Biomedical subjects

P Servais

Publications and source records attributed to P Servais.

At least 19 recordsLinked to original sources

PubMed2003

Impact of backwashing on nitrification in the biological activated carbon filters used in drinking water treatment.

Nitrification during biological filtration is currently used in drinking water production to remove ammonia, which is the source of several water quality problems during treatment and distribution. We evaluated here the impact of backwashing on nitrification efficiency in filters used for drinking water treatment. Two different granular activated carbon (one open and one closed carbon superstructure) were tested. Ammonia removal and fixed nitrifying bacterial biomass before and after backwashing were compared in first-stage pilot filters and full-scale second-stage filters. Backwashing has a greater impact on nitrification on first-stage than an second-stage filters. Backwashing improved the ammonia removal in warm (> or = 18 degrees C) water in a first-stage filter containing an open-superstructure granular activated carbon, whereas a closed-superstructure support showed a removal capacity that is less after a regular backwashing than before, or similar to it. In cold water (< or = 4 degrees C), backwashing had a negative impact on nitrification capacity in an open-superstructure medium first-stage filter. In full-scale second-stage filters, backwashing had a slight negative impact on filter performances for both open- and closed-superstructure media at temperatures between 8 degrees C and 12 degrees C. In colder waters (< or = 3 degrees C), nitrification was very poor both before and after backwashing. Sampling of fixed, nitrifying biomass in the pilot filter columns showed that in all cases (low and high expansion backwash; both media tested) and at 20 +/- 3 degrees C the overall biomass levels remained unchanged before and after backwash. In the full-scale second-stage filters, nitrifying bionass was similar before and after backwashing for both types of media tested.

Ammonia↗

PubMed2001

Using light scatter signal to estimate bacterial biovolume by flow cytometry.

BACKGROUND: In the past decade, flow cytometry has become a useful and precise alternative to microscopic bacterial cell counts in aquatic samples. However, little evidence of its usefulness for the evaluation of bacterial biovolumes has emerged in from the literature. METHODS: The light scattering and cell volume of starved bacterial strains and natural bacterial communities from the Black Sea were measured by flow cytometry and epifluorescence microscopy, respectively, in order to establish a relationship between light scattering and cell volume. RESULTS: With the arc-lamp flow cytometer, forward angle light scatter (FALS) was related to cell size in both the starved strains and natural communities, although regression parameters differed. We tested the predictive capacity of the FALS verous cell size relationship in a bacterial community from the North Sea. That analysis showed that a reliable bacterial biovolume prediction of a natural bacterial community can be obtained from FALS using a model generated from natural bacterial community data. CONCLUSIONS: Bacterial biovolume is likely to be related to FALS measurements. It is possible to establish a generally applicable model derived from natural bacterial assemblages for flow cytometric estimation of bacterial biovolumes by light scatter.

Aeromonas hydrophila↗

PubMed2001

Bacterial dynamics in the drinking water distribution system of Brussels.

Water samples and pipe coupons were collected from the Brussel's drinking water distribution system (DS). A treated surface water and various groundwaters feed this DS. Parameters related to bacterial regrowth have been measured on these samples: temperature, concentrations of free residual chlorine, concentration of biodegradable dissolved organic carbon (BDOC), abundance of suspended bacteria, densities of fixed bacteria and levels of bacterial activity. Results showed that groundwaters were less susceptible to favor bacterial regrowth in the DS pipes. Treated surface water and mixed waters had the highest potential of bacterial regrowth in the DS dead ends. Results also showed that the potential regrowth induced by the distribution of a treated surface water could be reduced if: (1) the BDOC levels were below 0.25 mg C/l at the outlet of the surface water treatment plant; (2) a significant free chlorine residual was present within the whole DS. Second-stage biological filtration using granular activated carbon is now under construction at the surface water treatment plant feeding a part of this DS. This treatment implementation should reduce BDOC levels and chlorine demand of the treated surface water and will further reduce the slight regrowth phenomena observed in this DS.

Belgium↗

PubMed2001

Impact of temperature on nitrification in biological activated carbon (BAC) filters used for drinking water treatment.

