Are bacterial spores activated by High Pressure treatment at 20°C ?

International audience

Combining heat treatment, control of water activity and pressure to preserve foods

Drying parameters greatly affect the destruction of Cronobacter sakazakii and Salmonella Typhimurium in standard buffer and milk

International audience; Salmonella Typhimurium and Cronobacter sakazakii are two foodborne pathogens involved in neonatal infections from milk powder and infant formula. Their ability to survive in low-moisture food and during processing from the decontamination to the dried state is a major issue in food protection. In this work, we studied the effects of the drying process on Salmonella Typhimurium and Cronobacter sakazakii, with the aim of identifying the drying parameters that could promote greater inactivation of these two foodborne pathogens. These two bacteria were dried under different atmospheric relative humidities in milk and phosphate-buffered saline, and the delays in growth re…

Effect of high pressure on the antimicrobial activity and secondary structure of the bacteriocin nisin

International audience; Effect of high pressure (HP) treatment on the antimicrobial properties and the structure of nisin was evaluated. Nisin solutions at pH 2.8 or 6.1 were treated by HP at 500 MPa – 10 min – 20 °C and their antimicrobial potency was determined. It appeared that HP clearly impacted the antimicrobial activity of nisin, with respective activity loss of 22.5% and 49.9% at pH 2.8 and 6.1. Structural analysis of nisin by circular dichroism and Fourier transform-infrared spectroscopies revealed that the decrease of nisin antimicrobial activity was likely due to the unfolding of the protein induced by HP. A loss of nisin β-turns structure, particularly significant at neutral pH,…

Viscosity mapping of the structures of Bacillus subtilis spores by fluorescence lifetime imaging

International audience; L’état de la membrane plasmique des cellules est un élément essentiel pour connaitre la conditionphysiologique des cellules. Sur des microorganismes, cette connaissance permet de mesurer l’impact d’uneperturbation sur la structure cellulaire et sur sa survie ultérieure. La fluidité membranaire résulte tout à lafois de la composition en phospholipides, de la présence et du rôle de certaines molécules comme lesstérols, les protéines transmembranaires mais aussi des conditions thermodynamiques et physico-chimiquesextérieures (P, T, aw). La bactérie Bacillus subtilis est capable dans des conditions défavorables de passerd’un état actif végétatif à l’état de spore, état d…

High pressure inactivation of Escherichia coli and its giant spheroplast at subzero temperature

International audience

Distributions of the growth rate of the germ tubes and germination time of Penicillium chrysogenum conidia depend on water activity

The effects of water activities for sporulation (a(wsp)) and germination (a(wge)) on the distributions of the growth rate of the germ tubes (mu) and the germination time (t(G)) of Penicillium chrysogenum conidia were determined by monitoring the length of the same germ tubes throughout the experiments automatically. No relationship between the individual t(G)'s and mu's could be established. Irrespective of the water activity for germination, mu was greater and t(G) was less for conidia produced at 0.95a(wsp) than that at 0.99a(wsp). At 0.99 a(wge) the mean and the standard deviation of t(G) were smaller than those obtained at 0.95a(wge). At 0.99a(wge), normal distributions for mu and t(G) …

Effect of Combined Physical Stresses on Cells: The Role of Water

International audience; The role of water in microorganism viability was assessed through the application of combined physical perturbations. The combination of different physical parameters could allow to balance the properties variations (especially water related) resulting from the increase of one parameter alone. Thus, it is possible to optimize the survival of cells in controlling these parameters. This was tested through two different examples. The first example shows that combination of osmotic level and temperature can allow optimizing yeast cell survival in following membrane fluidity variation. Moreover this analysis has allowed a better comprehension of cell inactivation during r…

Harnessing medically relevant metals onto water-soluble subphthalocyanines: towards bimodal imaging and theranostics

International audience; Subphthalocyanine (SubPc), a putative fluorophore for optical imaging (OI), was conjugated to chelating ligands (DOTA, DTPA) affording water-soluble conjugates complexed with (non-radioactive) metals relevant to the following medical imaging techniques/therapies: MRI (Gd), PET (Cu, Ga), SPECT (In, Ga, Lu), RIT (Cu, Lu, Y), and NCT (Gd). Magneto-optical properties of ditopic gadolinium species (and optical properties of other metal containing species) were examined (brightness (ε × Φ F) and relaxivity R 1) and fluorescence confocal/biphoton microscopy studies were conducted. † Electronic supplementary information (ESI) available: Experimental characterization, NMR and…

