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Desriac N.,ADRIA Developpement | Desriac N.,CNRS Microbial Ecology | Broussolle V.,French National Institute for Agricultural Research | Broussolle V.,University of Avignon | And 5 more authors.
Frontiers in Microbiology | Year: 2013

Microorganisms are able to adapt to different environments and evolve rapidly, allowing them to cope with their new environments. Such adaptive response and associated protections toward other lethal stresses, is a crucial survival strategy for a wide spectrum of microorganisms, including food spoilage bacteria, pathogens, and organisms used in functional food applications. The growing demand for minimal processed food yields to an increasing use of combination of hurdles or mild preservation factors in the food industry. A commonly used hurdle is low pH which allows the decrease in bacterial growth rate but also the inactivation of pathogens or spoilage microorganisms. Bacillus cereus is a well-known food-borne pathogen leading to economical and safety issues in food industry. Because survival mechanisms implemented will allow bacteria to cope with environmental changes, it is important to provide understanding of B. cereus stress response. Thus this review deals with the adaptive traits of B. cereus cells facing to acid stress conditions. The acid stress response of B. cereus could be divided into four groups (i) general stress response (ii) pH homeostasis, (iii) metabolic modifications and alkali production and (iv) secondary oxidative stress response. This current knowledge may be useful to understand how B. cereus cells may cope to acid environment such as encountered in food products and thus to find some molecular biomarkers of the bacterial behavior. These biomarkers could be furthermore used to develop new microbial behavior prediction tools which can provide insights into underlying molecular physiological states which govern the behavior of microorganisms and thus opening the avenue toward the detection of stress adaptive behavior at an early stage and the control of stress-induced resistance throughout the food chain. © 2013 Desriac, Broussolle, Postollec, Mathot, Sohier, Coroller and Leguerine.


PubMed | CNRS Microbial Ecology, ADRIA Developpement and University of Avignon
Type: | Journal: Research in microbiology | Year: 2016

Spore-forming bacteria are able to grow under a wide range of environmental conditions, to form biofilms and to differentiate into resistant forms: spores. This resistant form allows their dissemination in the environment; consequently, they may contaminate raw materials. Sporulation can occur all along the food chain, in raw materials, but also in food processes, leading to an increase in food contamination. However, the problem of sporulation during food processing is poorly addressed and sporulation niches are difficult to identify from the farm to the fork. Sporulation is a survival strategy. Some environmental factors are required to trigger this differentiation process and others act by modulating it. The efficiency of sporulation is the result of the combined effects of these two types of factors on vegetative cell metabolism. This paper aims to explain and help identify sporulation niches in the food chain, based on features of spore-former physiology.


Baril E.,CNRS Microbial Ecology | Coroller L.,CNRS Microbial Ecology | Postollec F.,ADRIA Developpement | Leguerinel I.,CNRS Microbial Ecology | And 3 more authors.
International Journal of Food Microbiology | Year: 2011

While bacterial spores are mostly produced in a continuous process, this study reports a two-step sporulation methodology. Even though spore heat resistance of numerous spore-forming bacteria is known to be dependent on sporulation conditions, this approach enables the distinction between the vegetative cell growth phase in nutrient broth and the sporulation phase in specific buffer. This study aims at investigating whether the conditions of growth of the vegetative cells, prior to sporulation, could affect spore heat resistance. For that purpose, wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores, produced via a two-step sporulation process, was determined from vegetative cells harvested at four different stages of the growth kinetics, i.e. early exponential phase, late exponential phase, transition phase or early stationary phase. To assess the impact of the temperature on spore heat resistance, sporulation was performed at 10. °C, 20. °C and 30. °C from cells grown during a continuous or a discontinuous temperature process, differentiating or not the growth and sporulation temperatures. Induction of sporulation seems possible for a large range of growth stages. Final spore concentration was not significantly affected by the vegetative cell growth stage while it was by the temperature during growing and sporulation steps. The sporulation temperature influences the heat resistance of B. weihenstephanensis KBAB4 spores much more than growth temperature prior to sporulation. Spores produced at 10. °C were up to 3 times less heat resistant than spores produced at 30. °C. © 2011 Elsevier B.V.