The impact of temperature on nitrification in biological granular activated carbon (GAC) filters was evaluated in order to improve the understanding of the nitrification process in drinking water treatment. The study was conducted in a northern climate where very cold water temperatures (below 2 degrees C) prevail for extended periods and rapid shifts of temperature are frequent in the spring and fall. Ammonia removals were monitored and the fixed nitrifying biomass was measured using a method of potential nitrifying activity. The impact of temperature was evaluated on two different filter media: an opened superstructure wood-based activated carbon and a closed superstructure activated carbon-based on bituminous coal. The study was conducted at two levels: pilot scale (first-stage filters) and full-scale (second-stage filters) and the results indicate a strong temperature impact on nitrification activity. Ammonia removal capacities ranged from 40 to 90% in pilot filters, at temperatures above 10 degrees C, while more than 90% ammonia was removed in the full-scale filters for the same temperature range. At moderate temperatures (4-10 degrees C), the first stage pilot filters removed 10-40% of incoming ammonia for both media (opened and closed superstructure). In the full-scale filters, a difference between the two media in nitrification performances was observed at moderate temperatures: the ammonia removal rate in the opened superstructure support (more than 90%) was higher than in the closed superstructure support (45%). At low temperatures (below 4 degrees C) both media performed poorly. Ammonia removal capacities were below 30% in both pilot- and full-scale filters.

Ammonia↗

PubMed2001

Microbial community dynamics in Mediterranean nutrient-enriched seawater mesocosms: changes in the genetic diversity of bacterial populations.

A mesocosm experiment was performed to study the influence of nutrients on activity and diversity of bacterial assemblages from the Mediterranean Sea. Changes in the diversity of the predominant bacterial populations were monitored by DGGE fingerprinting of PCR products derived from 16S rRNA encoding genes. Fluctuations in the diversity of the most active populations was inferred by performing the DGGE fingerprinting on the basis of the cellular rRNA after reverse transcription and PCR amplification. DNA-derived DGGE patterns obtained from duplicate control and nutrient-enriched mesocosms showed differences in the development of the bacterial communities between control and nutrient-enriched experimental mesocosms. Multidimensional scaling analysis of the DNA-derived DGGE fingerprints indicated that duplicate treatments were reproducible. DNA- and RNA-derived DGGE fingerprints of bacterial assemblages changed over time, showing that the composition of the bacterial assemblages, as well as the most active bacterial populations changed during different phases of the incubation. Sequences of predominant DGGE bands in RNA-derived patterns were similar to 16S rRNA gene sequences of members of the alpha-, gamma- and delta-Proteobacteria and of the Cytophaga-Flavobacterium-Bacteroides phylum (CFB). Bands corresponding to Ruegeria-like bacteria and members of the CFB became especially dominant during the course of incubation, suggesting that these populations were important contributors to bacterial production and activity in the post-grazing phase of the experiment.

Journal Article↗

PubMed2001

Microbial community dynamics in Mediterranean nutrient-enriched seawater mesocosms: changes in abundances, activity and composition.

Quantitative and qualitative changes in bacterial communities from the Mediterranean Sea were compared in duplicate batch mesocosms with or without addition of inorganic nutrients. Methods including traditional microbial ecology techniques, molecular biology and flow cytometry were combined to determine abundances, production, cell size, activity, culturability and taxonomic diversity of bacterial cells. Addition of nutrients and confinement resulted in an increase of bacterial densities which were rapidly controlled by protozoan grazing. Changes in bacterial activity and morphology were observed during the growth phase of bacteria and under grazing pressure. The proportion of medium-size and culturable cells increased during the growth phase. These cells were preferentially consumed by grazers resulting in a strong limitation of bacterial production. As a consequence of the grazing pressure, large cells were produced and contributed to the remaining bacterial productivity after grazing. Grazing had an effect on the taxonomic composition of bacterial communities by preferentially eliminating gamma-Proteobacteria, alpha-Proteobacteria were preserved. It seems that some species from the genera Ruegeria and Cytophaga may have developed defence strategies to escape predation.

Journal Article↗

PubMed2001

Are the actively respiring cells (CTC+) those responsible for bacterial production in aquatic environments?

The 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) staining method is commonly and increasingly used to detect and to enumerate actively respiring cells (CTC+ cells) in aquatic systems. However, this method remains controversial since some authors promote this technique while others pointed out several drawbacks of the method. Using flow cytometry (FCM), we showed that CTC staining kinetics vary greatly from one sample to another. Therefore, there is no universal staining protocol that can be applied to aquatic bacterial communities. Furthermore, using (3)H-leucine incorporation, it was shown that the CTC dye has a rapid toxic effect on bacterial cells by inhibiting protein synthesis, a key physiological function. The coupling of radioactive labelling with cell sorting by FCM suggested that CTC+ cells contribute to less than 60% of the whole bacterial activity determined at the community level. From these results, it is clearly demonstrated that the CTC method is not valid to detect active bacteria, i.e. cells responsible for bacterial production.

