bluuebunny/crossref_metadata_2025 huggingface dataset:
Absence of Junctional Glutamate Receptor Clusters in
Drosophila
Mutants Lacking Spontaneous Transmitter Release
Authors: Saitoe Minoru , Schwarz Thomas L. , Umbach Joy A. , Gundersen Cameron B. , Kidokoro Yoshiaki
Published: July 2002

Little is known about the functional significance of spontaneous miniature synaptic potentials, which are the result of vesicular exocytosis at nerve terminals. Here, by using
Drosophila
mutants with specific defects in presynaptic function, we found that glutamate receptors clustered normally at neuromuscular junctions of mutants that retained spontaneous transmitter secretion but had lost the ability to release transmitter in response to action potentials. In contrast, receptor clustering was defective in mutants in which both spontaneous and evoked vesicle exocytosis were absent. Thus, spontaneous vesicle exocytosis appears to be tightly linked to the clustering of glutamate receptors during development.
Hydrogen 21-Centimeter Emission from a Galaxy at Cosmological Distance
Authors: Zwaan M. A. , van Dokkum P. G. , Verheijen M. A. W.
Published: July 2002

We have detected the neutral atomic hydrogen (HI) emission line at a cosmologically significant distance [redshift (
z
) = 0.18] in the rich galaxy cluster Abell 2218 with the Westerbork Synthesis Radio Telescope. The HI emission originates in a spiral galaxy 2.0
h
65
−1
megaparsecs from the cluster core. No other significant detections have been made in the cluster, suggesting that the mechanisms that remove neutral gas from cluster galaxies are efficient. We infer that fewer than three gas-rich galaxies were accreted by Abell 2218 over the past 10
9
years. This low accretion rate is qualitatively consistent with low-density cosmological models in which clusters are largely assembled at
z
> 1.
A Cosmic Double Helix in the Archetypical Quasar 3C273
Authors: Lobanov A. P. , Zensus J. A.
Published: July 2002

Finding direct evidence for plasma instability in extragalactic jets is crucial for understanding the nature of relativistic outflows from active galactic nuclei. Our radio interferometric observations of the quasar 3C273 made with the orbiting radio telescope, HALCA, and an array of ground telescopes have yielded an image in which the emission across the jet is resolved, revealing two threadlike patterns that form a double helix inside the jet. This double helical structure is consistent with a Kelvin-Helmholtz instability, and at least five different instability modes can be identified and modeled by a light jet with a Lorentz factor of 2 and Mach number of 3.5. The model reproduces in detail the internal structure of the jet on scales of up to 30 milli–arc seconds (∼300 parsecs) and is consistent with the general morphology of the jet on scales of up to 1 kiloparsec.
Single-Molecule Analysis of Chemotactic Signaling in
Dictyostelium
Cells
Authors: Ueda Masahiro , Sako Yasushi , Tanaka Toshiki , Devreotes Peter , Yanagida Toshio
Published: July 2002

Single-molecule imaging techniques were used to reveal the binding of individual cyclic adenosine 3′,5′-monophosphate molecules to heterotrimeric guanine nucleotide–binding protein coupled receptors on the surface of living
Dictyostelium discoideum
cells. The binding sites were uniformly distributed and diffused rapidly in the plane of the membrane. The probabilities of individual association and dissociation events were greater for receptors at the anterior end of the cell. Agonist-induced receptor phosphorylation had little effect on any of the monitored properties, whereas G protein coupling influenced the binding kinetics. These observations illustrate the dynamic properties of receptors involved in gradient sensing and suggest that these may be polarized in chemotactic cells.
Evidence for Strengthening of the Tropical General Circulation in the 1990s
Authors: Chen Junye , Carlson Barbara E. , Del Genio Anthony D.
Published: July 2002

Satellite observations suggest that the thermal radiation emitted by Earth to space increased by more than 5 watts per square meter, while reflected sunlight decreased by less than 2 watts per square meter, in the tropics over the period 1985–2000, with most of the increase occurring after 1990. By analyzing temporal changes in the frequency of occurrence of emitted thermal and reflected solar fluxes, the effects of El Niño–Southern Oscillation are minimized, and an independent longer-time-scale variation of the radiation budget is identified. Similar analyses of upper tropospheric humidity, cloud amount, surface air temperature, and vertical velocity confirm that these flux changes are associated with a decadal-time-scale strengthening of the tropical Hadley and Walker circulations. Equatorial convective regions have intensified in upward motion and moistened, while both the equatorial and subtropical subsidence regions have become drier and less cloudy.
Developmental Control of Cell Cycle Regulators: A Fly's Perspective
Authors: Edgar Bruce A. , Lehner Christian F.
Published: July 2002

During early development in many species, maternally supplied gene products permit the cell cycle to run at maximum velocity, subdividing the fertilized egg into smaller and smaller cells. As development proceeds, zygotic controls are activated that first limit divisions to defined spatial and temporal domains, coordinating them with morphogenesis, and then halt proliferation altogether, to allow cell differentiation. Analysis of the regulation of cyclin-dependent kinases (Cdks) in
Drosophila
has provided insights into how this embryonic program of cell proliferation is controlled at the molecular level and how it is linked to developmental cues. Recent studies have also begun to reveal how cell proliferation is controlled during the second phase of
Drosophila
development, which occurs in imaginal tissues. In contrast to their embryonic progenitors, imaginal cells proliferate with a cycle that requires cell growth and is linked to patterning processes controlled by secreted cell signaling molecules. The functions of these signaling molecules appear to be nearly as conserved between vertebrates and invertebrates as the cell cycle control apparatus itself, suggesting that the mechanisms that coordinate growth, patterning, and cell proliferation in developing tissues have ancient origins.
Role of the Major Antigen of
Mycobacterium tuberculosis
in Cell Wall Biogenesis
Authors: Belisle John T. , Vissa Varalakshmi D. , Sievert Todd , Takayama Kuni , Brennan Patrick J. , Besra Gurdyal S.
Published: July 2002

