Quantification des bactéries histaminogènes et maîtrise de la formation d'histamine dans les produits marins par biopréservation

Histamine-producing bacteria were isolated from naturally contaminated seafood, some of responsible for histamine-poisoning. At the same time, lactic acid bacteria were isolated on the same products and clustered according to their inhibitory activity against 4 histamine-producing species. Most of the strains were identified as Lactobacillus fuchuensis or Lactobacillus sakei. Twelve lactic acid bacteria were selected for challenge-test on canned, cooked or smoked tuna. Challenge-test combined with sensory analysis performed on cooked vacuum-packed tuna against Morganella psychrotolerans and Morganella morganii, demonstrated an important inhibitory effect on growth and production of histamine with L. sakei CNCM I-4707. Bacterial count was reduced by 3 to 5 log CFU/g and histamine production was reduced under 50 mg/kg by L. sakei after 4 days of storage at 15°C and 11 days at 4°C (for M. psychrotolerans). Based on sensory evaluation, biopreservation performed with L. sakei also extended the shelf-life of cooked tuna up to 8 days at 15°C. A real-time PCR method specific of M. psychrotolerans and M. morganii with a selective enrichment step was developed. After enrichment, this method allowed to quantify M. psychrotolerans and M. morganii between 50 CFU/g to 104 CFU/g, while direct amplification quantified these bacteria between 104 CFU/g to 109 CFU/g. Finally, the development of a new RT-qPCR method was initiated to demonstrate an over-expression of the genes involved in the reduction of histidine into histamine under acidic stress.