Romain Briandet - Academia.edu (original) (raw)

Papers by Romain Briandet

Frontiers in Microbiology

Biopreservation is a sustainable approach to improve food safety and maintain or extend food shel... more Biopreservation is a sustainable approach to improve food safety and maintain or extend food shelf life by using beneficial microorganisms or their metabolites. Over the past 20 years, omics techniques have revolutionised food microbiology including biopreservation. A range of methods including genomics, transcriptomics, proteomics, metabolomics and meta-omics derivatives have highlighted the potential of biopreservation to improve the microbial safety of various foods. This review shows how these approaches have contributed to the selection of biopreservation agents, to a better understanding of the mechanisms of action and of their efficiency and impact within the food ecosystem. It also presents the potential of combining omics with complementary approaches to take into account better the complexity of food microbiomes at multiple scales, from the cell to the community levels, and their spatial, physicochemical and microbiological heterogeneity. The latest advances in biopreserva...

Food Microbiology, 2022

The spatial organisation of bacterial pathogens in food matrices remains poorly understood, but i... more The spatial organisation of bacterial pathogens in food matrices remains poorly understood, but is important in improving risk assessment and preventing infection of consumers by contaminated foodstuff. By combining confocal laser scanning microscopy with genetic fluorescent labelling of Listeria monocytogenes and Escherichia coli O157:H7, it was possible to investigate the spatial patterns of colonisation of both foodborne pathogens in gel matrices, alone or in combination, in various environmental conditions. Increasing low melting point agarose (LMPA) concentrations triggers the transition between a motile single-cell lifestyle to a sessile population spatially organised as microcolonies. The size, number and morphology of microcolonies were highly affected by supplementations in NaCl or lactic acid, two compounds frequently used in food products. Strikingly, single-cell motility was partially restored at higher LMPA concentration in the presence of lactic acid for Escherichia coli O157:H7 and in the presence of NaCl for Listeria monocytogenes. Co-culture of both species in the hydrogel affected pathogen colonisation features; Listeria monocytogenes was better able to colonise gel matrices containing lactic acid in the presence of Escherichia coli O157:H7. Altogether, this investigation provides insights into the spatial distribution and structural dynamics of bacterial pathogens in gel matrices. Potential impacts on food safety are discussed.

Bacteroides thetaiotaomicron is a gut symbiont that inhabits the mucus layer and adheres to and m... more Bacteroides thetaiotaomicron is a gut symbiont that inhabits the mucus layer and adheres to and metabolizes food particles, contributing to gut physiology and maturation. Whereas adhesion and biofilm formation could be key features for B. thetaiotaomicron stress resistance and gut colonization, little is known about the determinants of B. thetaiotaomicron biofilm formation. We previously showed that the B. thetaiotaomicron reference strain VPI-5482 is a poor in vitro biofilm former. Here we demonstrated that bile, a gut-relevant environmental cue, triggers the formation of biofilm in many B. thetaiotaomicron isolates and common gut Bacteroidales species. We identified the genetic determinants of this bile-dependent biofilm formation and showed that it involves the production of the DNase BT3563, degrading extracellular DNA, in biofilms formed in the presence of bile. Our study therefore identifies a physiologically relevant condition inducing B. thetaiotaomicron biofilm and shows th...

Applied and Environmental Microbiology, 1999

We determined the variations in the surface physicochemical properties of Listeria monocytogenes ... more 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 o...

Frontiers in Microbiology, 2019

Pseudomonas aeruginosa is an environmental bacterium and a nosocomial pathogen with clone C one o... more Pseudomonas aeruginosa is an environmental bacterium and a nosocomial pathogen with clone C one of the most prevalent clonal groups. The P. aeruginosa clone C specific genomic island PACGI-1 harbors a xenolog of ftsH encoding a functionally diverse membrane-spanning ATP-dependent metalloprotease on the core genome. In the aquatic isolate P. aeruginosa SG17M, the core genome copy ftsH1 significantly affects growth and dominantly mediates a broad range of phenotypes, such as secretion of secondary metabolites, swimming and twitching motility and resistance to aminoglycosides, while the PACGI-1 xenolog ftsH2 backs up the phenotypes in the ftsH1 mutant background. The two proteins, with conserved motifs for disaggregase and protease activity present in FtsH1 and FtsH2, have the ability to form homo-and hetero-oligomers with ftsH2 distinctively expressed in the late stationary phase of growth. However, mainly FtsH1 degrades a major substrate, the heat shock transcription factor RpoH. Pull-down experiments with substrate trap-variants inactive in proteolytic activity indicate both FtsH1 and FtsH2 to interact with the inhibitory protein HflC, while the phenazine biosynthesis protein PhzC was identified as a substrate of FtsH1. In summary, as an exception in P. aeruginosa, clone C harbors two copies of the ftsH metallo-protease, which cumulatively are required for the expression of a diversity of phenotypes.

