Liu W. J. , Jiang S. S. , Ding Y. , Wu X. S. , Wang J. Y. , Hu X. B. , Jiang J. H. 
Published: July 2002

In situwhite-beam synchrotron radiation topographic observations under an electric field have been made on the KTiOPO4(KTP) family of crystals. The investigation shows a strong enhancement of diffracted intensity forhklreflections (l ≠ 0) and topographic contrast in the form of fine striations when the external electric field is parallel to the polar axis. Several kinds of doped and undoped samples with various grown-in defects, such as domain boundaries, growth striations, growth-sector boundaries, dislocations,etc., have been studied in detail. The results suggest that these defects have very little effect on the field-induced striations. It is believed that the movement of K^+ ions driven by the electric field leads to a local accumulation of charges and a lattice distortion. The strongly anisotropic conductivity is a governing factor in the explanation of the field-related phenomena in this kind of quasi-one-dimensional conductor.
Using electron-microscopy images as a model for molecular replacement
Authors: Dodson Eleanor J. 
Published: July 2002

This review addresses the technical problems encountered while using models based on electron microscopy to generate initial phases for crystallographic studies. The test cases used were the gp6 portal protein with 13-fold rotational symmetry and the human hepatitis virus HepB, a viral assembly with T = 4 icosohedral symmetry.
XAFS investigations of tin nitrides
Authors: Lützenkirchen-Hecht Dirk , Scotti Nicole , Jacobs Herbert , Frahm Ronald 
Published: July 2002

Tin nitrides (Sn3N4) prepared by the reaction of Sn-halides with KNH2 in liquid ammonia and a subsequent vacuum annealing procedure were investigated with transmission mode XAFS experiments. While the near edge data suggest the presence of a univalent Sn-compound with a valency close to +4, the analysis of the extended X-ray absorption fine structure proves the presence of two different local Sn sites in this crystal structure: While Sn(1) is surrounded by 4 nitrogen in a distance of 2.06 Å, each Sn(2) ion is coordinated with 6 nitrogen at about 2.17 Å radial distance.
Random circular permutation leading to chain disruption within and near α helices in the catalytic chains of aspartate transcarbamoylase: Effects on assembly, stability, and function
Authors: Beernink Peter T. , Yang Ying R. , Graf Roney , King David S. , Shah Shaival S. , Schachman Howard K. 
Published: July 2002

AbstractA collection of circularly permuted catalytic chains of aspartate transcarbamoylase (ATCase) has been generated by random circular permutation of the pyrB gene. From the library of ATCases containing permuted polypeptide chains, we have chosen for further investigation nine ATCase variants whose catalytic chains have termini located within or close to an α helix. All of the variants fold and assemble into dodecameric holoenzymes with similar sedimentation coefficients and slightly reduced thermal stabilities. Those variants disrupted within three different helical regions in the wild‐type structure show no detectable enzyme activity and no apparent binding of the bisubstrate analog N‐phosphonacetyl‐l‐aspartate. In contrast, two variants whose termini are just within or adjacent to other α helices are catalytically active and allosteric. As expected, helical disruptions are more destabilizing than loop disruptions. Nonetheless, some catalytic chains lacking continuity within helical regions can assemble into stable holoenzymes comprising six catalytic and six regulatory chains. For seven of the variants, continuity within the helices in the catalytic chains is important for enzyme activity but not necessary for proper folding, assembly, and stability of the holoenzyme.
Plasmid-Mediated Florfenicol Resistance Encoded by the
floR
Gene in
Escherichia coli
Isolated from Cattle
Authors: Cloeckaert Axel , Baucheron Sylvie , Flaujac Geraldine , Schwarz Stefan , Kehrenberg Corinna , Martel Jean-Louis , Chaslus-Dancla Elisabeth 
Published: July 2002

ABSTRACT

A florfenicol resistance gene almost identical to
floR
of
Salmonella enterica
serovar Typhimurium DT104 was detected on 110- to 125-kb plasmids in
Escherichia coli
isolates of animal origin. Analysis of the
floR
gene flanking regions of one of the plasmids showed that they were different from those encountered in
S. enterica
serovar Typhimurium DT104.
Two New Mechanisms of Macrolide Resistance in Clinical Strains of
Streptococcus pneumoniae
from Eastern Europe and North America
Authors: Tait-Kamradt A. , Davies T. , Appelbaum P. C. , Depardieu F. , Courvalin P. , Petitpas J. , Wondrack L. , Walker A. , Jacobs M. R. , Sutcliffe J. 
Published: July 2002

