Effet de stress technologiques sur la survie de différents modèles bactériens (applications particulières aux stress thermique, osmotique, acide et la lumière pulsée)

Listeria monocytogenes est une bactérie très fréquemment rencontrée dans notre environnement. Ses capacités de résistance et de croissance lui permettent de contaminer très facilement nos aliments. Dans une première phase, l effet du stress (froid, salin et acide) généralement rencontré dans l industrie agroalimentaire sur le comportement de 3 souches de Listeria monocytogenes a été étudié dans un aliment et en milieux de culture. Nous avons montré que L. monocytogenes est capable de survivre mais pas de croître à la surface de saumon frais congelé durant une période d au moins 10 mois. De même, nous avons testé la capacité de croissance en présence de concentrations élevées en sel (10 % NaCl) à pH neutre et à pH acide à différentes températures d incubation (37, 25 et 4C). Dans une deuxième phase, l action de la lumière pulsée sur 3 micro-organismes cibles (L. monocytogenes, Ps. fluorescens, Ph. phosphoreum) a été étudiée en milieux de culture solide ou liquide. Les résultats de cette étude ont montré la grande efficacité de ce traitement. Cependant cette efficacité dépend de l exposition des microorganismes aux flashs de la lumière pulsée. Puis une évaluation de l action de la lumière pulsée a été effectuée sur l ADN. La lumière pulsée a entraîné des coupures simple et double brin au niveau de l ADN. Enfin, nous avons étudié l effet traitement par la lumière pulsée sur les protéines de lait. Ainsi, plusieurs méthodes d analyses (spectroscopie UV, fluorescence, électrophorèse par SDS-PAGE et HPLC) n ont pas montré des modifications significatives des composants des protéines après traitement.Listeria monocytogenes is an ubiquitous bacterial species known to be a major hazard in food safety. At first, we have assessed the behaviour of 3 strains of L. monocytogenes in relation to cold, saline and acid stress in food system and in laboratory conditions. Results of this study indicate that L. monocytogenes is capable of survival but not growth on the surface of frozen raw salmon for a period of at least 10 months. Nevertheless, freezing is a way of reducing the linked risk Listeria for the seafood products industry. These 3 strains are able to grow in the presence of high concentrations in salt (10 % NaCl) in neutral and acid pH at 37, 25 and 4C. Then, the effects of broad spectrum pulsed light on the survival of L. monocytogenes, Ps. fluorescens and Ph. phosphoreum populations on agar, in a liquid medium and on food were investigated. The present study clearly demonstrates the potential of pulsed light for bacterial inactivation. Complete inactivation of these bacteria can be achieved within a few microseconds. The microbicidal effect depends on the position of the microbes, so that any shadowing of target cells must be avoided. A solution of DNA was used to demonstrate DNA strand-breaking after pulsed light treatment. The influence of pulsed light treatment on protein components of milk was evaluated by means of spectroscopy ultraviolet, spectrofluorimetry, electrophoresis and HPLC. The pulsed light treatment did not produce any significant changes of protein components.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Effectiveness of Pulsed Ultraviolet-Light Treatment for Bacterial Inactivation on Agar Surface and Liquid Medium

International audienceIn the present study, the efficiency of a broad-spectrum pulsed ultraviolet (UV)-light for the inactivation of Listeria monocytogenes Scott A, L. monocytogenes CNL 895807, and Pseudomonas fluorescens MF37 populations as agar seeded or suspended cells was investigated. The bacterial populations were treated by pulsed UV-light at different number of pulses (1 to 3), dose of energy (162, 243, or 324J), and distance from the strobe (4, 9, or 12 cm). After pulsed UV-light treatment, the bacterial reduction was determined by standard plate count. The results showed that there was a significant reduction of population along with an increase of light energy and number of pulses. Decreasing the distance between the Petri dishes and the xenon lamp demonstrated an increase in bacterial reduction. Decontamination efficacy decreased significantly with the increase in level of contamination. This study demonstrates that pulsed UV-light can be used as an effective sterilizing method for the bacteria