The dominant exported proteins and protective antigens of
Mycobacterium tuberculosis
are a triad of related gene products called the antigen 85 (Ag85) complex. Each has also been implicated in disease pathogenesis through its fibronectin-binding capacities. A carboxylesterase domain was found within the amino acid sequences of Ag85A, B, and C, and each protein acted as a mycolyltransferase involved in the final stages of mycobacterial cell wall assembly, as shown by direct enzyme assay and site-directed mutagenesis. Furthermore, the use of an antagonist (6-azido-6-deoxy-α,α′-trehalose) of this activity demonstrates that these proteins are essential and potential targets for new antimycobacterial drugs.
Receptor-Mediated Activation of a MAP Kinase in Pathogen Defense of Plants
Authors: Ligterink Wilco , Kroj Thomas , Nieden Uta zur , Hirt Heribert , Scheel Dierk
Published: July 2002

Parsley cells recognize the fungal plant pathogen
Phytophthora sojae
through a plasma membrane receptor. A pathogen-derived oligopeptide elicitor binds to this receptor and thereby stimulates a multicomponent defense response through sequential activation of ion channels and an oxidative burst. An elicitor-responsive mitogen-activated protein (MAP) kinase was identified that acts downstream of the ion channels but independently or upstream of the oxidative burst. Upon receptor-mediated activation, the MAP kinase is translocated to the nucleus where it might interact with transcription factors that induce expression of defense genes.
Nanotube Nanodevice
Authors: Collins Philip G. , Zettl A. , Bando Hiroshi , Thess Andreas , Smalley R. E.
Published: July 2002

A scanning tunneling microscope (STM) was used to explore the local electrical characteristics of single-wall carbon nanotubes. As the STM tip was moved along the length of the nanotubes, well-defined positions were found where the transport current changes abruptly from a graphitic-like response to one that is highly nonlinear and asymmetrical, including near-perfect rectification. The observations are consistent with the existence of localized, on-tube nanodevices of a type proposed theoretically.
Chain Reactions Linking Acorns to Gypsy Moth Outbreaks and Lyme Disease Risk
Authors: Jones Clive G. , Ostfeld Richard S. , Richard Michele P. , Schauber Eric M. , Wolff Jerry O.
Published: July 2002

In eastern U.S. oak forests, defoliation by gypsy moths and the risk of Lyme disease are determined by interactions among acorns, white-footed mice, moths, deer, and ticks. Experimental removal of mice, which eat moth pupae, demonstrated that moth outbreaks are caused by reductions in mouse density that occur when there are no acorns. Experimental acorn addition increased mouse density. Acorn addition also increased densities of black-legged ticks, evidently by attracting deer, which are key tick hosts. Mice are primarily responsible for infecting ticks with the Lyme disease agent. The results have important implications for predicting and managing forest health and human health.
Switching Supramolecular Polymeric Materials with Multiple Length Scales
Authors: Ruokolainen J. , Mäkinen R. , Torkkeli M. , Mäkelä T. , Serimaa R. , Brinke G. ten , Ikkala O.
Published: July 2002

It was demonstrated that polymeric supramolecular nanostructures with several length scales allow straightforward tailoring of hierarchical order-disorder and order-order transitions and the concurrent switching of functional properties. Poly(4-vinyl pyridine) (P4VP) was stoichiometrically protonated with methane sulfonic acid (MSA) to form P4VP(MSA)
1.0
, which was then hydrogen-bonded to pentadecylphenol. Microphase separation, re-entrant closed-loop macrophase separation, and high-temperature macrophase separation were observed. When MSA and pentadecylphenol were complexed to the P4VP block of a microphase-separated diblock copolymer poly[styrene-
block
-(4-vinyl pyridine)], self-organized structures-in-structures were obtained whose hierarchical phase transitions can be controlled systematically. This microstructural control on two different length scales (in the present case, at 48 and 350 angstroms) was then used to introduce temperature-dependent transitions in electrical conductivity.
Magnetic Field Effect on Picosecond Electron Transfer
Authors: Gilch P. , Pöllinger-Dammer F. , Musewald C. , Michel-Beyerle M. E. , Steiner U. E.
Published: July 2002

The recombination dynamics of a transition metal redox system monitored by femtosecond pump-probe spectroscopy are shown to be sensitive to high magnetic fields at times shorter than 10 picoseconds. The effect, based on coherent population beats of different spin states, is quantitatively accounted for and allows direct access to spin relaxation rates far beyond the time resolution of the fastest electron paramagnetic resonance technique. The presence of this ultrafast magnetic field effect helps in understanding complex reaction schemes in transition metal chemistry, which occur in a wide range of fields, such as bioinorganic chemistry and catalysis.
Recruitment of a
hedgehog
Regulatory Circuit in Butterfly Eyespot Evolution
Authors: Keys David N. , Lewis David L. , Selegue Jane E. , Pearson Bret J. , Goodrich Lisa V. , Johnson Ronald L. , Gates Julie , Scott Matthew P. , Carroll Sean B.
Published: July 2002

The origin of new morphological characters is a long-standing problem in evolutionary biology. Novelties arise through changes in development, but the nature of these changes is largely unknown. In butterflies, eyespots have evolved as new pattern elements that develop from special organizers called foci. Formation of these foci is associated with novel expression patterns of the Hedgehog signaling protein, its receptor Patched, the transcription factor Cubitus interruptus, and the
engrailed
target gene that break the conserved compartmental restrictions on this regulatory circuit in insect wings. Redeployment of preexisting regulatory circuits may be a general mechanism underlying the evolution of novelties.
EIN2, a Bifunctional Transducer of Ethylene and Stress Responses in
Arabidopsis
Authors: Alonso Jose M. , Hirayama Takashi , Roman Gregg , Nourizadeh Saeid , Ecker Joseph R.
Published: July 2002

