14 research outputs found
In vitro activity of thiamphenicol against Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes clinical isolates
Objective.
To determine in vitro activity of thiamphenicol and other clinically available antimicrobials against clinical isolates of Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes.
Materials and Methods.
We included in the study 875 clinical isolates from 20 Russian cities during 2018–2019. Among tested strains, 126 were H. influenzae, 389 – S. pneumoniae, 360 – S. pyogenes. Antimicrobial susceptibility testing was performed using broth microdilution method according to ISO 20776-1:2006. AST results were interpreted according to EUCAST v.11.0 clinical breakpoints.
Results.
The minimum inhibitory concentrations (MICs) of thiamphenicol did not exceed 2 mg/L for 94.4% of H. influenzae strains (MIC50 and MIC90 were 0.5 and 1 mg/L, respectively). Thiamphenicol was active against 76.9% of ampicillin-resistant H. influenzae strains (MIC of thiamphenicol 0.06 mg/L) did not exceed 2 mg/L. A total of 88.1% of S. pneumoniae strains resistant to erythromycin were highly susceptible to thiamphenicol (MIC < 2 mg/L). The MIC of thiamphenicol did not exceed 8 mg/L for 96.1% of S. pyogenes strains (MIC50 and MIC90 were 2 and 4 mg/L, respectively).
Conclusions.
Thiamphenicol was characterized by relatively high in vitro activity, comparable to that of chloramphenicol, against tested strains of H. influenzae, S. pneumoniae and S. pyogenes, including S. pneumoniae isolates with reduced susceptibility to penicillin
Cosmic Numbers: A Physical Classification for Cosmological Models
We introduce the notion of the cosmic numbers of a cosmological model, and
discuss how they can be used to naturally classify models according to their
ability to solve some of the problems of the standard cosmological model.Comment: 3 pages, no figures. v2: Two references added, cosmetic changes.
Version to appear in Phys. Rev. D (Brief reports
2d Stringy Black Holes and Varying Constants
Motivated by the recent interest on models with varying constants and whether
black hole physics can constrain such theories, two-dimensional charged stringy
black holes are considered. We exploit the role of two-dimensional stringy
black holes as toy models for exploring paradoxes which may lead to constrains
on a theory. A two-dimensional charged stringy black hole is investigated in
two different settings. Firstly, the two-dimensional black hole is treated as
an isolated object and secondly, it is contained in a thermal environment. In
both cases, it is shown that the temperature and the entropy of the
two-dimensional charged stringy black hole are decreased when its electric
charge is increased in time. By piecing together our results and previous ones,
we conclude that in the context of black hole thermodynamics one cannot derive
any model independent constraints for the varying constants. Therefore, it
seems that there aren't any varying constant theories that are out of favor
with black hole thermodynamics.Comment: 12 pages, LaTeX, to appear in JHE
Time Variations in the Scale of Grand Unification
We study the consequences of time variations in the scale of grand
unification, , when the Planck scale and the value of the unified coupling
at the Planck scale are held fixed. We show that the relation between the
variations of the low energy gauge couplings is highly model dependent. It is
even possible, in principle, that the electromagnetic coupling varies,
but the strong coupling does not (to leading approximation). We
investigate whether the interpretation of recent observations of quasar
absorption lines in terms of time variation in can be accounted for by
time variation in . Our formalism can be applied to any scenario where a
time variation in an intermediate scale induces, through threshold corrections,
time variations in the effective low scale couplings.Comment: 14 pages, revtex4; Updated observational results and improved
statistical analysis (section IV); added reference
Search for varying constants of nature from astronomical observation of molecules
The status of searches for possible variation in the constants of nature from
astronomical observation of molecules is reviewed, focusing on the
dimensionless constant representing the proton-electron mass ratio
. The optical detection of H and CO molecules with large
ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as
the detection of H with the Cosmic Origins Spectrograph aboard the Hubble
Space Telescope is discussed in the context of varying constants, and in
connection to different theoretical scenarios. Radio astronomy provides an
alternative search strategy bearing the advantage that molecules as NH
(ammonia) and CHOH (methanol) can be used, which are much more sensitive to
a varying than diatomic molecules. Current constraints are
for redshift , corresponding to
look-back times of 10-12.5 Gyrs, and for
, corresponding to half the age of the Universe (both at 3
statistical significance). Existing bottlenecks and prospects for future
improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the
International Space Science Institute, Bern 201
Dimensionless cosmology
Although it is well known that any consideration of the variations of
fundamental constants should be restricted to their dimensionless combinations,
the literature on variations of the gravitational constant is entirely
dimensionful. To illustrate applications of this to cosmology, we explicitly
give a dimensionless version of the parameters of the standard cosmological
model, and describe the physics of Big Bang Neucleosynthesis and recombination
in a dimensionless manner. The issue that appears to have been missed in many
studies is that in cosmology the strength of gravity is bound up in the
cosmological equations, and the epoch at which we live is a crucial part of the
model. We argue that it is useful to consider the hypothetical situation of
communicating with another civilization (with entirely different units),
comparing only dimensionless constants, in order to decide if we live in a
Universe governed by precisely the same physical laws. In this thought
experiment, we would also have to compare epochs, which can be defined by
giving the value of any {\it one} of the evolving cosmological parameters. By
setting things up carefully in this way one can avoid inconsistent results when
considering variable constants, caused by effectively fixing more than one
parameter today. We show examples of this effect by considering microwave
background anisotropies, being careful to maintain dimensionlessness
throughout. We present Fisher matrix calculations to estimate how well the fine
structure constants for electromagnetism and gravity can be determined with
future microwave background experiments. We highlight how one can be misled by
simply adding to the usual cosmological parameter set