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It was shown in the literature that ethanol locks have a positive effect on preventing catheter-related infections in patients with central venous catheters without causing any microbial resistance. However, ethanol is known to interact with polyurethanes. The consequences of this interaction on the catheter surface properties were studied as it can impact the biocompatibility of the material and the adhesion phenomena onto the surface. No physical and chemical degradation was put into evidence, but low molecular weight compounds such as additives were extracted from the catheter bulk or migrated and exudated onto its surface. Nevertheless, as far as bacterial adhesion is concerned, after the catheter was locked and the lock removed, the surface modifications promoted no adhesion., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Afif Khzam reports financial support and equipment, drugs, or supplies were provided by Vygon., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Listeria monocytogenes presents a dimorphism associated to the SecA2 activity with cells having a normal rod shape or a dysmorphic elongated filamentous form. Besides variation of the cell and colony morphotype, this cell differentiation has profound ecophysiological and physiopathological implications with collateral effects on virulence and pathogenicity, biotope colonisation, bacterial adhesion and biofilm formation. This suggests the SecA2-only protein export could influence the listerial cell surface, which was investigated first by characterising its properties in L. monocytogenes wt and ΔsecA2. The degree of hydrophilicity and Lewis acid-base properties appeared significantly affected upon SecA2 inactivation. As modification of electrostatic properties would owe to modification in the composition of cell-surface proteins, the proteosurfaceome was further investigated by shotgun label-free proteomic analysis with a comparative relative quantitative approach. Following secretomic analysis, the protein secretion routes of the identified proteins were mapped considering the cognate transport and post-translocational maturation systems, as well as protein categories and subcellular localisation. Differential protein abundance profiles coupled to network analysis revealed the SecA2 dependence of 48 proteins, including some related to cell envelope biogenesis, translation and protein export, which could account for modifications of adhesion and surface properties of L. monocytogenes upon SecA2 inactivation. This investigation unravelled the profound influence of SecA2 activity on the cell surface properties and proteosurfaceome of L. monocytogenes, which provides advanced insights about its ecophysiopathology. SIGNIFICANCE: L. monocytogenes is a foodborne zoonotic pathogen and etiological agent of human listeriosis. This species presents a cellular dimorphism associated to the SecA2 activity that has profound physiopathological and ecophysiological implications with collateral effects on bacterial virulence and colonisation. To explore the influence of the SecA2-only protein export on the listerial cell, the surface properties of L. monocytogenes expressing or depleted of SecA2 was characterised by microelectrophoresis, microbial affinity to solvents and contact angles analyses. As modifications of hydrophilicity and Lewis acid-base electrostatic properties would owe to modification in the composition of cell-surface proteins, the proteinaceous subset of the surfaceome, i.e. the proteosurfaceome, was investigated further by shotgun label-free proteomic analysis. This subproteome appeared quite impacted upon SecA2 inactivation with the identification of proteins accounting for modifications in the cell surface properties. The profound influence of SecA2 activity on the cell surface of L. monocytogenes was unravelled, which provides advanced insights about its ecophysiopathology., (Copyright © 2021. Published by Elsevier B.V.)

Polyionenes (PI) with stable positive charges and tunable hydrophobic spacers in the polymer backbone, are shown to be particularly efficient regarding antimicrobial properties. This effect can be modulated since it increases with the length of hydrophobic spacers, i.e., the number of methylene groups between quaternary ammoniums. Now, to further explore these properties and provide efficient antimicrobial surfaces, polyionenes should be grafted onto materials. Here a robust grafting strategy to covalently attach polyionenes is described. The method consisted in a sequential surface chemistry procedure combining polydopamine coating, diazonium-induced polymerization, and polyaddition. To the best of knowledge, grafting of PI onto surfaces is not reported earlier. All chemical steps are characterized in detail via various surface analysis techniques (FTIR, X-ray photoelectron spectroscopy, contact angle, and surface energy measurements). The antibacterial properties of polyionene-grafted surfaces are then studied through bacterial adhesion experiments consisting in enumeration of adherent bacteria (total and viable cultivable cells). PI-grafted surfaces are showed to display effective and versatile bacteriostatic/bactericidal properties associated with a proadhesive effect., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The ready-to-eat products can be contaminated during processing by pathogen or spoilage bacteria, which persist in the industrial environment. Some bacterial species are able to form biofilms which protect them from environmental conditions. To check the bacterial contamination of the surfaces in the food industries, the professionals must regularly use surface sampling methods to detect the pathogen such as Listeria monocytogenes or the spoilage such as Pseudomonas fluorescens. In 2010, we designed and carried out a European survey to collect surface sampling information to detect or enumerate L. monocytogenes in food processing plants. A total of 137 questionnaires from 14 European Union Member States were returned. The outcome of this survey showed that the professionals preferred friction sampling methods with gauze pad, swab and sponges versus contact sampling methods. After this survey, we compared the effectiveness of these three friction sampling methods and the contact plates, as recommended in the standard EN ISO 18593 that was revised in 2018, on the recovery of L. monocytogenes and of P. fluorescens in mono-specie biofilms. This study showed no significant difference between the effectiveness of the four sampling methods to detach the viable and culturable bacterial population of theses mono-specie biofilms., (© FEMS 2020.)