ABSTRACT

Resistance to macrolides in pneumococci is generally mediated by methylation of 23S rRNA via
erm
(B) methylase which can confer a macrolide (M)-, lincosamide (L)-, and streptogramin B (S
B
)-resistant (MLS
B
) phenotype or by drug efflux via
mef
(A) which confers resistance to 14- and 15-membered macrolides only. We studied 20 strains with unusual ML or MS
B
phenotypes which did not harbor
erm
(B) or
mef
(A). The strains had been isolated from patients in Eastern Europe and North America from 1992 to 1998. These isolates were found to contain mutations in genes for either 23S rRNA or ribosomal proteins. Three strains from the United States with an ML phenotype, each representing a different clone, were characterized as having an A2059G (
Escherichia coli
numbering) change in three of the four 23S rRNA alleles. Susceptibility to macrolides and lincosamides decreased as the number of alleles in isogenic strains containing A2059G increased. Sixteen MS
B
strains from Eastern Europe were found to contain a 3-amino-acid substitution (
69
GTG
71
to TPS) in a highly conserved region of the ribosomal protein L4 (
63
KPWRQK
GTG
RAR
74
). These strains formed several distinct clonal types. The single MS
B
strain from Canada contained a 6-amino-acid L4 insertion (
69
GTG
REKGTG
RAR), which impacted growth rate and also conferred a 500-fold increase in MIC on the ketolide telithromycin. These macrolide resistance mechanisms from clinical isolates are similar to those recently described for laboratory-derived mutants.
Effect of Proinflammatory Cytokines on the Interplay between Roxithromycin, HMR 3647, or HMR 3004 and Human Polymorphonuclear Neutrophils
Authors: Vazifeh D. , Bryskier A. , Labro M. T. 
Published: July 2002

ABSTRACTCytokines, the hallmarks of infectious and inflammatory diseases, modify phagocyte activities and thus may interfere with the immunomodulating properties of antibacterial agents. We have investigated whether various proinflammatory cytokines (interleukin 1 [IL-1], IL-6, IL-8, gamma interferon, tumor necrosis factor alpha [TNF-α], and granulocyte-macrophage colony-stimulating factor [GM-CSF]) modify two macrolide properties, i.e., inhibition of oxidant production by polymorphonuclear neutrophils (PMN) and cellular uptake. Roxithromycin and two ketolides, HMR 3647 and HMR 3004, were chosen as the test agents. TNF-α and GM-CSF (but not the other cytokines) decreased the inhibitory effect of HMR 3647 only on oxidant production by PMN. Fifty percent inhibitory concentrations were, however, in the same range in control and cytokine-treated cells (about 60 to 70 μg/ml), suggesting that HMR 3647 acts downstream of the priming effect of cytokines. In contrast, the impairment of oxidant production by roxithromycin and HMR 3004 was unchanged (or increased) in cytokine-treated cells. This result suggests that HMR 3004 (the strongest inhibitory drug, likely owing to its quinoline side chain) and roxithromycin act on a cellular target upstream of cytokine action. In addition, TNF-α and GM-CSF significantly (albeit moderately) impaired (by about 20%) the uptake of the three molecules by PMN. The inhibitory effect of these two cytokines seems to be related to activation of the p38 mitogen-activated protein kinase. Our data also illuminate the mechanism underlying macrolide uptake: protein kinase A- and tyrosine kinase-dependent phosphorylation seems to be necessary for optimal uptake, while protein kinase C activation impairs it. The relevance of our data to the clinical setting requires further investigations, owing to the complexity of the cytokine cascade during infection and inflammation.
Antifungal Activity of Amphotericin B Cochleates against
Candida albicans
Infection in a Mouse Model
Authors: Zarif Leila , Graybill John R. , Perlin David , Najvar Laura , Bocanegra Rosie , Mannino Raphael J. 
Published: July 2002