Damage in Escherichia coli Cells Treated with a Combination of High Hydrostatic Pressure and Subzero Temperature

ABSTRACT The relationship between membrane permeability, changes in ultrastructure, and inactivation in Escherichia coli strain K-12TG1 cells subjected to high hydrostatic pressure treatment at room and subzero temperatures was studied. Propidium iodide staining performed before and after pressure treatment made it possible to distinguish between reversible and irreversible pressure-mediated cell membrane permeabilization. Changes in cell ultrastructure were studied using transmission electron microscopy (TEM), which showed noticeable condensation of nucleoids and aggregation of cytosolic proteins in cells fixed after decompression. A novel technique used to mix fixation reagents with the c…

Métrologie : calibrants de pression pour la gamme 0 - 2 GPA

International audience; La gamme des pressions moyennes 0-2 GPa est aujourd’hui couramment utilisée dans différents secteurs de recherche tels que biochimie et chimie, agroalimentaire, physique des matériaux et Sciences de l’Univers. Dans cette gamme de pression, les cellules optiques se sont fortement développées lors de la dernière décennie. Au cours des expériences en pression et en température contrôlées, une bonne maîtrise de la métrologie est un atout indispensable à l’obtention d’une mesure précise de la pression in situ, et donc d’une bonne reproductibilité des expériences. A ce jour, la mesure précise et conjuguée de ces deux paramètres reste une prouesse technique. Aucun des systè…

Influence of phytosterols on the structural and dynamic properties of plant plasma membrane

National audience; The complex mixture of sterols, namely phytosterols, found in the plasma membrane (PM) of plant cells is an intriguing characteristic. In the present work, we characterized the sterol composition of tobacco BY-2 cell PM, and we adapted a sterol manipulation method to this plant material. Methyl-b-cyclodextrin was found to induce a drastic reduction of the PM total free sterol content, with a low specificity for the different phytosterols, and without effect on steryl-conjugates. The consequences of phytosterols depletion were investigated by means of fluorescence spectroscopy and biochemical detergent resistant membrane (DRM) fraction purification methods. Data obtained w…

Multispectral fluorescence sensitivity to acidic and polyphenolic changes in Chardonnay wines – The case study of malolactic fermentation

International audience; In this study, stationary and time-resolvedfluorescence signatures, were statistically and chemometrically analyzed among three typologies of Chardonnay wines (A, B and C) with the objectives to evaluate their sensitivity to acidic and polyphenolic changes. For that purpose, a dataset was built using Excitation Emission Matrices of fluorescence (N = 103) decomposed by a Parallel Factor Analysis (PARAFAC), andfluorescence decays (N = 22), mathematically fitted, using the conventional exponential modeling and the phasor plot representation. Wine PARAFAC component C4 coupledwith its phasor plot g and s values enable the description of malolactic fermentation (MLF) occur…

Modification of Plasma Membrane Organization in Tobacco Cells Elicited by Cryptogein

Abstract Lipid mixtures within artificial membranes undergo a separation into liquid-disordered and liquid-ordered phases. However, the existence of this segregation into microscopic liquid-ordered phases has been difficult to prove in living cells, and the precise organization of the plasma membrane into such phases has not been elucidated in plant cells. We developed a multispectral confocal microscopy approach to generate ratiometric images of the plasma membrane surface of Bright Yellow 2 tobacco (Nicotiana tabacum) suspension cells labeled with an environment sensitive fluorescent probe. This allowed the in vivo characterization of the global level of order of this membrane, by which w…

Inactivation of dried spores of Bacillus subtilis 168 by a treatment combining high temperature and pressure

International audience; Specific treatments combining high temperatures of up to 150 °C and moderate pressure of up to 0.6 MPa have been applied to Bacillus subtilis 168 spores conditioned at different aw levels (between 0.10 and 0.70) corresponding to different residual water contents within the spore core. The spores were treated as a dry powder in a pressurized nitrogen environment or in water/glycerol solutions.These thermodynamic conditions were intended to prevent any water evaporation from the spore core during time/temperature treatments.Our results clearly show that retaining liquid water in the core by applying pressure during the treatment resulted in greater spore destruction (b…

Recovery Estimation of Dried Foodborne Pathogens Is Directly Related to Rehydration Kinetics.