In the marine environment, most solid surfaces are covered by microbial biofilms, mainly composed of bacteria and diatoms. The negative effects of biofilms on materials and equipment are numerous and pose a major problem for industry and human activities. Since marine micro-organisms are an important source of bioactive metabolites, it is possible that they synthesize natural ecofriendly molecules that inhibit the adhesion of organisms. In this work, the antibiofilm potential of marine bacteria was investigated using Flavobacterium sp. II2003 as a target. This strain is potentially a pioneer strain of bacteria that was previously selected from marine biofilms for its strong biofilm-forming ability. The culture supernatants of 86 marine heterotrophic bacteria were tested for their ability to inhibit Flavobacterium sp. II2003 biofilm formation and the Pseudomonas sp. IV2006 strain was identified as producing a strong antibiofilm activity. The Pseudomonas sp. IV2006 culture supernatant (SN IV2006 ) inhibited Flavobacterium sp. II2003 adhesion without killing the bacteria or inhibiting its growth. Moreover, SN IV2006 had no effect on the Flavobacterium sp. II2003 cell surface hydrophilic/hydrophobic and general Lewis acid-base characteristics, but modified the surface properties of glass, making it on the whole more hydrophilic and more alkaline and significantly reducing bacterial cell adhesion. The glass-coating molecules produced by Pseudomonas sp. IV2006 were found to probably be polysaccharides, whereas the antibiofilm molecules contained in SN IV2006 and acting during the 2 h adhesion step on glass and polystyrene surfaces would be proteinaceous. Finally, SN IV2006 exhibited a broad spectrum of antibiofilm activity on other marine bacteria such as Flavobacterium species that are pathogenic for fish, and human pathogens in both the medical environment, such as Staphylococcus aureus and Pseudomonas aeruginosa , and in the food industry, such as Yersinia enterocolitica . Thus, a wide range of applications could be envisaged for the SN IV2006 compounds, both in aquaculture and human health.

Enterococcus faecalis is an opportunistic pathogen with an intrinsically high resistance to lysozyme, a key effector of the innate immune system. This high level of resistance requires a complex network of transcriptional regulators and several genes (oatA, pgdA, dltA and sigV) acting synergistically to inhibit both the enzymatic and cationic antimicrobial peptide activities of lysozyme. We sought to identify novel genes modulating E. faecalis resistance to lysozyme. Random transposon mutagenesis carried out in the quadruple oatA/pgdA/dltA/sigV mutant led to the identification of several independent insertions clustered on the chromosome. These mutations were located in a locus referred to as the enterococcal polysaccharide antigen (EPA) variable region located downstream of the highly conserved epaA-epaR genes proposed to encode a core synthetic machinery. The epa variable region was previously proposed to be responsible for EPA decorations, but the role of this locus remains largely unknown. Here, we show that EPA decoration contributes to resistance towards charged antimicrobials and underpins virulence in the zebrafish model of infection by conferring resistance to phagocytosis. Collectively, our results indicate that the production of the EPA rhamnopolysaccharide backbone is not sufficient to promote E. faecalis infections and reveal an essential role of the modification of this surface polymer for enterococcal pathogenesis., Competing Interests: The authors have declared that no competing interests exist.

Enterococcus faecalis, an organism generally not pathogenic for healthy humans, has the potential to cause disease in susceptible hosts. While it seems to be equipped to interact with and circumvent host immune defense, most of the molecular and cellular mechanisms underlying the enterococcal infectious process remain elusive. Here, we investigated the role of the Enterococcal Leucine Rich protein A (ElrA), an internalin-like protein of E. faecalis also known as a virulence factor. ElrA was previously shown to prevent adhesion to macrophages. We show that ElrA does not inhibit the basic phagocytic process, but is able to prevent sensing and migration of macrophages toward E. faecalis. Presence or absence of FHL2, a eukaryotic partner of ElrA, does not affect the ElrA-dependent mechanism preventing macrophage migration. However, we highlight a partial contribution of FHL2 in ElrA-mediated virulence in vivo. Our results indicate that ElrA plays at least a dual role of which anti-phagocytic activity may contribute to dissemination of extracellular E. faecalis during infection.