Ethylene regulates plant growth, development, and responsiveness to a variety of stresses. Cloning of the
Arabidopsis EIN2
gene identifies a central component of the ethylene signaling pathway. The amino-terminal integral membrane domain of EIN2 shows similarity to the disease-related Nramp family of metal-ion transporters. Expression of the EIN2 CEND is sufficient to constitutively activate ethylene responses and restores responsiveness to jasmonic acid and paraquat-induced oxygen radicals to mutant plants. EIN2 is thus recognized as a molecular link between previously distinct hormone response pathways. Plants may use a combinatorial mechanism for assessing various stresses by enlisting a common set of signaling molecules.
Chiral Magnetic Domain Structures in Ultrathin FePd Films
Authors: Dürr H. A. , Dudzik E. , Dhesi S. S. , Goedkoop J. B. , van der Laan G. , Belakhovsky M. , Mocuta C. , Marty A. , Samson Y.
Published: July 2002

The magnetization profile of magnetically ordered patterns in ultrathin films was determined by circular dichroism in x-ray resonant magnetic scattering (CDXRMS). When this technique was applied to single crystalline iron palladium alloy layers, magnetic flux closure domains were found whose thickness can constitute a large fraction (∼25 percent) of the total film.
Requirement of ATM-Dependent Phosphorylation of Brca1 in the DNA Damage Response to Double-Strand Breaks
Authors: Cortez David , Wang Yi , Qin Jun , Elledge Stephen J.
Published: July 2002

The Brca1 (breast cancer gene 1) tumor suppressor protein is phosphorylated in response to DNA damage. Results from this study indicate that the checkpoint protein kinase ATM (mutated in ataxia telangiectasia) was required for phosphorylation of Brca1 in response to ionizing radiation. ATM resides in a complex with Brca1 and phosphorylated Brca1 in vivo and in vitro in a region that contains clusters of serine-glutamine residues. Phosphorylation of this domain appears to be functionally important because a mutated Brca1 protein lacking two phosphorylation sites failed to rescue the radiation hypersensitivity of a Brca1-deficient cell line. Thus, phosphorylation of Brca1 by the checkpoint kinase ATM may be critical for proper responses to DNA double-strand breaks and may provide a molecular explanation for the role of ATM in breast cancer.
Electronic Structures of Single-Walled Carbon Nanotubes Determined by NMR
Authors: Tang X.-P. , Kleinhammes A. , Shimoda H. , Fleming L. , Bennoune K. Y. , Sinha S. , Bower C. , Zhou O. , Wu Y.
Published: July 2002

Single-walled carbon nanotubes were studied by
13
C nuclear magnetic resonance (NMR). Two types of
13
C nuclear spins were identified with different spin-lattice relaxation rates. The fast-relaxing component, assigned to metallic tubes, followed the relaxation behavior expected in metals, and the density-of-states at the Fermi level increased with decreasing tube diameter. The slow-relaxing component has a significantly lower density-of-states at the Fermi level. Exposure to oxygen has a substantial effect on relaxation rates of both components.
The Solar Wind-Magnetosphere-Ionosphere System
Authors: Lyon John G.
Published: July 2002

The solar wind, magnetosphere, and ionosphere form a single system driven by the transfer of energy and momentum from the solar wind to the magnetosphere and ionosphere. Variations in the solar wind can lead to disruptions of space- and ground-based systems caused by enhanced currents flowing into the ionosphere and increased radiation in the near-Earth environment. The coupling between the solar wind and the magnetosphere is mediated and controlled by the magnetic field in the solar wind through the process of magnetic reconnection. Understanding of the global behavior of this system has improved markedly in the recent past from coordinated observations with a constellation of satellite and ground instruments.
A Link Between RNA Interference and Nonsense-Mediated Decay in
Caenorhabditis elegans
Authors: Domeier Mary Ellen , Morse Daniel P. , Knight Scott W. , Portereiko Michael , Bass Brenda L. , Mango Susan E.
Published: July 2002

Double-stranded RNA (dsRNA) inhibits expression of homologous genes by a process involving messenger RNA degradation. To gain insight into the mechanism of degradation, we examined how RNA interference is affected by mutations in the
smg
genes, which are required for nonsense-mediated decay. For three of six
smg
genes tested, mutations resulted in animals that were initially silenced by dsRNA but then recovered; wild-type animals remained silenced. The levels of target messenger RNAs were restored during recovery, and RNA editing and degradation of the dsRNA were identical to those of the wild type. We suggest that persistence of RNA interference relies on a subset of
smg
genes.
CD95/CD95 Ligand Interactions on Epithelial Cells in Host Defense to
Pseudomonas aeruginosa
Authors: Grassmé Heike , Kirschnek Susanne , Riethmueller Joachim , Riehle Andrea , von Kürthy Gabriele , Lang Florian , Weller Michael , Gulbins Erich
Published: July 2002

Pseudomonas aeruginosa
causes severe infections, particularly of the lung, that are life threatening. Here, we show that
P. aeruginosa
infection induces apoptosis of lung epithelial cells by activation of the endogenous CD95/CD95 ligand system. Deficiency of CD95 or CD95 ligand on epithelial cells prevented apoptosis of lung epithelial cells in vivo as well as in vitro. The importance of CD95/CD95 ligand–mediated lung epithelial cell apoptosis was demonstrated by the rapid development of sepsis in CD95- or CD95 ligand–deficient mice, but not in normal mice, after
P. aeruginosa
infection.
Bioavailability of Praziquantel Increases with Concomitant Administration of Food
Authors: Castro Nelly , Medina Roberto , Sotelo Julio , Jung Helgi
Published: July 2002