Journal Article↗

PubMed2001

Does the high nucleic acid content of individual bacterial cells allow us to discriminate between active cells and inactive cells in aquatic systems?

The nucleic acid contents of individual bacterial cells as determined with three different nucleic acid-specific fluorescent dyes (SYBR I, SYBR II, and SYTO 13) and flow cytometry were compared for different seawater samples. Similar fluorescence patterns were observed, and bacteria with high apparent nucleic acid contents (HNA) could be discriminated from bacteria with low nucleic acid contents (LNA). The best discrimination between HNA and LNA cells was found when cells were stained with SYBR II. Bacteria in different water samples collected from seven freshwater, brackish water, and seawater ecosystems were prelabeled with tritiated leucine and then stained with SYBR II. After labeling and staining, HNA, LNA, and total cells were sorted by flow cytometry, and the specific activity of each cellular category was determined from leucine incorporation rates. The HNA cells were responsible for most of the total bacterial production, and the specific activities of cells in the HNA population varied between samples by a factor of seven. We suggest that nucleic acid content alone can be a better indicator of the fraction of growing cells than total counts and that this approach should be combined with other fluorescent physiological probes to improve detection of the most active cells in aquatic systems.

Bacteria↗

PubMed2001

Use of rapid enzymatic assays to study the distribution of faecal coliforms in the Seine river (France).

In 1997 and 1998 faecal contamination of the Seine river and its estuary was studied for the first time by rapid enzymatic methods, based on the presence of the beta-D-glucuronidase enzyme in E. coli, in parallel with traditional plate counts of faecal coliforms on specific culture medium. Our study focused on a 450 km stretch of the river, including the Parisian area, and presenting highly variable levels of faecal pollution. Both methods showed that wastewater outfalls of the Parisian area and the presence of a maximum turbidity zone (at the mouth of the estuary) had a strong impact on the abundance of faecal coliforms in the river. Downstream from the Parisian outfalls, beta-D-glucuronidase activity measurements decreased 5-6x less rapidly than plate counts suggesting that rapid enzymatic assays could detect enzymatically-active but non-culturable bacteria.

Biological Assay↗

PubMed2001

Use of beta-D-galactosidase and beta-D-glucuronidase activities for quantitative detection of total and fecal coliforms in wastewater.

Two enzymatic methods based on the measurement of the beta-D-galactosidase activity of total coliforms and the beta-D-glucuronidase activity of Escherichia coli were used to assess coliform levels in wastewater alongside traditional culture-based techniques, which can be biased by the aggregation of bacteria or their attachment to particles. Enzymatic methods were precise (i.e., coefficients of variation were 9%-15%), rapid (response in 20 min), and correlated well (in log units) with traditional techniques for raw and treated sewage (r2 > 0.75). They were used for rapid assessment of coliform removal efficiency in two different wastewater treatments. These methods could be useful for the estimation of the abundance of coliforms in domestic sewage and their removal by wastewater treatment processes.

Bacteriological Techniques↗

PubMed2000

Successional changes in the genetic diversity of a marine bacterial assemblage during confinement.

The successional changes in the genetic diversity of Mediterranean bacterioplankton subjected to confinement were studied in an experimental 300 1 seawater enclosure. Five samples were taken at different times and analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting to rapidly monitor changes in the bacterial genetic diversity. DGGE analysis clearly showed variations between the samples. Three of the five samples, with different DGGE banding patterns, were further analyzed by cloning and sequencing of 16S rRNA genes. Comparative sequence analysis indicated a shift from a mixed bacterial assemblage to a community dominated by bacteria closely affiliated to a single genus, Alteromonas. Sequences obtained at the start of the experiment were affiliated with two alpha-proteobacterial and three gamma-proteobacterial lineages known from other studies of marine picoplankton. One sequence was affiliated with the Verrucomicrobiales. After 161 h of incubation two sequences represented a gamma-proteobacterial lineage also present at 0 h, but the majority of sequences clustered around that of Alteromonas macleodii. After 281 h only the dominant Alteromonas-like bacteria and bacteria distantly related to Legionella were found by cloning and sequencing. Mortality rates of bacteria indicated that grazing was the dominant mortality process when heterotrophic protozoa were abundant. Hence, changes in the genetic diversity of bacteria were partly influenced by the differential mortality of bacterial populations during the course of incubation.

