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Inhibition of Listeria monocytogenes by a combination of chitosan and divergicin M35

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The antimicrobial activities of the class IIa bacteriocin divergicin M35 and several types of chitosan against Listeria monocytogenes were quantified by agar diffusion, critical micro-dilution, and viable count and observed by electron microscopy. Antimicrobial activity of chitosan depended on its molecular mass (MM) and the pH. Three chitosans with MM values of 2, 20, and 100 kDa and 87.4% degree of deacetylation (DDA) were chosen for further study, based on high anti-listerial activity at pH 4.5. Electron microscopy suggested that the mechanism of anti-listerial activity also varied with the MM. Low-MM chitosan appeared to inhibit L. monocytogenes by affecting cell permeability and growth, whereas medium- and high-MM chitosan may form a barrier on the cell surface that prevents entry of nutrients. The minimum inhibitory concentrations (MICs) of 2, 20, and 100 kDa chitosan and divergicin M35 against a divergicin-resistant strain of L. monocytogenes (LSD 535) were 2.5, 2.5, 0.625, and 0.25 mg/mL, respectively. The combination of any of these 3 chitosans and divergicin M35 appeared to have an additive effect against L. monocytogenes, as determined by fractional inhibitory concentration (FIC) index. This study provides useful data for the development of chitosan films incorporating divergicin M35 for inhibiting L. monocytogenes in foods.

Les effets antimicrobiens de la divergicine M35, une bactériocine de classe IIa, et de plusieurs types de chitosane envers Listeria monocytogenes ont été quantifiés par la méthode de diffusion sur gélose, la méthode de dilution sur microplaques, le dénombrementdes cellules viables et par observation en microscopie électronique. L’activité antimicrobienne des chitosanes dépendait de leur masse moléculaire (MM) et du pH. Trois chitosanes de 2, 20 et 100 kDa, déacétylés à 87.4 %, ont été choisis dans les études subséquentes, à cause de leur forte activité anti-listeria à pH 4.5. La microscopie électronique a suggéré que le mécanisme associé à l’activité anti-listeria variait aussi en fonction du MM. Le chitosane de faible MM semblait inhiber L. monocytogenes en affectant la perméabilité et la croissance cellulaires, alors que les chitosanes de MM moyenne ou élevée peuvent former une barrière à la surface de la cellule, empêchant ainsi l’entrée des nutriments. Les concentrations minimales inhibitrices (CMI) des chitosanes de 2, 20 et 100 kDa et de la divergicine M35 envers une souche de L. monocytogenes résistante à la divergicine (LSD 535) étaient de 2.5, 2.5, 0.625 et 0.25 mg/mL respectivement. La combinaison d’un des 3 chitosanes et de la divergicine M35 semblait avoir un effet additif envers L. monocytogenes, tel que déterminé par l’indice de concentration inhibitrice fractionnée « FIC index ». Cette étude fournit des données utiles pour le développement de films de chitosane où la divergicine M35 est incorporée afin d’inhiber L. monocytogenes dans les aliments.

Document Type: Research Article

Publication date: 2009-04-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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