Evaluation of the novel substrate RUGtm for the detection of Escherichia coli in water from temperate (Zurich, Switzerland) and tropical (Bushenyi, Uganda) field sites

Direct testing of water quality to promote drinking water safety contributes to the sustainable development goals, which call for universal access to safely-managed drinking water services by 2030. Enzyme–substrate tests offer a potentially simple and reliable approach for the detection and quantification of fecal indicator bacteria, including Escherichia coli (E. coli). The novel aquatest (AT) based on resorufin-β-D-glucuronide methyl ester (RUG™) (AT-RUG) is an enzyme–substrate test that overcomes several drawbacks of other established tests. In this study, AT-RUG was used to detect and quantify E. coli in water from temperate (Zurich, Switzerland) and tropical (Bushenyi, Uganda) regions. Quantitative results of AT-RUG were compared with IDEXX Colilert-18® (C-18), m-TEC and m-ColiBlue24®. In temperate waters, AT-RUG was found to be as sensitive as m-TEC (97.0%) and C-18 (98.5%) and showed strong agreement with the reference methods. The false-positive rate for E. coli detection in temperate waters using AT-RUG was 6%. AT-RUG performed well at incubation temperatures of 37 °C and 45 °C, but not at 24 °C. In tropical waters, AT-RUG sensitivity was 94.1% compared to m-ColiBlue24®. AT-RUG detected significantly more E. coli than m-ColiBlue24®, suggesting it is a more conservative estimate. At both field sites, AT-RUG was able to effectively indicate categorical concentrations of E. coli in water samples indicating the level of risks of fecal contamination of water supplies. This study indicates that AT-RUG is a reliable and accurate medium for the detection and quantification of E. coli in temperate and tropical waters

Dual Role for Pilus in Adherence to Epithelial Cells and Biofilm Formation in Streptococcus agalactiae

Streptococcus agalactiae is a common human commensal and a major life-threatening pathogen in neonates. Adherence to host epithelial cells is the first critical step of the infectious process. Pili have been observed on the surface of several gram-positive bacteria including S. agalactiae. We previously characterized the pilus-encoding operon gbs1479-1474 in strain NEM316. This pilus is composed of three structural subunit proteins: Gbs1478 (PilA), Gbs1477 (PilB), and Gbs1474 (PilC), and its assembly involves two class C sortases (SrtC3 and SrtC4). PilB, the bona fide pilin, is the major component; PilA, the pilus associated adhesin, and PilC, are both accessory proteins incorporated into the pilus backbone. We first addressed the role of the housekeeping sortase A in pilus biogenesis and showed that it is essential for the covalent anchoring of the pilus fiber to the peptidoglycan. We next aimed at understanding the role of the pilus fiber in bacterial adherence and at resolving the paradox of an adhesive but dispensable pilus. Combining immunoblotting and electron microscopy analyses, we showed that the PilB fiber is essential for efficient PilA display on the surface of the capsulated strain NEM316. We then demonstrated that pilus integrity becomes critical for adherence to respiratory epithelial cells under flow-conditions mimicking an in vivo situation and revealing the limitations of the commonly used static adherence model. Interestingly, PilA exhibits a von Willebrand adhesion domain (VWA) found in many extracellular eucaryotic proteins. We show here that the VWA domain of PilA is essential for its adhesive function, demonstrating for the first time the functionality of a prokaryotic VWA homolog. Furthermore, the auto aggregative phenotype of NEM316 observed in standing liquid culture was strongly reduced in all three individual pilus mutants. S. agalactiae strain NEM316 was able to form biofilm in microtiter plate and, strikingly, the PilA and PilB mutants were strongly impaired in biofilm formation. Surprisingly, the VWA domain involved in adherence to epithelial cells was not required for biofilm formation

Apport diagnostique et thérapeutique des prélèvements microbiologiques des abcès de cornées avec critères de gravité au CHU de Reims entre 2012 et 2014

International audienc

Principal Component Analysis for the characterisation of spatiotemporal variations of the solar resource in urban environments

