Evaluation of PCR-based methods for the identification of enteroaggregative hemorrhagic Escherichia coli in sprouts

Abstract

In this study real-time PCR assays were evaluated for the detection of enteroaggregative hemorrhagic Escherichia coli (EAHEC) O104:H4 in artificially contaminated mung bean and/alfalfa sprouts inoculated with 1, 10, and 100 CFU of EAHEC O104:H4 per 25 g sample (20, 10, and 2 replicates respectively). After selective culture enrichment the samples were tested using commercial real-time PCR kits detecting aggR/aaiC, stx/eae, and wzxO104. Using the commercial real-time PCR kits, the artificially contaminated samples were detected in the range of 75–80% positive results when contaminated with approximately 1 CFU, and 100% at 10 and 100 CFU. Microbiological detection employing O104-specific immunomagnetic capture and plating onto chromogenic media (modified Rainbow Agar and CHROMagar STEC) and confirmation by latex agglutination and PCR gave similar results (Cohen's kappa value between 0.61 and 1). In addition, the real-time PCR assay targeting the aggR and aaiC genes, indicative of enteroaggregative Escherichia coli (EAggEC), was tested against a panel of 60 bacterial strains and demonstrated 100% exclusivity (54 strains) and 100% inclusivity (6 strains). This study demonstrates the efficacy of the real-time PCR assays for the specific and sensitive detection of EAHEC from spouts.