Assessing the Nonlinearity of Karst Response Function under Variable Boundary Conditions.

The hydraulic and transfer response of karst aquifers is complex and often highly nonlinear: due to their high transmissivity and connection with the surface, such systems are very sensitive to modifications of their boundary conditions. The aim of this study was to assess the variation of the response depending on both upstream and downstream parameters, and propose a methodology to simulate the response of the karst system depending on those parameters. The impact of the variations of multiple environmental parameters on the response of a karstic system submitted to tidal variations (Normandy, France) was investigated after a campaign of artificial tracer tests acquired in very different hydrologic conditions (rainfall events, low tide, high tide, low/high piezometric level, and low/high waters). Principal components analysis and hierarchical clustering were applied on both environmental variables and karstic system response variables (parameters of the residence time distribution [RTD] curves). Equations between the RTD parameters and the most relevant variables were established using a symbolic regression algorithm. It appeared that the variations of the RTD parameters depend mainly on the cumulated rainfall preceding the injection, the piezometric level of the aquifer, and on the tide parameters. The hydraulic conditions downstream of the aquifer have a strong influence on the hydraulic and transfer response of the aquifer. The response of the aquifer in various and extreme conditions has been simulated using the equations resulting from the symbolic regression algorithm. Such relationships can be useful for management of water resources in karst media, and support decision making.

Occurrence of multi-antibiotic resistant Pseudomonas spp. in drinking water produced from karstic hydrosystems.

Aquatic environments could play a role in the spread of antibiotic resistance genes by enabling antibiotic-resistant bacteria transferred through wastewater inputs to connect with autochthonous bacteria. Consequently, drinking water could be a potential pathway to humans and animals for antibiotic resistance genes. The aim of this study was to investigate occurrences of Escherichia coli and Pseudomonas spp. in drinking water produced from a karst, a vulnerable aquifer with frequent increases in water turbidity after rainfall events and run-offs. Water samples were collected throughout the system from the karstic springs to the drinking water tap during three non-turbid periods and two turbid events. E. coli densities in the springs were 10- to 1000-fold higher during the turbid events than during the non-turbid periods, indicating that, with increased turbidity, surface water had entered the karstic system and contaminated the spring water. However, no E. coli were isolated in the drinking water. In contrast, Pseudomonas spp. were isolated from the drinking water only during turbid events, while the densities in the springs were from 10- to 100-fold higher than in the non-turbid periods. All the 580 Pseudomonas spp. isolates obtained from the sampling periods were resistant (to between 1 and 10 antibiotics), with similar resistance patterns. Among all the Pseudomonas isolated throughout the drinking water production system, between 32% and 86% carried the major resistance pattern: ticarcillin, ticarcillin-clavulanic acid, cefsulodin, and/or aztreonam, and/or sulfamethoxazol-trimethoprim, and/or fosfomycin. Finally, 8 Pseudomonas spp. isolates, related to the Pseudomonas putida and Pseudomonas fluorescens species, were isolated from the drinking water. Thus, Pseudomonas could be involved in the dissemination of antibiotic resistance via drinking water during critical periods.

Antibiotic-resistant Escherichia coli in karstic systems: a biological indicator of the origin of fecal contamination?

Occurrences of antibiotic-resistant Escherichia coli in two springs of a karstic system (NW France) providing drinking water were determined to study the role of aquifers in the dissemination of the resistance genes. Water samples were collected during wet and dry periods and after a heavy rainfall event to investigate E. coli density, antibiotic resistance patterns, and occurrences of class 1, 2, and 3 integrons. By observing patterns of the resistant isolates (i.e. number and type of resistances) and their occurrences, we were able to define two resistant subpopulations, introduced in the aquifer via surface water: (1) R1-2, characterized by one or two resistance(s), essentially to chloramphenicol and/or tetracycline (96.5%), was always found during the heavy rainfall event; (2) R3-10, characterized by three or more resistances, mostly resistant to tetracycline (94.1%) and beta-lactams (86%), was found transiently. Class 1 and 2 integrons were detected, mostly in the R3-10 subpopulation for class 1 integrons. The characteristics of these two subpopulations strongly suggest that the contamination originates from pasture runoff for the R1-2 subpopulation and from wastewater treatment plant effluents for the R3-10 subpopulation. These two subpopulations of E. coli could be used as biological indicators to determine the origin of groundwater contamination.

Cryptosporidium parvum isolate-dependent postinfectious jejunal hypersensitivity and mast cell accumulation in an immunocompetent rat model.