In the present study we found that after a single oral dose of 1,800 mg of praziquantel, following a high-lipid diet and a high-carbohydrate diet, the maximum levels in plasma increased 243 and 515% and the area under the plasma concentration curve from 0 to 8 h increased 180 and 271%, respectively.
The Triple Combination Indinavir-Zidovudine-Lamivudine Is Highly Synergistic
Authors: Snyder Stuart , D'Argenio D. Z. , Weislow Owen , Bilello John A. , Drusano G. L.
Published: July 2002

Administration of the combination of indinavir-zidovudine-lamivudine has been demonstrated to cause a large fraction of treated patients to have a decline in human immunodeficiency virus type 1 (HIV-1) copy number to below the detectability of sensitive assays. A recent investigation (G. L. Drusano, J. A. Bilello, D. S. Stein, M. Nessly, A. Meibohm, E. A. Emini, P. Deutsch, J. Condra, J. Chodakewitz, and D. J. Holder, J. Infect. Dis. 178:360–367, 1998) demonstrated that the durability of the antiviral effect was affected by combination chemotherapy. Zidovudine-lamivudine-indinavir differed significantly from the combination of zidovudine plus indinavir. We hypothesized that the addition of lamivudine might alter the regimen, producing a synergistic anti-HIV effect. In vitro analysis of drug interaction demonstrated that zidovudine-indinavir interacted additively. The addition of lamivudine in concentrations which suppressed viral replication by 20% or less by itself demonstrated marked increases in the synergy volume, increasing the synergy volume 20-fold with the addition of 320 nM lamivudine (which does not suppress HIV by itself) and 40-fold with the addition of 1,000 nM lamivudine (20% viral inhibition as a single agent). A fully parametric analysis with a newly developed model for three-drug interaction confirmed and extended these observations. The interaction term (α
IND,AZT,3TC
) for all three drugs showed the greatest degree of synergy. This marked synergistic interaction among the three agents may explain some of the clinical results which differentiate this regimen from the double-drug regimen of zidovudine plus indinavir.
Induction of Fibronectin-Binding Proteins and Increased Adhesion of Quinolone-ResistantStaphylococcus aureusby Subinhibitory Levels of Ciprofloxacin
Authors: Bisognano Carmelo , Vaudaux Pierre , Rohner Peter , Lew Daniel P. , Hooper David C.
Published: July 2002

We recently reported that strain EN1252a, a fluoroquinolone-resistant derivative ofStaphylococcus aureusNCTC8325 with mutations ingrlAandgyrA, expressed increased levels of fibronectin-binding proteins (FnBPs) and showed a significantly higher attachment to fibronectin-coated polymer surfaces after growth in the presence of subinhibitory concentrations of ciprofloxacin. The present study evaluated the occurrence and frequency of fluoroquinolone-induced FnBP-mediated adhesion in clinical isolates of fluoroquinolone-resistant methicillin-resistantS. aureus(MRSA) and methicillin-susceptibleS. aureus(MSSA). Eight of ten MRSA isolates and four of six MSSA isolates withgrlAandgyrAmutations exhibited significant increases in attachment to fibronectin-coated surfaces after growth in the presence of one-quarter the MIC of ciprofloxacin. Fluoroquinolone-induced FnBP-mediated adhesion of one clinical MRSA strain and the double mutant strain EN1252a also occurred on coverslips removed from the subcutaneous space of guinea pigs. For strain EN1252a, the regulation offnbtranscription by sub-MICs of ciprofloxacin was studied on reporter plasmids carryingfnb-luxABfusions. One-quarter of the MIC of ciprofloxacin significantly increasedfnbB, but notfnbA, promoter activity of the fluoroquinolone-resistant mutant but not its fluoroquinolone-susceptible parent ISP794. This response was abolished by pretreatment with rifampin, indicating an effect at the level of transcription. Activation of thefnbBpromoter was not due to an indirect effect of ciprofloxacin on growth rate and still occurred in anagrmutant of strain EN1252a. These data suggest that sub-MIC levels of ciprofloxacin activate thefnbBpromoter of some laboratory and clinical isolates, thus contributing to increased production of FnBP(s) and leading to higher levels of bacterial attachment to fibronectin-coated or subcutaneously implanted coverslips.
Therapeutic Responses to Quinine and Clindamycin in Multidrug-Resistant Falciparum Malaria
Authors: Pukrittayakamee Sasithon , Chantra Arun , Vanijanonta Sirivan , Clemens Ralf , Looareesuwan Sornchai , White Nicholas J.
Published: July 2002

Therapeutic responses to clindamycin in combination with quinine were assessed in adult Thai patients with uncomplicated multidrug-resistant
Plasmodium falciparum
malaria. In total 204 patients were randomized to receive a 7-day oral treatment regimen of quinine (Q
7
) either alone (
n
= 68), in combination with clindamycin (Q
7
C
7
;
n
= 68), or in combination with tetracycline (Q
7
T
7
;
n
= 68). All patients had uncomplicated recoveries with no serious adverse effects. Fever clearance times for both of the two combination regimens (median of 47 h and range of 8 to 120 h for Q
7
C
7
and median of 36 h and range of 8 to 117 h for Q
7
T
7
) were significantly shorter than that for the Q
7
-only regimen (median, 56; range, 4 to 152 h) (
P
= 0.002). Parasite clearance times (overall mean ± standard deviation, 78 ± 23 h) were not significantly different between the three treatment groups (
P
= 0.98). The cure rates assessed at 28 days of follow-up were 100% for Q
7
C
7
and 98% for Q
7
T
7
, whereas the cure rate was 87% for the Q
7
-only regimen (
P
≤ 0.04). Clindamycin in combination with quinine is a safe and effective treatment for multidrug-resistant
P. falciparum
malaria. This combination may be of particular value in children and pregnant women, in whom tetracyclines are contraindicated.
Activities of Imipenem and Cephalosporins against Clonally Related Strains of
Escherichia coli
Hyperproducing Chromosomal β-Lactamase and Showing Altered Porin Profiles
Authors: Martínez-Martínez L. , Conejo M. C. , Pascual A. , Hernández-Allés S. , Ballesta S. , Ramírez de Arellano-Ramos E. , Benedí V. J. , Perea E. J.
Published: July 2002

