135 research outputs found
The High Angular Resolution Multiplicity of Massive Stars
We present the results of a speckle interferometric survey of Galactic
massive stars that complements and expands upon a similar survey made over a
decade ago. The speckle observations were made with the KPNO and CTIO 4 m
telescopes and USNO speckle camera, and they are sensitive to the detection of
binaries in the angular separation regime between 0.03" and 5" with relatively
bright companions (Delta V < 3). We report on the discovery of companions to 14
OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37
Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary
sample that we selected for future orbital determinations). We made a
statistical analysis of the binary frequency among the subsample that are
listed in the Galactic O Star Catalog by compiling published data on other
visual companions detected through adaptive optics studies and/or noted in the
Washington Double Star Catalog and by collecting published information on
radial velocities and spectroscopic binaries. We find that the binary frequency
is much higher among O-stars in clusters and associations compared to the
numbers for field and runaway O-stars, consistent with predictions for the
ejection processes for runaway stars. We present a first orbit for the O-star
Delta Orionis, a linear solution of the close, apparently optical, companion of
the O-star Iota Orionis, and an improved orbit of the Be star Delta Scorpii.
Finally, we list astrometric data for another 249 resolved and 221 unresolved
targets that are lower mass stars that we observed for various other science
programs.Comment: 76 pages, 6 figures, 11 table
Visual orbit for the low-mass binary Gliese 22 AC from speckle interferometry
Based on 14 data points obtained with near-infrared speckle interferometry
and covering an almost entire revolution, we present a first visual orbit for
the low-mass binary system Gliese 22 AC. The quality of the orbit is largely
improved with respect to previous astrometric solutions. The dynamical system
mass is 0.592 +- 0.065 solar masses, where the largest part of the error is due
to the Hipparcos parallax. A comparison of this dynamical mass with
mass-luminosity relations on the lower main sequence and theoretical
evolutionary models for low-mass objects shows that both probably underestimate
the masses of M dwarfs. A mass estimate for the companion Gliese 22 C indicates
that this object is a very low-mass star with a mass close to the hydrogen
burning mass limit.Comment: Accepted by Astronomy and Astrophysics, 6 pages, 2 figure
Orbit Determination of Close Binary Systems using Lucky Imaging
We present relative positions of visual binaries observed during 2009 with
the FastCam "lucky-imaging" camera at the 1.5-m Carlos Sanchez Telescope (TCS)
at the Observatorio del Teide. We obtained 424 CCD observations (averaged in
198 mean relative positions) of 157 binaries with angular separations in the
range 0.14-15.40", with a median separation of 0.51". For a given system, each
CCD image represents the sum of the best 10-25% images from 1000-5000
short-exposure frames. Derived internal errors were 7 mas in r and 1.2^{\circ}
(9 mas) in q. When comparing to systems with very well-known orbits, we find
that the rms deviation in r residuals is 23 mas, while the rms deviation in q
residuals is 0.73 deg/r. We confirmed 18 Hipparcos binaries and we report new
companions to BVD 36 A and J 621 B. For binaries with preliminary orbital
parameters, the relative radial velocity was estimated as well. We also present
four new revised orbits computed for LDS 873, BU 627 A-BC, BU 628 and HO 197
AB. This work is the first results on visual binaries using the FastCam
lucky-imaging camera.Comment: 23 pages, 10 figures, 14 tables, accepted August 18th, 2011, to be
published in MNRA
Effect of RecA inactivation and detoxification systems on the evolution of ciprofloxacin resistance in Escherichia coli
Background
Suppression of SOS response and overproduction of reactive oxygen species (ROS) through detoxification system suppression enhance the activity of fluoroquinolones.
Objectives
To evaluate the role of both systems in the evolution of resistance to ciprofloxacin in an isogenic model of Escherichia coli.
Methods
Single-gene deletion mutants of E. coli BW25113 (wild-type) (ÎrecA, ÎkatG, ÎkatE, ÎsodA, ÎsodB), double-gene (ÎrecA-ÎkatG, ÎrecA-ÎkatE, ÎrecA-ÎsodA, ÎrecA-ÎsodB, ÎkatG-ÎkatE, ÎsodB-ÎsodA) and triple-gene (ÎrecA-ÎkatG-ÎkatE) mutants were included. The response to sudden high ciprofloxacin pressure was evaluated by mutant prevention concentration (MPC). The gradual antimicrobial pressure response was evaluated through experimental evolution and antibiotic resistance assays.
Results
For E. coli BW25113 strain, ÎkatE, ÎsodB and ÎsodB/ÎsodA mutants, MPC values were 0.25 mg/L. The ÎkatG, ÎsodA, ÎkatG/katE and ÎrecA mutants showed 2-fold reductions (0.125 mg/L). The ÎkatG/ÎrecA, ÎkatE/ÎrecA, ÎsodA/ÎrecA, ÎsodB/ÎrecA and ÎkatG/ÎkatE/ÎrecA strains showed 4â8-fold reductions (0.03â0.06 mg/L) relative to the wild-type. Gradual antimicrobial pressure increased growth capacity for ÎsodA and ÎsodB and ÎsodB/ÎsodA mutants (no growth in 4 mg/L) compared with the wild-type (no growth in the range of 0.5â2 mg/L). Accordingly, increased growth was observed with the mutants ÎrecA/ÎkatG (no growth in 2 mg/L), ÎrecA/ÎkatE (no growth in 2 mg/L), ÎrecA/ÎsodA (no growth in 0.06 mg/L), ÎrecA/ÎsodB (no growth in 0.25 mg/L) and ÎrecA/ÎkatG/ÎkatE (no growth in 0.5 mg/L) compared with ÎrecA (no growth in the range of 0.002â0.015 mg/L).