International audienceUrban areas are serious candidates for the production of solar energy but their intrinsic complexity makes it challenging. The heterogeneity in the geometries and radiative properties of the different elements composing the urban fabric, specifically induces important spatiotemporal variations of the distribution of incident solar radiations. Besides, Principal Component Analysis (PCA) has been widely validated as an efficient tool to identify the principal behavioural features of a high-dimensional physical model. This paper proposes a novel approach to analyse and characterise the spatiotemporal variability of the solar resource within an urban context by means of PCA. A theoretical 100 × 100 m² asymmetric urban district made of nine cuboids with various heights is studied. The distribution of the incident field of irradiances is modelled via backward Monte-Carlo ray tracing over a full year on the facets of the central building under a clear sky, with a 15 min timestep and 1 m spatial resolution. PCA is subsequently applied to the simulated model to analyse its spatial and temporal variabilities. First results validate modal decomposition as a powerful technique for the analysis of the variability distribution, allowing the identification of the district areas subjected to important spatial and temporal variations of the solar resource. Characteristic scales are clearly represented by orders of decomposition. The contribution of surrounding geometries is also transcribed by particular spatial modes and similar influential variables are encountered across multiple evaluated surfaces but at different modal ranks

AC/TiO2 granular photocatalysts optical properties: Material composition effect on the radiative transfer in a photoreactor

International audienceThe radiative transfer analysis in photoreactor with heterogeneous media is still a challenge for reasons relative to solid particles structural complexity or materials complex optical properties. This article aims to study the radiative transfer in a photoreactor containing Activated-Carbon/Titanium Dioxide (AC/TiO2) composite particulate media. A focus was made on the analysis of the photon rate absorbed by these media, which is a key value for the further study of chemical photo-reaction for which they are intended into the system. The radiative properties of these media were first consistently defined using different mixing laws for refractive index calculation, coupled to Mie theory. A validation of the radiative properties was achieved by solving the radiative transfer equation using a Monte Carlo algorithm and by comparing the results of transmittance modelling of each media with transmittance experiments. The second part of the work consisted in the use of a second Monte Carlo algorithm for modelling local radiant energy repartition in the studied photoreactor and access the rate of energy absorbed. These parameters are some key tools for the description and the assessment of reactions in a defined photoreactor. An originality of the study comes from the wide range of AC/TiO2 composition studied through the work which allows to analyze the evolution of the radiative properties, radiant energy repartition and rate of energy absorbed as a function of the AC/TiO2 material composition

Quantification of uncertainties of radiative transfer calculation in urban canopy models

International audienceUrban canopy models simplify urban morphology and physical processes such as radiative transfer to calculate the urban surface energy balance as a lower boundary condition for atmospheric models at low computational cost. The present study uses a reference model of urban radiative transfer based on the Monte Carlo method, which solves the radiative transfer equation by taking into account the complex geometry of buildings and vegetation. Procedurally-generated urban morphologies similar to the Local Climate Zones (LCZ) are studied to cover the variety of urban forms that exist globally. The uncertainties arising from the simplification of the urban morphology as an infinitely-long street canyon or a regular array of square blocks are quantified. In addition, uncertainties due to the neglect of specular or spectral material reflectivities and the involved atmosphere are investigated. It is found that for all LCZ, the street canyon and block morphologies lead to a systematic overestimation (underestimation) of the fraction of solar radiation absorbed by the walls (ground). The neglect of pitched roofs has a strong influence on the simulated urban solar radiation budget for low solar elevation angles. Neglecting the spectral reflectivity of urban materials does not lead to relevant uncertainties in the broadband radiative fluxes. Specularly reflecting windows only change the urban solar radiation budget for a central business district morphology with a high glazing ratio. The participating atmosphere can strongly influence the urban terrestrial radiation budget, especially for high-rise districts. Future urban canopy models should therefore improve the realism of the urban morphology, and consider a participating atmosphere for the calculation ofterrestrial radiation

Résolution de l’approximation de schiff par la méthode de monte carlo pour l’évaluation des propriétés radiatives : application aux micro-organismes photosynthétiques

National audienc

Experimental and theoretical coupled approaches for the analysis of radiative transfer in photoreactors containing particulate media: Case study of TiO2 powders for photocatalytic reactions

International audienceThe analysis of radiative transfer in photoreactors is often crucial for operating efficient photoreactions. This article aims to present a complete experimental and theoretical coupled approach allowing radiative transfer analysis of photoreactors containing particulate media. TiO 2 powder, widely used in photocatalysis, was selected as a case study material for this work. First, Mie theory was used and adapted to assess the effective properties of heterogenous powders. A home-made experimental bench allowing normal-hemispheric transmittance measurement was settled. Theoretical and experimental evaluations of the radiative properties were compared and appear to match each other. The second part of the work consisted in both transmittance and local radiant energy modeling through Monte Carlo and Two Flux models using the previously defined radiative properties as entry parameters. The comparison of experimental and modeled transmittance highlighted the consistence of these models which were then used to describe the radiant energy evolution inside a parallelplane photoreactor