PubMed Health⌕ Search

Biomedical subjects

P De Boever

Publications and source records attributed to P De Boever.

13 recordsLinked to original sources
PubMed2006

Radiation dosimetry for microbial experiments in the International Space Station using different etched track and luminescent detectors.

The laboratory of Microbiology at SCK.CEN, in collaboration with different universities, participates in several ESA programmes with bacterial experiments that are carried out in the International Space Station (ISS). The main objective of these programmes is to study the effects of space flight conditions such as microgravity and cosmic radiation on the general behaviour of model bacteria. To measure the radiation doses received by the bacteria, different detectors accompanied the microbiological experiments. The results obtained during two space flight missions are discussed. This dosimetry experiment was a collaboration between different institutes so that the doses could be estimated by different techniques. For measurement of the high linear energy transfer (LET) doses (>10 keV microm(-1)), two types of etched track detectors were used. The low LET part of the spectrum was measured by three types of thermoluminescent detectors ((7)LiF:Mg,Ti; (7)LiF:Mg,Cu,P; Al(2)O(3):C) and by the optically stimulated luminescence technique using Al(2)O(3):C detectors.

Cosmic Radiation↗
PubMed2002

Assessment of the estrogenic activity of flue gases from burning processes by means of the yeast based human estrogen receptor (hER) bioassay.

Combustion processes are known to produce organic micro-pollutants in the flue gas at concentrations ranging over several orders of magnitude. Some organic micro-pollutants are suspected of being pseudo-estrogens and as such they can affect the public health. In this study, the possible application of the yeast based human estrogen receptor (hER) bioassay to screen flue gas streams for the presence of estrogenic active micro-pollutants was explored. Specifically, the protocol was modified to allow the detection and quantification of the potential estrogenic active non-polar organic micro-pollutants contained in the flue gas matrix. The modified assay was calibrated using a model estrogenic compound (17-alpha-ethinylestradiol (EE2)) dissolved in methylene chloride at concentrations ranging from 3 ng l(-1) to 3000 ng l(-1). The effective concentration to elucidate a 50% response (EC50) was 87 ng l(-1) of equivalent dissolved in methylene chloride. Samples of methylene chloride used to trap non-polar micro-pollutants in flue gas from combustion of pine wood were found to clearly register estrogenic activity by the bioassay under certain conditions. The combustion tests were performed with pinewood alone and with pine wood in the presence of both Copper-naphthenate and copper(II)chloride at 600 degrees C and 1000 degrees C. These conditions must be considered as experimental rather than practical. Overall, the results suggest that, by means of this modified assay, it is possible and warranted to screen systematically for estrogens in flue gas combustion processes.

Air Pollutants↗
PubMed2001

Combined use of Lactobacillus reuteri and soygerm powder as food supplement.

AIMS: The survival of Lactobacillus reuteri when challenged with glycodeoxycholic acid (GDCA), deoxycholic acid (DCA) and soygerm powder was investigated. Moreover, the impact of Lact. reuteri on the bioavailability of isoflavones present in soygerm powder was examined. METHODS AND RESULTS: The strain experienced a die-off when adding 2 or 3 mmol l-1 bile salts, with more pronounced effects in the case of DCA. By means of a haemolysis test it was shown that toxicity could be due to membrane damage. When 4 g l-1 soygerm powder was added, the Lactobacillus strain survived the bile salt burden better (P < or = 0.05) and the membrane damage in the haemolysis test decreased (P < or = 0.05). The Lact. strain cleaved beta-glycosidic isoflavones during fermentation of milk supplemented with soygerm powder. CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: The interactions between the Lactobacillus strain and soygerm powder suggest that combining both in fermented milk can exhibit advantageous probiotic effects. The relevance of the combination of the strain and the soygerm powder should be studied under more relevant physiological conditions.

Animals↗
PubMed2001

Optimization of a yeast estrogen screen and its applicability to study the release of estrogenic isoflavones from a soygerm powder.

