Immunoconcentration of Shiga toxin-producing Escherichia coli O157 from animal faeces and raw meats by using Dynabeads anti-E. coli O157 and the VIDAS system

Abstract

To identify the reservoirs and routes of transmission of Shiga toxin-producing Escherichia coli (STEC) O157, sensitive detection and isolation methods are necessary. The sensitivity of traditional culture methods can be improved significantly by the inclusion of an immunoconcentration step, resulting in less false-negatives. In this report, we evaluated the results of two commercially available test systems: Dynabeads anti-E. coli O157 and the Vitek Immunodiagnostic Assay System (VIDAS) Immuno-Concentration E. coli O157 (ICE) kit. Additionally, we compared two selective isolation media for STEC O157. Statistical analysis of the results obtained for animal faecal samples (n=637) examined by both immunoconcentration methods showed that by the manual Dynabeads anti-E. coli O157 procedure systematically more samples were identified as positive than by the VIDAS ICE. In case of meat samples (n=360), no difference between the results of the two methods was found. In addition to being accurate, the Dynabeads anti-E. coli O157 method is a less expensive method than the VIDAS ICE. But, the Dynabeads method is laborious and there is a risk of cross-contamination. The VIDAS ICE procedure on the other hand is fully automated with a standardised performance; fast and safe for the user. Irrespective of the type of sample (faeces or meat) and the immunoconcentration technique applied (Dynabeads anti-E. coli O157 or VIDAS ICE) more samples were found positive after plating onto CHROMagar O157 with cefixime (0.025 mg l(-1)) and tellurite (1.25 mg l(-1)) than after plating onto sorbitol-MacConkey agar with cefixime (0.05 mg l(-1)) and tellurite (2.5 mg l(-1)). However, only in case of meat samples examined by the VIDAS ICE the difference between the isolation media was not statistically significant.