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Optimisation de la recherche des Escherichia coli producteurs de Shiga-toxines (STEC)

Abstract : The Shiga toxin producing E. coli (STEC) are an emerging cause of food-borne illness and have become a public health priority. Paradoxically, there is no European microbiological criteria for detecting STEC in foodstuffs.
The aim of our study is to investigate the current main protocols used for detecting STEC, in order to suggest new optimized protocols to the manufacturers, which could limit the risk of distributing contaminated foodstuffs. Thus, growth follow-up and modeling of the simultaneous growth of several STEC strains and the background microflora of different matrices were carried out in various enrichment conditions.
The present study shows that when the level of STEC contamination is low, a short enrichment step (e.g. 6 hours for the IMS protocol (ISO EN 16654)) is not sufficient to detect STEC and could lead to false-negative results. However in particular conditions, it is not useful to extend the duration of the enrichment step because a simple competition between the STEC and the background microflora stops the STEC growth. The STEC growth duration depends on the matrix analysed and on its density in background flora. The growth duration varies between 4 and 7h for bovine faecal samples, and from 10 and 12h for ground beef samples in our experiments. For milk samples, another kind of interaction stops the STEC growth before that of the background flora (from 8,5 to 11h in our experiments).
Selective ingredients are often added to enrichment broths in order to improve the growth of STEC by limiting the growth of background microflora. The use of bile salts in enrichment broths has a positive impact for detecting STEC from bovine faecal and milk samples, but has little effect for detecting STEC from ground beef. However, the addition of novobiocin into enrichment broths inhibits the growth of some non-O157:H7 STEC strains, and slows down the growth of some E. coli O157:H7 strains. In order to avoid false-negative results, we strongly suggest that novobiocin should not be systematically added into enrichment broths for detecting STEC from food.
Finally, an optimisation of the current French testing protocol is proposed to detect E. coli O157:H7 in ground beef [ISO 16140] with a higher sample size and a reduced testing duration, while maintaining accuracy and taking into account the industry work flow and its economic constraints.
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https://tel.archives-ouvertes.fr/tel-00139179
Contributor : Antoine Vimont <>
Submitted on : Thursday, March 29, 2007 - 4:13:08 PM
Last modification on : Monday, October 19, 2020 - 11:06:39 AM
Long-term archiving on: : Tuesday, April 6, 2010 - 10:42:25 PM

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  • HAL Id : tel-00139179, version 1

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Antoine Vimont. Optimisation de la recherche des Escherichia coli producteurs de Shiga-toxines (STEC). Sciences du Vivant [q-bio]. Université Claude Bernard - Lyon I, 2007. Français. ⟨tel-00139179⟩

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