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International audience; Pathogenic bacterial biofilms invading surfaces in food and medical fields are a challenge to overcome. Despite all the strategies applied to fight their formation, the microbiological risk associated to bacterial biofilms remains an important threat for at risk population and for food and healthcare sectors. The prevention of biofilm formation might be an effective approach to confront this problem. In this study, stainless steel surfaces were functionalized by nisin, a natural antimicrobial peptide. The mechanism of action of immobilized nisin against sensitive bacteria is not fully understood. Therefore, nisin was grafted onto the surface by either its carboxylic group or its amino group. The generated coating's chemical, topographical and antibacterial properties were studied to understand the nisin mode of action, when immobilized, and identify the section of the bacteriocin responsible for the antimicrobial activity. The antimicrobial activity of the elaborated coatings was tested against Listeria monocytogenes. Indeed, the surfaces coated with nisin linked by its amino group showed an efficient antibacterial activity while the surface with nisin linked by its carboxylic group showed less antimicrobial effect. The antimicrobial results showed almost 2 log reduction of colony forming units for efficient antibacterial coatings while the other showed no bacterial reduction. The surface properties analysis permitted to understand the chemical and topographical characteristics of treated surfaces including nisin conformation and quantification. A tight relation was concluded between the surface topography, the nisin conformation, and the antibacterial activity of the bacteriocin-coated surfaces.

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International audience; The persistence of Salmonella enterica on abiotic surfaces in hospitals and the agri-food industries leads to several infections worldwide. In this context, this work aimed to study the adhesion of S. Enteritidis on plasma-modified stainless steel to prevent biofilm-associated-infections. Surface modification was achieved by the elaboration of organosilicon coatings from the monomer 1,1,3,3-tetramethyldisiloxane, mixed with oxygen, using a flowing nitrogen microwave post-discharge plasma polymerization technique. The effect of cold plasma parameters on the properties of the coatings, the coated surface topography and S. Enteritidis cell adhesion was studied. The results showed that the surface topography influenced the bacterial adhesion rate. Indeed, rough surfaces did not repel S. Enteritidis since the number of attached cells on these coatings was between 30 ± 4 to 65 ± 4 bacteria per microscopic field. Otherwise, smoother surfaces demonstrated an anti-adhesive character since the number of attached cells was almost nil on these coatings.

International audience; The biofilm formation on food-contact-surfaces is a serious threat for public health and often results in huge human and economic losses. Thus, it is of importance to develop new strategies that allow the monitoring of the biofilm formation on food-contact-surfaces. Such strategies permit effective and timely countermeasures and, therefore, to avoid the microbiological risk and associated environmental impact due to cleaning processes. Therefore, this work investigated a non-invasive method for monitoring and detection of the biofilm formation using Coda Wave Interferometry (CWI) method. The principle of this method and the calculation of decorrelation coefficient based on the ultrasonic measurements were explained. The results underlined that our developed method is able to detect the early stage of the biofilm formation of Staphylococcus aureus on the stainless steel. Namely, it is shown that the bacterial cell kinetic is well captured by the evolution of the decorrelation coefficient as a function of incubation times. Overall, this work showed that this cost effective CWI method is a promising tool for the detection of early stage biofilm formation on food-contact-surfaces.

Power generation from renewable energy sources, in particular solar photovoltaics (PV), has become extremely attractive thanks to its very low levelized cost of electricity (LCoE). In desert-like environments, the energy yield is drastically reduced due to dust accumulation. While effective and affordable cleaning strategies can be implemented in large, MW-size PV power plants, soiling remains an economic and logistic challenge. In this article, we analyze the soiling loss rates of PV modules for different tilt angles measured during a period of 15 months in the Western Region of Saudi Arabia. We observe a strong correlation between weather parameters like humidity and wind speed and the mechanism of dust accumulation. Our measurements show that, for specific weather conditions, soiled modules undergo a partial cleaning process. As a consequence, and for the first time, the soiling loss rates are shown to have a clear dependence on the current soiling state of the modules, with clean modules soiling twice as fast as soiled ones. This dependency is a key for predicting the correct cleaning frequency of a PV power plant. Finally, the results obtained for vertically mounted modules (90 deg), where dust accumulation is negligible, point to a favorable case for the use of bifacial PV modules.