International Journal of Food Microbiology, 2018

This work investigated the effects of diamond-like carbon (DLC) coatings on the architecture and ... more This work investigated the effects of diamond-like carbon (DLC) coatings on the architecture and biocide reactivity of dual-species biofilms mimicking food processing contaminants. Biofilms were grown using industrial isolates of Escherichia coli and Pantoea agglomerans on bare stainless steel (SST) and on two DLC surface coatings (a-C:H:Si:O designated by SICON® and a-C:H:Si designated by SICAN) in order to evaluate their antifouling activities. Quantification and spatial organization in single- and dual-species biofilms were examined by confocal laser scanning microscopy (CLSM) using a strain specific labelling procedure. Those assays revealed that the E. coli isolate exhibited a higher adhesion to the modified surfaces and a decreased susceptibility to disinfectant in presence of P. agglomerans than alone in axenic culture. While SICON® reduced the short-term growth of E. coli in axenic conditions, both DLC surfaces increased the E. coli colonization in presence of P. agglomerans. However, both modified surfaces triggered a significantly higher log reduction of E. coli cells within mixed-species biofilms, thus the use of SICON® and SICAN surfaces may be a good approach to facilitate the disinfection process in critical areas of food processing plants. This study presents a new illustration of the importance of interspecies interactions in surface-associated community functions, and of the need to evaluate the effectiveness of hygienic strategies with relevant multi-species consortia.

Molecules, 2019

Acinetobacter baumannii is a nosocomial human pathogen of increasing concern due to its multidrug... more Acinetobacter baumannii is a nosocomial human pathogen of increasing concern due to its multidrug resistance profile. The outer membrane protein A (OmpA) is an abundant bacterial cell surface component involved in A. baumannii pathogenesis. It has been shown that the C-terminal domain of OmpA is located in the periplasm and non-covalently associates with the peptidoglycan layer via two conserved amino acids, thereby anchoring OmpA to the cell wall. Here, we investigated the role of one of the respective residues, D268 in OmpA of A. baumannii clinical strain Ab169, on its virulence characteristics by complementing the ΔompA mutant with the plasmid-borne ompAD268A allele. We show that while restoring the impaired biofilm formation of the ΔompA strain, the Ab169ompAD268A mutant tended to form bacterial filaments, indicating the abnormalities in cell division. Moreover, the Ab169 OmpA D268-mediated association to peptidoglycan was required for the manifestation of twitching motility, de...

Journal of Food Protection, 2004

Although liquid egg white may be subjected to limited heat treatment when it is used in the fabri... more Although liquid egg white may be subjected to limited heat treatment when it is used in the fabrication of various foodstuffs, pathogenic bacteria such Salmonella Enteritidis could persist in this environment. Liquid egg white is not a favorable medium for Salmonella growth because of its alkaline pH and iron deficiency and the presence of ovotransferrin. Microorganisms adapted to a nonfavorable environment are often more resistant to stresses than are their laboratory-cultured counterparts. The objective of this study was to determine whether Salmonella exposed to an environment mimicking egg white conditions exhibited modified behavior that could have an impact on food safety. A medium resembling egg white (filtrate of egg white with added ovotransferrin) was used as an adaptation treatment to mimic the stress imparted by the egg white environment. There were no changes in resistance to heat and disinfection, in stainless steel adhesion, or in the virulence of Salmonella Enteritid...

Journal of Food Protection, 2002

Growth kinetics and physicochemical surface properties were compared for three Listeria strains w... more Growth kinetics and physicochemical surface properties were compared for three Listeria strains with differing degrees of virulence: L. monocytogenes LO28; its isogenic, nonhemolytic mutant L. monocytogenes Bof415; and a nonvirulent species, L. innocua (strain Lin9). The influences of growth stage (mid-exponential phase, early stationary phase, and mid-stationary phase) and culture temperature (20 and 37°C) were assessed by determining the electrical properties and the hydrophobic-hydrophilic and Lewis acid-base characteristics of the three strains. L. innocua, although taxonomically very similar to L. monocytogenes, exhibited physicochemical surface properties that differed significantly from those of L. monocytogenes LO28 and L. monocytogenes Bof415. Indeed, under our experimental conditions, L. innocua cells presented a more marked electro-negative character (particularly when cultured at 20°C), as well as greater variability in their Lewis acid-base characteristics as a function...