Pseudomonas aeruginosa is a pathogenic micro-organism responsible for many hospital-acquired infections. It is able to adhere to solid surfaces and develop an immobilized community or so-called biofilm. Many studies have been focusing on the use of specific materials to prevent the formation of these biofilms, but the reactivity of the bacteria in contact to surfaces remains unknown. The aim of this study was to evaluate the impact of the abiotic surface on the physiology of adherent bacteria. Three different materials, stainless steel (SS), glass (G), and polystyrene (PS) that were relevant to industrial or medical environments were characterized at the physicochemical level in terms of their hydrophobicity and roughness. We showed that SS was moderately hydrophilic and rough, potentially containing crevices, G was hydrophilic and smooth while PS was hydrophobic and smooth. We further showed that P. aeruginosa cells were more likely able to adhere to SS and G rather than PS surfaces under our experimental conditions. The physiological response of P. aeruginosa when adhering to each of these materials was then evaluated by global proteomic analysis. The abundance of 70 proteins was shown to differ between the materials suggesting that their abundance was modified as a function of the material to which bacteria adhered. Our data lead to enabling the identification of abundance patterns that appeared to be specific to a given surface. Taken together, our data showed that P. aeruginosa is capable of sensing and responding to a surface probably via specific programmes to adapt its physiological response accordingly.

Commercial infusion tubing and blood storage devices (tubing, blood and platelets bags) made of plasticized PVC were analyzed by spectroscopic, chromatographic and microscopic techniques in order to identify and quantify the additives added to the polymer (lubricants, thermal stabilizers, plasticizers) and to put into evidence their blooming onto the surface of the devices. For all the samples, deposits were observed on the surface but with different kinds of morphologies. Ethylene bis amide lubricant and metallic stearate stabilizers were implicated in the formation of these layers. In contact with aqueous media, these insoluble deposits were damaged, suggesting a possible particulate contamination of the infused solutions., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Reducing bacterial adhesion on substrates is fundamental for various industries. In this work, new superhydrophobic surfaces are created by electrodeposition of hydrophobic polymers (PEDOT-F 4 or PEDOT-H 8 ) on stainless steel with controlled topographical features, especially at a nano-scale. Results show that anti-bioadhesive and anti-biofilm properties require the control of the surface topographical features, and should be associated with a low adhesion of water onto the surface (Cassie-Baxter state) with limited crevice features at the scale of bacterial cells (nano-scale structures)., (Copyright © 2016. Published by Elsevier B.V.)

Medical device-related infections are a major problem in hospital. The risk of developing an infection is linked to the bacterial adhesion ability of pathogen strains on the device and their ability to form a biofilm. Here we focused on polymer surfaces exhibiting a blooming of antioxidant (Irganox 3114® and Irganox 1076®) on their surface. We tried to put into evidence the effect of such a phenomenon on the bacterial adhesion in terms of number of viable cultivable bacteria and bacteria localization on the surface. We showed that the blooming has a tendency to increase the Staphylococcus aureus adhesion phenomenon in part for topographic reasons., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Over the last decades, surface biocontamination has become a major concern in food industries and medical environments where its outcomes could vary from financial losses to public health issues. Understanding adhesion mechanisms of involved microorganisms is essential to develop new strategies of prevention and control. Adhesion of Pseudomonas aeruginosa, a nosocomial pathogenic bacterium, relies on several bacterial features, among which are bacterial appendages such as flagella and type IV pili. Here, we examine the role of P. aeruginosa PAO1 flagella and type IV pili in the adhesion to abiotic surfaces with various hydrophobicities. Adhesion kinetics showed, that after 60min, flagella increased the adhesion of the strain to surfaces with high hydrophobicity while no effect was observed on hydrophilic surfaces. Flagella of adherent bacteria exhibited specific and conserved pattern on the surfaces that suggested a higher affinity of flagella for hydrophobic surfaces. Based on these results and on previous studies in the literature, we proposed a model of flagella-mediated adhesion onto hydrophobic surfaces where these appendages induce the first contact and promote the adhesion of the bacterial body. These findings suggest that anti-bioadhesive surface design should take into consideration the presence of bacterial appendages., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In most habitats, microbial life is organized in biofilms, three-dimensional edifices sustained by extracellular polymeric substances that enable bacteria to resist harsh and changing environments. Under multispecies conditions, bacteria can benefit from the polymers produced by other species ("public goods"), thus improving their survival under toxic conditions. A recent study showed that a Bacillus subtilis hospital isolate (NDmed) was able to protect Staphylococcus aureus from biocide action in multispecies biofilms. In this work, we identified ypqP, a gene whose product is required in NDmed for thick-biofilm formation on submerged surfaces and for resistance to two biocides widely used in hospitals. NDmed and S. aureus formed mixed biofilms, and both their spatial arrangement and pathogen protection were mediated by YpqP. Functional ypqP is present in other natural B. subtilis biofilm-forming isolates. However, the gene is disrupted by the SPβ prophage in the weak submerged-biofilm-forming strains NCIB3610 and 168, which are both less resistant than NDmed to the biocides tested. Furthermore, in a 168 laboratory strain cured of the SPβ prophage, the reestablishment of a functional ypqP gene led to increased thickness and resistance to biocides of the associated biofilms. We therefore propose that YpqP is a new and important determinant of B. subtilis surface biofilm architecture, protection against exposure to toxic compounds, and social behavior in bacterial communities., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