Forty clonally related clinical isolates of
Escherichia coli
from hospitalized patients were resistant to cefoxitin (MICs, >256 μg/ml) and ceftazidime (MICs, 32 to 256 μg/ml) and were intermediate or resistant to cefotaxime (MICs, 16 to 128 μg/ml) but susceptible to both cefepime (MICs, 0.5 to 2 μg/ml) and imipenem (MICs, 0.125 to 0.25 μg/ml). Resistance to β-lactams was related to high-level production of AmpC β-lactamase and loss of OmpF porin.
Drug Susceptibility Testing of Anaerobic Protozoa
Authors: Upcroft Jacqueline A. , Upcroft Peter
Published: July 2002

A simple technique for routine, reproducible global surveillance of the drug susceptibility status of the anaerobic protozoa
Trichomonas, Entamoeba
, and
Giardia
is described. Data collected using this technique can be readily compared among different laboratories and with previously reported data. The technique employs a commercially available sachet and bag system to generate a low-oxygen environment and log
2
drug dilutions in microtiter plates, which can be monitored without aerobic exposure, to assay drug-resistant laboratory lines and clinically resistant isolates. MICs (after 2 days) of 3.2 and 25 μM indicated metronidazole-sensitive and highly clinically resistant isolates of
T. vaginalis
in anaerobic assays, respectively. The aerobic MICs were 25 and >200 μM. MICs (1 day) of 12.5 to 25 μM were found for axenic lines of
E. histolytica
, and MICs for
G. duodenalis
(3 days) ranged from 6.3 μM for metronidazole-sensitive isolates to 50 μM for laboratory metronidazole-resistant lines. This technique should encourage more extensive monitoring of drug resistance in these organisms.
Susceptibilities of
Mycobacterium
marinum
to Gatifloxacin, Gemifloxacin, Levofloxacin, Linezolid, Moxifloxacin, Telithromycin, and Quinupristin-Dalfopristin (Synercid) Compared to Its Susceptibilities to Reference Macrolides and Quinolones
Authors: Bråbäck Martin , Riesbeck Kristian , Forsgren Arne
Published: July 2002

The susceptibility pattern of
Mycobacterium
marinum
was determined. Quinupristin-dalfopristin and telithromycin were less active than clarithromycin. Linezolid showed good antimicrobial activity at clinically achievable concentrations. Gatifloxacin, levofloxacin, and moxifloxacin displayed activities similar to those of ciprofloxacin. Gemifloxacin was less active. The Etest method showed variable agreement with the reference method.
Site-Specific Recombination with the Chromosomal tRNA
Leu
Gene by the Large Conjugative
Haemophilus
Resistance Plasmid
Authors: Dimopoulou Ioanna D. , Russell Joanne E. , Mohd-Zain Zaini , Herbert Rebecca , Crook Derrick W.
Published: July 2002

Characterization of the sequences involved in recombination of the
Haemophilus
plasmid p1056 with the
Haemophilus influenzae
chromosome produced evidence indicating site-specific recombination with chromosomal tRNA
Leu
.
attP
sequences identical to those of p1056 were found in six plasmids of diverse origin, suggesting that a family of
Haemophilus
plasmids recombines with chromosomal tRNA
Leu
.
Resistance Determinants and Clonal Diversity in Group A Streptococci Collected during a Period of Increasing Macrolide Resistance
Authors: Cresti Stefania , Lattanzi Maria , Zanchi Alessandra , Montagnani Francesca , Pollini Simona , Cellesi Carla , Rossolini Gian Maria
Published: July 2002

Susceptibility to macrolides and lincosamides was investigated with 299 consecutive nonduplicate
Streptococcus pyogenes
clinical isolates collected over a 6-year period (1992 to 1997) from an area of central Italy. During this period, macrolide resistance rates steadily increased (from 9% in 1992 to 53% in 1997;
P
< 0.001). The increase was caused by isolates with a macrolide-lincosamide-streptogramin B resistance phenotype, carrying mostly
erm
(B) but also
erm
(TR) genes, that were not detected in the first 2 years and were detected with increasing prevalence (8, 5, 26, and 37%, respectively) during the following 4 years. During the same period, the prevalence of isolates with a macrolide resistance phenotype, carrying
mef
(A) determinants, did not vary significantly; on average it was 13%, with modest rate fluctuations in different years and no definite trend. Molecular typing revealed a remarkable clonal diversity among susceptible and resistant isolates and a notable heterogeneity of the genetic environment of the resistance genes. The analysis of clonal diversity in relation with resistance phenotypes and genotypes revealed that increased macrolide resistance rates were due to a complex interplay of different mechanisms, with a relevant contribution played by an “epidemic” spread of genetic elements carrying the
erm
(B) gene among the circulating streptococcal population.
Role of
rpoS
in Acid Resistance and Fecal Shedding of
Escherichia coli
O157:H7
Authors: Price Stuart B. , Cheng Chorng-Ming , Kaspar Charles W. , Wright James C. , DeGraves Fred J. , Penfound Thomas A. , Castanie-Cornet Marie-Pierre , Foster John W.
Published: July 2002

