Scientific Publications - Work Done by Microbiology Reader Bioscreen C

H. Bergis, A. Beaufort, M. Cornu, S. Rudelle, Variability of growth  of Listeria monocytogenes  in smoked salmon Artificially, 5th ASEPT International Conference, Laval, 17-18 mars 2004 / March 17-18, 2004, France, Food Safety, Abstracts of Posters, p. 6

ABSTRACT

Context : Within the framework of an assessment of the exposure to Listeria monocytogenes in smoked salmon, a study concerning the variability between strains of L. monocytogenes growth, was carried out. The experimental data obtained on the heterogeneity of growth of L. monocytogenes will be then used to validate predictive models of microbiology.

Methodology : Two methods allowing to estimate the variability between strains growth were used. The first one by spectrophotometry in a liquid medium and the second one by challenge-tests in smoked salmon. The study of the variability of growth in liquid medium was carried out with 25 strains of L. monocytogenes isolated from smoked salmon. The growth of these strains was followed at 12°C by measurement of optical density at 600 nm in TSB medium (Tryptone Soya Broth) with the automatic spectrophotometer Bioscreen C. The challenge-tests were carried out with 5 strains of L. monocytogenes selected among the 25 strains studied in liquid medium. These 5 strains were selected according to their characteristics of growth in broth. The challenge-tests were carried out at the temperatures of 4°C and 8°C in smoked salmon of known physicochemical characteristics. Results : The method by spectrophotometry made it possible to classify the 25 strains of L. monocytogenes according to their kinetic of growth in liquid medium while revealing significant differences between these strains. At 12°C, 23 strains have an identical behavior and 2 strains differ from this group: a slow strain with a µmax of 0.15 h^-1 and a fast strain with a µmax of 0.18 h^-1. The adjustment of a primary model to growth curves obtained by challenge-tests allowed to estimate the growth rates of L. monocytogenes at the 2 studied temperatures. At 8°C, the growth rates estimated vary between 0.58 d^-1 and 1.17 d^-1. At 4°C, the highest growth rate is 0.46 d^-1 and slowest is about 0.27 d^-1. The differences in kinetic of growth observed at 8°C seem of greater amplitude than to 4°C.

Conclusion : These results highlight a variability of behavior of the strains within the species of L. monocytogenes and show that it is important to take into account this strain effect in growth modeling. It comes out from this study that the classification of the strains established according to their speed of growth is different in TSB medium and in smoked salmon. This shows the importance in elaborating a liquid medium having characteristics close to the food studied to obtain a good adequacy between the 2 methods.

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Last modified: May 25, 2005