Here we describe a redesigned protocol of the yeast estrogen screen developed by Routledge and Sumpter. The redesigned test comprises two steps. First, a large amount of yeast with estrogenic compounds is incubated for 24 hr. Subsequently, a mixture of cycloheximide and the chromogenic substrate chlorophenol red-beta-d-galactopyranoside (CPRG) is added. The cycloheximide stops protein synthesis and allows for an end-point measurement of beta-galactosidase activity generated during the first 24 hr. CPRG is converted to chlorophenol red and reflects beta-galactosidase activity, which is indicative of the estrogenic activity. The modifications shorten the duration of the assay at least 1 day and avoid interference of the estrogenic CPRG or chlorophenol red. The redesigned and the original protocol were used to study the estrogenic activity of bisphenol A, methoxychlor, p,p'-DDT, and isoflavones (genistein, daidzein, and glycitein). Bisphenol A, methoxychlor, and genistein triggered higher levels of beta-galactosidase activity in the redesigned protocol. Estrogenic activity of p,p'-DDT could only be demonstrated with the redesigned protocol. Glycitein and daidzein failed to give a response with both protocols. We also studied deconjugation of beta-glycosidic isoflavones present in soygerm powder. Treatment of the soygerm powder with beta-glycosidase released isoflavones. The estrogenic response of the samples was confirmed with the redesigned protocol and correlated with the amount of genistein present. The release of isoflavones under conditions prevailing in the intestines was studied. Bacterial beta-glycosidase present in the large intestine released isoflavones, and moderate estrogenic activity could be demonstrated.

Biological Assay↗
PubMed2001

Probiotic removal of herbicides with endocrine disrupting potential from aqueous matrices.

Water dosed with 50 mg/L of 2,4-D and atrazine was treated to remove the herbicides which both are reported to have endocrine disrupting potential. Both chemicals could be removed effectively with activated carbon. Yet, traces of endocrine disrupter remained in the water and are able to enter the food chain. The further biological elimination of these compounds was investigated. Milk alone did not decrease the amount of chemicals present in the aqueous supernatant. Yet, the probiotic products Bifidus yoghurt (GB), Actimel (Danone) and Yakult (Yakult Honsha) appeared to bind a substantial amount of the endocrine disrupting chemicals to the particulate fraction and thus render them potentially less bio-available in the aqueous phase.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2000

Protective effect of the bile salt hydrolase-active Lactobacillus reuteri against bile salt cytotoxicity.

Bacterial bile salt hydrolysis is considered a risk factor for the development of colon cancer because of the risk of forming harmful secondary bile salts after an initial deconjugation step. In this study, the influence of enhanced bacterial bile salt transformation by the bile salt hydrolase-active Lactobacillus reuteri was studied in batch culture using the microbial suspension of the Simulator of the Human Intestinal Microbial Ecosystem; (SHIME), which was supplemented with oxgall at 5 g/l or 30 g/l. Changes in the fermentative capacity of the microbial ecosystem and the (geno)toxic properties of the SHIME supernatants were investigated. Increasing concentrations of oxgall inhibited the fermentation. Transient cell toxicity was observed for samples supplemented with 5 g oxgall/l, while samples with 30 g oxgall/l exhibited toxicity. The results of the haemolysis test suggest that the detrimental effects were probably due to the membrane-damaging effects of bile salts. In all cases, the adverse effects could be counteracted by the addition of 7.5 +/- 0.5 log10 CFU L. reuteri/ml. Plausible mechanisms for the protective properties of L. reuteri could involve a precipitation of the deconjugated bile salts and a physical binding of bile salts by the bacterium, thereby making the harmful bile salts less bioavailable.

Amidohydrolases↗
PubMed2000

Influence of a synbiotic mixture consisting of Lactobacillus acidophilus 74-2 and a fructooligosaccharide preparation on the microbial ecology sustained in a simulation of the human intestinal microbial ecosystem (SHIME reactor).