International audience; Drying is a common process which is used to preserve food products and technological microorganisms, but which is deleterious for the cells. The aim of this study is to differentiate the effects of drying alone from the effects of the successive and necessary rehydration. Rehydration of dried bacteria is a critical step already studied in starter culture but not for different kinetics and not for pathogens. In the present study, the influence of rehydration kinetics was investigated for three foodborne pathogens involved in neonatal diseases caused by the consumption of rehydrated milk powder: Salmonella enterica subsp. enterica serovar Typhimurium, Salmonella enteri…

Effect of high hydrostatic pressure on extraction of B-phycoerythrin from Porphyridium cruentum: Use of confocal microscopy and image processing

International audience; The aim of the study was to extract B-phycoerythrin from Porphyridium cruentum while preserving its structure. The high hydrostatic pressure treatments were chosen as extraction technology. Different methods have been used to observe the effects of the treatment: spectrophotometry and confocal laser scanning microscopy followed by image processing analysis. Image processing led to the generation of masks used for the identification of three clusters: intra, extra and intercellular. All methods showed that high hydrostatic pressure treatments between 50 and 500 MPa failed to extract B-phycoerythrin from Porphyridium cruentum cells. The fluorescence emission was negati…

Interaction Between Osmotic and Hydrostatic Pressure in Yeast Inactivation

The protective effect of an osmotic perturbation on high-pressure inactivation has been investigated using a yeast strain:Saccharomyces cerevisiae. Osmotic shocks have been carried out with binary medium (glycerol/sorbitol and water) with or without glucose. Variations of osmotic level, osmotic shift kinetics and time between osmotic and hydrostatic treatment (350 MPa/10 min) have allowed the characterization of cell baroprotection. Two different cumulative baroprotection effects have been distinguished: one conferred by the solute on biological structures and the other related to the osmotic stress, cell volume variations and stress metabolism response (HSP, trehalose). These experiments h…

Modeling the heat inactivation of foodborne pathogens in milk powder : High relevance of the substrate water activity

International audience; Due to the ability of foodborne pathogens to survive in low moisture foods, the decontamination of these products is an important issue in food hygiene. Up to now, such decontamination has mostly been achieved through empirical methods. The intention of this work is to establish a more rational use of heat treatment cycles. The effects of thermal treatment cycles on the inactivation of dried Salmonella Typhimurium, Salmonella Senftenberg, Cronobacter sakazakii and Escherichia coli were assessed. Bacteria were mixed with whole milk powder and dried down to different water activity levels (0.11, 0.25, 0.44 and 0.58). The rate of inactivated bacteria was determined afte…

La biopréservation: une stratégie d’avenir pour la conservation des aliments

N° d'article 201511121820; La demande grandissante des consommateurs pour des produits alimentaires à teneur réduite en conservateurs pousse les industriels de l’agroalimentaire à rechercher des méthodes de conservation alternatives. Dans ce contexte, la bioprotection s’impose comme un procédé à fort potentiel. Cette technique consiste à inoculer sur les aliments des cultures de bactéries protectrices. Celles-ci, par l’intermédiaire de plusieurs mécanismes, vont inhiber la croissance de bactéries pathogènes et d’altération telles que Listeria monocytogenes et Salmonella. Cependant, cette technique n’a pas d’effet sur les spores bactériennes. Ainsi, l’objet central du projet de recherche ANR…

Liquid ordered domains of tobacco cell plasma membrane : in vivo visualization, spatial distribution and modulation upon elicitation

SPE IPM; International audience; The ability of lipids in complex mixtures to form liquid-ordered, sterol-rich phases, together with the association of specific proteins with sterol-enriched biochemical fractions extracted from biological membranes, gave raise to the "lipid rafts" hypothesis. This suggests the presence within biological membranes of small-sized, ordered domains, of particular lipid and protein composition, which could serve as signal transduction platforms, particularly during plant-microorganisms interactions. However, the precise organization of living cell plasma membrane is still poorly described and the spatial distribution of segregating liquid-disordered and liquid-o…