Animals↗

PubMed2000

Relationships among Bacterial Cell Size, Productivity, and Genetic Diversity in Aquatic Environments using Cell Sorting and Flow Cytometry.

The study of relationships between cell size and productivity is of key importance in microbial ecology to understand which members of natural aquatic communities are responsible for the overall activity and/or productivity. Flow sorting of microorganisms from different environmental samples was used to analyze the activity of bacterial cells depending on their biovolume. Bacterial cells from five different natural samples taken along the Mediterranean coast including fresh- and seawaters were incubated with tritiated leucine, then stained with SYTO 13 and sorted by flow cytometry according to their average side-angle-scattered (SSC) light. In all samples, a bell-shaped relationship was found between cell biovolume and activity, whereas activity of a given cell-size class varied between samples. In contrast, an inverse relationship was found between biovolumes and abundances. These results suggest that medium-sized cells with highest growth rates are probably submitted to intense grazing. For one sample, bacteria within five different size classes were sorted and the genetic diversity of cells within each sorted size class and that of the whole community were analyzed by the denaturing gradient gel electrophoresis (DGGE) method. The genetic diversity, as determined at the community level was highly represented into the pool of small cells, whereas only few species were present into larger cell subpopulations. The results suggest that only a few genotypes may be dominant within the largest and most productive cells. Furthermore, cell size polymorphism as well as heterogeneous cellular activities were found within some species.

Journal Article↗

PubMed2000

Use of enzymatic methods for rapid enumeration of coliforms in freshwaters.

Rapid enumeration methods based on the enzymatic hydrolysis of 4-methylumbelliferyl-beta-D-galactoside and 4-methylumbelliferyl-beta-D-glucuronide were optimized for freshwaters. The enzymes beta-D-galactosidase (GALase) and beta-D-glucuronidase (GLUase) were shown to be already induced in freshwaters when tested, respectively, with the inducers isopropyl-beta-D-thiogalactopyranoside and methyl-beta-D-glucuronide. Both enzymatic activities were compared, respectively, with plate counts of total and faecal coliforms in freshwaters. Enzymatic methods and reference plate counts were significantly correlated in log-log plots. Moreover, the GLUase method allowed the detection of viable (presenting a detectable GLUase activity) but nonculturable Escherichia coli.

Bacteriological Techniques↗

PubMed2000

Survival of Escherichia coli in freshwater: beta-D-glucuronidase activity measurements and characterization of cellular states.

A rapid enzyme assay measuring beta-D-glucuronidase activity of Escherichia coli was tested in survival experiments after discharge of E. coli in river water. Enzyme activity was compared with several analyses performed to characterize cellular states under stressful conditions. Enzyme activity remained stable under starvation and light stress conditions despite losses of culturability, respiratory activity, and cytoplasmic membrane integrity. beta-D-Glucuronidase activity followed the pattern of genetic and morphologic cell integrity. The tested enzyme assay seems well adapted to study the fate of fecal coliforms in survival experiments, and appears to be a rapid and efficient way to estimate the microbiological quality of surface waters.

Bacteriological Techniques↗

PubMed1999

Coupling Bacterial Activity Measurements with Cell Sorting by Flow Cytometry.

> Abstract A new procedure to investigate the relationship between bacterial cell size and activity at the cellular level has been developed; it is based on the coupling of radioactive labeling of bacterial cells and cell sorting by flow cytometry after SYTO 13 staining. Before sorting, bacterial cells were incubated in the presence of tritiated leucine using a procedure similar to that used for measuring bacterial production by leucine incorporation and then stained with SYTO 13. Subpopulations of bacterial cells were sorted according to their average right-angle light scatter (RALS) and fluorescence. Average RALS was shown to be significantly related to the average biovolume. Experiments were performed on samples collected at different times in a Mediterranean seawater mesocosm enriched with nitrogen and phosphorus. At four sampling times, bacteria were sorted in two subpopulations (cells smaller and larger than 0.25 µm(3)). The results indicate that, at each sampling time, the growth rate of larger cells was higher than that of smaller cells. In order to confirm this tendency, cell sorting was performed on six subpopulations differing in average biovolume during the mesocosm follow-up. A clear increase of the bacterial growth rates was observed with increasing cell size for the conditions met in this enriched mesocosm.http://link.springer-ny.com/link/service/journals/00248/bibs/38n2p180.html

Journal Article↗

PubMed1998

Effects of the farnesyltransferase inhibitor UCF-1C/manumycin on growth and p21-ras post-translational processing in NIH3T3 cells.