Techniques Hospitalieres, 1999

Procedia Environmental Sciences, 2015

The biofilm ubiquitously exists on most wet surfaces. It is a protective shield of the bacteria a... more The biofilm ubiquitously exists on most wet surfaces. It is a protective shield of the bacteria and causes the difficulty in the disinfection. The irrigation of the biofilm by the specific swimmer bacteria can exacerbate killing of biofilm bacteria. Therefore, we precisely investigate the tunneling of swimmers bacteria within biofilms. These bacterial stealth swimmers create transient opened spaces in the biofilm. We found that these opened spaced in the biofilm is the obvious indication of the motion of the swimmers. We exploit both detected swimmer in one swimmer channel and the opened space in the other biofilm channel of confocal microscope video, in order to interactively improve the tracking of the swimmer's motion in the biofilm, which is implemented by improving a successful algorithm of single particle tracking. Moreover, we quantitatively study the swimmer trajectory, the opened space and their relation in the large-scale microscope video when the biofilm is separately irrigated by many different species of bacteria. We try to discover the influence of the irrigated bacteria on the biofilm.

Clinical and Biomedical Spectroscopy and Imaging II, 2011

The diffusion capabilities of free fluorophores inside the heterogeneous three dimensional struct... more The diffusion capabilities of free fluorophores inside the heterogeneous three dimensional structure of Staphylococcus aureus biofilm were studied by an original image-based Fluorescence Recovery After Photobleaching method. The study was extended to BODIPY-vancomycin in order to better understand the mechanisms involved in the high tolerance of the bacteria embedded in a biofilm to the antibiotic.

Spectroscopy: An International Journal, 2012

In biomedical and food industry, surface colonization by bacteria is harmful: it leads to biofilm... more In biomedical and food industry, surface colonization by bacteria is harmful: it leads to biofilm formation, a microbial consortia more resistant to antibiotics than planktonic bacteria. In order to design materials able to limit the biofilm formation, the effect of bacteria on materials has to be well characterized. In this work, a well-defined surface composed of a self-assembled monolayer (SAM) of octadecanethiol (ODT) onto a gold surface is probedin situ. The SAM conformation is obtained using the femtosecond vibrational sum frequency generation (SFG) spectroscopy. This technique provides selectively the molecular vibrational signature of the interface. The behaviour of the ODT SAM is studied in different environments: in air, in water, and upon exposure to hydrophilic or hydrophobicLactococcus lactisbacteria. Modelling the experimental SFG spectra reveals a measurable change of the SAM conformation which depends on the environment, especially on the hydrophilic-hydrophobic char...

Cellular Microbiology, 2014

The predominant form of life for microorganisms in their natural habitats is the biofilm mode of ... more The predominant form of life for microorganisms in their natural habitats is the biofilm mode of growth. The adherence and colonization of probiotic bacteria are considered as essential factors for their immunoregulatory function in the host. Here, we show that Lactobacillus casei ATCC334 adheres to and colonizes the gut of zebrafish larvae. The abundance of pro-inflammatory cytokines and the recruitment of macrophages were low when inflammation was induced in probiotic-fed animals, suggesting that these bacteria have anti-inflammatory properties. We treated human macrophage-differentiated monocytic THP-1 cells with supernatants of L. casei ATCC334 grown in either biofilm or planktonic cultures. TNF-α production was suppressed and the NF-κB pathway was inhibited only in the presence of supernatants from biofilms. We identified GroEL as the biofilm supernatant compound responsible, at least partially, for this anti-inflammatory effect. Gradual immunodepletion of GroEL demonstrated that the abundance of GroEL and TNF-α were inversely correlated. We confirmed that biofilm development in other Lactobacillus species affects the immune response. The biofilms supernatants of these species also contained large amounts of GroEL. Thus, our results demonstrate that the biofilm enhances the immunomodulatory effects of Lactobacillus sp. and that secreted GroEL is involved in this beneficial effect.

Advances in experimental medicine and biology, 2011

In natural, industrial and medical environments, microorganisms mainly live as structured and org... more 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 fluorescenc...

Molecular Microbiology, 2011

LeuO, the regulator of leucine biosynthesis operon of Escherichia coli, is involved in the regula... more LeuO, the regulator of leucine biosynthesis operon of Escherichia coli, is involved in the regulation of as yet unspecified genes affecting the stress response and pathogenesis expression. To get insights into the regulatory role(s) of LeuO, Genomic SELEX screening has been performed to identify the whole set of its regulation targets. A total of 140 LeuO-binding sites were identified on the E. coli genome, of which as many as 133 (95%) were found to contain the binding sites of H-NS, the universal silencer of stressresponse genes, supporting the concept that LeuO plays an antagonistic role with anti-silencing activity. Western blot analysis indicated that H-NS predominates in growing phase; however, after prolonged culture for 1 week, H-NS decreased instead LeuO increased, supporting the anti-silencing role of LeuO. In concert with this model, a set of stress-response genes including cryptic chaperone/usher-type fimbriae operons are under the control of antagonistic interplay between LeuO and H-NS. Confocal laser scanning microscopic observation in flow-chambers showed that the mutants lacking leuO and some fimbriae genes are defective in biofilm formation or form altered biofilm architecture. Taken together we propose that LeuO is a major player in antagonistic interplay against the universal silencer H-NS.