5èmes Journées Scientifiques et Techniques du Réseau des Microscopistes INRA. « Imagerie cellulaire en science du vivant : Cryo-microscopies, Dynamiques in vivo et Interactions moléculaires »

National audience; L’imagerie cellulaire, dans le domaine des sciences du vivant, est essentielle à la compréhension des phénomènes cellulaires subcellulaires régulant le fonctionnement des cellules et tissus. En microscopie électronique, la mise en oeuvre de cryo-méthodes permet de préserver l’intégrité moléculaire et spatiale des protéines et lipides intracellulaires ou membranaires (de faible poids moléculaire, présentes en faible quantité ou très labiles) dont la localisation in situ est recherchée afin de caractériser leur organisation, participer à la détermination de leur fonction au sein de la cellule et d’analyser leur distribution. Ces techniques, en pleine évolution, seront abord…

Biopréservation et hautes pressions : des outils pour la maîtrise des dangers microbiologiques dans les aliments

L’utilisation d’additifs conservateurs est souvent nécessaire pour assurer la sécurité microbiologique des produits carnés réfrigérés faiblement acides. Le projet ANR BLac HP (2014-2019) a étudié une nouvelle stratégie de stabilisation des produits carnés réfrigérés pour assurer le contrôle des flores indésirables à la fois végétatives et sporulées. Grâce à une approche pluridisciplinaire, les travaux ont montré que la combinaison de la biopréservation par des bactéries lactiques et d’un traitement hautes pressions permettait d’assurer la qualité microbiologique de dés de jambon cuits à teneur réduite en nitrite pendant toute leur durée de vie. Le traitement permet de plus une qualité senso…

Subphthalocyanines: addressing water-solubility, nano-encapsulation, and activation for optical imaging of B16 melanoma cells

Water-soluble disulfonato-subphthalocyanines (SubPcs) or hydrophobic nano-encapsulated SubPcs are efficient probes for the fluorescence imaging of cells. 20 nm large liposomes (TEM and DLS) incorporated about 13% SubPc. Moreover, some of these fluorophores were found to be pH activatable.

L’imagerie microscopique et la spectroscopie de fluorescence : outils essentiels pour l’étude de modèles cellulaires sous haute pression

National audience

Synergistic and Antagonistic Effects of Combined Subzero Temperature and High Pressure on Inactivation of Escherichia coli

ABSTRACT The combined effects of subzero temperature and high pressure on the inactivation of Escherichia coli K12TG1 were investigated. Cells of this bacterial strain were exposed to high pressure (50 to 450 MPa, 10-min holding time) at two temperatures (−20°C without freezing and 25°C) and three water activity levels (a w ) (0.850, 0.992, and ca. 1.000) achieved with the addition of glycerol. There was a synergistic interaction between subzero temperature and high pressure in their effects on microbial inactivation. Indeed, to achieve the same inactivation rate, the pressures required at −20°C (in the liquid state) were more than 100 MPa less than those required at 25°C, at pressures in t…

Caco-2 Invasion by Cronobacter sakazakii and Salmonella enterica Exposed to Drying and Heat Treatments in Dried State in Milk Powder

International audience; Due to the ability of foodborne pathogens to survive in low moisture food, the decontamination of milk powder is an important issue in food protection. The safety of food products is, however, not always insured and the different steps in the processing of food involve physiological and metabolic changes in bacteria. Among these changes, virulence properties may also be affected. In this study, the effect of drying and successive thermal treatments on the invasion capacity of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii was assessed. Bacteria were dried on milk powder at three different water activity levels (0.25, 0.58, and 0.80) and hea…

Proton dynamics in bacterial spores, a neutron scattering investigation

International audience; Results from first neutron scattering experiments on bacterial spores are reported. The elastic intensities and mean square displacements have a non-linear behaviour as function of temperature, which is in agreement with a model presenting more pronounced variations at around 330 K (57 • C) and 400 K (127 • C). Based on the available literature on thermal properties of bacterial spores, mainly referring to differential scanning calorimetry, they are suggested to be associated to main endothermic transitions induced by coat and/or core bacterial response to heat treatment.

