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

Molecular studies of the intestinal mucosal barrier physiopathology using co-cultures of epithelial and immune cells: a technical update.

Peyer's patch lymphocytes cocultured with Caco-2 cells trigger the phenotypic conversion of enterocytes into cells that express morphological and functional M-cell properties. We report a technical update for setting up this model, which will enable the study of M-cell biology, the identification by biochemical approaches of molecules involved in the interaction of microorganisms with M cells, and the development of vectors that would efficiently target the mucosal immune system

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

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

Water supply and sanitation services in small towns in rural–urban transition zones: The case of Bushenyi-Ishaka Municipality, Uganda

Small towns lag behind cities in drinking water and sanitation access globally. Closing this gap requires developing service models for areas with both urban and rural characteristics. This study assessed Bushenyi-Ishaka, a municipality in Uganda situated at the rural–urban transition, with a focus on service ladder indictors. Data sources included household interviews (n = 500) and water quality samples from sources and storage containers. Households in more urban (as compared to rural) cells were more likely to use improved water sources (including piped water on-premises), make regular payments for water, rely on shared sanitation facilities, and make use of manual sludge emptying services. Most households (72%) used an unlined pit latrine not intended for emptying and reuse. These findings suggest that small town servicing models should prioritize non-sewered sanitation management, including incentives for safe excreta containment and disposal opportunities. This study also highlights a need for integrated services models to expand rural–urban water and sanitation coverage