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Détection et étude de l'expression de gènes de bactériocines de Bactéries lactiques dans les fromages

Abstract : We examined the presence of lactic acid bacteria (LAB) able to produce different bacteriocins in traditional Slovenian cheeses. In five samples of Tolminc cheese (from cows' milk) and four samples of Kraški ovčji sir (from ewes' milk) we looked for the presence 19 LAB bacteriocins' gene determinants using PCR. The DNA analysed was extracted directly from cheese samples as well as from cultivable microbial consortia of cheese which were isolated on CATC, Rogosa and M17 agar media. We used diffusion tests to determine the antimicrobial activity of microbial consortia against different indicator bacteria. Anti-staphylococcal activity was also determined in situ in milk and cheese. Competitive advantage of bacteriocinogenic strains was examined by consecutive propagation of microbial consortia in milk. During this we followed the presence of different bacteriocin gene determinants and antimicrobial activity of microbial consortia. The same properties were also determined for individual bacteriocinogenic strains that were isolated from initial consortia and from consortia obtained after propagation in milk. The success of finding bacteriocin gene determinants with PCR depended greatly on the efficiency of DNA extraction. The extraction of total DNA was the most successful when sodium citrate was used for cheese homogenisation. In DNA of different cheeses and microbial consortia we detected a number of bacteriocin gene determinants. Their number was reduced during the process of propagation in milk, which indicates a poor competitive advantage of some bacteriocinogenic strains. The results demonstrated competitive advantage only for strains that carried gene determinants for cytolysin. We detected bacteriocin activity in cheese only when monoculture of nisin A producer was added. The discrepancy between detected bacteriocin gene determinants and antimicrobial activity shows the complexity that links these two properties. This method will be very useful in the future studies of the role of bacteriocins in cheese.
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  • HAL Id : pastel-00711965, version 1
  • PRODINRA : 317134

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Aljosa Trmcic. Détection et étude de l'expression de gènes de bactériocines de Bactéries lactiques dans les fromages. Sciences agricoles. AgroParisTech, 2011. Français. ⟨NNT : 2011AGPT0038⟩. ⟨pastel-00711965⟩

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