Cryptosporidium spp. are a cause of self-limited diarrhea in immunocompetent hosts. In immunocompetent rats, Cryptosporidium parvum infection induced digestive hypersensitivity, a key pathophysiological factor in functional digestive disorders such as irritable bowel syndrome (IBS). In such a rat model, we sought to document whether jejunal hypersensitivity depends on C. parvum isolate and is associated with a mast cell accumulation. Five-day-old rats were orally administered 10(5) oocysts of either Nouzilly (NoI) or Iowa (IoI) C. parvum isolate. NoI-infected rats exhibited the lowest food intake on days 7 and 14 postinfection (p.i.). On day 7 p.i., small intestine villus atrophy, crypt hyperplasia, and inflammatory cell infiltration were prominent in NoI-infected rats, with higher numbers of Cryptosporidium forms than in IoI-infected rats. Compared to uninfected control rats, jejunal intraepithelial lymphocytes (IELs) were increased only in NoI-infected rats on day 14 p.i. On day 50 p.i., jejunal hypersensitivity to distension was found only in NoI-infected rats; this hypersensitivity is associated with activated mast cell accumulation. The number of mast cells in the jejunal lamina propria was increased from day 36 p.i. in NoI-infected rats and only at day 120 p.i. in IoI-infected rats. Our data suggest that both the severity of infection (weight loss, reduced food intake, villus atrophy, and IEL accumulation) and the onset of a jejunal hypersensitivity after infection in association with an activated mast cell accumulation are isolate dependent and related to NoI infection. This cryptosporidiosis rat model is a relevant model for the study of underlying mechanisms of postinfectious IBS-like symptoms.

Chemical characterization of porewaters in an intertidal mudflat of the Seine estuary: relationship to erosion-deposition cycles.

A seasonal field study was carried out in the Seine estuary to determine the chemistry of sediment porewaters using the 'peeper' technique and changes in the elevation of the mudflats using the 'Altus' technique. This approach allowed us to evaluate the release of nutrients and to link these releases to the sediment hydrodynamics. Our results show that nutrient and organic matter cycling in a Seine estuary mudflat exhibits a seasonal behaviour, which is mainly influenced by variations in hydrodynamics. Sediments, rich organic matter, were input during floods and they were mineralized during summer and autumn, releasing nutrients and dissolved organic carbon into the sediment porewaters. The nutrient release, including ammonium, is mainly linked to the mineralization of organic matter, while the release of phosphate is delayed. The delay could be the result of phosphate association with organic matter and/or its co-precipitation with calcium and iron.

Biofilm proteome: homogeneity or versatility?

The problems associated with biofilm infections in humans result from the distinct characteristics of biofilms, in particular their high level of resistance to antibiotics. One of the hypotheses that have been advanced to explain this resistance to antimicrobials is the phenotypic differentiation of biofilm cells. Although many studies on biofilms have highlighted physiological alterations following the attachment of bacteria to a surface, no studies have explicitly demonstrated a "biofilm" physiology. To contribute to this topical debate, we used principal component analysis to interpret spot quantity variations observed on electropherograms obtained by two-dimensional gel electrophoresis of crude protein extracts from planktonic and sessile Pseudomonas aeruginosa cells. These analyses showed that the proteome of attached P. aeruginosa cells differs from that of their planktonic counterparts. Furthermore, we found that the proteome of sessile P. aeruginosa is strongly dependent on the nature of the biofilm substratum.

Transport of particulate material and dissolved tracer in a highly permeable porous medium: comparison of the transfer parameters.

We are experimentally studying, by means of short-pulse injection, the transport and deposition kinetics of suspended particles (silts of the order of 10 microm) in a highly permeable medium consisting of a column of gravel. In our experiments, the breakthrough curves (BTCs) are well described by analytical solutions of a convection/dispersion model with first-order deposition kinetics. All the transport parameters calculated by the model for both particles and dissolved tracer depend on the flow rate. We demonstrate the existence of a critical flow rate, determined experimentally, beyond which the transfer time for the particles is longer than that for the tracer. This phenomenon is unusual in comparison with the results available in the literature. The increase in transfer time of particles in comparison to tracer leads us to assume a purely mechanical phenomenon, that is, collision between particles and grains of the medium with instantaneous reset in motion when the flow rate is sufficient to avoid settling. Thanks to the polydispersivity of the injected suspension and the control of grain size at the outlet, it can also be determined that the coarser particles are recovered before the finer particles, as expected when one considers the size-exclusion effect.