Are bacterial spores activated by High Pressure treatment at 20°C ?

Visualization of RNA-Quadruplexes in Live Cells

Visualization of DNA and RNA quadruplex formation in human cells was demonstrated recently with different quadruplex-specific antibodies. Despite the significant interest in these immunodetection approaches, dynamic detection of quadruplex in live cells remains elusive. Here, we report on NaphthoTASQ (N-TASQ), a next-generation quadruplex ligand that acts as a multiphoton turn-on fluorescent probe. Single-step incubation of human and mouse cells with N-TASQ enables the direct detection of RNA-quadruplexes in untreated cells (no fixation, permeabilization or mounting steps), thus offering a unique, unbiased visualization of quadruplexes in live cells.

High gas pressure: An innovative method for the inactivation of dried bacterial spores

In this article, an original non-thermal process to inactivate dehydrated bacterial spores is described. The use of gases such as nitrogen or argon as transmission media under high isostatic pressure led to an inactivation of over 2 logs CFU/g of Bacillus subtilis spores at 430 MPa, room temperature, for a 1 min treatment. A major requirement for the effectiveness of the process resided in the highly dehydrated state of the spores. Only a water activity below 0.3 led to substantial inactivation. The solubility of the gas in the lipid components of the spore and its diffusion properties was essential to inactivation. The main phenomenon involved seems to be the sorption of the gas under pres…

The role of water in bacteria spore resistance

Advanced fluorescence technologies help to resolve long-standing questions about microbial vitality

International audience; Advances in fundamental physical and optical principles applied to novel fluorescence methods are currently resulting in rapid progress in cell biology and physiology. Instrumentation devised in pioneering laboratories is becoming commercially available, and study findings are now becoming accessible. The first results have concerned mainly higher eukaryotic cells but many more developments can be expected, especially in microbiology. Until now, some important problems of cell physiology have been difficult to investigate due to interactions between probes and cells, excretion of probes from cells and the inability to make in situ observations deep within the cell, w…

Direct investigation of viscosity of an atypical inner membrane of Bacillus spores: A molecular rotor/FLIM study

Abstract We utilize the fluorescent molecular rotor Bodipy-C12 to investigate the viscoelastic properties of hydrophobic layers of bacterial spores Bacillus subtilis. The molecular rotor shows a marked increase in fluorescence lifetime, from 0.3 to 4 ns, upon viscosity increase from 1 to 1500 cP and can be incorporated into the hydrophobic layers within the spores from dormant state through to germination. We use fluorescence lifetime imaging microscopy to visualize the viscosity inside different compartments of the bacterial spore in order to investigate the inner membrane and relate its compaction to the extreme resistance observed during exposure of spores to toxic chemicals. We demonstr…

Cellular Injuries in Cronobacter sakazakii CIP 103183T and Salmonella enterica Exposed to Drying and Subsequent Heat Treatment in Milk Powder

International audience; Because of the ability of foodborne pathogens to survive in low-moisture foods, their decontamination is an important issue in food protection. This study aimed to clarify some of the cellular mechanisms involved in inactivation of foodborne pathogens after drying and subsequent heating. Individual strains of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii were mixed into whole milk powder and dried to different water activity levels (0.25 and 0.58); the number of surviving cells was determined after drying and subsequent thermal treatments in closed vessels at 90 and 100 degrees C, for 30 and 120 s. For each condition, the percentage of unc…

Understanding low hydration state of bacteria spores

Cryopreservation of Escherichia coli K12TG1: Protection from the damaging effects of supercooling by freezing

Injuries in living cells caused by water freezing during a freeze-thaw process have been extensively reported. In particular, intracellular water freezing has long been incriminated in cell death caused by a high cooling rate, but this supposition could not always be demonstrated. This work aims to discriminate the role of water freezing, dehydration and cold-induced injuries in cellular damage occuring during cryopreservation. For this purpose, Escherichia coli K12TG1 suspensions were maintained in a supercooled or frozen state at -20°C for times ranging from 10 min to 5 h. The supercooled state was maintained for a long period at -20°C by applying a non-injurious isostatic pressure (P<40 …

