Detection and isolation of Shiga-Toxin producing Escherichia coli in flour in Germany between 2014 and 2017

Dietrich Mäde,Rainer Imming,Amal Wicke,Anne-Catrin Geuthner

doi:10.1007/s00003-017-1113-1

Abstract

Official control samples of wheat and rye flour were analyzed for the presence of Shiga-toxin producing Escherichia coli (STEC) in 25 g. The detection procedure was based on enrichment in buffered peptone water and Tryptone Bile X-Glucuronide agar, followed by multiplex real-time PCR with an internal positive control. Positive samples were sub-cultured for strain isolation by a two-step procedure. In the first step, ten colonies were picked from each plate, pooled, and analyzed by real-time PCR. In addition, a bacterial material from the part with heavy growth was analyzed. If the 1st isolation attempt failed, in a second step all colonies from molecular positive plates were picked, sub-cultured, pooled and analyzed. 39% of test samples were positive by real-time PCR. STEC was isolated from 17 test samples corresponding to 19%. Molecular detection is linked to the presence of quantifiable numbers of E. coli, whereas the grain species did not have an influence. There is a non-significant correlation with some mills indicating some technological or hygienic problems in those facilities. Increasing the number of subsamples did improve the detection rate. Our findings show the frequent presence of STEC in flour in Germany.

Highlights

Shiga-Toxin producing Escherichia coli (STEC) is a major cause of severe human gastroenteritis (Karmali 2004; EFSA Panel on Biological Hazrads (BIOHAZ) 2013; Karch et al 2015)
Our findings show the frequent presence of Shiga-toxin producing Escherichia coli (STEC) in flour in Germany
This paper describes the molecular detection and microbial isolation of STEC in flour samples

Summary

Introduction

Shiga-Toxin producing Escherichia coli (STEC) is a major cause of severe human gastroenteritis (Karmali 2004; EFSA Panel on Biological Hazrads (BIOHAZ) 2013; Karch et al 2015). Since 2016, reports of the presence of STEC in contaminated flour have been published (CDC 2016; Gieraltowski et al 2017; Wu et al 2017). Neil et al (2012) reported STEC in uncooked cookie dough first, but could not trace back this contamination to flour unambiguously. A U.S company initiated a voluntary recall of wheat flour and products contaminated with STEC O121 and O26 (CDC 2016). These findings highlight the risk of pathogenic STEC in flour and flour products. Risky consumption of raw cookie dough or cake batter is quite

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