Environmental Microbiology, 2013

SummaryListeria monocytogenes has a dichotomous lifestyle, existing as an ubiquitous saprophytic ... more SummaryListeria monocytogenes has a dichotomous lifestyle, existing as an ubiquitous saprophytic species and as an opportunistic intracellular pathogen. Besides its capacity to grow in a wide range of environmental and stressful conditions, L. monocytogenes has the ability to adhere to and colonize surfaces. Morphotype variation to elongated cells forming rough colonies has been reported for different clinical and environmental isolates, including biofilms. This cell differentiation is mainly attributed to the reduced secretion of two SecA2‐dependent cell‐wall hydrolases, CwhA and MurA. SecA2 is a non‐essential SecA paralogue forming an alternative translocase with the primary Sec translocon. Following investigation at temperatures relevant to its ecological niches, i.e. infection (37°C) and environmental (20°C) conditions, inactivation of this SecA2‐only protein export pathway led, despite reduced adhesion, to the formation of filamentous biofilm with aerial structures. Compared to...

Le Lait, 1995

Nineteen bacteriophages infecting P freudenreichii have been isolated from 32 Swisstype cheeses. ... more Nineteen bacteriophages infecting P freudenreichii have been isolated from 32 Swisstype cheeses. They ail present a similar morphology and belong to the B1 group of Bradley's classification. According to their restriction patterns, obtained with the endonuclease Ps~, they can be grouped into 3 clusters, 1 of which contains the majority of the phages. Sixteen of the 32 cheeses studied were infected with bacteriophages. We observed that ail the cheeses made from raw milk and ripened in a warm curing room for several weeks which are known to contain high concentrations of propionibacteria, were infected with bacteriophages. Moreover, the multiplication of bacteriophages occurred in cheese during the multiplication stage of propionibacteria in a warm curing room. We have shown that raw milk contains bacteriophages and thus it can be a source of phages in factories. However, these bacteriophages are sensitive to the milk heat treatment used for cheesemaking. bacteriophage 1 Propionibacterium 1Swiss-type cheese Résumé-Bactériophages infectant les bactéries propioniques laitières. Dix-neuf bactériophages actifs sur P freudenreichii ont été isolés à partir de 32 fromages à pâte pressée cuite. Leur morphologie est similaire et permet de les classer dans le groupe B1 de la classification de Bradley. L'étude du profil de restriction de leur chromosome obtenu avec l'endonucléase Pstl a permis de les classer en 3 groupes, dont un en rassemble la grande majorité. Seize fromages parmi les 32 étudiés étaient contaminés par des bactériophages. Nous avons remarqué que tous les fromages faits avec du lait cru, affinés en cave chaude et qui par conséquent montrent une haute concentration en bactéries propionlaues, contenaient des bactériophages. De plus, la multiplication de ceux-ci se produisait parallèlement à celle des bactéries lors de l'affinage. Nous avons aussi montré que le lait cru pouvait véhiculer des bactériophages et donc constituer une voie d'entrée des phages dans les usines. Ces phages sont cependant sensibles aux traitements thermiques appliqués au lait avant la fabrication fromagère. bactériophage IPropionibacterium Ifromage à pâte pressée cuite

Biofouling, 2003

The development of antifouling strategies in seawater requires knowledge of the physico-chemical ... more The development of antifouling strategies in seawater requires knowledge of the physico-chemical properties of the cell surfaces of early adherent bacteria. The hydrophilic, electrostatic and the Lewis acid-base cell surface properties of eleven marine bacteria were characterized. Although these bacteria adhered to a hydrophilic support immersed for 3 and 6 h, they presented various physico-chemical properties. Eleven strains possessed a hydrophilic surface and five a hydrophobic surface. Although the majority of the bacteria presented an electron-donating character, some could not generate Lewis acid-base interactions with the support. On the other hand, all strains possessed an isoelectric point ranging from 2.2 to 3.4 and were negatively charged at the pH of seawater. Hydrophilicity was a preponderant property among these bacteria, but other properties should not be ignored. The development of new antifouling paints must take account all the possible interaction levels used by the bacteria to adhere to an immersed surface.

Frontiers in Microbiology

In the One Health concept, the use of beneficial bacteria to form positive biofilms that prevent ... more In the One Health concept, the use of beneficial bacteria to form positive biofilms that prevent the settlement of undesirable bacteria is a promising solution to limit the use of antimicrobials on farms. However, there is a lack of field studies reporting the onset of these beneficial bacteria after application and the effects on autochthonous surface microbiota. In the study reported here, the inner surfaces of commercial broiler chicken houses were treated or not with a bacterial consortium composed of Bacillus spp. and Pediococcus spp. strains, able to form covering biofilms in different laboratory models. Preinstalled coupons were sampled over time to capture microbial biofilm dynamics on-farm surfaces. The results showed that the bacterial consortium can establish on the farm surfaces, modulate microbial communities, and limit the implantation of Enterobacteriaceae and Enterococcaceae, two families containing potential pathogens.