Examination of the effect of the farnesylprotein transferase (FPTase) inhibitor UCF1-C/manumycin on NIH3T3 cells transfected with a normal N-ras gene and expressing high levels of the corresponding p21-ras protein showed that 10 microm UCF1-C immediately and reversibly inhibited growth in these cells, without modifying cell-death rate, thus acting as a cytostatic. There was also a 98% reduction of p21-ras neofarnesylation and a 3-fold decrease in total content in p21-ras products, yet without gross modification of the relative content in the post-translational products and without accumulation of the native protein to detectable levels. UCF1-C likewise reversibly inhibited growth in parental NIH3T3 cells, as well as in sub-strains expressing a transfected normal or mutated H-ras gene. Together with the fact that the well-developed network of actin stress fibers present in the NIH3T3 (N-ras) cells was not affected by the FPTase inhibitor, these data indicate that its growth-inhibitory effect is not necessarily in direct relation with that exerted on p21-ras processing. Alternatively, it might be causally related to the decreased prenylation of other cellular proteins, perhaps included among the 13 proteins, unrelated to p21-ras, of which the farnesylation was also reduced under UCF1-C treatment. Some cells transformed by a ras or non-ras oncogene might exhibit higher susceptibility towards FPTase inhibitors than normal cells, but this might then be attributable to differences in the pattern of expression and/or in the functional importance of non-ras farnesylated proteins.

3T3 Cells↗

PubMed1995

Dissociation of two actions in the positive effect of prior partial hepatectomy on the induction of the hepatocarcinogenic process by diethylnitrosamine.

The present study was aimed at re-evaluating the mechanism by which partial hepatectomy (PH) and the resulting mitogenic stimulation act to positively modulate the action of a chemical hepatocarcinogen applied 24 hours after surgery. Using as a marker the immunocytochemical expression of glutathione S-transferase placental form (GST-P), we compared the early incidence of single altered hepatocytes and the time-course of appearance and growth of subsequently developed liver neoplasia in diethylnitrosamine (DENA) treated sham-operated or partially hepatectomized animals. The data showed that, compared to sham-operation, partial hepatectomy increases the frequency of early GST-P positive single hepatocytes appearing 72 h after treatment with DENA (50 mg/kg b.w.), indicating a positive (co-carcinogenic) effect of PH on the frequency of the initiation event. At 2 months after this treatment, foci of altered hepatocytes were about 5 times more numerous in PH-pretreated than in sham-operated animals and their average volume about four times greater. The latter difference persisted for up to 10 months after carcinogen treatment, indicating that the lesions had grown at similar rates in the meantime. The simplest hypothesis to account for this difference in size of the lesions is that it is due to the 2-3 waves of normal-like cell division the altered hepatocytes underwent during the very first days after removal of part of the liver mass, rather than to true promotion or to an intrinsic difference in proliferative phenotype of the initiated cells. The increased size and higher frequency of the lesions in PH-pretreated rats concur to increase the population of cells at risk towards subsequent events implied in multistep progression and, by this, to positively modulate the latter. Accordingly, only PH treated rats had developed neoplastic nodules at 10 months and tumours at 15 months. This can therefore be explained without resorting to the currently held view that cell divisions in PH would increase the carcinogenic efficiency of DENA, due to the fact that resulting cell divisions would intervene before full repair of DENA-induced DNA damages.

Animals↗

PubMed1994

[The population of the big university hospitals in Belgium from the early nineteenth century to the end of the twentieth century].

This paper is the synthesis of researches concerning the university hospitals of Gand, Liège and Louvain in Belgium. First, you will find an abstract of the analysis and main results. The interpretation topics are then approached with three different points of view: the sources, being hospital or medical records, their qualities and their limits; the structure of the institutions and their consequences on the social structure of the patients; the impact of the demographic transition. The hospital, which was one reserved to poor adults, has progressively been authorized to "non-profitables", children first, then old people, so that the ageing of patients largely exceeds that of the population itself.

Belgium↗