The aim of this paper is to study the impact of the substrate stiffness on the bacterial adhesion. For this purpose, agarose hydrogels are used as substrates with controlled mechanical properties. Indeed, the elastic modulus of these hydrogels, more precisely the shear storage moduli G', evolves with the agarose concentration (in this study from 0.75% to 3%). Other physico-chemical characteristics of the surface, known to be involved in bacterial adhesion, as hydrophobicity, were confirmed to remain constant. Two marine bacterial strains, a positive Gram Bacillus sp. 4J6 and a negative Gram Pseudoalteromonas sp. D41 were selected. Their retention on the substrates was analysed by confocal laser scanning microscopy and by counting of viable adhered bacteria. It was demonstrated that surface elastic modulus correlated with bacterial retention. Bacteria D41 adhered in higher numbers to rigid surfaces. For 4J6, bacterial adhesion patterns were changed: clusterings were observed on surfaces with lower elastic modulus. Furthermore, a proteomic study, based on the total soluble proteome of D41 strain, highlights an impact of elastic modulus on proteins synthesis. These data demonstrated an adapted response of adhering bacteria on hydrogels of varying mechanical properties., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Biofilms can cause severe problems in industrial paper mills, particularly of economic and technological types (clogging of filters, sheet breaks or holes in the paper, machine breakdowns, etc.). We present here some promising results on the use of essential oil compounds to control these biofilms. Biofilms were grown on stainless-steel coupons with a microbial white water consortium sampled from an industrial paper mill. Five essential oil compounds were screened initially in the laboratory in terms of their antimicrobial activity against planktonic cells and biofilms. The three most active compounds were selected and then tested in different combinations. The combination finally selected was tested at the pilot scale to confirm its efficiency under realistic conditions. All the compounds tested were as active against biofilms as they were against planktonic cells. The most active compounds were thymol, carvacrol, and eugenol, and the most efficient combination was thymol-carvacrol. At a pilot scale, with six injections a day, 10 mM carvacrol alone prevented biocontamination for at least 10 days, and a 1 mM thymol-carvacrol combination enabled a 67 % reduction in biofilm dry matter after 11 days. The use of green antimicrobials could constitute a very promising alternative or supplement to the treatments currently applied to limit biofilm formation in the environment of paper mill machines.

Antivirulence strategies targeting bacterial behavior, such as adhesion and biofilm formation, are expected to exert low selective pressure and have been proposed as alternatives to biocidal antibiotic treatments to avoid the rapid occurrence of bacterial resistance. Here, we tested this hypothesis using group 2 capsule polysaccharide (G2cps), a polysaccharidic molecule previously shown to impair bacterium-surface interactions, and we investigated the nature of bacterial resistance to a nonbiocidal antibiofilm strategy. We screened an Escherichia coli mutant library for an increased ability to form biofilm in the presence of G2cps, and we identified several mutants displaying partial but not total resistance to this antibiofilm polysaccharide. Our genetic analysis showed that partial resistance to G2cps results from multiple unrelated mutations leading to modifications in surface physicochemical properties that counteract the changes in ionic charge and Lewis base properties induced by G2cps. Moreover, some of the identified mutants harboring improved biofilm formation in the presence of G2cps were also partially resistant to other antibiofilm molecules. This study therefore shows that alterations of bacterial surface properties mediate only partial resistance to G2cps. It also experimentally validates the potential value of nonbiocidal antibiofilm strategies, since full resistance to antibiofilm compounds is rare and potentially unlikely to arise in clinical settings.