The aim of the present work was to study and compare the effect of growth temperature (20, 30, and 37 degrees C) and surface type (stainless steel and polycarbonate) on the production of virulence factors, such as proteases and siderophores, and the risk of surface contamination associated with Pseudomonas aeruginosa biofilm and planktonic cells. The increase of growth temperature from 20 to 37 degrees C increased (approximately twofold) the electronegative charge and the hydrophobicity of the P. aeruginosa biofilm cell surface. P. aeruginosa biofilm cell adhesion to stainless steel and polycarbonate was 5- and 1.5-fold higher than their planktonic counterparts at 20 and 30 degrees C, respectively. The increase of growth temperature from 20 to 37 degrees C increased the production of proteases (twofold) and siderophores (twofold) and the cytotoxicity (up to 30-fold) against the HeLa cell line in the supernatants of P. aeruginosa planktonic and biofilm cultures. This study also highlighted that biofilm and planktonic P. aeruginosa cells exhibited distinct physiological properties with respect to the production of virulence factors and the cytotoxicity against the Hela cell line. Therefore, effective disinfection procedures should be adapted to inactivate bacteria detached from biofilms.

The aim of the present work was to study and compare the effect of growth temperature (20, 30, and 37°C) and surface type (stainless steel and polycarbonate) on the production of virulence factors, such as proteases and siderophores, and the risk of surface contamination associated with

International audience; This study investigated the effect of the growth temperature (20 and 37 degrees C) of Escherichia coli strains isolated from pigs on their adhesion to stainless steel and polycarbonate. This study also evaluated the ability of the DLVO and XDLVO mathematical models to predict this adhesion. The rise of growth temperature from 20 to 37 degrees C significantly influenced the adhesion of studied E. coli strains. The data also underlined that the mathematical prediction did not fully match with the experimental bacterial adhesion to surfaces. Furthermore, results showed that the colistin-resistant and sensitive E. coli strains adhesion depends on the type of abiotic surface. Based on these results, the mathematical models are limited in the prediction of the bacterial adhesion to abiotic surfaces. The surface roughness is a major parameter of the bacterial adhesion and should be included in the future mathematical models predicting the bacterial adhesion.

International audience; The present study investigated and compared the effect of growth temperature on the susceptibility of biofilm-detached andplanktonic Staphylococcus aureus cells, to benzalkonium chloride (BAC). This study also highlights the impact of BAC on the bacterial physiology and the role of membrane fluidity regulation as a bacterial resistance mechanism. The minimum inhibitory concentration of BAC was characterized with micro-dilution growth inhibition assay. The BAC treatment was performed on S. aureus cultured at 20 degrees C and 37 degrees C, for 24h. The morphology of S. aureus cells was examined using scanning electron microscopy. The loss of bacterial membrane integrity after BAC treatment was studied by monitoring the intracellular potassium ion leakage using the atomic absorption spectroscopy. The bacterial membrane total fatty acid composition, controlling the membrane fluidity, was analyzed by GC/MS. The results showed that the resistance of S. aureus cells to BAC increased with the increase of growth temperature. The planktonic cells were more susceptible to BAC than biofilm-detached ones. The rise of growth temperature resulted in an increase of S. aureus membrane rigidity. Furthermore, a higher membrane fluidity was observed in planktonic cells when compared to that in the biofilm-detached ones. The resistance of S. aureus seems to depend on the growth temperature. Compared to planktonic cells, biofilm-detached cells showed a greater resistance to BAC. The BAC targets and disturbs the bacterial membrane. Membrane fluidity modulation is likely a one of resistance mechanisms for S. aureus to BAC at the cellular scale. Therefore, disinfection procedures, in food sector, should be adapted for bacteria detached from biofilm.