Pulsed light system as a novel food decontamination technology: a review

International audienceIn response to consumer preferences for high quality foods that are as close as possible to fresh products, athermal technologies are being developed to obtain products with high levels of organoleptic and nutritional quality but free of any health risks. Pulsed light is a novel technology that rapidly inactivates pathogenic and food spoilage microorganisms. It appears to constitute a good alternative or a complement to conventional thermal or chemical decontamination processes. This food preservation method involves the use of intense, short-duration pulses of broad-spectrum light. The germicidal effect appears to be due to both photochemical and photothermal effects. Several high intensity flashes of broad spectrum light pulsed per second can inactivate microbes rapidly and effectively. However, the efficacy of pulsed light may be limited by its low degree of penetration, as microorganisms are only inactivated on the surface of foods or in transparent media such as water. Examples of applications to foods are presented, including microbial inactivation and effects on food matrices

Bacterial inactivation using pulsed light

Pulsed light is a new method intended for the decontamination of food surfaces using short, high frequency pulses of an intense broad spectrum. The effects of broad spectrum pulsed light on the survival of Listeria monocytogenes Scott A, Listeria monocytogenes CNL, Pseudomonas fluorescens MF37 and Photobacterium phosphoreum SF680 populations on agar and in a liquid medium were investigated during this study. The sterilisation system generated 1.5 J cm−2 per pulse with eight lamps for 300 μs. In the case of surface-seeded cells, a 7.8, 8.14 and >7.14 log reduction was obtained for L. monocytogenes, Ps. fluorescens MF37 and Ph. phosphoreum, respectively, after a single pulse of treatment. Inactivation levels were lower for depth-plated cells: indeed, 10 pulses of treatment achieved 1.6, 2.03 and 4.78 log reductions for L. monocytogenes ScottA, L. monocytogenes CNL and Ps. fluorescens MF37, respectively. After 5 pulses, Ph. phosphoreum exhibited a 4.6 log reduction. Similarly, bacterial cells in suspension treated with 3 pulses were reduced by 0.52, 0.8, 2.07 and 2.05 for L. monocytogenes Scott A, L. monocytogenes CNL, Ps. fluorescens MF37 and Ph. phosphoreum, respectively. No resistance to pulsed light was observed during our experiments

Effect of pulsed-light treatment on milk proteins and lipids

International audiencePulsed-light treatment offers the food industry a new technology for food preservation. It allows the inactivation of numerous micro-organisms including most infectious foodborne pathogens. In addition to microbial destruction, one can also question whether pulsed-light treatment induced conformational changes in food components. To investigate this question, the influence of pulsed-light treatment on protein components of milk was evaluated by using UV spectroscopy, spectrofluorometry, electrophoresis, and determination of amino acid composition. Pulsed-light treatment resulted in an increase of UV absorbance at 280 nm. The intrinsic tryptophan fluorescence of P-lactoglobulin (BLG) showed a 7 nm red shift after 10 pulses. SIDS-PAGE showed the formation of dimers after treatment of BLG by 5 pulses and more. No significant changes in the amino acid composition of proteins and lipid oxidation were observed after pulsed-light treatment. The obtained results indicated changes in! the polarity of the tryptophanyl residue microenvironment of BLG solutions or changes in the tryptophan indole structure and some aggregation of studied proteins. Hence, pulsed-light treatment did not lead to very significant changes in protein components; consequently, it could be applied to process protein foods for their better preservation

Réponse adaptative de Listeria monocytogenes au stress osmotique et froid: implication en sécurité des aliments

National audienceListeria monocytogenes est un pathogène psychrotrophe d’origine alimentaire, responsable d’infections humaines invasives. C’est un micro-organisme ubiquitaire et capable de survivre dans des conditions de stress froid et salin rencontrés dans l’industrie de la transformation et le traitement des aliments. Une stratégie utilisée par plusieurs bactéries et en particulier par L. monocytogenes pour l’adaptation au stress osmotique est l’accumulation des solutés compatibles. Ce pathogène utilise deux types de réponses adaptatives aux basses températures : l’ajustement de la fluidité membranaire par un changement de la composition des acides gras membranaires et l’accumulation d’osmolytes de l’environnement. Nous décrivons dans cette revue les mécanismes mis en jeu par L. monocytogenes pour répondre aux stress froid et osmotique liés aux procédés de fabrication alimentaire, et à montrer l’implication de cette adaptation en sécurité des aliments