Lactobacillus acidophilus 74-2, which is used in probiotic products, was administered, with fructo-oligosaccharide in a milk-based product, to the second vessel (duodenum/jejunum) of the SHIME reactor, an in vitro simulation of the human intestinal microbial ecology. The main focus of this study was to monitor the changes of the population density of selected bacterial species in the intestine and the changes of metabolic activities during the supplementation of L. acidophilus and fructooligosaccharide in the SHIME reactor. Interestingly, the addition of L. acidophilus 74-2 with fructooligosaccharide gave rise to an increase of bifidobacteria. Moreover, major positive changes occurred in the production of volatile fatty acids: a strong upward trend was observed especially in the case of butyric acid and propionic acid. Furthermore a noticeable increase of beta-galactosidase activity was monitored, while the activity of beta-glucuronidase, generally considered undesirable, declined.

Animals↗
PubMed2000

Fermentation by gut microbiota cultured in a simulator of the human intestinal microbial ecosystem is improved by supplementing a soygerm powder.

An in vitro model, designated the Simulator of the Human Intestinal Microbial Ecosystem (SHIME), was used to study the effect of a soygerm powder rich in beta-glycosidic phytoestrogenic isoflavones on the fermentation pattern of the colon microbiota and to determine to what extent the latter metabolize the conjugated phytoestrogens. Initially, an inoculum prepared from human feces was introduced into the reactor vessels and stabilized over 3 wk using a culture medium. This stabilization period was followed by a 2-wk control period during which the microbiota were monitored. The microbiota were then subjected to a 2-wk treatment period by adding 2.5 g/d soygerm powder to the culture medium. The addition resulted into an overall increase of bacterial marker populations (Enterobacteriaceae:, coliforms, Lactobacillus: sp., Staphylococcus: sp. and Clostridium: sp.), with a significant increase of the Lactobacillus: sp. population. The short-chain fatty acid (SCFA) concentration increased approximately 30% during the supplementation period; this was due mainly to a significant increase of acetic and propionic acids. Gas analysis revealed that the methane concentration increased significantly. Ammonium and sulfide concentrations were not influenced by soygerm supplementation. Use of an electronic nose apparatus indicated that odor concentrations decreased significantly during the treatment period. The beta-glycosidic bonds of the phytoestrogenic isoflavones were cleaved under the conditions prevailing in the large intestine. The increased bacterial fermentation after addition of the soygerm powder was paralleled by substantial metabolism of the free isoflavones (genistein, daidzein and glycitein), resulting in recovery of only 12-17% of the supplemented isoflavones.

Bioreactors↗
PubMed1998

Cholesterol lowering in pigs through enhanced bacterial bile salt hydrolase activity.

The effect of feeding live Lactobacillus reuteri cells containing active bile salt hydrolase (BSH) on plasma cholesterol levels was studied in pigs. During an experiment lasting 13 weeks, twenty pigs were fed on a high-fat, high-cholesterol, low-fibre for the first 10 weeks, and a regular pig diet for the last 3 weeks. One group of animals received, twice daily, 11.25 (SD 0.16) log10 colony forming units of the potential probiotic bacteria for 4 weeks (from week 3 until week 7). From week 8 onwards, the treated group was again fed on the same diet as the control group without additions. The total faecal Lactobacillus counts were only significantly higher in the treated pigs during the first 2 weeks of L reuteri feeding. Based on limited data, it was suggested that the administered Lactobacillus species had caused a temporary shift within the indigenous Lactobacillus population rather than permanently colonizing the intestinal tract. The probiotic feeding brought about significant lowering (P < or = 0.05) of total and LDL-cholesterol concentrations in the treated pigs compared with the control pigs, while no change in HDL-cholesterol concentration was observed. The data for faecal output of neutral sterols and bile salts were highly variable between the animals of each group, yet they indicated an increased output in the treated pigs. Although the blood cholesterol levels went up in both groups during the 3 weeks following the Lactobacillus administration period, significantly lower serum total and LDL-cholesterol levels were observed in the treated pigs. During the final 3 weeks of normalization to the regular diet, cholesterol concentrations significantly decreased in both animal groups and the differences in total and LDL-cholesterol concentrations between the groups largely disappeared.