International audience; This work aims at studying the impact of silane-based coatings, generated by atmospheric pressure plasma spraying (APPS) of a liquid precursor (hexamethydisiloxane – HMDSO), on dairy antifouling and antibacterial properties of food-grade 316L stainless steel. The influence of the manufacturing parameters (precursor flow rate, nozzle-to-substrate distance and scanning speed) on the coatings properties was investigated using a wide range of characterization techniques (drop shape analysis, X-Ray Mappings, Scanning Electron Microscopy, Fourier-Transformed Infrared Spectroscopy, Atomic Force Microscopy). Coating’s roughness in particular was shown to strongly increase when precursor flow rate increases. A pilot pasteurizer, fed with a model foulant solution (whey protein and calcium), allowed performing two consecutive industrial-like isothermal dairy fouling tests, revealing the promising anti-fouling properties of the HMDSO-coated steel. A fouling reduction of up to 90% compared to bare stainless steel was achieved after first cycle for all samples. The second fouling run allowed to select the best-performing sample, which kept the same antifouling properties as in the first test. Its mechanism of action was investigated, which revealed that a nanostructured, Si-O-Si rich surface was efficient to prevent isothermal dairy fouling. The adhesion of the pathogenic bacterium Staphylococcus aureus also proved to be impacted by this plasma coating, with a significant decrease of adhered cells (−30% compared to native stainless steel).

International audience; Dairy industries are burdened by fouling phenomena that increase costs and environmental impacts of thermal processes. One remedial solution could be to replace stainless-steel equipment by other materials less prone to fouling. This work studied the fouling behaviour and hygienic features of two hydrophobic and non-polar commercial graphite-based composites (Graphilor (R) XC and XTH) that were exposed to isothermal whey protein fouling in an industrial pasteurisation unit and to foodborne pathogenic bacterial strains, namely Staphylococcus aureus, Listeria monocytogenes and Salmonella enterica. Both composites exhibited impressive fouling-release properties: a simple 20 min water rinse was enough to remove all dairy deposit after 1.5 h of pasteurisation, as opposed to usual heavy clean-in-place procedures. The composites also showed a significant effect on bacterial adhesion, exhibiting lower cell counts than stainless-steel surfaces. These results suggest that graphite-based materials might successfully replace stainless steel as equipment material to reduce fouling in dairy fouling industries.

International audience; The goal of this study was to investigate the effect of growth conditions such as the temperature (20, 30 and 37 °C), incubation duration (24 and 48 h) and surface type (stainless steel and polycarbonate) on the cell surface physicochemical properties and adhesion to abiotic surfaces of biofilm-detached and planktonic Staphylococcus aureus cells. This study tested also the hypothesis that S. aureus planktonic cells exhibit distinct pathogenic properties compared with their sessile counterparts. The results showed that the changes of the growth conditions promoted changes in the zeta potential, hydrophobicity, electron donor/acceptor character of the studied cell populations. Biofilm-detached cells showed a greater adhesion to stainless steel and polycarbonate compared with planktonic cells. Compared with planktonic cells, sessile ones showed higher cytotoxic effect against HeLa cells, DNase activity, and siderophore levels. The higher cytotoxic effect and production of DNase and siderophore increased with the increase of temperature and duration of incubations. Based on the obtained data, the S. aureusbiofilm-detached cells were found to be distinct in many physiological properties compared with their planktonic counterparts.