Frontiers in Microbiology

Biopreservation is a sustainable approach to improve food safety and maintain or extend food shel... more Biopreservation is a sustainable approach to improve food safety and maintain or extend food shelf life by using beneficial microorganisms or their metabolites. Over the past 20 years, omics techniques have revolutionised food microbiology including biopreservation. A range of methods including genomics, transcriptomics, proteomics, metabolomics and meta-omics derivatives have highlighted the potential of biopreservation to improve the microbial safety of various foods. This review shows how these approaches have contributed to the selection of biopreservation agents, to a better understanding of the mechanisms of action and of their efficiency and impact within the food ecosystem. It also presents the potential of combining omics with complementary approaches to take into account better the complexity of food microbiomes at multiple scales, from the cell to the community levels, and their spatial, physicochemical and microbiological heterogeneity. The latest advances in biopreserva...

Food Microbiology, 2022

The spatial organisation of bacterial pathogens in food matrices remains poorly understood, but i... more The spatial organisation of bacterial pathogens in food matrices remains poorly understood, but is important in improving risk assessment and preventing infection of consumers by contaminated foodstuff. By combining confocal laser scanning microscopy with genetic fluorescent labelling of Listeria monocytogenes and Escherichia coli O157:H7, it was possible to investigate the spatial patterns of colonisation of both foodborne pathogens in gel matrices, alone or in combination, in various environmental conditions. Increasing low melting point agarose (LMPA) concentrations triggers the transition between a motile single-cell lifestyle to a sessile population spatially organised as microcolonies. The size, number and morphology of microcolonies were highly affected by supplementations in NaCl or lactic acid, two compounds frequently used in food products. Strikingly, single-cell motility was partially restored at higher LMPA concentration in the presence of lactic acid for Escherichia coli O157:H7 and in the presence of NaCl for Listeria monocytogenes. Co-culture of both species in the hydrogel affected pathogen colonisation features; Listeria monocytogenes was better able to colonise gel matrices containing lactic acid in the presence of Escherichia coli O157:H7. Altogether, this investigation provides insights into the spatial distribution and structural dynamics of bacterial pathogens in gel matrices. Potential impacts on food safety are discussed.

Bacteroides thetaiotaomicron is a gut symbiont that inhabits the mucus layer and adheres to and m... more Bacteroides thetaiotaomicron is a gut symbiont that inhabits the mucus layer and adheres to and metabolizes food particles, contributing to gut physiology and maturation. Whereas adhesion and biofilm formation could be key features for B. thetaiotaomicron stress resistance and gut colonization, little is known about the determinants of B. thetaiotaomicron biofilm formation. We previously showed that the B. thetaiotaomicron reference strain VPI-5482 is a poor in vitro biofilm former. Here we demonstrated that bile, a gut-relevant environmental cue, triggers the formation of biofilm in many B. thetaiotaomicron isolates and common gut Bacteroidales species. We identified the genetic determinants of this bile-dependent biofilm formation and showed that it involves the production of the DNase BT3563, degrading extracellular DNA, in biofilms formed in the presence of bile. Our study therefore identifies a physiologically relevant condition inducing B. thetaiotaomicron biofilm and shows th...

Applied and Environmental Microbiology, 1999

We determined the variations in the surface physicochemical properties of Listeria monocytogenes ... more 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 o...

Frontiers in Microbiology, 2019

Pseudomonas aeruginosa is an environmental bacterium and a nosocomial pathogen with clone C one o... more Pseudomonas aeruginosa is an environmental bacterium and a nosocomial pathogen with clone C one of the most prevalent clonal groups. The P. aeruginosa clone C specific genomic island PACGI-1 harbors a xenolog of ftsH encoding a functionally diverse membrane-spanning ATP-dependent metalloprotease on the core genome. In the aquatic isolate P. aeruginosa SG17M, the core genome copy ftsH1 significantly affects growth and dominantly mediates a broad range of phenotypes, such as secretion of secondary metabolites, swimming and twitching motility and resistance to aminoglycosides, while the PACGI-1 xenolog ftsH2 backs up the phenotypes in the ftsH1 mutant background. The two proteins, with conserved motifs for disaggregase and protease activity present in FtsH1 and FtsH2, have the ability to form homo-and hetero-oligomers with ftsH2 distinctively expressed in the late stationary phase of growth. However, mainly FtsH1 degrades a major substrate, the heat shock transcription factor RpoH. Pull-down experiments with substrate trap-variants inactive in proteolytic activity indicate both FtsH1 and FtsH2 to interact with the inhibitory protein HflC, while the phenazine biosynthesis protein PhzC was identified as a substrate of FtsH1. In summary, as an exception in P. aeruginosa, clone C harbors two copies of the ftsH metallo-protease, which cumulatively are required for the expression of a diversity of phenotypes.