Different polymeric surfaces have been modified in order to reach a high hydrophobic character, indeed the superhydrophobicity property. For this purpose, polypropylene and polystyrene have been treated by RF or μwaves CF4 plasma with different volumes, the results were compared according to the density of injected power. The effect of pretreatment such as mechanical abrasion or plasma activation was also studied. The modified surfaces were shown as hydrophobic, or even superhydrophobic depending of defects density. They were characterized by measurement of wettability and roughness at different scales, i.e. macroscopic, mesoscopic and atomic. It has been shown that a homogeneous surface at the macroscopic scale could be heterogeneous at lower mesoscopic scale. This was associated with the crystallinity of the material. The bioadhesion tests were performed with Gram positive and negative pathogenic strains: Listeria monocytogenes, Pseudomonas aeruginosa and Hafnia alvei. They have demonstrated an antibacterial efficiency of very hydrophobic and amorphous PS treated for all strains tested and a strain-dependent efficiency with modified PP surface being very heterogeneous at the mesoscopic scale. Thus, these biological results pointed out not only the respective role of the surface chemistry and topography in bacterial adhesion, but also the dependence on the peaks and valley distribution at bacteria dimension scale., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A new rheo-optical shearing device was designed to investigate the structural evolution of complex material under shear flow. Seeking to keep the area under study constantly within the field of vision, it was conceived to produce shear flow by relying on the uniaxial translation of two parallel plates. The device features three modes of translation motion: step strain (0.02-320), constant shear rate (0.01-400 s(-1)), and oscillation (0.01-20 Hz) flow. Because the temperature is controlled by using a Peltier module coupled with a water cooling system, temperatures can range from 10 to 80 °C. The sample is loaded onto a user-friendly plate on which standard glasses can be attached with a depression vacuum pump. The principle innovation of the proposed rheo-optical shearing device lies in the fact that this suction system renders the microscopy glasses one with the plates, thereby ensuring their perfect planarity and parallelism. The gap width between the two plates can range from 0 to 5 mm. The device was designed to fit on any inverted confocal laser scanning microscope. In terms of controlled deformation, the conception and technical solutions achieve a high level of accuracy. Moreover, user-friendly software has been developed to control both shear flow parameters and temperature. The validation of specifications as well as the three modes of motion was carried out, first of all without a sample, and then by tracking fluorescent particles in a model system, in our case a micro-gel. Real values agreed well with those we targeted. In addition, an experiment with bread dough deformation under shear flow was initiated to gain some insight into the potential use of our device. These results show that the RheOptiCAD(®) promises to be a useful tool to better understand, from both a fundamental and an industrial point of view, the rheological behavior of the microstructure of complex fluids under controlled thermo-mechanical parameters in the case of food and non-food systems.

The interaction of hydrophilic and hydrophobic ovococcoid bacteria and bovine serum albumin (BSA) proteins with a well ordered surface of octadecanethiol (ODT) self assembled monolayer (SAM) has been studied in different situations where proteins were either preadsorbed on ODT or adsorbed simultaneously with bacterial adhesion as in life conditions. The two situations lead to very different antimicrobial behavior. Bacterial adhesion on preadsorbed BSA is very limited, while the simultaneous exposure of ODT SAM to proteins and bacteria lead to a markedly weaker antimicrobial effect. The combination of sum frequency generation spectroscopy and fluorescence confocal microscopy experiments allow one to draw conclusions on the factors that govern the ODT SAM or BSA film interaction with bacteria at the molecular level. On the hydrophobic ODT surface, interaction with hydrophobic or hydrophilic biomolecules results in opposite effects on the SAM, namely, a flattening or a raise of the terminal methyl groups of ODT. On an amphiphilic BSA layer, the bacterial adhesion strength is weakened by the negative charges carried by both BSA and bacteria. Surprisingly, preadsorbed BSA that cover part of the bacteria cell walls increase the adhesion strength to the BSA film and reduce hydrophobic interactions with the ODT SAM. Finally, bacterial adhesion on a BSA film is shown to modify the BSA proteins in some way that change their interaction with the ODT SAM. The antimicrobial effect is much stronger in the case of a preadsorbed BSA layer than when BSA and bacteria are in competition to colonize the ODT SAM surface.

The genome of Lactococcus lactis strain IL1403 harbors a putative pilus biogenesis cluster consisting of a sortase C gene flanked by 3 LPxTG protein encoding genes (yhgD, yhgE, and yhhB), called here pil. However, pili were not detected under standard growth conditions. Over-expression of the pil operon resulted in production and display of pili on the surface of lactococci. Functional analysis of the pilus biogenesis machinery indicated that the pilus shaft is formed by oligomers of the YhgE pilin, that the pilus cap is formed by the YhgD pilin and that YhhB is the basal pilin allowing the tethering of the pilus fibers to the cell wall. Oligomerization of pilin subunits was catalyzed by sortase C while anchoring of pili to the cell wall was mediated by sortase A. Piliated L. lactis cells exhibited an auto-aggregation phenotype in liquid cultures, which was attributed to the polymerization of major pilin, YhgE. The piliated lactococci formed thicker, more aerial biofilms compared to those produced by non-piliated bacteria. This phenotype was attributed to oligomers of YhgE. This study provides the first dissection of the pilus biogenesis machinery in a non-pathogenic Gram-positive bacterium. Analysis of natural lactococci isolates from clinical and vegetal environments showed pili production under standard growth conditions. The identification of functional pili in lactococci suggests that the changes they promote in aggregation and biofilm formation may be important for the natural lifestyle as well as for applications in which these bacteria are used.

