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24, chemin de Borde Rouge –Auzeville – CS52627
31326 Castanet Tolosan CEDEX - France

Dernière mise à jour : Mai 2018

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PhD thesis of Taous Saraoui (2013-2016)

Taous Saraoui
Mechanisms of interaction between a bioprotective bacterium with a seafood biopreservation interest "Lactococcus piscium CNCMI-4031" and the pathogenic bacterium Listeria monocytogenes (M.F. Pilet, F. Leroi)

Abstract :

Lactococcus piscium CNCM I-4031, a psychrotrophic lactic acid bacterium isolated from raw salmon, is able to inhibit the growth of Listeria monocytogenes by 3 to 4 log CFU g-1 in peeled cooked shrimp. To characterize this inhibition a chemically defined medium was developed and the inhibition reproduced. In addition of growth inhibition, L. piscium reduced virulence of L. monocytogenes. Scan electronics microscopy showed that L. monocytogenes cells were elongated and cell walls damaged in presence of L. piscium. The mechanism involved in this inhibition are not due to excretion of antimicrobial molecules nor nutritional competition. It requires cell-to-cell contact and may be controlled by quorum-sensing. To elucidate the mechanism involved in this inhibition, the genome of L. piscium CNCM I-4031 was sequenced and expert annotation was performed. In addition, the gene expression of L. piscium in pure culture and in co-culture with L. monocytogenes using RNA-Seq approach was compared. By compiling the results of both approaches, 13 potential target genes clusters were highlighted. There are involved in biosynthesis and transport of bacteriocins, quorum sensing mechanism, pili formation, bacterial competence and CAZymes. Deeper investigation of the results is necessary to select potential target genes for a functional approach with construction of mutant of L. piscium. At last, applied trial of L. piscium in association with Carnobacterium divergens V41, a bioprotective strain producing a bacteriocin, proved the efficiency of this cocktail to improve the quality and security of peeled cooked shrimp.

Valorisation :

  • Saraoui, T., P. A. Fall, F. Leroi, J.-P. Antignac, S. Chéreau and M. F. Pilet 2016. Inhibition mechanism of Listeria monocytogenes by a bioprotective bacteria Lactococcus piscium CNCM I-4031. Food Microbiology 53: 70-78. Ranking du JCR: Q1.
  • Saraoui, T., F. Leroi, J. Björkroth and M. F. Pilet 2016. Lactococcus piscium: a psychrotrophic lactic acid bacterium with bioprotective or spoilage activity in food—a review. Journal of Applied Microbiology 121(4): 907-918. Ranking du JCR: Q3.
  • Saraoui, T., J. Cornet, E. Guillouet, M. F. Pilet, F. Chevalier, J.-J. Joffraud and F. Leroi 2017. Improving simultaneously the quality and safety of cooked and peeled shrimp using a cocktail of bioprotective lactic acid bacteria. International Journal of Food Microbiology 241: 69-77. Ranking du JCR: Q1.
  • Saraoui, T., F. Leroi, F. Chevalier, J.-M. Cappelier, D. Passerini and M.-F. Pilet 2018. Bioprotective Effect of Lactococcus piscium CNCM I-4031 Against Listeria monocytogenes Growth and Virulence. Frontiers in Microbiology 9(1564). Ranking du JCR: Q1.