Conclusions
After RecA inactivation, gradual exposure to ciprofloxacin reduces the evolution of resistance. After suppression of RecA and detoxification systems, sudden high exposure to ciprofloxacin reduces the evolution of resistance in E. coli.Plan Nacional de I+D+i 2013-2016 and the Instituto de Salud Carlos III (projects and PI17/01501 and PI20-00239)SubdirecciĂłn General de Redes y Centros de InvestigaciĂłn Cooperativa, Ministerio de EconomĂa, Industria y Competitividad, Spanish Network for Research in Infectious Diseases (REIPI; RD16/0016/0001 and REIPI RD16/ 0016/0009
Quinolone Resistance Reversion by Targeting the SOS Response
Suppression of the SOS response has been postulated as a therapeutic strategy for potentiating antimicrobial agents. We aimed to evaluate the impact of its suppression on reversing resistance using a model of isogenic strains of Escherichia coli representing multiple levels of quinolone resistance. E. coli mutants exhibiting a spectrum of SOS activity were constructed from isogenic strains carrying quinolone resistance mechanisms with susceptible and resistant phenotypes. Changes in susceptibility were evaluated by static (MICs) and dynamic (killing curves or flow cytometry) methodologies. A peritoneal sepsis murine model was used to evaluate in vivo impact. Suppression of the SOS response was capable of resensitizing mutant strains with genes encoding three or four different resistance mechanisms (up to 15-fold reductions in MICs). Killing curve assays showed a clear disadvantage for survival (Îlog10 CFU per milliliter [CFU/ml] of 8 log units after 24 h), and the in vivo efficacy of ciprofloxacin was significantly enhanced (Îlog10 CFU/g of 1.76 log units) in resistant strains with a suppressed SOS response. This effect was evident even after short periods (60 min) of exposure. Suppression of the SOS response reverses antimicrobial resistance across a range of E. coli phenotypes from reduced susceptibility to highly resistant, playing a significant role in increasing the in vivo efficacy
Impaired Virulence and In Vivo Fitness of Colistin-Resistant Acinetobacter baumannii
4 pĂĄginas, 2 figuras. Presentado en parte: 20 Âș Congreso Europeo de MicrobiologĂa ClĂnica y Enfermedades Infecciosas, Resumen 1389, Viena, Austria, 10-13 de abril de 2010.Acinetobacter baumannii (American Type Culture Collection strain 19606) acquires mutations in the pmrB gene during the in vitro development of resistance to colistin. The colistin-resistant strain has lower affinity for colistin, reduced in vivo fitness (competition index, .016), and decreased virulence, both in terms of mortality (0% lethal dose, 6.9 vs 4.9 log colony-forming units) and survival in a mouse model of peritoneal sepsis. These results may explain the low incidence and dissemination of colistin resistance in A. baumannii in clinical settings.This work was supported by the European Development Regional Fund âA way to achieve Europeâ (ERDF); the Spanish Network for the Research in Infectious Diseases (REIPI RD06/0008), Instituto de Salud Carlos III, Ministerio de Ciencia e InnovaciĂłn, Spain; and the Autonomous government of Madrid (COMBACT S-BIO-0260/2006, L.R.).Peer reviewe
Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage
The nearby high-mass star binary system Theta 1 Orionis C is the brightest
and most massive of the Trapezium OB stars at the core of the Orion Nebula
Cluster, and it represents a perfect laboratory to determine the fundamental
parameters of young hot stars and to constrain the distance of the Orion
Trapezium Cluster. Between January 2007 and March 2008, we observed T1OriC with
VLTI/AMBER near-infrared (H- and K-band) long-baseline interferometry, as well
as with bispectrum speckle interferometry with the ESO 3.6m and the BTA 6m
telescopes (B'- and V'-band). Combining AMBER data taken with three different
3-telescope array configurations, we reconstructed the first VLTI/AMBER
closure-phase aperture synthesis image, showing the T1OriC system with a
resolution of approx. 2 mas. To extract the astrometric data from our
spectrally dispersed AMBER data, we employed a new algorithm, which fits the
wavelength-differential visibility and closure phase modulations along the H-
and K-band and is insensitive to calibration errors induced, for instance, by
changing atmospheric conditions. Our new astrometric measurements show that the
companion has nearly completed one orbital revolution since its discovery in
1997. The derived orbital elements imply a short-period (P=11.3 yrs) and
high-eccentricity orbit (e=0.6) with periastron passage around 2002.6. The new
orbit is consistent with recently published radial velocity measurements, from
which we can also derive the first direct constraints on the mass ratio of the
binary components. We employ various methods to derive the system mass
(M_system=44+/-7 M_sun) and the dynamical distance (d=410+/-20 pc), which is in
remarkably good agreement with recently published trigonometric parallax
measurements obtained with radio interferometry.Comment: 15 pages, 15 figures, accepted by A&
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