Metrics Proposed To Prevent the Harvest of Leafy Green Crops Exposed to Floodwater Contaminated with Escherichia coli

Abstract

, 2012). Further, previously flooded soils should not be replanted for 60 days. In this study, the suitability of the LGMA metrics for farms in the Mid-Atlantic region of the United States was evaluated. The upper end of a spinach bed (in Beltsville, MD) established on a ؊5% grade was flooded with water containing 6 log CFU/ml Escherichia coli to model a worst-case scenario of bacterial movement through soil. Escherichia coli prevalence in soil and on foliar tissue was determined by most probable number (MPN) analysis at distances up to 9 m from the edge of the flood for 63 days. While E. coli was quickly detected at the 9-m distance within 1 day in the spring trial and within 3 days in the fall trial, no E. coli was detected on plants outside the flood zone after 14 days. On day 63 for the two trials, E. coli populations in the flood zone soil were higher in the fall than in the spring. Regression analysis predicted that the time required for a 3-log MPN/g (dry weight) decrease in E. coli populations inside the flood zone was within the 60-day LGMA guideline in the spring but would require 90 days in the fall. Overall, data suggest that the current guidelines should be revised to include considerations of field and weather conditions that may promote bacterial movement and survival. IMPORTANCEThis study tracked the movement of Escherichia coli from floodwater across a horizontal plane of soil and the potential for the contamination of distant leafy green produce. The purpose of this study was to address the validity of the California Leafy Green Products Handler Marketing Agreement recommendations for the harvest of leafy green crops after a flooding event. These recommendations were based on the turning radius of farming equipment but did not take into consideration the potential subsurface movement of pathogens in the water through soil. This research shows that further considerations of field slope, temperature, and additional rainfall events may be necessary to provide appropriate guidelines to prevent the harvest of leafy green crops contaminated by enteric pathogens in floodwaters. This study may be used to provide a framework for comprehensive recommendations to growers for good harvesting practices after a flooding event.L eafy green vegetables are vulnerable to contamination from a variety of sources, including contaminated manure, soil, irrigation water, and contact with wildlife and/or their feces. This vulnerability is partly due to the fact that edible plant portions grow low to the ground and have no protective layers such as peels, shells, or skins (1). The California Leafy Green Products Handler Marketing Agreement (LGMA) has recommended that farmers not harvest any leafy green crops within a minimum of 30 ft (9 m) from the edge of a flood and that they wait 60 days before replanting the soil that had been underwater (2). The 9-m buffer zone was based on the turning radius of farming equipment to prevent cross contamination, via the tires, between flooded crops and leafy greens that had not cont...

Survival of Escherichia coli in Manure-Amended Soils Is Affected by Spatiotemporal, Agricultural, and Weather Factors in the Mid-Atlantic United States

“…Other work evaluating the survival of a multistrain inoculum of nonpathogenic E. coli in soils flooded with diluted dairy manure runoff has shown that survival durations in a clay loam soil were longer in a fall season compared to spring season (38). In that study, slow die-off E. coli in manure-amended soils in the fall season compared to a spring season was attributed to lower temperatures and exposure to less UV (i.e., UV-B) radiation.…”

A System Model for Understanding the Role of Animal Feces as a Route of Contamination of Leafy Greens before Harvest

“…Although the Weibull model was used for E. coli O157:H7 survival in soil (11), we used the log-linear survival models for model simplification and an increase in computational efficiency. Log-linear survival models have been reported previously for survival of E. coli O157:H7 in soil (32,33).…”

Overview of the Potential Impacts of Climate Change on the Microbial Safety of the Dairy Industry

“…In turn, extreme weather events, such as flooding, were shown to increase the prevalence of Escherichia coli and Salmonella spp. [26,27]. In addition, rain splashing and storm water runoffs were also shown to facilitate the dispersal of microbial contamination from soil to crops [22,28].…”