Influence d'un bio-adjuvant sur les propriétés mécaniques et la porosité de mortiers

National audienceABSTRACT: the purpose of this paper is to examine the influence of a bio-admixture on compressive strength, flexion strength, as well as porosity of mortars at constant water on cement ratio (W/C = 0.5). The results showed that, for a long curing period (120 days), the addition of bioadmixture (2 and 2.5%) leads to an improvement of compressive strength of mortars. The porosity of mortars is not significantly affected by the addition of bioadmixture. However, increasing of curing period caused a decrease of the kinetics of capillary imbibition.RESUME: l'objectif de cette étude est d'évaluer l'effet d'un nouveau bio-adjuvant sur les propriétés mécaniques et la porosité de mortiers. Différentes concentrations de bio-adjuvant (0 ; 0,5 ; 1 ; 1,5 ; 2 et 2,5%) ont été ajoutées à des mortiers contenant du ciment CEM I (E/C = 0,5). La résistance en compression, la résistance en flexion, la porosité totale à l'eau et l'imbibition capillaire des mortiers ont été évaluées. Après 120 jours de cure dans l'eau, les mortiers avec 2 et 2,5% de bio-adjuvant présentent des résistances à la compression supérieures à celle des mortiers sans bio-adjuvant. Les essais de porosité totale à l'eau et d'imbibition capillaire des mortiers montrent une faible influence du bio-adjuvant utilisé sur la structure poreuse des mortiers. Cependant, le temps de cure à partir de 30 jours et jusqu'à 120 jours a entraîné une diminution de la cinétique d'imbibition capillaire

INFLUENCE DE BIOSURFACTANTS SUR L'ADHESION DE LISTERIA MONOCYTOGENES A DES SURFACES INERTES (CONSEQUENCES SUR LA DESINFECTION (DOCTORAT : MICROBIOLOGIE))

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Influence of a bioadmixture on standardized parameters of cementitious materials

International audienceA lipopeptide bioadmixture was used to modify the surface bio-contamination of concrete and their durability. Experimental investigations were intended to establish the influence of this bioproduct regarding different properties of mortar and/or cement paste samples. Standardized tests, such as slump test, flexural and compressive strength measurements as well as porosity determination, aim to confirm the ability of this bioproduct to be used as an admixture in cementitious materials. The bioadmixture introduced an effect on the workability of fresh samples with a plasticizing action. The bioproduct can improve the mechanical strength of Portand cement mortars depending on its content in samples and allows to reach resistances consistent with the standard strength class of samples. If the bioadmixture does not influence the total porosity available to water of the cement pastes, the mercury injection porosimetry has revealed the existence of a threshold from which the porous network of samples changes. The evolution of the surface roughness is also impacted by the bioadmixture, due to both curing time and interactions of the surface with water. The bioadmixture inhibits the development and the formation of crystals on the sample surfaces and modifies hydric transfers within the porous network of the samples

Corrosion behaviour of AISI 304 stainless steel in presence of a biosurfactant produced by Pseudomonas fluorescens

International audienceUnder certain conditions, some microorganisms are able to synthesize surface active compounds called biosurfactants (BS), which reduce the surface tension of water. BS characteristics depend on which microorganism produce them and therefore, on the microorganism culture conditions (temperature, pH, C, N-source,...). Numerous applications are known for these biomolecules, such as cleaning, bioremediation, and their use as a detergent, or in cosmetic formulations.Recently, a large amount of literature has been edited on the influence of BS on the interactions between pathogenic bacteria and inert surfaces. It has been shown that the modifications of surface properties by the adsorption of BS can reduce microbial adhesion.Some other studies on chemical surfactants have shown that the adsorption of surface-active compounds plays a major role in corrosion; they are indeed used as an interesting corrosion inhibition tool. Therefore, it seems very interesting to study the impact of BS as environment-friendly (since biological and biodegradable) corrosion inhibitors.In the present work, an attempt was made to study the corrosion behaviour of AISI 304 stainless steel in presence of BS produced by a Gram-negative bacteria, Pseudomonas fluorescens (Pf495). Corrosion tests were achieved on several surface oxidation states. The surface morphology of the corroded specimens was investigated using SEM

