PhD thesis of Gaëtan Podeur (2011-2014)

Abstract:

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. M. psychrotolerans count was reduced by 3 to 5 log UFC/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. 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.

Valorisation:

• Podeur, G., P. Dalgaard, F. Leroi, H. Prevost, J. Emborg, J. Martinussen, L. H. Hansen and M. F. Pilet 2015. Development of a real-time PCR method coupled with a selective pre-enrichment step for quantification of Morganella morganii and Morganella psychrotolerans in fish products. International Journal of Food Microbiology 203: 55-62. https://doi.org/10.1016/j.ijfoodmicro.2015.03.005. Ranking du JCR: Q1.