Augustin J.-C.,National Veterinary School of Alfort | Bergis H.,Agence francaise de securite sanitaire des aliments AFSSA | Midelet-Bourdin G.,Agence francaise de securite sanitaire des aliments AFSSA | Cornu M.,Agence francaise de securite sanitaire des aliments AFSSA | And 8 more authors.
Food Microbiology | Year: 2011

The assessment of the evolution of micro-organisms naturally contaminating food must take into account the variability of biological factors, food characteristics and storage conditions. A research project involving eight French laboratories was conducted to quantify the variability of growth parameters of Listeria monocytogenes obtained by challenge testing in five food products. The residual variability corresponded to a coefficient of variation (CV) of approximately 20% for the growth rate (μmax) and 130% for the parameter K = μmax × lag. The between-batch and between-manufacturer variability of μmax was very dependent on the food tested and mean CV of approximately 20 and 35% were observed for these two sources of variability, respectively. The initial physiological state variability led to a CV of 100% for the parameter K. It appeared that repeating a limited number of three challenge tests with three different batches (or manufacturers) and with different initial physiological states seems often necessary and adequate to accurately assess the variability of the behavior of L. monocytogenes in a specific food produced by a given manufacturer (or for a more general food designation). © 2010 Elsevier Ltd.


PubMed | Aerial, Montpellier University, ACTALIA, LNE and 2 more.
Type: | Journal: Food microbiology | Year: 2016

Predicting microbial safety of fresh products in modified atmosphere packaging implies to take into account the dynamic of O2, CO2 and N2 exchanges in the system and its effect on microbial growth. In this paper a mechanistic model coupling gas transfer and predictive microbiology was validated using dedicated challenge-tests performed on poultry meat, fresh salmon and processed cheese, inoculated with either Listeria monocytogenes or Pseudomonas fluorescens and packed in commercially used packaging materials (tray+lid films). The model succeeded in predicting the relative variation of O2, CO2 and N2 partial pressure in headspace and the growth of the studied microorganisms without any parameter identification. This work highlighted that the respiration of the targeted microorganism itself and/or that of the naturally present microflora could not be neglected in most of the cases, and could, in the particular case of aerobic microbes contribute to limit the growth by removing all residual O2 in the package. This work also confirmed the low sensitivity of L. monocytogenes toward CO2 while that of P. fluorescens permitted to efficiently prevent its growth by choosing the right combination of packaging gas permeability value and initial % of CO2 initially flushed in the pack.


Ziane M.,Abou Bekr Belkaid University Tlemcen | Desriac N.,ADRIA Developpement | Le Chevalier P.,University of Western Brittany | Couvert O.,University of Western Brittany | And 2 more authors.
Food Control | Year: 2014

Aims: In this study, species taxonomy, heat resistance and growth potential of mesophilic aerobic spore-forming Bacillus strains isolated from commercially available couscous were determined. Methods and results: Aerobic spore-forming bacteria were isolated from three Algerian retail couscous samples heated at 80°C for 10min. Plate counting of spore-forming bacteria showed a mean concentration of 20CFU/g. By monitoring 16S gene sequencing, ten Bacillus strains were identified, belonging to 3 different species: five Bacillus licheniformis strains, four Bacillus cereus group strains sensu lato and one Bacillus subtilis strain. According to the panC gene sequencing, the four B.cereus strains were assigned to the group IV (mesophilic and heat resistant group, associated with cases of foodborne illness). B.cereus cells growth kinetics in moistened couscous semolina showed a specific growth rate of 0.33h-1 at 30°C, confirming their growth ability in this media.The heat resistance (δ value i.e. the first decimal reduction time) and heat sensitivity (zT values i.e. the temperature increase leading a ten-fold reduction of the δ value) of spores of B.cereus and B.subtilis strains were determined using Weibull and Bigelow models, respectively. δ100°C values are ranged from 0.14 to 7.90min and estimated zT values ranged from 7.52°C to 10.38°C. Moreover, the estimate four decimal reduction times at 90°C (t4D) of spores of isolated B.cereus strains were from 0.58h to 3.73h. Conclusions: B.cereus strains isolated from retail packaged couscous semolina are resistant to heat treatment both during the industrial food process and can easily grow in moistened couscous semolina. These observations could explain numerous B.cereus outbreaks associated with couscous semolina consumption. © 2014 Elsevier Ltd.


