Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 9, 2010
Publication Date: August 1, 2010
Citation: Patel, J.R., Darlington, L.K. 2010. Survival of Salmonella on spinach leaves treated with contaminated irrigation water. International Association for Food Protection Proceedings. p.3-29.
Introduction: Salmonella outbreaks have been associated with the consumption of fresh produce. The produce may be contaminated with Salmonella during on-farm contact with contaminated water. Transmission of Salmonella from contaminated irrigation water to spinach plants in growth chamber settings requires further valuation.
Purpose: The purpose of this study was to evaluate the efficacy of the California Leafy Green Marketing Agreement (LGMA) establishing water quality criteria for irrigation water applied to spinach plants.
Methods: A green fluorescent protein-labeled Salmonella Typhimurium was cultivated in water extracts of dairy manure solids. Spinach cultivar “Whale” was grown in pasteurized sandy loom soil (3% organic matter) in BL-2 growth chamber (14 h day 21'C, 10 h night at 16'C, 50% RH). The individual 3-week old spinach plants were spray inoculated every 2 week with ~ 5 ml water containing 130 (low) or 13000 (high) Salmonella per 100 ml. Plants were also irrigated with potable water every week to maintain rigor. Four replicates of each plant shoot were analyzed on day 1 and weekly for up to 6 weeks for Salmonella populations by direct plating on XLT4 agar and MPN (enrichment in BPW followed by selective enrichment in tetrathionate broth and subsequent spot plating on XLT4 agar).
Results: Salmonella were not detected on spinach leaves after 1 day or after 6 weeks when irrigation water was contaminated at low or high level. A single irrigation event with very high level of contaminated water (1.3 x 107 Salmonella per 100 ml) resulted in survival of 8 x 104 Salmonella per plant after 1 day. Salmonella persisted on spinach leaves for at least 2 weeks when plants were irrigated at very high level.
Significance: Results may aid in understanding the role of irrigation water in Salmonella contamination on spinach leaves. The Persistence of Salmonella should be studied at the field levels to determine the efficacy of California LGMA Irrigation water standards.