The standard test methods used to assess the efficiency of a disinfectant applied to surfaces are often based on counting the microbial survivors sampled in a liquid, but total cell removal from surfaces is seldom achieved. One might therefore wonder whether evaluations of microbial survivors in liquid-sampled cells are representative of the levels of survivors in whole populations. The present study was thus designed to determine the "damaged/undamaged" status induced by a peracetic acid disinfection for Bacillus atrophaeus spores deposited on glass coupons directly on this substrate and to compare it to the status of spores collected in liquid by a sampling procedure. The method utilized to assess the viability of both surface-associated and liquid-sampled spores included fluorescence labeling with a combination of Syto 61 and Chemchrome V6 dyes and quantifications by analyzing the images acquired by confocal laser scanning microscopy. The principal result of the study was that the viability of spores sampled in the liquid was found to be poorer than that of surface-associated spores. For example, after 2 min of peracetic acid disinfection, less than 17% ± 5% of viable cells were detected among liquid-sampled cells compared to 79% ± 5% or 47% ± 4%, respectively, when the viability was evaluated on the surface after or without the sampling procedure. Moreover, assessments of the survivors collected in the liquid phase, evaluated using the microscopic method and standard plate counts, were well correlated. Evaluations based on the determination of survivors among the liquid-sampled cells can thus overestimate the efficiency of surface disinfection procedures.

Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials., (© 2011 American Chemical Society)

In natural, industrial and medical environments, microorganisms mainly live as structured and organised matrix-encased communities known as biofilms. In these communities, microorganisms demonstrate coordinated behaviour and are able to perform specific functions such as dramatic resistance to antimicrobials, which potentially lead to major public health and industrial problems. It is now recognised that the appearance of such specific biofilm functions is intimately related to the three-dimensional organisation of the biological edifice, and results from multifactorial processes. During the last decade, the emergence of innovative optical microscopy techniques such as confocal laser scanning microscopy in combination with fluorescent labelling has radically transformed imaging in biofilm research, giving the possibility to investigate non-invasively the dynamic mechanisms of formation and reactivity of these biostructures. In this chapter, we discuss the contribution of fluorescence analysis and imaging to the study at different timescales of various processes: biofilm development (hours to days), antimicrobial reactivity within the three-dimensional structure (minutes to hours) or molecular diffusion/reaction phenomena (pico- to milliseconds).

Aims: To evaluate the impact of the mode of contamination in relation with the nature of solid substrates on the resistance of spores of Bacillus atrophaeus -selected as surrogates of Bacillus anthracis- to a disinfectant, peracetic acid., Methods and Results: Six materials confronted in urban and military environments were selected for their different structural and physicochemical properties. In parallel, two modes of contamination were examined, i.e. deposition and immersion. Deposition was used to simulate contamination by an aerosol and immersion by an extended contact with liquids. A pronounced difference in the biocontamination levels and spatial organization of spores was observed depending on the mode of contamination and the nature of the solid substrate considered, with consequences on decontamination. Contamination by immersion led to lower efficiency of peracetic acid decontamination than contamination by deposition. Infiltration of spores into porous materials after immersion is one reason. In contrast, the deposition mode aggregates cells at the surface of materials, explaining the similar disinfecting behaviour of porous and nonporous substrates when considering this inoculation route., Conclusions: The inoculation route was shown to be as influential a parameter as material characteristics (porosity and wettability) for decontamination efficacy., Significance and Impact of the Study: These results provide comparative information for the decontamination of B. atrophaeus spores in function of the mode of contamination and the nature of solid substrates., (Journal of Applied Microbiology © 2010 The Society for Applied Microbiology. No claim to French government works.)

Electrical discharges in humid air at atmospheric pressure (nonthermal quenched plasma) generate long-lived chemical species in water that are efficient for microbial decontamination. The major role of nitrites was evidenced together with a synergistic effect of nitrates and H(2)O(2) and matching acidification. Other possible active compounds are considered, e.g., peroxynitrous acid.

The adhesion forces holding micron-sized particles to solid surfaces can be studied through the detachment forces developed by the transit of an air-liquid interface in a capillary. Two key variables affect the direction and magnitude of the capillary detachment force: (i) the thickness of the liquid film between the bubble and the capillary walls, and (ii) the effective angle of the triple phase contact between the particles and the interface. Variations in film thickness were calculated using a two-phase flow model. Film thickness was used to determine the time-variation of the capillary force during transit of the bubble. The curve for particle detachment was predicted from the calculated force. This curve proved to be non-linear and gave in situ information on the effective contact angle developing at the particle-bubble interface during detachment. This approach allowed an accurate determination of the detachment force. This theoretical approach was validated using latex particles 2 microm in diameter.

