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

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.

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“…A recent report suggests that the frequency and level of flour contamination may be much higher than previously believed (Mäde et al, 2017). The presence of pathogenic bacteria poses a serious risk to consumers because of cross contamination or consumers handling habits such as ingesting raw cookie dough (Rose et al, 2012).…”

Safety assessment and microbiological quality of homemade soy‐cheese in Nigeria

“…Additionally, Camino Feltes, Arisseto‐Bragotto, and Block () documented that it is one of the commonly known agents which causes diarrhea, abdominal pain, vomiting, and/or nausea. Mäde, Geuthner, Imming, and Wicke () and de Quadros Rodrigues et al () independently confirmed the prevalence of E. coli in cereals and legumes.…”

Microbiological Survey of Wheat Flour Sold at Retail in Canada, 2018 to 2019

“…A study has suggested that the level of STEC in contaminated flour samples were below 1 MPN/100g (23). Another study results revealed that isolation of STEC was independent on the presence of generic E. coli of flour samples (34). Therefore, it is not surprising that non-O157 STEC positive samples had generic E. coli below the limit of detection (<0.48 log CFU/g).…”

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