[1] Ecole Natl Vet Lyon, Unite Microbiol Alimentaire & Previsionnelle, F-69280 Marcy Letoile, France
[2] INRA, Microbiol Lab, Ctr Rech, F-63122 St Genes Champanelle, France
[3] Univ Auvergne Clermont 1, Grp Rech Pathogenie Bacterienne Intestinale, Fac Pharm, F-63001 Clermont Ferrand, France
[4] Robert Koch Inst, Div Microbial Toxins, D-13353 Berlin, Germany