Desriac N.,ADRIA Developpement | Desriac N.,CNRS Microbial Ecology | Postollec F.,ADRIA Developpement | Coroller L.,CNRS Microbial Ecology | And 3 more authors.
International Journal of Food Microbiology | Year: 2013

Exposure to mild stress conditions can activate stress adaptation mechanisms and provide cross-resistance towards otherwise lethal stresses. In this study, an approach was followed to select molecular biomarkers (quantitative gene expressions) to predict induced acid resistance after exposure to various mild stresses, i.e. exposure to sublethal concentrations of salt, acid and hydrogen peroxide during 5. min to 60. min. Gene expression patterns of unstressed and mildly stressed cells of Bacillus weihenstephanensis were correlated to their acid resistance (3D value) which was estimated after exposure to lethal acid conditions. Among the twenty-nine candidate biomarkers, 12 genes showed expression patterns that were correlated either linearly or non-linearly to acid resistance, while for the 17 other genes the correlation remains to be determined. The selected genes represented two types of biomarkers, (i) four direct biomarker genes ( lexA, spxA, narL, bkdR) for which expression patterns upon mild stress treatment were linearly correlated to induced acid resistance; and (ii) nine long-acting biomarker genes ( spxA, BcerKBAB4_0325, katA, trxB, codY, lacI, BcerKBAB4_1716, BcerKBAB4_2108, relA) which were transiently up-regulated during mild stress exposure and correlated to increased acid resistance over time. Our results highlight that mild stress induced transcripts can be linearly or non-linearly correlated to induced acid resistance and both approaches can be used to find relevant biomarkers. This quantitative and systematic approach opens avenues to select cellular biomarkers that could be incremented in mathematical models to predict microbial behaviour. © 2013 Elsevier B.V.


Desriac N.,ADRIA Developpement | Desriac N.,CNRS Microbial Ecology | Coroller L.,CNRS Microbial Ecology | Sohier D.,ADRIA Developpement | Postollec F.,ADRIA Developpement
Food Microbiology | Year: 2012

The aim of this study was to define an integrative approach to identify resistance biomarkers using gene expression quantification and mathematical modelling. Mid-exponentially growing cells were transferred into acid conditions (BHI, pH 4.6) to obtain inactivation kinetics, performed in triplicate. The inactivation curve was fitted with a mixed Weibull model. This model allowed to differentiate two subpopulations with various acid resistances among the initial population. In parallel, differential gene expression was quantified by RT-qPCR. While narL was down-regulated throughout acid inactivation, sigB and katA were up-regulated. sigB expression up-regulation peak was correlated to the less resistant subpopulation when katA up-regulation, was correlated to the more resistant subpopulation. Moreover, differences in population structure were highlighted between each replicate. The higher proportion of the more resistant subpopulation was linked to a higher katA gene expression. These results suggest that sigB and katA might be used as different types of biomarkers, for instance to track moderate and high acid-resistance, respectively. The use of this approach combining RT-qPCR and predictive modelling to track cellular biomarker variations appears as an interesting tool to take into account physiological cell responses into mathematical modelling, allowing an accurate prediction of microbial behaviour. © 2012 Elsevier Ltd.


Huchet V.,ADRIA Developpement | Pavan S.,ADRIA Developpement | Lochardet A.,ADRIA Developpement | Divanac'h M.L.,ADRIA Developpement | And 2 more authors.
Food Microbiology | Year: 2013

Molds are responsible for spoilage of bakery products during storage. A modeling approach to predict the effect of water activity (aw) and temperature on the appearance time of Aspergillus candidus was developed and validated on cakes. The gamma concept of Zwietering was adapted to model fungal growth, taking into account the impact of temperature and aw. We hypothesized that the same model could be used to calculate the time for mycelium to become visible (tv), by substituting the matrix parameter by tv. Cardinal values of A.candidus were determined on potato dextrose agar, and predicted tv were further validated by challenge-tests run on 51 pastries. Taking into account the aw dynamics recorded in pastries during reasonable conditions of storage, high correlation was shown between predicted and observed tv when the aw at equilibrium (after 14 days of storage) was used for modeling (Af=1.072, Bf=0.979). Validation studies on industrial cakes confirmed the experimental results and demonstrated the suitability of the model to predict tv in food as a function of aw and temperature. © 2013 Elsevier Ltd.


Trademark
Adria Developpement | Date: 2010-08-31

Computer software for forecasting the state and activity of water in the field of industry, agro-industry and living beings. Software design for use in the field of forecasting the state and activity of water, in the field of industry of living beings.

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