1,993 research outputs found
The Conserved nhaAR Operon Is Drastically Divergent between B2 and Non-B2 Escherichia coli and Is Involved in Extra-Intestinal Virulence
The Escherichia coli species is divided in phylogenetic groups that differ in their virulence and commensal distribution. Strains belonging to the B2 group are involved in extra-intestinal pathologies but also appear to be more prevalent as commensals among human occidental populations. To investigate the genetic specificities of B2 sub-group, we used 128 sequenced genomes and identified genes of the core genome that showed marked difference between B2 and non-B2 genomes. We focused on the gene and its surrounding region with the strongest divergence between B2 and non-B2, the antiporter gene nhaA. This gene is part of the nhaAR operon, which is in the core genome but flanked by mobile regions, and is involved in growth at high pH and high sodium concentrations. Consistently, we found that a panel of non-B2 strains grew faster than B2 at high pH and high sodium concentrations. However, we could not identify differences in expression of the nhaAR operon using fluorescence reporter plasmids. Furthermore, the operon deletion had no differential impact between B2 and non-B2 strains, and did not result in a fitness modification in a murine model of gut colonization. Nevertheless, sequence analysis and experiments in a murine model of septicemia revealed that recombination in nhaA among B2 strains was observed in strains with low virulence. Finally, nhaA and nhaAR operon deletions drastically decreased virulence in one B2 strain. This effect of nhaAR deletion appeared to be stronger than deletion of all pathogenicity islands. Thus, a population genetic approach allowed us to identify an operon in the core genome without strong effect in commensalism but with an important role in extra-intestinal virulence, a landmark of the B2 strains
Electron transport through multilevel quantum dot
Quantum transport properties through some multilevel quantum dots sandwiched
between two metallic contacts are investigated by the use of Green's function
technique. Here we do parametric calculations, based on the tight-binding
model, to study the transport properties through such bridge systems. The
electron transport properties are significantly influenced by (a) number of
quantized energy levels in the dots, (b) dot-to-electrode coupling strength,
(c) location of the equilibrium Fermi energy and (d) surface disorder. In
the limit of weak-coupling, the conductance () shows sharp resonant peaks
associated with the quantized energy levels in the dots, while, they get
substantial broadening in the strong-coupling limit. The behavior of the
electron transfer through these systems becomes much more clearly visible from
our study of current-voltage (-) characteristics. In this context we also
describe the noise power of current fluctuations () and determine the Fano
factor () which provides an important information about the electron
correlation among the charge carriers. Finally, we explore a novel transport
phenomenon by studying the surface disorder effect in which the current
amplitude increases with the increase of the surface disorder strength in the
strong disorder regime, while, the amplitude decreases in the limit of weak
disorder. Such an anomalous behavior is completely opposite to that of bulk
disordered system where the current amplitude always decreases with the
disorder strength. It is also observed that the current amplitude strongly
depends on the system size which reveals the finite quantum size effect.Comment: 12 pages, 7 figure
Surgical management of multilevel lumbar spondylolysis: A case report and review of the literature
AbstractMultilevel lumbar spondylolysis accounts for less than 6% of the cases of lumbar spondylolysis and its treatment, as reported in the literature, has not been consistent. Fewer than ten cases presenting triple lumbar spondylosis have been published. We describe the case of a 33-year-old male presenting bilateral L3, L4, and L5 isthmic lysis with no spondylolisthesis or disc degeneration. The MRI and CT of the lumbar spine were decisive elements in the therapeutic choice and the surgical treatment performed was bilateral L3 and L4 isthmic repair via a combined anterior and posterior L5S1 approach. The clinical and radiological results were good at the last follow-up visit
Heterodyne Spectroscopy of the 63 m O I Line in M42
We have used a laser heterodyne spectrometer to resolve the emission line
profile of the 63 micron 3P1 - 3P2 fine-structure transition of O I at two
locations in M42. Comparison of the peak antenna temperature with that of the
158 micron C II fine-structure line shows that the gas kinetic temperature in
the photodissociation region near theta1C is 175 - 220 K, the density is
greater than 2x10 ^5 cm-3, and the hydrogen column density is about 1.5x10 ^22
cm-2. A somewhat lower temperature and column density are found in the IRc2
region, most likely reflecting the smaller UV flux. The observed width of the O
I line is 6.8 km/s (FWHM) at theta1C, which is slightly broadened over the
intrinsic linewidth by optical depth effects. No significant other differences
between the O I and C II line profiles are seen, which shows that the narrow
emission from both neutral atomic oxygen and ionized carbon comes from the PDR.
The O I data do not rule out the possibility of weak broad-velocity emission
from shock-excited gas at IRc2, but the C II data show no such effect, as
expected from non-ionizing shock models.Comment: 11 pages including 2 postscript figures, uses aaspp4.st
Design and stability study of a paediatric oral solution of methotrexate 2mg/ml
Oral paediatric forms development by pharmaceutical industry is still insufficient. The present study was performed to propose an adapted and pleasant formulation of liquid oral formulation of MTX. The solution is composed of injectable methotrexate, water, Ora Sweet(®) and sodium bicarbonate. After 120 days storage, pH remained stable at about 8 in all formulations, insuring no risk of MTX precipitation. MTX content in solution formulation, determined by high performance liquid chromatography measurements, remained in the specifications of >90% of the initial concentration when stored at 4 and 25°C. Forced degradation of MTX by heat and acidic conditions allowed formation and detection of degradation products by the analytical method. Microbial study of the preparation shows that the solution remains in the specifications during all the storage, or after one sample each week during one month, eventually indicating the microbial properties are not affected by patient use. To conclude, we here propose a new MTX liquid formulation stable for at least 120 days
Low temperature heat capacity of Fe_{1-x}Ga_{x} alloys with large magneostriction
The low temperature heat capacity C_{p} of Fe_{1-x}Ga_{x} alloys with large
magnetostriction has been investigated. The data were analyzed in the standard
way using electron () and phonon () contributions. The
Debye temperature decreases approximately linearly with increasing
Ga concentration, consistent with previous resonant ultrasound measurements and
measured phonon dispersion curves. Calculations of from lattice
dynamical models and from measured elastic constants C_{11}, C_{12} and C_{44}
are in agreement with the measured data. The linear coefficient of electronic
specific heat remains relatively constant as the Ga concentration
increases, despite the fact that the magnetoelastic coupling increases. Band
structure calculations show that this is due to the compensation of majority
and minority spin states at the Fermi level.Comment: 14 pages, 6 figure
Early Hospital Discharge of Older Adults Admitted to the Emergency Department: Effect of Different Types of Recommendations Made by a Mobile Geriatric Team
International audienc
The cosmic microwave background radiation temperature at z = 3.025 toward QSO 0347--3819
From the analysis of the CII fine-structure population ratio in the damped
Ly_alpha system at z = 3.025 toward the quasar Q0347--3819 we derive an upper
bound of 14.6 (+/- 0.2) K on the cosmic microwave background temperature
regardless the presence of other different excitation mechanisms. The analysis
of the ground state rotational level populations of H_2 detected in the system
reveals a Galactic-type UV radiation field ruling out UV pumping as an
important excitation mechanism for CII. The low dust content estimated from the
Cr/Zn ratio indicates that the IR dust emission can also be neglected. When the
collisional excitation is considered, we measure a temperature for the cosmic
background radiation of T = 12.1 (+1.7, -3.2) K. The results are in agreement
with the T = 10.968 (+/-) 0.004 K predicted by the hot Big Bang cosmology at z
= 3.025.Comment: Accepte
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