Aim: To evaluate the microbial disinfection efficacy of a plasmachemical solution obtained by the activation of water with gliding electric discharges., Methods and Results: Distilled water was activated for 5 min by a nonthermal quenched plasma of the glidarc type operating in humid air and at atmospheric pressure. The plasma-activated water (PAW) was then used to treat planktonic and adherent cells of Staphylococcus epidermidis, Leuconostoc mesenteroides (as models of Gram-positive bacteria), Hafnia alvei (a Gram-negative bacteria) and Saccharomyces cerevisiae (as a yeast model). The treatments were less efficient on adherent cells than on planktonic cells in the case of bacteria, but not of S. cerevisiae. Inactivation was more effective for bacteria than for the yeast., Conclusions: Significant reductions in microbial populations were achieved in all cases, demonstrating the effectiveness of this new approach to treat contaminated media., Significance and Impact of the Study: PAW is a promising solution with potential application to the decontamination of equipment and surfaces.

This paper describes the effects of initial microbial concentration and planktonic/adherent/detached states on the efficiency of plasma-activated water. This disinfecting solution was obtained by treating distilled water with an atmospheric pressure plasma produced by gliding electric discharges in humid air. The inactivation kinetics of planktonic cells of Hafnia alvei (selected as a bacterial model) were found to be of the first order. They were influenced by the initial microbial concentration. Efficiency decreased when the initial viable population N(0) increased, and the inactivation rate k(max) was linearly modified as a function of Log(10) (N(0)). This relation was used to compare planktonic, adherent, and detached cells independently from the level of population. Bacteria adhering to stainless steel and high-density polyethylene were also sensitive to treatment, but at a lower rate than their free-living counterparts. Moreover, cells detached from these solid substrates exhibited an inactivation rate lower than that of planktonic cells but similar to adherent bacteria. This strongly suggests the induction of a physiological modification to bacteria during the adhesion step, rendering adherent--and further detached--bacteria less susceptible to the treatment, when compared to planktonic bacteria.

Aims: To determine the efficiency of an electric discharge of the gliding arc type for the destruction of Staphylococcus epidermidis planktonic, adherent and biofilm cells., Methods and Results: Bacterial cells were treated in humid air and at atmospheric pressure by a nonthermal quenched plasma of the glidarc type. The kinetics of destruction (followed by plating) were modelled by an Add-inn for Microsoft Excel, GInaFiT. For planktonic cells, log-linear destruction was obtained, whereas biphasic kinetics were observed for sessile cells. An increased resistance of biofilm cells was observed: the reduction of 6 logarithm units of the population was obtained in 15, 30 and 70 min for planktonic, adherent and biofilm cells, respectively. The experiments also show that the cells destruction did not depend on the adhesion surface but was governed by the gap between the target and the plasma source., Conclusion: The complete destruction of planktonic, adherent and more resistant biofilm cells of Staph. epidermidis is achieved by a glidarc air plasma at atmospheric pressure., Significance and Impact of the Study: The glidarc plasma technology is a promising candidate among the emerging nonthermal techniques for decontamination, as it can destroy even biofilms that are known as particularly resistant to various antimicrobials.

Correlation between microbial surface thermodynamics using the extended DLVO (XDLVO) theory and kinetic adhesion of various bacterial cells to sand was investigated. Two experimental setups were utilized. Adhesion tests were conducted in batch reactors with slow agitation. Also, bacteria were circulated through small sand columns in a closed loop and the results were analyzed with a simple model which accounted for the rate of the adhesion phenomena (omega in h(-1)) and adhesion percentage. Cells surface properties were derived from contact angle measurements. The wicking method was utilized to characterize the sand. Zeta potentials were measured for the sand and the cells. Kinetic of bacterial retention by the porous media was largely influenced by the electrostatic interactions which are correlated with omega from the model (R(2)=0.71). Negative zeta potentials resulted in electrostatic repulsions occurring between the sand and the bacterial cells which in result delayed bacterial adhesion. While no correlation was found between the adhesion percentage and the total interaction energy calculated with the XDLVO theory the respective behavior of hydrophobic and hydrophilic bacteria as well as the importance of electrostatic interactions was evidenced. All the bacterial strains studied adhered more in the column experiments than in the adhesion tests, presumably due to enhanced collision efficiency and wedging in porous media, while filtration could be ignored except for the larger Bacillus strains. Approximate XDLVO calculations due to solid surface nanoscale roughness, retention in a secondary minimum and population heterogeneity are discussed. Our results obtained with a large variety of different physicochemical bacterial strains highlights the influence of both surface thermodynamics and porous media related effects as well as the limits of using the XDLVO theory for evaluating bacterial retention through porous media.