The Impact of Drying on Foodborne Pathogens Salmonella enterica and Cronobacter sakazakii

International audience; [Technical Session 1 – Intervention Strategies] Introduction: Salmonella enterica and Cronobacter sakazakii are foodborne pathogens responsible for severe infant illness. Their ability to survive in harsh environmental conditions make these species a matter of concern for the low moisture food industry. Purpose: This study aimed to evaluate and understand the impact of drying conditions on survival, physiology, and invasion capacity of Salmonella Typhimurium and C. sakazakii.Methods: Salmonella Typhimurium and C. sakazakii were mixed into whole milk powder and dried at different water activity (aw) levels (0.25, 0.58 and 0.80). For each strain, the impact of each dry…

High gas pressure survival/reactivation of soil microorganisms

International audience; Deep sea sediments constitute a considerable reserve of microorganisms belonging to different microbial communities. Our researches aimed to better understand cellular mechanisms related to cellular plasticity involved in resistance of such microbial communities to extreme conditions and more particularly to high level of pressure (> 50 MPa). Obviously, the first step is to isolate microorganisms present in deep sea sediments and then cultivate. The comparison of the cultivation of such microorganisms under atmospheric conditions and under pressure conditions will afford a possible reactivation of specific piezotolerants and/or piezophiles organisms from dormancy. Th…

High pressure treatment at mild temperature induces irreversible sensitization of bacterial spores to antimicrobial agents

Behavior of plant plasma membranes under hydrostatic pressure as monitored by fluorescent environment-sensitive probes.

International audience; We monitored the behavior of plasma membrane (PM) isolated from tobacco cells (BY-2) under hydrostatic pressures up to 3.5 kbar at 30 °C, by steady-state fluorescence spectroscopy using the newly introduced environment-sensitive probe F2N12S and also Laurdan and di-4-ANEPPDHQ. The consequences of sterol depletion by methyl-β-cyclodextrin were also studied. We found that application of hydrostatic pressure led to a marked decrease of hydration as probed by F2N12S and to an increase of the generalized polarization excitation (GPex) of Laurdan. We observed that the hydration effect of sterol depletion was maximal between 1 and 1.5 kbar but was much less important at hig…

Understanding the Effects of High Pressure on Bacterial Spores Using Synchrotron Infrared Spectroscopy

International audience; Bacterial spores are extremely resistant life-forms that play an important role in food spoilage and foodborne disease. The return of spores to a vegetative cell state is a three-step process, these being activation, germination, and emergence. High-pressure (HP) processing is known to induce germination in part of the spore population and even to inactivate a high number of Bacillus spores when combined with other mild treatments such as the addition of nisin. The aim of the present work was to investigate the mechanisms involved in the sensitization of spores to nisin following HP treatment at ambient temperature or with moderate heating leading to a heterogeneous …

Applications des hautes pressions hydrostatiques en agroalimentaire

Effects of hydrostatic pressure on yeasts isolated from deep-sea hydrothermal vents

International audience; Hydrostatic pressure plays a significant role in the distribution of life in the biosphere. Knowledge of deep-sea piezotolerant and (hyper)piezophilic bacteria and archaea diversity has been well documented, along with their specific adaptations to cope with high hydrostatic pressure (HHP). Recent investigations of deep-sea microbial community compositions have shown unexpected micro-eukaryotic communities, mainly dominated by fungi. Molecular methods such as next-generation sequencing have been used for SSU rRNA gene sequencing to reveal fungal taxa. Currently, a difficult but fascinating challenge for marine mycologists is to create deep-sea marine fungus culture c…

Cellular imaging using BODIPY-, pyrene- and phthalocyanine-based conjugates

International audience; Fluorescent Probes aimed at absorbing in the blue/green region of the spectrum and emitting in the green/red have been synthesized (as the form of dyads-pentads), studied by spectrofluorimetry, and used for cellular imaging. The synthesis of phthalocyanine-pyrene 1 was achieved by cyclotetramerization of pyrenyldicyanobenzene, whereas phthalocyanine-BODIPY 2c was synthesized by Sonogashira coupling between tetraiodophthalocyanine and meso-alkynylBODIPY. The standard four-steps BODIPY synthesis was applied to the BODIPY-pyrene dyad 3 starting from pyrenecarbaldehyde and dimethylpyrrole. H-1, C-13, F-19, (BNMR)-B-11, ICP, MS, and UV/Vis spectroscopic analyses demonstra…