International Journal of Food Microbiology, 2018

This work investigated the effects of diamond-like carbon (DLC) coatings on the architecture and ... more This work investigated the effects of diamond-like carbon (DLC) coatings on the architecture and biocide reactivity of dual-species biofilms mimicking food processing contaminants. Biofilms were grown using industrial isolates of Escherichia coli and Pantoea agglomerans on bare stainless steel (SST) and on two DLC surface coatings (a-C:H:Si:O designated by SICON® and a-C:H:Si designated by SICAN) in order to evaluate their antifouling activities. Quantification and spatial organization in single- and dual-species biofilms were examined by confocal laser scanning microscopy (CLSM) using a strain specific labelling procedure. Those assays revealed that the E. coli isolate exhibited a higher adhesion to the modified surfaces and a decreased susceptibility to disinfectant in presence of P. agglomerans than alone in axenic culture. While SICON® reduced the short-term growth of E. coli in axenic conditions, both DLC surfaces increased the E. coli colonization in presence of P. agglomerans. However, both modified surfaces triggered a significantly higher log reduction of E. coli cells within mixed-species biofilms, thus the use of SICON® and SICAN surfaces may be a good approach to facilitate the disinfection process in critical areas of food processing plants. This study presents a new illustration of the importance of interspecies interactions in surface-associated community functions, and of the need to evaluate the effectiveness of hygienic strategies with relevant multi-species consortia.

Molecules, 2019

Acinetobacter baumannii is a nosocomial human pathogen of increasing concern due to its multidrug... more Acinetobacter baumannii is a nosocomial human pathogen of increasing concern due to its multidrug resistance profile. The outer membrane protein A (OmpA) is an abundant bacterial cell surface component involved in A. baumannii pathogenesis. It has been shown that the C-terminal domain of OmpA is located in the periplasm and non-covalently associates with the peptidoglycan layer via two conserved amino acids, thereby anchoring OmpA to the cell wall. Here, we investigated the role of one of the respective residues, D268 in OmpA of A. baumannii clinical strain Ab169, on its virulence characteristics by complementing the ΔompA mutant with the plasmid-borne ompAD268A allele. We show that while restoring the impaired biofilm formation of the ΔompA strain, the Ab169ompAD268A mutant tended to form bacterial filaments, indicating the abnormalities in cell division. Moreover, the Ab169 OmpA D268-mediated association to peptidoglycan was required for the manifestation of twitching motility, de...

Journal of Food Protection, 2004

Although liquid egg white may be subjected to limited heat treatment when it is used in the fabri... more Although liquid egg white may be subjected to limited heat treatment when it is used in the fabrication of various foodstuffs, pathogenic bacteria such Salmonella Enteritidis could persist in this environment. Liquid egg white is not a favorable medium for Salmonella growth because of its alkaline pH and iron deficiency and the presence of ovotransferrin. Microorganisms adapted to a nonfavorable environment are often more resistant to stresses than are their laboratory-cultured counterparts. The objective of this study was to determine whether Salmonella exposed to an environment mimicking egg white conditions exhibited modified behavior that could have an impact on food safety. A medium resembling egg white (filtrate of egg white with added ovotransferrin) was used as an adaptation treatment to mimic the stress imparted by the egg white environment. There were no changes in resistance to heat and disinfection, in stainless steel adhesion, or in the virulence of Salmonella Enteritid...

Journal of Food Protection, 2002

Growth kinetics and physicochemical surface properties were compared for three Listeria strains w... more Growth kinetics and physicochemical surface properties were compared for three Listeria strains with differing degrees of virulence: L. monocytogenes LO28; its isogenic, nonhemolytic mutant L. monocytogenes Bof415; and a nonvirulent species, L. innocua (strain Lin9). The influences of growth stage (mid-exponential phase, early stationary phase, and mid-stationary phase) and culture temperature (20 and 37°C) were assessed by determining the electrical properties and the hydrophobic-hydrophilic and Lewis acid-base characteristics of the three strains. L. innocua, although taxonomically very similar to L. monocytogenes, exhibited physicochemical surface properties that differed significantly from those of L. monocytogenes LO28 and L. monocytogenes Bof415. Indeed, under our experimental conditions, L. innocua cells presented a more marked electro-negative character (particularly when cultured at 20°C), as well as greater variability in their Lewis acid-base characteristics as a function...

Techniques Hospitalieres, 1999

Procedia Environmental Sciences, 2015

The biofilm ubiquitously exists on most wet surfaces. It is a protective shield of the bacteria a... more The biofilm ubiquitously exists on most wet surfaces. It is a protective shield of the bacteria and causes the difficulty in the disinfection. The irrigation of the biofilm by the specific swimmer bacteria can exacerbate killing of biofilm bacteria. Therefore, we precisely investigate the tunneling of swimmers bacteria within biofilms. These bacterial stealth swimmers create transient opened spaces in the biofilm. We found that these opened spaced in the biofilm is the obvious indication of the motion of the swimmers. We exploit both detected swimmer in one swimmer channel and the opened space in the other biofilm channel of confocal microscope video, in order to interactively improve the tracking of the swimmer's motion in the biofilm, which is implemented by improving a successful algorithm of single particle tracking. Moreover, we quantitatively study the swimmer trajectory, the opened space and their relation in the large-scale microscope video when the biofilm is separately irrigated by many different species of bacteria. We try to discover the influence of the irrigated bacteria on the biofilm.