This study aimed to characterize the bacterium-destroying properties of a gliding arc plasma device during electric discharges and also under temporal postdischarge conditions (i.e., when the discharge was switched off). This phenomenon was reported for the first time in the literature in the case of the plasma destruction of microorganisms. When cells of a model bacterium, Hafnia alvei, were exposed to electric discharges, followed or not followed by temporal postdischarges, the survival curves exhibited a shoulder and then log-linear decay. These destruction kinetics were modeled using GinaFiT, a freeware tool to assess microbial survival curves, and adjustment parameters were determined. The efficiency of postdischarge treatments was clearly affected by the discharge time (t*); both the shoulder length and the inactivation rate k(max) were linearly modified as a function of t*. Nevertheless, all conditions tested (t* ranging from 2 to 5 min) made it possible to achieve an abatement of at least 7 decimal logarithm units. Postdischarge treatment was also efficient against bacteria not subjected to direct discharge, and the disinfecting properties of "plasma-activated water" were dependent on the treatment time for the solution. Water treated with plasma for 2 min achieved a 3.7-decimal-logarithm-unit reduction in 20 min after application to cells, and abatement greater than 7 decimal logarithm units resulted from the same contact time with water activated with plasma for 10 min. These disinfecting properties were maintained during storage of activated water for 30 min. After that, they declined as the storage time increased.

The ability of adsorbed biosurfactants (Pf and Lb) obtained from gram-negative bacterium (Pseudomonas fluorescens) or gram-positive bacterium (Lactobacillus helveticus) to inhibit adhesion of four listerial strains to stainless steel was investigated. These metallic surfaces were characterized using the following complementary analytical techniques: contact-angle measurements (CAM), atomic force microscopy (AFM), polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). Contact-angles with polar liquids (water and formamide) indicated that the stainless steel surface covered with adsorbed biosurfactant was more hydrophilic and electron-donating than bare stainless steel. The surface characterization by XPS and PM-IRRAS revealed that conditioning the stainless steel changes the substrate in two ways, by modifying the surface alloy composition and by leaving an thin adsorbed organic layer. AFM observations enabled to say that the layer covered entirely the surface and was probably thicker (with patches) in the case of Pf-conditioned surfaces compared to the Lb-conditioned ones, which seemed to be less homogeneous. Though the added layer was thin, significant chemical changes were observed that can account for drastic modifications in the surface adhesive properties. As a matter of fact, adhesion tests showed that both used biosurfactants were effective by decreasing strongly the level of contamination of stainless steel surfaces by the four strains of Listeria monocytogenes. The more important decrease concerned the CIP104794 and CIP103573 strains (>99.7%) on surface conditioned by L. helveticus biosurfactant. A less reduced phenomenon (75.2%) for the CIP103574 strain on stainless steel with absorbed biosurfactant from P. fluorescens was observed. Whatever the strain of L. monocytogenes and the biosurfactant used, this antiadhesive biologic coating reduced both total adhering flora and viable and cultivable adherent bacteria on stainless steel surfaces. This study confirms that biosurfactants constitute an effective strategy to prevent microbial colonization of metallic surfaces by pathogenic bacteria like the food-borne pathogen L. monocytogenes.

Immunosensors, based on the immobilization of a model rabbit antibody on mixed self-assembled monolayers and Protein A as a linking agent on gold transducers, were elaborated and characterized at each step by modulated polarization-infrared spectroscopy (PM-IRRAS) and occasionally by atomic force microscopy (AFM) and quartz crystal microbalance (QCM). By testing two different mixed SAMs comprising 11-mercaptoundecanoic acid (MUA), together with either decanethiol (C9CH3) or mercaptohexanol (C6OH), the role of the chemical composition and structure of the antibody attachment layer upon the sensor performance was demonstrated.

As an alternative to the use of chemicals for cleaning and disinfecting surfaces of equipment in food industry, the efficacy of pulsed laser beams for removal and killing of adherent bacteria from stainless steel surfaces was assessed. Escherichia coli biofilms were produced under dynamic conditions in diluted nutritive medium incubated at 37 degrees C for 24 h. Influence of energy density and number of shots were tested at three wavelengths (1064, 532 and 355 nm). With one 20 ns pulse, results range from 3.5 decimal reductions of the microbial load with < or = 50 MW cm-2 without visible alteration of the surface, to more than 6 decimal reductions with < or = 600 MW cm-2. The measured effect was largely attributed to removal of the micro-organisms and transfer to the surrounding air. The treatment could therefore be improved with respect to the numbers remaining associated with the surface by venting.