Acid resistance (AR) is important to survival of
Escherichia coli
O157:H7 in acidic foods and may play a role during passage through the bovine host. In this study, we examined the role in AR of the
rpoS
-encoded global stress response regulator ς
S
and its effect on shedding of
E. coli
O157:H7 in mice and calves. When assayed for each of the three AR systems identified in
E. coli
, an
rpoS
mutant (
rpoS
::pRR10) of
E. coli
O157:H7 lacked the glucose-repressed system and possessed reduced levels of both the arginine- and glutamate-dependent AR systems. After administration of the
rpoS
mutant and the wild-type strain (ATCC 43895) to ICR mice at doses ranging from 10
1
to 10
4
CFU, we found the wild-type strain in feces of mice given lower doses (10
2
versus 10
3
CFU) and at a greater frequency (80% versus 13%) than the mutant strain. The reduction in passage of the
rpoS
mutant was due to decreased AR, as administration of the mutant in 0.05 M phosphate buffer facilitated passage and increased the frequency of recovery in feces from 27 to 67% at a dose of 10
4
CFU. Enumeration of
E. coli
O157:H7 in feces from calves inoculated with an equal mixture of the wild-type strain and the
rpoS
mutant demonstrated shedding of the mutant to be 10- to 100-fold lower than wild-type numbers. This difference in shedding between the wild-type strain and the
rpoS
mutant was statistically significant (
P
≤ 0.05). Thus, ς
S
appears to play a role in
E. coli
O157:H7 passage in mice and shedding from calves, possibly by inducing expression of the glucose-repressed RpoS-dependent AR determinant and thus increasing resistance to gastrointestinal stress. These findings may provide clues for future efforts aimed at reducing or eliminating this pathogen from cattle herds.
Effect of Temperature and Salinity Stress on Growth and Lipid Composition of
Shewanella gelidimarina
Authors: Nichols David S. , Olley June , Garda Horacio , Brenner Rodolfo R. , McMeekin Tom A.
Published: July 2002

The maximum growth temperature, the optimal growth temperature, and the estimated normal physiological range for growth of
Shewanella gelidimarina
are functions of water activity (a
w
), which can be manipulated by changing the concentration of sodium chloride. The growth temperatures at the boundaries of the normal physiological range for growth were characterized by increased variability in fatty acid composition. Under hyper- and hypoosmotic stress conditions at an a
w
of 0.993 (1.0% [wt/vol] NaCl) and at an a
w
of 0.977 (4.0% [wt/vol] NaCl) the proportion of certain fatty acids (monounsaturated and branched-chain fatty acids) was highly regulated and was inversely related to the growth rate over the entire temperature range. The physical states of lipids extracted from samples grown at stressful a
w
values at the boundaries of the normal physiological range exhibited no abrupt gel-liquid phase transitions when the lipids were analyzed as liposomes. Lipid packing and adaptational fatty acid composition responses are clearly influenced by differences in the temperature-salinity regime, which are reflected in overall cell function characteristics, such as the growth rate and the normal physiological range for growth.
Motility of
Marichromatium gracile
in Response to Light, Oxygen, and Sulfide
Authors: Thar Roland , Kühl Michael
Published: July 2002

The motility of the purple sulfur bacterium
Marichromatium gracile
was investigated under different light regimes in a gradient capillary setup with opposing oxygen and sulfide gradients. The gradients were quantified with microsensors, while the behavior of swimming cells was studied by video microscopy in combination with a computerized cell tracking system.
M. gracile
exhibited photokinesis, photophobic responses, and phobic responses toward oxygen and sulfide. The observed migration patterns could be explained solely by the various phobic responses. In the dark,
M. gracile
formed an ∼500-μm-thick band at the oxic-anoxic interface, with a sharp border toward the oxic zone always positioned at ∼10 μM O
2
. Flux calculations yielded a molar conversion ratio S
tot
/O
2
of 2.03:1 (S
tot
= [H
2
S] + [HS
−
] + [S
2−
]) for the sulfide oxidation within the band, indicating that in darkness the bacteria oxidized sulfide incompletely to sulfur stored in intracellular sulfur globules. In the light,
M. gracile
spread into the anoxic zone while still avoiding regions with >10 μM O
2
. The cells also preferred low sulfide concentrations if the oxygen was replaced by nitrogen. A light-dark transition experiment demonstrated a dynamic interaction between the chemical gradients and the cell's metabolism. In darkness and anoxia,
M. gracile
lost its motility after ca. 1 h. In contrast, at oxygen concentrations of >100 μM with no sulfide present the cells remained viable and motile for ca. 3 days both in light and darkness. Oxygen was respired also in the light, but respiration rates were lower than in the dark. Observed aggregation patterns are interpreted as effective protection strategies against high oxygen concentrations and might represent first stages of biofilm formation.
Isolation and Characterization of a Novel As(V)-Reducing Bacterium: Implications for Arsenic Mobilization and the Genus
Desulfitobacterium
Authors: Niggemyer Allison , Spring Stefan , Stackebrandt Erko , Rosenzweig R. Frank
Published: July 2002

Dissimilatory arsenate-reducing bacteria have been implicated in the mobilization of arsenic from arsenic-enriched sediments. An As(V)-reducing bacterium, designated strain GBFH, was isolated from arsenic-contaminated sediments of Lake Coeur d'Alene, Idaho. Strain GBFH couples the oxidation of formate to the reduction of As(V) when formate is supplied as the sole carbon source and electron donor. Additionally, strain GBFH is capable of reducing As(V), Fe(III), Se(VI), Mn(IV) and a variety of oxidized sulfur species. 16S ribosomal DNA sequence comparisons reveal that strain GBFH is closely related to
Desulfitobacterium hafniense
DCB-2
T
and
Desulfitobacterium frappieri
PCP-1
T
. Comparative physiology demonstrates that
D
.
hafniense
and
D
.
frappieri
, known for reductively dechlorinating chlorophenols, are also capable of toxic metal or metalloid respiration. DNA-DNA hybridization and comparative physiological studies suggest that
D. hafniense
,
D. frappieri
, and strain GBFH should be united into one species. The isolation of an Fe(III)- and As(V)-reducing bacterium from Lake Coeur d'Alene suggests a mechanism for arsenic mobilization in these contaminated sediments while the discovery of metal or metalloid respiration in the genus
Desulfitobacterium
has implications for environments cocontaminated with arsenious and chlorophenolic compounds.
Effects of Hydrophobic and Electrostatic Cell Surface Properties of Bacteria on Feeding Rates of Heterotrophic Nanoflagellates
Authors: Matz Carsten , Jürgens Klaus
Published: July 2002