Clinical and Biomedical Spectroscopy and Imaging II, 2011

The diffusion capabilities of free fluorophores inside the heterogeneous three dimensional struct... more The diffusion capabilities of free fluorophores inside the heterogeneous three dimensional structure of Staphylococcus aureus biofilm were studied by an original image-based Fluorescence Recovery After Photobleaching method. The study was extended to BODIPY-vancomycin in order to better understand the mechanisms involved in the high tolerance of the bacteria embedded in a biofilm to the antibiotic.

Spectroscopy: An International Journal, 2012

In biomedical and food industry, surface colonization by bacteria is harmful: it leads to biofilm... more In biomedical and food industry, surface colonization by bacteria is harmful: it leads to biofilm formation, a microbial consortia more resistant to antibiotics than planktonic bacteria. In order to design materials able to limit the biofilm formation, the effect of bacteria on materials has to be well characterized. In this work, a well-defined surface composed of a self-assembled monolayer (SAM) of octadecanethiol (ODT) onto a gold surface is probedin situ. The SAM conformation is obtained using the femtosecond vibrational sum frequency generation (SFG) spectroscopy. This technique provides selectively the molecular vibrational signature of the interface. The behaviour of the ODT SAM is studied in different environments: in air, in water, and upon exposure to hydrophilic or hydrophobicLactococcus lactisbacteria. Modelling the experimental SFG spectra reveals a measurable change of the SAM conformation which depends on the environment, especially on the hydrophilic-hydrophobic char...

Cellular Microbiology, 2014

The predominant form of life for microorganisms in their natural habitats is the biofilm mode of ... more The predominant form of life for microorganisms in their natural habitats is the biofilm mode of growth. The adherence and colonization of probiotic bacteria are considered as essential factors for their immunoregulatory function in the host. Here, we show that Lactobacillus casei ATCC334 adheres to and colonizes the gut of zebrafish larvae. The abundance of pro-inflammatory cytokines and the recruitment of macrophages were low when inflammation was induced in probiotic-fed animals, suggesting that these bacteria have anti-inflammatory properties. We treated human macrophage-differentiated monocytic THP-1 cells with supernatants of L. casei ATCC334 grown in either biofilm or planktonic cultures. TNF-α production was suppressed and the NF-κB pathway was inhibited only in the presence of supernatants from biofilms. We identified GroEL as the biofilm supernatant compound responsible, at least partially, for this anti-inflammatory effect. Gradual immunodepletion of GroEL demonstrated that the abundance of GroEL and TNF-α were inversely correlated. We confirmed that biofilm development in other Lactobacillus species affects the immune response. The biofilms supernatants of these species also contained large amounts of GroEL. Thus, our results demonstrate that the biofilm enhances the immunomodulatory effects of Lactobacillus sp. and that secreted GroEL is involved in this beneficial effect.

Advances in experimental medicine and biology, 2011

In natural, industrial and medical environments, microorganisms mainly live as structured and org... more 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 fluorescenc...

Molecular Microbiology, 2011

LeuO, the regulator of leucine biosynthesis operon of Escherichia coli, is involved in the regula... more LeuO, the regulator of leucine biosynthesis operon of Escherichia coli, is involved in the regulation of as yet unspecified genes affecting the stress response and pathogenesis expression. To get insights into the regulatory role(s) of LeuO, Genomic SELEX screening has been performed to identify the whole set of its regulation targets. A total of 140 LeuO-binding sites were identified on the E. coli genome, of which as many as 133 (95%) were found to contain the binding sites of H-NS, the universal silencer of stressresponse genes, supporting the concept that LeuO plays an antagonistic role with anti-silencing activity. Western blot analysis indicated that H-NS predominates in growing phase; however, after prolonged culture for 1 week, H-NS decreased instead LeuO increased, supporting the anti-silencing role of LeuO. In concert with this model, a set of stress-response genes including cryptic chaperone/usher-type fimbriae operons are under the control of antagonistic interplay between LeuO and H-NS. Confocal laser scanning microscopic observation in flow-chambers showed that the mutants lacking leuO and some fimbriae genes are defective in biofilm formation or form altered biofilm architecture. Taken together we propose that LeuO is a major player in antagonistic interplay against the universal silencer H-NS.

