Purpose: The objective of this study was to evaluate four different STEC detection methods for their efficiency in identifying STEC in environmental samples.
Methods: For this objective, culturing method on Sorbitol MacConkey agar (CT-SMAC) or rainbow agar, multiplex PCR detecting stx1/2 and rfb genes for STEC and O157 serotype respectively, immunomagnetic bead-based immuno-fluorescent assay (IFA), and commercial Dryspot E. coliSeroscreen kit were compared for their sensitivity and specificity in identifying STEC in various environmental samples including rectal swabs, water, soil and feed.
Results: Of 482 samples tested, 127 were positive for O157 STEC and 196 were positive for non-O157 STEC. All positive samples were detected by multiplex PCR (100%); however, culture methods, IFA, and commercial Dryspot Seroscreen kit could detect only 68%, 86%, and 39% of the positive samples, respectively. Additionally, culture methods showed higher false-positive rates (23%) than other three methods tested. To our knowledge, this is the first study which compared multiple STEC detection methods for environmental samples.
Significance: Our results indicate that PCR is the most reliable method for detection of STEC in complex samples with highest specificity and sensitivity than other methods. Also it is suggested culture method alone is not sufficient to detect STEC in complex samples. Further study will be needed to confirm the efficiency of PCR in STEC detection from food samples. We believe employing PCR as a routine STEC monitoring system will improve food safety.