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 (∼0.5-0.7 CFU/25 mL) or high level (∼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.

Highlights: This study is the first to compare a wide range of commercial test kits for detection of Salmonella and E. coli O157:H7 in SSIW.