Purpose: Compare the performance of AOAC certified rapid methods with the FDA BAM method for detection of Escherichia coli O157:H7 in artificially inoculated alfalfa sprout spent irrigation water. The methods selected include four lateral flow tests (Reveal, RapidChek, Singlepath, VIP Gold), three enzyme immunoassays (VIDAS UP, Assurance EIA, TECRA VIA), and six DNA-based assays (BAX MP, GeneDisc, iQ-Check, MicroSEQ, foodproof, Assurance GDS).
Methods: Twenty-five ml of spent irrigation water collected from a commercial sprouting facility was inoculated with 0, 1, or 10 CFU of E. coli O157:H7 and was subjected to the recommended enrichment and assay protocols, including both the shorter version (6-10h) and the 16-24h enrichment. Regardless of assay results, the presence of E. coli O157:H7 in the enrichments was determined using procedures outlined in the FDA BAM.
Results: Following the 16-24h enrichment protocols, all the DNA-based methods were able to detect the presence of E. coli O57:H7 at the 10 CFU/25 ml level, although performances differed when testing samples spiked at the 1 CFU/25 ml level. Assurance GDS and BAX performed better, probably due to the use of more selective enrichment media. For the immunoassay-based methods, using the shorter enrichment protocols, all methods underperformed when compared with the BAM, with VIP Gold and Assurance EIA performing better than others. When the longer enrichment protocols were followed, Reveal, RapidChek, VIDAS UP, and Tecra performed equally or better than the BAM.
Significance: Not all AOAC certified methods can perform well for testing low levels of E. coli O157:H7 in sprout spent irrigation water. Enrichment media used by each test kit play a key role in determining the sensitivity of the method.