Shiga Toxin producing E.coli (STEC, syn. VTEC) have been detected by the FSVO laboratories in swiss wheat and spelt flours. The isolated strains (except one) do not belong to serovars typically associated with human infections. To better understand the entry, horizontal transfer, and persistence of these bacteria in grain, flour, milling by-products, dough and semi-finished products, we aim to sample the fabrication process in swiss mills. In addition, the persistence of STECs in the mentioned products will be studied appliying challenge tests. Finally, a quantitative real time PCR based detection procedure of STEC from these products will be established with a particular focus on sampling, sample size and sample preparation.