1,103 research outputs found
Enterohemorrhagic Escherichia coli colonization of human colonic epithelium in vitro and ex vivo
Enterohemorrhagic E. coli (EHEC) are important foodborne pathogens causing gastroenteritis and more severe complications such as hemorrhagic colitis and hemolytic uremic syndrome. Pathology is most pronounced in the colon, but to date there is no direct clinical evidence showing EHEC binding to colonic epithelium in patients. In this study, we investigated EHEC adherence to the human colon by using in vitro organ culture (IVOC) of colonic biopsies and polarized T84 colon carcinoma cells. We showed for the first time that EHEC colonized human colonic biopsies by forming typical attaching/effacing (A/E) lesions which were dependent on EHEC type III secretion (T3S) and binding of the outer membrane protein intimin to the Translocated intimin receptor (Tir). A/E lesion formation was dependent on oxygen levels and suppressed under oxygen-rich culture conditions routinely used for IVOC. In contrast, EHEC adherence to polarized T84 cells occurred independently of T3S and intimin and did not involve Tir translocation into the host cell membrane. Neither colonization of biopsies nor T84 cells was significantly affected by expression of Shiga toxins. Our study suggests that EHEC colonize and form stable A/E lesions on the human colon which is likely to contribute to intestinal pathology during infection. Furthermore, care needs to be taken when using cell culture models as they might not reflect the in vivo situation
Time-Resolved Studies of a Rolled-Up Semiconductor Microtube Laser
We report on lasing in rolled-up microtube resonators. Time-resolved studies
on these semiconductor lasers containing GaAs quantum wells as optical gain
material reveal particularly fast turn-on-times and short pulse emissions above
the threshold. We observe a strong red-shift of the laser mode during the pulse
emission which is compared to the time evolution of the charge-carrier density
calculated by rate equations
Hepatic Artery Infusion Chemotherapy
Hepatic artery chemotherapy was given to 36 patients, using totally implantable devices consisting of a port
and external pump. Twenty-seven patients had inoperable liver metastases of colorectal origin. The infusion
system was inserted by laparotomy into the hepatic artery via the gastroduodenal artery. There was no
operative mortality. Thirteen infusion systems could not be used for chemotherapy due to dislodgement,
early death and lack of follow-up. FUdR was infused every two weeks. There were minor local
complications like thrombosis of the system and dislodgement of the port. Toxic effects could be managed
by reducing the dose. Response to chemotherapy was evaluated by survival, clinical condition, CEA,
ultrasound and CT six months after onset of arterial chemotherapy. Ten/twenty-three patients (43%)
responded to therapy, eight of them died on the average 19 months after initial chemotherapy. Six patients
were non-responders, seven had stable disease. Five/ten patients developed extrahepatic metastases. Mean
survival time was 13.1 months, mean interval until relapse 10.6 months
Spin dephasing and photoinduced spin diffusion in high-mobility 110-grown GaAs-AlGaAs two-dimensional electron systems
We have studied spin dephasing and spin diffusion in a high-mobility
two-dimensional electron system, embedded in a GaAs/AlGaAs quantum well grown
in the [110] direction, by a two-beam Hanle experiment. For very low excitation
density, we observe spin lifetimes of more than 16 ns, which rapidly decrease
as the pump intensity is increased. Two mechanisms contribute to this decrease:
the optical excitation produces holes, which lead to a decay of electron spin
via the Bir-Aranov-Pikus mechanism and recombination with spin-polarized
electrons. By scanning the distance between the pump and probe beams, we
observe the diffusion of spin-polarized electrons over more than 20 microns.
For high pump intensity, the spin polarization in a distance of several microns
from the pump beam is larger than at the pump spot, due to the reduced
influence of photogenerated holes.Comment: 4 pages, 3 figure
Identification and characterisation of enteroaggregative Escherichia coli subtypes associated with human disease
Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence
Statics and Dynamics of the Wormlike Bundle Model
Bundles of filamentous polymers are primary structural components of a broad
range of cytoskeletal structures, and their mechanical properties play key
roles in cellular functions ranging from locomotion to mechanotransduction and
fertilization. We give a detailed derivation of a wormlike bundle model as a
generic description for the statics and dynamics of polymer bundles consisting
of semiflexible polymers interconnected by crosslinking agents. The elastic
degrees of freedom include bending as well as twist deformations of the
filaments and shear deformation of the crosslinks. We show that a competition
between the elastic properties of the filaments and those of the crosslinks
leads to renormalized effective bend and twist rigidities that become
mode-number dependent. The strength and character of this dependence is found
to vary with bundle architecture, such as the arrangement of filaments in the
cross section and pretwist. We discuss two paradigmatic cases of bundle
architecture, a uniform arrangement of filaments as found in F-actin bundles
and a shell-like architecture as characteristic for microtubules. Each
architecture is found to have its own universal ratio of maximal to minimal
bending rigidity, independent of the specific type of crosslink induced
filament coupling; our predictions are in reasonable agreement with available
experimental data for microtubules. Moreover, we analyze the predictions of the
wormlike bundle model for experimental observables such as the tangent-tangent
correlation function and dynamic response and correlation functions. Finally,
we analyze the effect of pretwist (helicity) on the mechanical properties of
bundles. We predict that microtubules with different number of protofilaments
should have distinct variations in their effective bending rigidity
Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures
For the realisation of scalable solid-state quantum-bit systems, spins in
semiconductor quantum dots are promising candidates. A key requirement for
quantum logic operations is a sufficiently long coherence time of the spin
system. Recently, hole spins in III-V-based quantum dots were discussed as
alternatives to electron spins, since the hole spin, in contrast to the
electron spin, is not affected by contact hyperfine interaction with the
nuclear spins. Here, we report a breakthrough in the spin coherence times of
hole ensembles, confined in so called natural quantum dots, in narrow
GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently,
time-resolved Faraday rotation and resonant spin amplification techniques
deliver hole-spin coherence times, which approach in the low magnetic field
limit values above 70 ns. The optical initialisation of the hole spin
polarisation, as well as the interconnected electron and hole spin dynamics in
our samples are well reproduced using a rate equation model.Comment: 16 pages, 6 figure
Theory of Resonant Raman Scattering in One Dimensional Electronic systems
A theory of resonant Raman scattering spectroscopy of one dimensional
electronic systems is developed on the assumptions that (i) the excitations of
the one dimensional electronic system are described by the Luttinger Liquid
model, (ii) Raman processes involve virtual excitations from a filled valence
band to an empty state of the one dimensional electronic system and (iii)
excitonic interactions between the valence and conduction bands may be
neglected. Closed form analytic expressions are obtained for the Raman
scattering cross sections, and are evaluated analytically and numerically for
scattering in the polarized channel, revealing a "double-peak" structure with
the lower peak involving multispinon excitations with total spin S=0 and the
higher peak being the conventional plasmon. A key feature of our results is a
nontrivial power law dependence, involving the Luttinger Liquid exponents, of
the dependence of the Raman cross sections on the difference of the laser
frequency from resonance. We find that near resonance the calculated ratio of
intensity in the lower energy feature to the intensity in the higher energy
feature saturates at a value of the order of unity (times a factor of the ratio
of the velocities of the two modes). We explicate the differences between the
'Luttinger liquid' and 'Fermi liquid' calculations of RRS spectra and argue
that excitonic effects, neglected in all treatments so far, are essential for
explaining the intensity ratios observed in quantum wires. We also discuss
other Luttinger liquid features which may be observed in future RRS
experiments
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