The influence of cell surface hydrophobicity and electrostatic charge of bacteria on grazing rates of three common species of interception-feeding nanoflagellates was examined. The hydrophobicity of bacteria isolated from freshwater plankton was assessed by using two different methods (bacterial adhesion to hydrocarbon and hydrophobic interaction chromatography). The electrostatic charge of the cell surface (measured as zeta potential) was analyzed by microelectrophoresis. Bacterial ingestion rates were determined by enumerating bacteria in food vacuoles by immunofluorescence labelling via strain-specific antibodies. Feeding rates varied about twofold for each flagellate species but showed no significant dependence on prey hydrophobicity or surface charge. Further evidence was provided by an experiment involving flagellate grazing on complex bacterial communities in a two-stage continuous culture system. The hydrophobicity values of bacteria that survived protozoan grazing were variable, but the bacteria did not tend to become more hydrophilic. We concluded that variability in bacterial cell hydrophobicity and variability in surface charge do not severely affect uptake rates of suspended bacteria or food selection by interception-feeding flagellates.
Yeast Species Associated with Orange Juice: Evaluation of Different Identification Methods
Authors: Arias Covadonga R. , Burns Jacqueline K. , Friedrich Lorrie M. , Goodrich Renee M. , Parish Mickey E.
Published: July 2002

Five different methods were used to identify yeast isolates from a variety of citrus juice sources. A total of 99 strains, including reference strains, were identified using a partial sequence of the 26S rRNA gene, restriction pattern analysis of the internal transcribed spacer region (5.8S-ITS), classical methodology, the RapID Yeast Plus system, and API 20C AUX. Twenty-three different species were identified representing 11 different genera. Distribution of the species was considerably different depending on the type of sample. Fourteen different species were identified from pasteurized single-strength orange juice that had been contaminated after pasteurization (PSOJ), while only six species were isolated from fresh-squeezed, unpasteurized orange juice (FSOJ). Among PSOJ isolates,
Candida intermedia
and
Candida parapsilosis
were the predominant species.
Hanseniaspora occidentalis
and
Hanseniaspora uvarum
represented up to 73% of total FSOJ isolates. Partial sequence of the 26S rRNA gene yielded the best results in terms of correct identification, followed by classical techniques and 5.8S-ITS analysis. The commercial identification kits RapID Yeast Plus system and API 20C AUX were able to correctly identify only 35 and 13% of the isolates, respectively. Six new 5.8S-ITS profiles were described, corresponding to
Clavispora lusitaniae
,
Geotrichum citri-aurantii
,
H. occidentalis
,
H. vineae
,
Pichia fermentans
, and
Saccharomycopsis crataegensis
. With the addition of these new profiles to the existing database, the use of 5.8S-ITS sequence became the best tool for rapid and accurate identification of yeast isolates from orange juice.
Engineering the
Rhizobium leguminosarum
bv. viciae Hydrogenase System for Expression in Free-Living Microaerobic Cells and Increased Symbiotic Hydrogenase Activity
Authors: Brito B. , Palacios J. M. , Imperial J. , Ruiz-Argüeso T.
Published: July 2002

Rhizobium leguminosarum
bv. viciae UPM791 induces hydrogenase activity in pea (
Pisum sativum
L.) bacteroids but not in free-living cells. The symbiotic induction of hydrogenase structural genes (
hupSL
) is mediated by NifA, the general regulator of the nitrogen fixation process. So far, no culture conditions have been found to induce NifA-dependent promoters in vegetative cells of this bacterium. This hampers the study of the
R. leguminosarum
hydrogenase system. We have replaced the native NifA-dependent
hupSL
promoter with the FnrN-dependent
fixN
promoter, generating strain SPF25, which expresses the
hup
system in microaerobic free-living cells. SPF25 reaches levels of hydrogenase activity in microaerobiosis similar to those induced in UPM791 bacteroids. A sixfold increase in hydrogenase activity was detected in merodiploid strain SPF25(pALPF1). A time course induction of hydrogenase activity in microaerobic free-living cells of SPF25(pALPF1) shows that hydrogenase activity is detected after 3 h of microaerobic incubation. Maximal hydrogen uptake activity was observed after 10 h of microaerobiosis. Immunoblot analysis of microaerobically induced SPF25(pALPF1) cell fractions indicated that the HupL active form is located in the membrane, whereas the unprocessed protein remains in the soluble fraction. Symbiotic hydrogenase activity of strain SPF25 was not impaired by the promoter replacement. Moreover, bacteroids from pea plants grown in low-nickel concentrations induced higher levels of hydrogenase activity than the wild-type strain and were able to recycle all hydrogen evolved by nodules. This constitutes a new strategy to improve hydrogenase activity in symbiosis.
AhpC, AhpD, and a Secreted 14-Kilodalton Antigen from
Mycobacterium avium
subsp.
paratuberculosis
Distinguish between Paratuberculosis and Bovine Tuberculosis in an Enzyme-Linked Immunosorbent Assay
Authors: Olsen Ingrid , Tryland Morten , Wiker Harald G. , Reitan Liv J.
Published: July 2002

