Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 24, 2011
Publication Date: July 30, 2011
Citation: Patel, J.R., Singh, M., Darlington, L.K. 2011. Persistence of poultry associated Salmonella spp. on spinach plants [abstract]. International Association for Food Protection Proceedings. 2011 IAFP Abstract Book# P2-76.
Introduction: Pre-harvest spinach contamination can occur via irrigation water and can influence the persistence of Salmonella on spinach leaves. Salmonella persistence on spinach plants should be evaluated as nearby poultry farms can be a critical source of contaminated water run-off.
Purpose: The purpose of this study was to compare the persistence of Salmonella on spinach leaves when contaminated with strains isolated from produce and poultry. Further, efficacy of the California Leafy Green Marketing Agreement (LGMA) irrigation water quality criteria applied to spinach plants was also evaluated.
Methods: Five strain mixtures of Salmonella; poultry and produce isolates were cultivated in water extracts of dairy manure solids. The individual 3-week old spinach plants (‘Tyee Fe” cultivar) grown in BL-2 growth chamber were spray inoculated every 2 week with ~ 3 ml water containing 2.12 (low) or 4.12 (high) log Salmonella per ml. Plants were also irrigated with potable water every week to maintain plant turgidity. Three 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 undetectable (< 1.1 MPN/g) on spinach leaves throughout the study when irrigation water was contaminated at low level of poultry or produce isolates. However, Salmonella were recovered every week from spinach leaves (4-5 log MPN/g) when inoculated at high level. Salmonella persisted at significantly higher numbers on spinach plants when contaminated with produce isolates.
Significance: Longer persistence of Salmonella on spinach leaves when contaminated at a high inoculum level reinforces need for water quality standards such as the California LGMA. Comparative evaluation of contamination sources (irrigation water) should be studied at the field levels.