ABSTRACT

Cochleates are lipid-based supramolecular assemblies composed of natural products, negatively charged phospholipid, and a divalent cation. Cochleates can encapsulate amphotericin B (AmB), an important antifungal drug. AmB cochleates (CAMB) have a unique shape and the ability to target AmB to fungi. The minimal inhibitory concentration and the minimum lethal concentration against
Candida albicans
are similar to that for desoxycholate AmB (DAMB; Fungizone). In vitro, CAMB induced no hemolysis of human red blood cells at concentrations of as high as 500 μg of AmB/ml, and DAMB was highly hemolytic at 10 μg of AmB/ml. CAMB protect ICR mice infected with
C. albicans
when the agent is administered intraperitoneally at doses of as low as 0.1 mg/kg/day. In a tissue burden study, CAMB, DAMB, and AmBisome (liposomal AmB; LAMB) were effective in the kidneys, but in the spleen CAMB was more potent than DAMB at 1 mg/kg/day and was equivalent to LAMB at 10 mg/kg/day. In summary, CAMB are highly effective in treating murine candidiasis and compare well with AmBisome and AmB.
Antiviral
l
-Nucleosides Specific for Hepatitis B Virus Infection
Authors: Bryant Martin L. , Bridges Edward G. , Placidi Laurent , Faraj Abdesslem , Loi Anna-Giulia , Pierra Claire , Dukhan David , Gosselin Gilles , Imbach Jean-Louis , Hernandez Brenda , Juodawlkis Amy , Tennant Bud , Korba Brent , Cote Paul , Marion Pat , Cretton-Scott Erika , Schinazi Raymond F. , Sommadossi Jean-Pierre 
Published: July 2002

ABSTRACT

A unique series of simple “unnatural” nucleosides has been discovered to inhibit hepatitis B virus (HBV) replication. Through structure-activity analysis it was found that the 3′-OH group of the β-
l
-2′-deoxyribose of the β-
l-
2′-deoxynucleoside confers specific antihepadnavirus activity. The unsubstituted nucleosides β-
l-
2′-deoxycytidine, β-
l
-thymidine, and β-
l
-2′-deoxyadenosine had the most potent, selective, and specific antiviral activity against HBV replication. Human DNA polymerases (α, β, and γ) and mitochondrial function were not affected. In the woodchuck model of chronic HBV infection, viral load was reduced by as much as 10
8
genome equivalents/ml of serum and there was no drug-related toxicity. In addition, the decline in woodchuck hepatitis virus surface antigen paralleled the decrease in viral load. These investigational drugs, used alone or in combination, are expected to offer new therapeutic options for patients with chronic HBV infection.
Identification and Expression of Cephamycinase
bla
CMY
Genes in
Escherichia coli
and
Salmonella
Isolates from Food Animals and Ground Meat
Authors: Zhao Shaohua , White David G. , McDermott Patrick F. , Friedman Sharon , English Linda , Ayers Sherry , Meng Jianghong , Maurer John J , Holland Robert , Walker Robert D. 
Published: July 2002

ABSTRACT

Twenty-one
Salmonella
and 54
Escherichia coli
isolates, recovered from food animals and retail ground meats, that exhibited decreased susceptibilities to ceftiofur and ceftriaxone were shown to possess a
bla
CMY
gene. The
bla

CMY
-
4

gene was identified in an
E. coli
isolate recovered from retail chicken and was further shown to be responsible for resistance to cephalothin, ampicillin, and amoxicillin-clavulanic acid and elevated MICs of ceftriaxone, cefoxitin, and ceftiofur.
Antimicrobial Activity of Quinupristin-Dalfopristin Combined with Other Antibiotics against Vancomycin-Resistant Enterococci
Authors: Eliopoulos G. M. , Wennersten C. B. 
Published: July 2002