Impact of water activity of diverse media on spore germination of Aspergillus and Penicillium species

International audience; The effects of water activity (aw) of diverse media i/ culture medium for sporogenesis, aw sp ii/ liquid spore suspension medium, aw su and iii/ medium for germination, aw ge, on the germination time tG of Aspergillus carbonarius, Aspergillus flavus, Penicillium chrysogenum and Penicillium expansum were assessed according to a screening matrix at 0.95 and 0.99 aw. It was shown that i/ reduced tGs were obtained at 0.95 aw sp except for P. expansum ii/ a significant effect of aw su on tG was demonstrated for A. carbonarius, P. chrysogenum and P. expansum iii/ the most important factor for controlling the germination time was the medium for germination except for A. car…

Absolute Humidity Influences the Seasonal Persistence and Infectivity of Human Norovirus

ABSTRACT Norovirus (NoV) is one of the main causative agents of acute gastroenteritis worldwide. In temperate climates, outbreaks peak during the winter season. The mechanism by which climatic factors influence the occurrence of NoV outbreaks is unknown. We hypothesized that humidity is linked to NoV seasonality. Human NoV is not cultivatable, so we used cultivatable murine norovirus (MNV) as a surrogate to study its persistence when exposed to various levels of relative humidity (RH) from low (10% RH) to saturated (100% RH) conditions at 9 and 25°C. In addition, we conducted similar experiments with virus-like particles (VLPs) from the predominant GII-4 norovirus and studied changes in bin…

Cell inactivation and membrane damage after long-term treatments at sub-zero temperature in the supercooled and frozen states.

The survival of cells subjected to cooling at sub-zero temperature is of paramount concern in cryobiology. The susceptibility of cells to cryopreservation processes, especially freeze-thawing, stimulated considerable interest in better understanding the mechanisms leading to cell injury and inactivation. In this study, we assessed the viability of cells subjected to cold stress, through long-term supercooling experiments, versus freeze-thawing stress. The viability of Escherichia coli, Saccharomyces cerevisiae, and leukemia cells were assessed over time. Supercooled conditions were maintained for 71 days at -10 degrees C, and for 4 h at -15 degrees C, and -20 degrees C, without additives or…

Survie et/ou réactivation de microorganismes du sol sous hautes pressions gazeuses

National audience; Le sol constitue une réserve considérable de microorganismes représentatifs de nombreuses communautés cellulaires. Les recherches reposent sur l’hypothèse qu’il existe, dans les échantillons de sol, des communautés microbiennes adaptées à des conditions physiques (pression, température) très différentes de celles rencontrées dans nos laboratoires : soit parce que les conditions de milieu ont changé (sol), soit parce que les conditions de prélèvement sont très différentes des conditions de culture (grands fonds marins). Dans cette optique, l’utilisation des hautes pressions gazeuses (200-1000 bars dans un premier temps) est envisagée afin d’essayer de réactiver des microor…

Can pressure-induced cell inactivation be related to cell volume compression? A case study for Saccharomyces cerevisiae

In this paper, emphasis has been put on the relationship between volume compression and cell inactivation for the Saccharomyces cerevisiae strain CBS 1171 submitted to high hydrostatic pressure treatments. The influence of cell dehydration on pressure inactivation was first investigated. Inactivation was found to be strongly limited, or even completely prevented for cells with a water content of 60% w/w or below. Moreover, the volume compression undergone by a single yeast cell was assessed as a function of pressure and hydration conditions using a high-pressure setup for pressure-volume-temperature measurements. Direct measurements of volume compression were performed on cell pellets after…

CCDC 1014064: Experimental Crystal Structure Determination

Related Article: Yann Bernhard, Pascale Winckler, Remi Chassagnon, Philippe Richard, Élodie Gigot, Jean-Marie Perrier-Cornet, Richard A. Decréau|2014|Chem.Commun.|50|13975|doi:10.1039/C4CC05503A