Amidohydrolases↗
PubMedDate not supplied

Polycyclic aromatic hydrocarbons (PAHs) and estrogenic compounds in experimental flue gas streams.

The importance of combustion processes as a source of substances with estrogenic activity in the environment was investigated. Wood (nontreated and treated with wood preservatives), barbecue charcoal, meat, and kitchen waste were combusted in a laboratory-scale incinerator. Flue gas emissions (particulates and gaseous pollutants) were trapped in polyurethane foam cartridges. The cartridges were subjected to Soxhlet extraction and part of the extracts redissolved in dimethylsulfoxide (DMSO) for analyses of estrogenic activity by means of the yeast-based human estrogen receptor (hER) bioassay. A synthetic estrogen, 17-alpha-ethinylestradiol (EE2), was used as the reference estrogenic compound. Part of the extracts was analyzed for the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs). Estrogenic compounds in the flue gas (wood) were as high as 234 +/- 25 ng m(-3) EE2 equivalent compared with 27 to 81 ng m(-3) EE2 equivalent in flue gas from combustion of barbecue charcoal. Concentrations of polycyclic aromatic hydrocarbons in both flue gas streams were in the range of 21,000 +/- 2000 and 240 +/- 110 ng m(-3), respectively. In general, the concentrations of EE2 equivalent in the flue gas samples were at least a factor of 1000 lower than total PAH concentration. The EE2 levels were not related to the concentration of PAHs in any flue gas sample.

Air Pollutants↗
PubMedDate not supplied

Space flight effects on bacterial physiology.

The study of bacterial behavior under space flight conditions is highly important for the early detection of changes in bacterial communities and bacteria with medical, environmental, or life support consequences for survival of the crew in closed space environments. Although many species of prokaryotes have been studied in ground simulation facilities or have been flown in space flights, at present only few hard research data are available to predict the effects of cosmic radiation, microgravity, vibration and hypervelocity on microbial behavior in space flight. The results that are available tend to be fragmentary and often lack a classical, controlled experimental context to interpret them. Thus, many basic questions concerning the effects of space on microbial behavior have yet to be resolved.

Bacteria↗
PubMedDate not supplied

Physiological changes induced in four bacterial strains following oxidative stress.

In order to study the behaviour and resistance of bacteria under extreme conditions, physiological changes associated with oxidative stress were monitored using flow cytometry. The study was conducted to assess the maintenance of membrane integrity and potential as well as the esterase activity, the intracellular pH and the production of superoxide anions in four bacterial strains (Ralstonia metallidurans, Escherichia coli, Shewanella oneidensis and Deinococcus radiodurans). The strains were chosen for their potential usefulness in bioremediation. Suspensions of R. metallidurans, E. coli, S. oneidensis and D. radiodurans were submitted to 1 h oxidative stress (H2O2 at various concentrations from 0 to 880 mM). Cell membrane permeability (propidium iodide) and potential (rhodamine-123, 3,3'-dihexyloxacarbocyanine iodide), intracellular esterase activity (fluorescein diacetate), intracellular reactive oxygen species concentration (hydroethidine) and intracellular pH (carboxyflurorescein diacetate succinimidyl ester (5(6)) were monitored to evaluate the physiological state and the overall fitness of individual bacterial cells under oxidative stress. The four bacterial strains exhibited varying sensitivities towards H2O2. However, for all bacterial strains, some physiological damage could already be observed from 13.25 mM H2O2 onwards, in particular with regard to their membrane permeability. Depending on the bacterial strains, moderate to high physiological damage could be observed between 13.25 mM and 220 mM H2O2. Membrane potential, esterase activity, intracellular pH and production of superoxide anion production were considerably modified at high H2O2 concentrations in all four strains. In conclusion, we show that a range of significant physiological alterations occurs when bacteria are challenged with H2O2 and fluorescent staining methods coupled with flow cytometry are useful for monitoring the changes induced not only by oxidative stress but also by other stresses like temperature, radiation, pressure, pH, etc....

Bacteria↗