ABSTRACT

Interactions between quinupristin-dalfopristin and six other antimicrobials were examined by checkerboard arrays against 50 clinical isolates of vancomycin-resistant
Enterococcus faecium
selected to represent a range of susceptibilities to individual agents. Unequivocal synergistic or antagonistic interactions at clinically relevant concentrations were infrequently encountered when the streptogramin was combined with chloramphenicol, ampicillin, imipenem, vancomycin, or teicoplanin. Combinations with doxycycline resulted in synergistic inhibition in 36% of checkerboards. Against 10 strains of
Enterococcus faecalis
, synergistic interactions were found when quinupristin-dalfopristin was combined with doxycycline (four strains), either glycopeptide (three strains), or ampicillin (two strains). Combination with quinupristin-dalfopristin increased the ampicillin MIC from 1 to 4 μg/ml for one strain. For 10 strains of
E. faecium
, interactions were also assessed by time-kill methods using concentrations of the agents attainable in human serum. Most of these antimicrobials augmented killing by quinupristin-dalfopristin to a minor degree. Against 2 of the 12 strains in this collection that were not highly resistant to gentamicin, the combination of quinupristin-dalfopristin (2 μg/ml) plus gentamicin (5 μg/ml) resulted in killing approaching 3 log
10
CFU/ml. With the exception of doxycycline, inhibitory interactions between quinupristin-dalfopristin and other agents tested against vancomycin-resistant strains of
E. faecium
were uncommon at clinically relevant concentrations.
Comparison of Levofloxacin, Alatrofloxacin, and Vancomycin for Prophylaxis and Treatment of Experimental Foreign-Body-Associated Infection by Methicillin-Resistant
Staphylococcus aureus
Authors: Vaudaux Pierre , Francois Patrice , Bisognano Carmelo , Schrenzel Jacques , Lew Daniel P. 
Published: July 2002

ABSTRACT

The prophylactic and therapeutic activities of two fluoroquinolones, levofloxacin and alatrofloxacin (the
l
-Ala-
l
-Ala prodrug of trovafloxacin), were compared to those of vancomycin in two different experimental models of foreign-body-associated infections caused by methicillin-resistant but quinolone-susceptible
Staphylococcus aureus
(MRSA) isolates. In a guinea pig model of prophylaxis, subcutaneously implanted tissue cages were infected with 10
3
CFU of MRSA, which was a 100% infectious dose in control animals. A single dose of 50 mg of levofloxacin per kg of body weight, administered intraperitoneally 3 h before bacterial challenge, was more efficient than vancomycin for the prevention of infections in tissue cages with MRSA inocula of 10
4
and 10
5
CFU. In a rat model used to evaluate therapy of chronic tissue cage infection caused by MRSA, the efficacies of 7-day high-dose regimens of levofloxacin (100 mg/kg once a day [q.d.] or 50 mg/kg twice a day [b.i.d.]) or alatrofloxacin (50 mg/kg q.d.) were compared to the efficacy of vancomycin (50 mg/kg b.i.d.). Active levels of levofloxacin, trovafloxacin, and vancomycin were continuously present in tissue cage fluid, with the levels exceeding the minimal bactericidal concentrations for MRSA during therapy. The q.d. and b.i.d. regimens of levofloxacin had equivalent activities and were significantly (
P
< 0.05) more active than alatrofloxacin or vancomycin in decreasing the viable counts of MRSA in tissue cage fluids. No quinolone-resistant mutants emerged during therapy with either fluoroquinolone. The mechanisms explaining the inferior activity of alatrofloxacin compared to the activity of levofloxacin against chronic foreign-body-associated infections by MRSA are unknown.
Substrate Specificity of Atrazine Chlorohydrolase and Atrazine-Catabolizing Bacteria
Authors: Seffernick Jennifer L. , Johnson Gilbert , Sadowsky Michael J. , Wackett Lawrence P. 
Published: July 2002

ABSTRACT

Bacterial atrazine catabolism is initiated by the enzyme atrazine chlorohydrolase (AtzA) in
Pseudomonas
sp. strain ADP. Other triazine herbicides are metabolized by bacteria, but the enzymological basis of this is unclear. Here we begin to address this by investigating the catalytic activity of AtzA by using substrate analogs. Purified AtzA from
Pseudomonas
sp. strain ADP catalyzed the hydrolysis of an atrazine analog that was substituted at the chlorine substituent by fluorine. AtzA did not catalyze the hydrolysis of atrazine analogs containing the pseudohalide azido, methoxy, and cyano groups or thiomethyl and amino groups. Atrazine analogs with a chlorine substituent at carbon 2 and
N
-alkyl groups, ranging in size from methyl to
t
-butyl, all underwent dechlorination by AtzA. AtzA catalyzed hydrolytic dechlorination when one nitrogen substituent was alkylated and the other was a free amino group. However, when both amino groups were unalkylated, no reaction occurred. Cell extracts were prepared from five strains capable of atrazine dechlorination and known to contain
atzA
or closely homologous gene sequences:
Pseudomonas
sp. strain ADP,
Rhizobium
strain PATR,
Alcaligenes
strain SG1,
Agrobacterium radiobacter
J14a, and
Ralstonia picketti
D. All showed identical substrate specificity to purified AtzA from
Pseudomonas
sp. strain
ADP
. Cell extracts from
Clavibacter michiganensis
ATZ1, which also contains a gene homologous to
atzA
, were able to transform atrazine analogs containing pseudohalide and thiomethyl groups, in addition to the substrates used by AtzA from
Pseudomonas
sp. strain ADP. This suggests that either (i) another enzyme(s) is present which confers the broader substrate range or (ii) the AtzA itself has a broader substrate range.
Improved Template Preparation for PCR-Based Assays for Detection of Food-Borne Bacterial Pathogens
Authors: Lampel Keith A. , Orlandi Palmer A. , Kornegay Leroy 
Published: July 2002

