Articles scientifiques

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15 octobre 2006

Biofilm Formation and Biocides Sensitivity of Pseudomonas marginalis Isolated from a Maple Sap Collection System

Auteurs : Lagacé, L., Jacques, M., Mafu, A. A. et D. Roy

Cet article est disponible seulement en anglais (Journal of Food Protection, Vol. 69, No 10, October 2006, pp. 2320-2566, pp. 2411-2416(6)).

The susceptibility of planktonic and biofilm cells of Pseudomonas marginalis toward four commonly used biocides at different temperatures (15 and 30°C) and biofilm growth times (24 and 48 h) was assessed. Using the MBEC biofilm device, biofilm production in maple sap was shown to be highly reproducible for each set of conditions tested. Biofilm formation was influenced by growth temperature and time. A temperature of 15°C and incubation time of 24 h yielded fewer CFU per peg and showed fewer adhered cells and typical biofilm structures, based on scanning electron microscopy observations as compared with other conditions. Minimal biofilm eradication concentration values for P. marginalis were significantly greater (P < 0.001) than were MBCs for planktonic cells and for every biocide tested, with the exception of minimal biofilm eradication concentration values for peracetic acid at 15°C and 24 h. Sodium hypochlorite and peracetic acid sanitizers were able to eliminate P. marginalis biofilms at lower concentrations as compared with hydrogen peroxide- and quaternary ammonium-based sanitizers (P < 0.001). According to the results obtained, sodium hypochlorite and peracetic acid sanitizers would be more appropriate for maple sap collection system sanitation.

01 mai 2006

Compositions of maple sap microflora and collection system biofilms evaluated by scanning electron microscopy and denaturing gradient gel electrophoresis

Auteurs : L. Lagacé, M. Jacques, A. A. Mafu et D. Roy

Cet article est disponible seulement en anglais (International Journal of Food Microbiology, Volume 109, Issues 1–2, 25 May 2006, Pages 9–18). Le numéro de référence (Digital Object Identifier (DOI)) est le : 10.1016/j.ijfoodmicro.2006.01.004.

The bacterial microflora of maple sap and biofilms in collection system tubing were studied through the use of bacterial counts, scanning electron microscopy (SEM) of surfaces and the analysis of 16S rRNA gene by denaturing gradient gel electrophoresis (DGGE). Samples were taken at five times during the 2002 and 2003 seasons in order to follow the changes in the microflora of this complex ecosystem. Bacterial counts showed the growth of bacterial populations as the season advanced. These populations were mainly composed of psychrotrophic bacteria and Pseudomonas spp. SEM results confirmed the suspected presence of biofilms on the inner surfaces of tubing samples. Bacterial colonization and biofilm formation progressively increased during the season for both lateral and main line surfaces, and biofilms were mainly composed of rod shape bacteria. The bacterial microflora profiles obtained for sap and corresponding biofilm by DGGE showed up to 12 major bands. The Shannon-Weaver index of diversity (H) calculated from DGGE bands were statistically higher for sap samples compared to biofilm. The diversity index was relatively stable or increasing for lateral line sap and biofilm samples during the season while the diversity index for sap and biofilm samples of the main line showed a decreasing profile as the season progressed. Sequence analysis of major DGGE bands revealed the predominance of bacteria from the genera Pseudomonas, Rahnella and another, unidentified genus. The results describe the composition of sap collection system microflora as well as the formation of biofilms and will be useful for further studies on factors affecting maple product quality.

02 janvier 2006

Microbiology of maple sap and biofilm formation in maple sap collection system

Auteur : Luc Lagacé

Cet article est disponible seulement en anglais. Vous pouvez obtenir l'article auprès de l'Hokkaido University Press. L'article est  tiré de : M. Terazawa (ed) Tree sap III, Proceedings of the 3rd international symposium on sap utilization (ISSU) in Bifuka 2005, Hokkaido University Press, Sapporo, Japan.

Maple sap is the sweet exudate collected from maple trees during the spring season to produce maple syrup. It is a rich medium composed mainly of organic compounds and minerals that can support the growth of many species of microorganisms. These microorganisms are bacteria, yeasts and moulds that can develop in the taphole of maple trees as well as in the sap collection system in the form of a biofilm. The biofilm can be thought of as a reservoir of microorganisms that will continuously inoculate the sap and consequently modify its chemical composition. Microbial growth in maple sap as been known for a long time to be detrimental for maple syrup quality with regards to its colour, texture and taste. The microbial community of maple sap and biofilm was recently studied using molecular tools such as the amplified ribosomal DNA restriction analysis (ARDRA) and scanning electron microscopy. These methods have permitted the observation of the biofilm formation on the interior surface of tubing of the sap collection system and the characterization of maple sap microbiota by the identification of many species of bacteria in which, Pseudomonas species occupied an important place. A review of the results obtained with these techniques will therefore be presented here along with a comprehensive discussion on the relevant impact of these findings.

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