2,444 research outputs found
The effect of a multispecies probiotic on the composition of the faecal microbiota and bowel habits in chronic obstructive pulmonary disease patients treated with antibiotics
Short-term antibiotic treatment profoundly affects the intestinal microbiota, which may lead to sustained changes in microbiota composition. Probiotics may restore such a disturbance. The objective of the present study was to investigate the effect of a multispecies probiotic on the faecal microbiota during and after antibiotic intake in patients with a history of frequent antibiotic use. In this randomised, placebo-controlled, double-blind study, thirty chronic obstructive pulmonary disease (COPD) patients treated with antibiotics for a respiratory tract infection received 5 g of a multispecies probiotic or placebo twice daily for 2 weeks. Faecal samples were collected at 0, 7, 14 and 63 d. Changes in the composition of the dominant faecal microbiota were determined by PCR-denaturing gradient gel electrophoresis (DGGE). Changes in bacterial subgroups were determined by quantitative PCR and culture. Bowel movements were scored daily according to the Bristol stool form scale. During and after antibiotic treatment, DGGE-based similarity indices (SI) were high ( >/= 84 %) and band richness was relatively low, both remaining stable over time. No difference in SI was observed between patients with and without diarrhoea-like bowel movements. The multispecies probiotic had a modest effect on the bacterial subgroups. Nevertheless, it affected neither the composition of the dominant faecal microbiota nor the occurrence of diarrhoea-like bowel movements. The dominant faecal microbiota was not affected by antibiotics in this COPD population, suggesting an existing imbalance of the microbiota, which may also have contributed to the lack of effect by probiotic intak
Pyrimidine biosynthesis is not an essential function for trypanosoma brucei bloodstream forms
<p>Background: African trypanosomes are capable of both pyrimidine biosynthesis and salvage of preformed pyrimidines from the host, but it is unknown whether either process is essential to the parasite.</p>
<p>Methodology/Principal Findings: Pyrimidine requirements for growth were investigated using strictly pyrimidine-free media, with or without single added pyrimidine sources. Growth rates of wild-type bloodstream form Trypanosoma brucei brucei were unchanged in pyrimidine-free medium. The essentiality of the de novo pyrimidine biosynthesis pathway was studied by knocking out the PYR6-5 locus that produces a fusion product of orotate phosphoribosyltransferase (OPRT) and Orotidine Monophosphate Decarboxylase (OMPDCase). The pyrimidine auxotroph was dependent on a suitable extracellular pyrimidine source. Pyrimidine starvation was rapidly lethal and non-reversible, causing incomplete DNA content in new cells. The phenotype could be rescued by addition of uracil; supplementation with uridine, 2′deoxyuridine, and cytidine allowed a diminished growth rate and density. PYR6-5−/− trypanosomes were more sensitive to pyrimidine antimetabolites and displayed increased uracil transport rates and uridine phosphorylase activity. Pyrimidine auxotrophs were able to infect mice although the infection developed much more slowly than infection with the parental, prototrophic trypanosome line.</p>
<p>Conclusions/Significance: Pyrimidine salvage was not an essential function for bloodstream T. b. brucei. However, trypanosomes lacking de novo pyrimidine biosynthesis are completely dependent on an extracellular pyrimidine source, strongly preferring uracil, and display reduced infectivity. As T. brucei are able to salvage sufficient pyrimidines from the host environment, the pyrimidine biosynthesis pathway is not a viable drug target, although any interruption of pyrimidine supply was lethal.</p>
Propagation of nuclear data uncertainties for ELECTRA burn-up calculations
The European Lead-Cooled Training Reactor (ELECTRA) has been proposed as a
training reactor for fast systems within the Swedish nuclear program. It is a
low-power fast reactor cooled by pure liquid lead. In this work, we propagate
the uncertainties in Pu-239 transport data to uncertainties in the fuel
inventory of ELECTRA during the reactor life using the Total Monte Carlo
approach (TMC). Within the TENDL project the nuclear models input parameters
were randomized within their uncertainties and 740 Pu-239 nuclear data
libraries were generated. These libraries are used as inputs to reactor codes,
in our case SERPENT, to perform uncertainty analysis of nuclear reactor
inventory during burn-up. The uncertainty in the inventory determines
uncertainties in: the long-term radio-toxicity, the decay heat, the evolution
of reactivity parameters, gas pressure and volatile fission product content. In
this work, a methodology called fast TMC is utilized, which reduces the overall
calculation time. The uncertainty in the long-term radiotoxicity, decay heat,
gas pressure and volatile fission products were found to be insignificant.
However, the uncertainty of some minor actinides were observed to be rather
large and therefore their impact on multiple recycling should be investigated
further. It was also found that, criticality benchmarks can be used to reduce
inventory uncertainties due to nuclear data. Further studies are needed to
include fission yield uncertainties, more isotopes, and a larger set of
benchmarks.Comment: 4 pages, 4 figures, Proc. 2013 International Conference on Nuclear
Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be
published in Nuclear Data Sheet
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