ABSTRACT

Shigella flexneri
,
Salmonella enterica
serotype Typhimurium, and
Listeria monocytogenes
were applied to FTA filters, and the filters were used directly as templates to demonstrate their sensitivity and applicability in PCR-based detection assays. With pure cultures, the sensitivities of detection by FTA filter-based PCR were 30 to 50 and 200 CFU for the gram-negative enterics and
Listeria
, respectively. Different numbers of
S. flexneri
cells were used in controlled contamination experiments with several different foods (produce, beef, and apple cider). Aliquots from concentrated food washes subsequently spotted onto FTA filters and assayed by PCR gave consistently positive results and detection limits similar to those observed with pure-culture dilutions. This universal method for PCR template preparation from bacterial cells is rapid and highly sensitive and reduces interference from food-associated inhibitors of PCR. In addition, its broad applicability eliminates the need for multiple methods for analysis of food matrices.
Development of a Single-Reaction Multiplex PCR Toxin Typing Assay for
Staphylococcus aureus
Strains
Authors: Sharma Naresh K. , Rees Catherine E. D. , Dodd Christine E. R. 
Published: July 2002

ABSTRACT

We describe here the development of a single-reaction multiplex PCR assay for the enterotoxin genes from
Staphylococcus aureus
that utilizes a universal toxin gene primer in combination with toxin-specific primers to amplify characteristic toxin gene products. In combination with a new DNA purification method, the assay can detect enterotoxin genes A to E from a pure culture within 3 to 4 h. The test was used to characterize a diverse set of environmental
S. aureus
isolates, and a 99% correlation with toxin typing using standard immunological tests was found. The design of the assay allows it to be extended to include both newly characterized and as-yet-unknown toxin genes.
A New System for Three-Dimensional Tracking of Motile Microorganisms
Authors: Thar Roland , Blackburn Nicholas , Kühl Michael 
Published: July 2002

ABSTRACT
A new three-dimensional (3D)-tracking system with optimized dark-field illumination is presented. It allows simultaneous 3D tracking of several free-swimming microorganisms with diameters of >10 μm. Resolution limits and illumination efficiencies for different size classes of microorganisms are treated analytically. First applications for 3D tracking of protists are demonstrated.
Geranic Acid Formation, an Initial Reaction of Anaerobic Monoterpene Metabolism in Denitrifying
Alcaligenes defragrans
Authors: Heyen Udo , Harder Jens 
Published: July 2002

ABSTRACT

Monoterpenes with an unsaturated hydrocarbon structure are mineralized anaerobically by the denitrifying β-proteobacterium
Alcaligenes defragrans
. Organic acids occurring in cells of
A. defragrans
and culture medium were characterized to identify potential products of the monoterpene activation reaction. Geranic acid (
E
,
E
-3,7-dimethyl-2,6-octadienoic acid) accumulated to 0.5 mM in cells grown on α-phellandrene under nitrate limitation. Cell suspensions of
A. defragrans
65Phen synthesized geranic acid in the presence of β-myrcene, α-phellandrene, limonene, or α-pinene. Myrcene yielded the highest transformation rates. The alicyclic acid was consumed by cell suspensions during carbon limitation. Heat-labile substances present in cytosolic extracts catalyzed the formation of geranic acid from myrcene. These results indicated that a novel monoterpene degradation pathway must be present in
A. defragrans.