Les biosurfactants, des biomolécules à forte potentialité d'application

Biosurfactants are surface-active molecules synthesized by certain microorganisms. Their chemical nature as well as their surface-active properties are dramatically dependent on the type of microorganism (bacteria, yeasts, moulds), on the individual strain tested and on the available nutrients. The various known biosurfactants comprise glycolipids, lipopeptides, phospholipids, neutral lipids, fatty acids or lipopolysaccharides. As their chemical synthetic counterparts, they may exhibit emulsifying, foaming, wetting or dispersing properties, as well as more specific characteristics i.e. antibiotic activity. Such properties may be still efficient in extreme conditions such as acidic pH and high temperatures. In regard to their potentiality and their low toxicity, they are nowadays used in different applications such as environmental protection, petroleum industry, agronomy or cosmetology and should shortly settle in new sectors such as food processing, pharmaceutical industries or health care. The main objective of the following review is to synthesize the present knowledge in this research area.Les biosurfactants sont des molécules tensioactives produites par certains micro-organismes. Leur nature tout comme leur pouvoir tensioactif sont fortement dépendants du type de micro-organisme utilisé (bactéries, levures, champignons), de la souche testée ainsi que du substrat nutritif disponible pour le développement cellulaire. Parmi les différents biosurfactants recensés, on trouve aujourd’hui des glycolipides, des lipopeptides, des phospholipides, des lipides neutres, des acides gras ou des lipopolysaccharides. Tout comme leurs homologues de synthèse chimique, ils peuvent avoir des propriétés émulsifiantes, moussantes, mouillantes ou encore dispersantes, mais également des propriétés plus spécifiques (i.e. propriétés antibiotiques). Certaines de ces propriétés peuvent, de plus, être conservées dans des conditions extrêmes utilisation telles que pH acides, températures élevées, etc. Compte tenu de leurs potentialités et de leur innocuité, ils sont aujourd’hui utilisés dans différents domaines d’application tels que l’environnement, l’industrie pétrolière, l’agronomie ou encore la cosmétologie et devraient rapidement trouver leur place dans de nouveaux secteurs d’applications tels que les industries agroalimentaires, pharmaceutiques ou encore le domaine médical. La revue présentée ici a pour principal objectif de synthétiser les connaissances acquises à ce jour dans ce domaine

Pit formation on stainless steel surfaces pre-treated with biosurfactants produced by Pseudomonas fluorescens

International audienceToday, it is widely established that the surface tension of water can be reduced by some microorganisms capable of synthesizing surface-active compounds called biosurfactants (BS). BS characteristics depend on the microorganism that produces them and therefore, on the microorganism culture conditions.Some studies on chemical surfactants have shown that the adsorption of surface-active compounds plays a major role in corrosion: indeed they are used as a good corrosion inhibition tool.The purpose of this study was first, to estimate the importance and behavior of the stainless steels passive film on the adsorption of BS, produced by the Gram negative bacteria Pseudomonas fluorescens, and secondly, to study the impact of these treatments on the pitting corrosion.In this paper, the galvanostatic polarization technique. used as accelerated method for determining the characteristic pit potentials on stainless steels, is examined. Pit growth, shape and cover formation were also observed. The surface topography of the corroded specimens was investigated using field emission scanning electron microscopy (FESEM)

Genetic Features of Resident Biofilms Determine Attachment of Listeria monocytogenes▿

Planktonic Listeria monocytogenes cells in food-processing environments tend most frequently to adhere to solid surfaces. Under these conditions, they are likely to encounter resident biofilms rather than a raw solid surface. Although metabolic interactions between L. monocytogenes and resident microflora have been widely studied, little is known about the biofilm properties that influence the initial fixation of L. monocytogenes to the biofilm interface. To study these properties, we created a set of model resident Lactococcus lactis biofilms with various architectures, types of matrices, and individual cell surface properties. This was achieved using cell wall mutants that affect bacterial chain formation, exopolysaccharide (EPS) synthesis and surface hydrophobicity. The dynamics of the formation of these biofilm structures were analyzed in flow cell chambers using in situ time course confocal laser scanning microscopy imaging. All the L. lactis biofilms tested reduced the initial immobilization of L. monocytogenes compared to the glass substratum of the flow cell. Significant differences were seen in L. monocytogenes settlement as a function of the genetic background of resident lactococcal biofilm cells. In particular, biofilms of the L. lactis chain-forming mutant resulted in a marked increase in L. monocytogenes settlement, while biofilms of the EPS-secreting mutant efficiently prevented pathogen fixation. These results offer new insights into the role of resident biofilms in governing the settlement of pathogens on food chain surfaces and could be of relevance in the field of food safety controls

Listeria monocytogenes Scott A: Cell Surface Charge, Hydrophobicity, and Electron Donor and Acceptor Characteristics under Different Environmental Growth Conditions

We determined the variations in the surface physicochemical properties of Listeria monocytogenes Scott A cells that occurred under various environmental conditions. The surface charges, the hydrophobicities, and the electron donor and acceptor characteristics of L. monocytogenes Scott A cells were compared after the organism was grown in different growth media and at different temperatures; to do this, we used microelectrophoresis and the microbial adhesion to solvents method. Supplementing the growth media with glucose or lactic acid affected the electrical, hydrophobic, and electron donor and acceptor properties of the cells, whereas the growth temperature (37, 20, 15, or 8°C) primarily affected the electrical and electron donor and acceptor properties. The nonlinear effects of the growth temperature on the physicochemical properties of the cells were similar for cells cultivated in two different growth media, but bacteria cultivated in Trypticase soy broth supplemented with 6 g of yeast extract per liter (TSYE) were slightly more hydrophobic than cells cultivated in brain heart infusion medium (P < 0.05). Adhesion experiments conducted with L. monocytogenes Scott A cells cultivated in TSYE at 37, 20, 15, and 8°C and then suspended in a sodium chloride solution (1.5 × 10(−1) or 1.5 × 10(−3) M NaCl) confirmed that the cell surface charge and the electron donor and acceptor properties of the cells had an influence on their attachment to stainless steel