Two hundred and thirty individual clones of microorganisms were recovered from milk tanks and milking machine surfaces at two distinct farms (Bejaja City, Algeria). Of these clones, 130 were identified as lactic acid bacteria (LAB). In addition Escherichia coli, Salmonella, Staphylococcus aureus and Pseudomonas aeruginosa species were identified in the remaining 100 isolates-spoilage isolate. These isolates were assayed for ability to form biofilms. S. aureus, Lactobacillus brevis strains LB1F2, LB14F1 and LB15F1, and Lactobacillus pentosus strains LB2F2 and LB3F2 were identified as the best biofilm formers. Besides, these LAB isolates were able to produce proteinaceous substances with antagonism against the aforementioned spoilage isolates, when grown in MRS or TSB-YE media. During the screening, L. pentosus LB3F2 exhibited the highest antibacterial activity when grown in TSB-YE medium at 30 °C. Additionally, L. pentosus LB3F2 was able to strongly hamper the adhesion of S. aureus SA3 on abiotic surfaces as polystyrene and stainless steel slides. LAB isolates did not show any hemolytic activity and all of them were sensitive to different families of antibiotic tested. It should be pointed out that LB3F2 isolate was not cytotoxic on the intestinal cells but could stimulate their metabolic activity. This report unveiled the potential of LB1F2, LB14F1, LB15F1, LB2F2, and LB3F2 isolates to be used as natural barrier or competitive exclusion organism in the food processing sector as well as a positive biofilm forming bacteria.

This study investigated the effect of growth temperature changes (20, 30, and 37°C) on the adhesion behavior of Pseudomonas aeruginosa and Staphylococcus aureus to stainless steel and polycarbonate. Adhesion assays were performed under static conditions at 20°C. In addition, the validity of the thermodynamic and extended Derjaguin, Landau, Verwey, and Overbeek theories as predictive tools of bacterial adhesion were studied. The surface properties of the bacterial cells and the substrates of attachment were characterized, and atomic force microscopy was used to analyze the surface topography. The results indicated that the highest adhesion rate of P. aeruginosa and S. aureus on both surfaces was observed when the cells were grown at 37°C. The bacterial adhesion to stainless steel was found to be two times higher than to polycarbonate for both bacteria, whatever the condition used. The present study underlined that the thermodynamic and the extended Derjaguin, Landau, Verwey, and Overbeek theories were able to partially predict the empirical results of P. aeruginosa adhesion. However, these theories failed to predict the adhesion behavior of S. aureus to both surfaces when the growth temperature was changed. The results of the microbial adhesion to solvent indicated that the adhesion rate to abiotic surfaces may correlate with the hydrophobicity of bacterial surfaces. The effect of surface topography on bacterial adhesion showed that surface roughness, even on the very low nanometer scale, has a significant effect on bacterial adhesion behavior.

The goal of this study was to investigate the effect of the environmental conditions such as the temperature change, incubation time and surface type on the resistance of Staphylococcus aureus biofilms to disinfectants. The antibiofilm assays were performed against biofilms grown at 20 °C, 30 °C and 37 °C, on the stainless steel and polycarbonate, during 24 and 48 h. The involvement of the biofilm matrix and the bacterial membrane fluidity in the resistance of sessile cells were investigated. Our results show that the efficiency of disinfectants was dependent on the growth temperature, the surface type and the disinfectant product. The increase of growth temperature from 20 °C to 37 °C, with an incubation time of 24 h, increased the resistance of biofilms to cationic antimicrobials. This change of growth temperature did not affect the major content of the biofilm matrix, but it decreased the membrane fluidity of sessile cells through the increase of the anteiso-C19 relative amount. The increase of the biofilm resistance to disinfectants, with the rise of the incubation time, was dependent on both growth temperature and disinfectant product. The increase of the biofilm age also promoted increases in the matrix production and the membrane fluidity of sessile cells. The resistance of S. aureus biofilm seems to depend on the environment of the biofilm formation and involves both extracellular matrix and membrane fluidity of sessile cells. Our study represents the first report describing the impact of environmental conditions on the matrix production, sessile cells membrane fluidity and resistance of S. aureus biofilms to disinfectants.

The relationship between the environmental conditions of biofilm formation and resistance to disinfectants was studied. Anti-biofilm assays were performed against biofilms grown at 20, 30 and 37°C on stainless steel and polycarbonate, over 24 and 48 h. A rise in growth temperature increased the resistance of 24 h biofilms to disinfectants containing didecyldimethylammonium chloride and decreased it to a disinfectant containing alkyldimethylbenzylammonium chloride. The increase in growth temperature coupled with an incubation time of 24 h promoted increases in both matrix production and the membrane rigidity of sessile cells. An increase in incubation time also increased both matrix production and the membrane rigidity of sessile cells. Such phenomena resulted in an increased resistance to disinfectants of biofilms grown at 20 and 30°C. The resistance of 48 h biofilms to disinfectants decreased with an increase in growth temperature despite the increase in matrix production and the membrane rigidity of sessile cells.

Biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus on food-contact-surfaces represents a significant risk for the public health. In this context, the present study investigates the relationship between the environmental conditions of biofilm formation and the resistance to disinfectants. Therefore, a static biofilm reactor, called NEC-Biofilm System, was established in order to study the effect of growth temperature (20,30 and 37 degrees C), and of the surface type (stainless steel and polycarbonate), on biofilm resistance to disinfectants. These conditions were selected to mimic the biofilm formation on abiotic surfaces of food processing industries. The antibiofilm assays were performed on biofilms grown during 24 h. The results showed that the growth temperature influenced significantly the biofilm resistance to disinfectants. These data also revealed that the growth temperature has a significant effect on the biofilm structure of both bacteria. Furthermore, the increase of the biofilm growth temperature increased significantly the algD transcript level in sessile P. aeruginosa cells, whereas the icaA one was not affected in S. aureus cells. Overall, our findings show that the biofilm structure and matrix cannot fully explain the biofilm resistance to disinfectant agents. Nevertheless, it underlines the intimate link between environmental conditions, commonly met in food sectors, and the biofilm resistance to disinfectants.

The biofilm formation on abiotic surfaces in food and medical sectors constitutes a great public health concerns. In fact, biofilms present a persistent source for pathogens, such as Pseudomonas aeruginosa and Staphylococcus aureus, which lead to severe infections such as foodborne and nosocomial infections. Such biofilms are also a source of material deterioration and failure. The environmental conditions, commonly met in food and medical area, seem also to enhance the biofilm formation and their resistance to disinfectant agents. In this regard, this review highlights the effect of environmental conditions on bacterial adhesion and biofilm formation on abiotic surfaces in the context of food and medical environment. It also describes the current and emergent strategies used to study the biofilm formation and its eradication. The mechanisms of biofilm resistance to commercialized disinfectants are also discussed, since this phenomenon remains unclear to date.

Background Eosinophils are key players in T H 2-driven pathologies, such as allergic lung inflammation. After IL-5– and eotaxin-mediated tissue recruitment, they release several cytotoxic and inflammatory mediators. However, their exact contribution to asthma remains controversial. Indeed, in human subjects anti–IL-5 treatment inhibits eosinophilia but not antigen-induced airway hyperresponsiveness (AHR). Likewise, lung fibrosis is abrogated in 2 strains of eosinophil-deficient mice, whereas AHR is inhibited in only one of them. Finally, eosinophils have been shown to attract T H 2 lymphocytes at the inflammatory site. Objective The ability of eosinophils to promote AHR and lung inflammation independently of lymphocytes was investigated. Methods Adoptive transfers of resting or activated eosinophils from IL-5 transgenic mice were performed into naive BALB/c mice, mice with severe combined immunodeficiency, and IFN-γ–deficient BALB/c recipients. Results Adoptively transferred eosinophils induced lung inflammation, fibrosis, collagen deposition, and AHR not only in BALB/c mice but also in recipient mice with severe combined immunodeficiency. Surprisingly, IFN-γ expression was increased in lungs from eosinophil-transferred animals. Furthermore, IFN-γ neutralization in recipients partially inhibited eosinophil-induced AHR. Moreover, IFN-γ–deficient eosinophils or eosinophils treated with a blocking anti–IFN-γ receptor antibody failed to induce AHR in IFN-γ–deficient recipients. Finally, in vitro and at low concentrations, IFN-γ increased eosinophil peroxidase release, potentiated chemotaxis, and prolonged survival, suggesting the existence of an autocrine mechanism. Conclusions These results support the important and previously unsuspected contribution of eosinophils to lung inflammation independently of lymphocytes through production of IFN-γ, the prototypical T H 1 cytokine.