Comparison of Commercial Test Kits for Detection of Salmonella and E. coli O157:H7 in Alfalfa Spent Sprout Irrigation Water

Background Sprout growers in the United States are required to test spent sprout irrigation water (SSIW) or in-process sprouts for Escherichia coli O157:H7 and Salmonella species. Pathogen screening kits are commercially available; however, few have been validated for analysis of sprouts or SSIW. Objective This study evaluated AOAC-certified test kits (lateral flow devices [LFDs], enzyme immunoassays [EIAs], and molecular assays) in comparison with culture methods described in the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) for detection of Salmonella and E. coli O157:H7 in alfalfa SSIW. Method Twenty-five milliliter aliquots of alfalfa SSIW, either uninoculated or inoculated with Salmonella or E. coli O157:H7 at a low (similar to 0.5-0.7 CFU/25 mL) or high level (similar to 10-20 CFU/25 mL), were subjected to the enrichment and assay protocols recommended by each test. Pathogen presence was confirmed following FDA BAM procedures and, if applicable, test kit manufacturer protocols. Results Twelve of the 13 Salmonella test kits evaluated (except VIDAS UP) performed well and detected Salmonella in 100% of SSIW samples contaminated at 0.61 CFU/mL. Performance varied among E. coli O157:H7 test kits, with four (Reveal, MicroSEQ, GDS, MDA) of 12 kits designed for next-day detection, and four (Reveal, VIP Gold, MicroSEQ, GDS) of seven kits designed for same-day detection capable of detecting the pathogen in 100% samples contaminated at 0.90 CFU/mL. Conclusions Enrichment conditions play a key role in determining the performance of test kits and the success of confirmation.