Ergebnisse, Schlussfolgerungen und Empfehlungen aus zwei Ringversuchen zum Nachweis und zur Isolierung von Shiga (Vero) Toxin bildenden Escherichia coli (STEC) aus Hackfleischproben

For quality assurance the National Reference Laboratory for Escherichia coli at the Federal Institute for Risk Assessment had organized two ring trials in 2008 and 2009 (called RV2008 and RV2009) on the detection and isolation of Shiga toxin producing Escherichia coli (STEC) from minced beef samples. There were 23 (RV2008) and 26 (RV2009) participants from institutions dealing with the microbiological control of food. For the analysis, the participants received five samples of minced meat containing STEC and four samples without STEC. By comparing the results, a significant improvement of detection sensitivity and specificity was observed for RV2009. In RV2008, only 4 (17.4%) of the participants had identified all STEC-positive samples, compared to 14 (53.8%) in RV2009. The number of false-positive findings decreased from 17.4% (RV2008) to 3.8% (RV2009). Statistically significant differences between the participating laboratories were found by determination of concordance odds ratios. Most participants used methods for detection and isolation of STEC based on protocols that are officially recommended in Germany (§64 LFGB), such as Shiga toxin (Stx) ELISA/Colony Immunoblot, or stx-PCR/DNA colony hybridization. A strikingly low sensitivity when using the Stx-ELISA as detection method was observed for RV2008. This finding could be attributed to the use of a commercial Stx-ELISA (Novitek Veterinär) that showed deficiencies for identification of Stx1 and some variants of Stx2. It is recommended to use only detection systems that have been independently evaluated for their specificity and sensitivity. Real-time stx-PCR as a new method has been increasingly used and proved to be promising. The detection of enterohaemorrhagic E. coli O157: [H7] as the most common cause of Haemorrhagic Colitis (HC) and Haemolytic Uraemic Syndrome (HUS) should be improved by introduction of specific procedures (ISO16654), since only 2 of 26 participants successfully isolated this agent from a minced meat sample that contained two STEC strains.