Environmental Microbiology, 2013

SummaryListeria monocytogenes has a dichotomous lifestyle, existing as an ubiquitous saprophytic ... more SummaryListeria monocytogenes has a dichotomous lifestyle, existing as an ubiquitous saprophytic species and as an opportunistic intracellular pathogen. Besides its capacity to grow in a wide range of environmental and stressful conditions, L. monocytogenes has the ability to adhere to and colonize surfaces. Morphotype variation to elongated cells forming rough colonies has been reported for different clinical and environmental isolates, including biofilms. This cell differentiation is mainly attributed to the reduced secretion of two SecA2‐dependent cell‐wall hydrolases, CwhA and MurA. SecA2 is a non‐essential SecA paralogue forming an alternative translocase with the primary Sec translocon. Following investigation at temperatures relevant to its ecological niches, i.e. infection (37°C) and environmental (20°C) conditions, inactivation of this SecA2‐only protein export pathway led, despite reduced adhesion, to the formation of filamentous biofilm with aerial structures. Compared to...

Le Lait, 1995

Nineteen bacteriophages infecting P freudenreichii have been isolated from 32 Swisstype cheeses. ... more Nineteen bacteriophages infecting P freudenreichii have been isolated from 32 Swisstype cheeses. They ail present a similar morphology and belong to the B1 group of Bradley's classification. According to their restriction patterns, obtained with the endonuclease Ps~, they can be grouped into 3 clusters, 1 of which contains the majority of the phages. Sixteen of the 32 cheeses studied were infected with bacteriophages. We observed that ail the cheeses made from raw milk and ripened in a warm curing room for several weeks which are known to contain high concentrations of propionibacteria, were infected with bacteriophages. Moreover, the multiplication of bacteriophages occurred in cheese during the multiplication stage of propionibacteria in a warm curing room. We have shown that raw milk contains bacteriophages and thus it can be a source of phages in factories. However, these bacteriophages are sensitive to the milk heat treatment used for cheesemaking. bacteriophage 1 Propionibacterium 1Swiss-type cheese Résumé-Bactériophages infectant les bactéries propioniques laitières. Dix-neuf bactériophages actifs sur P freudenreichii ont été isolés à partir de 32 fromages à pâte pressée cuite. Leur morphologie est similaire et permet de les classer dans le groupe B1 de la classification de Bradley. L'étude du profil de restriction de leur chromosome obtenu avec l'endonucléase Pstl a permis de les classer en 3 groupes, dont un en rassemble la grande majorité. Seize fromages parmi les 32 étudiés étaient contaminés par des bactériophages. Nous avons remarqué que tous les fromages faits avec du lait cru, affinés en cave chaude et qui par conséquent montrent une haute concentration en bactéries propionlaues, contenaient des bactériophages. De plus, la multiplication de ceux-ci se produisait parallèlement à celle des bactéries lors de l'affinage. Nous avons aussi montré que le lait cru pouvait véhiculer des bactériophages et donc constituer une voie d'entrée des phages dans les usines. Ces phages sont cependant sensibles aux traitements thermiques appliqués au lait avant la fabrication fromagère. bactériophage IPropionibacterium Ifromage à pâte pressée cuite

Biofouling, 2003

The development of antifouling strategies in seawater requires knowledge of the physico-chemical ... more The development of antifouling strategies in seawater requires knowledge of the physico-chemical properties of the cell surfaces of early adherent bacteria. The hydrophilic, electrostatic and the Lewis acid-base cell surface properties of eleven marine bacteria were characterized. Although these bacteria adhered to a hydrophilic support immersed for 3 and 6 h, they presented various physico-chemical properties. Eleven strains possessed a hydrophilic surface and five a hydrophobic surface. Although the majority of the bacteria presented an electron-donating character, some could not generate Lewis acid-base interactions with the support. On the other hand, all strains possessed an isoelectric point ranging from 2.2 to 3.4 and were negatively charged at the pH of seawater. Hydrophilicity was a preponderant property among these bacteria, but other properties should not be ignored. The development of new antifouling paints must take account all the possible interaction levels used by the bacteria to adhere to an immersed surface.

Frontiers in Microbiology

In the One Health concept, the use of beneficial bacteria to form positive biofilms that prevent ... more In the One Health concept, the use of beneficial bacteria to form positive biofilms that prevent the settlement of undesirable bacteria is a promising solution to limit the use of antimicrobials on farms. However, there is a lack of field studies reporting the onset of these beneficial bacteria after application and the effects on autochthonous surface microbiota. In the study reported here, the inner surfaces of commercial broiler chicken houses were treated or not with a bacterial consortium composed of Bacillus spp. and Pediococcus spp. strains, able to form covering biofilms in different laboratory models. Preinstalled coupons were sampled over time to capture microbial biofilm dynamics on-farm surfaces. The results showed that the bacterial consortium can establish on the farm surfaces, modulate microbial communities, and limit the implantation of Enterobacteriaceae and Enterococcaceae, two families containing potential pathogens.