Sera from cattle naturally infected with
Mycobacterium avium
subsp.
paratuberculosis
(
n
= 56) and naturally (
n
= 4) and experimentally (
n
= 8) infected with
Mycobacterium bovis
were tested for the presence of antibodies against paratuberculosis antigens. An enzyme-linked immunosorbent assay (ELISA) was established based on absorption of
M. avium
subsp.
paratuberculosis
antigens on a hyperimmune antiserum against
M. avium
subsp.
avium
proteins in order to remove cross-reacting antigens. This absorbed-antigen ELISA recognized 66% of animals with paratuberculosis (37 of 56), while none of the animals with naturally occurring bovine tuberculosis (TB) had detectable antibodies. However, the animals with experimental bovine TB also responded in this ELISA. Similar results were found in a commercial ELISA, showing that neither of these tests was able to distinguish between paratuberculosis and bovine TB. The sera were further tested for antibody activities against purified AhpC and AhpD, which are proteins constitutively expressed by
M. avium
subsp.
paratuberculosis,
and against a secreted 14-kDa protein present in culture filtrates from the
M. avium
complex. Elevated antibody levels to AhpC, AhpD, and the 14-kDa antigen were found in 27% (13 of 48), 15% (7 of 48), and 27% (13 of 48), respectively, of the cattle with paratuberculosis. Together these ELISAs were positive with 35% (17 of 48) of the animals. None of the animals with bovine TB had detectable antibodies against any of the purified proteins despite their high levels of cross-reacting antibodies. These results show that purified specific antigens are needed to differentiate between paratuberculosis and bovine TB in ELISA.
Laboratory-Acquired Parasitic Infections from Accidental Exposures
Authors: Herwaldt Barbara L.
Published: July 2002

Parasitic diseases are receiving increasing attention in developed countries in part because of their importance in travelers, immigrants, and immunocompromised persons. The main purpose of this review is to educate laboratorians, the primary readership, and health care workers, the secondary readership, about the potential hazards of handling specimens that contain viable parasites and about the diseases that can result. This is accomplished partly through discussion of the occupationally acquired cases of parasitic infections that have been reported, focusing for each case on the type of accident that resulted in infection, the length of the incubation period, the clinical manifestations that developed, and the means by which infection was detected. The article focuses on the cases of infection with the protozoa that cause leishmaniasis, malaria, toxoplasmosis, Chagas' disease (American trypanosomiasis), and African trypanosomiasis. Data about 164 such cases are discussed, as are data about cases caused by intestinal protozoa and by helminths. Of the 105 case-patients infected with blood and tissue protozoa who either recalled an accident or for whom the likely route of transmission could be presumed, 47 (44.8%) had percutaneous exposure via a contaminated needle or other sharp object. Some accidents were directly linked to poor laboratory practices (e.g., recapping a needle or working barehanded). To decrease the likelihood of accidental exposures, persons who could be exposed to pathogenic parasites must be thoroughly instructed in safety precautions before they begin to work and through ongoing training programs. Protocols should be provided for handling specimens that could contain viable organisms, using protective clothing and equipment, dealing with spills of infectious organisms, and responding to accidents. Special care should be exercised when using needles and other sharp objects.
T-Cell Epitopes and Human Leukocyte Antigen Restriction Elements of an Immunodominant Antigen ofBlastomyces dermatitidis
Authors: Chang W. L. , Audet R. G. , Aizenstein B. D. , Hogan L. H. , DeMars R. I. , Klein B. S.
Published: July 2002

Humans infected with the dimorphic fungusBlastomyces dermatitidisdevelop strong T-lymphocyte responses to WI-1, an immunodominant antigen that has been shown to elicit protective immunity in mice. In the present study, the T-cell epitopes of WI-1 and human leukocyte antigen (HLA) restricting elements that display them were investigated. Peripheral blood mononuclear cells (PBMC) from 37 patients with a confirmed history of blastomycosis were tested for a response to WI-1 in primary proliferation assays; PBMC from 35 (95%) responded. Six patients whose PBMC proliferated strongly in response to WI-1 (defined as a stimulation index greater than 50) were tested further for responses to subcloned, recombinant fragments of the antigen. These patients responded chiefly to sequences within the N terminus and the 25-amino-acid tandem repeat. Cloned CD4+T cells from an infected individual were used to delineate more precisely the peptide epitopes in the fragments and HLA restricting elements that present them. A majority of the T-cell clones recognized an epitope spanning amino acids 149 to 172 within the N terminus, displayed by HLA-DR 15. A minority of the clones, which have been shown to perform a cytolytic function in vitro, recognized an epitope in the tandem repeat displayed by HLA-DPw4, an uncommon restricting element. Tandem repeat epitopes required display by the β chain of DPw4 heterodimers. Thus, human T cells with different functions in vitro also recognize distinct regions of WI-1, raising the possibility that HLA restricting elements that present them could modulate immunity during blastomycosis by selection and display of WI-1 peptides.
DNA Adenine Methylase Is Essential for Viability and Plays a Role in the Pathogenesis of
Yersinia pseudotuberculosis
and
Vibrio cholerae
Authors: Julio Steven M. , Heithoff Douglas M. , Provenzano Daniele , Klose Karl E. , Sinsheimer Robert L. , Low David A. , Mahan Michael J.
Published: July 2002

Salmonella
strains that lack or overproduce DNA adenine methylase (Dam) elicit a protective immune response to different
Salmonella
species. To generate vaccines against other bacterial pathogens, the
dam
genes of
Yersinia pseudotuberculosis
and
Vibrio cholerae
were disrupted but found to be essential for viability. Overproduction of Dam significantly attenuated the virulence of these two pathogens, leading to, in
Yersinia
, the ectopic secretion of virulence proteins (
Yersinia
outer proteins) and a fully protective immune response in vaccinated hosts. Dysregulation of Dam activity may provide a means for the development of vaccines against varied bacterial pathogens.