Callahan Mary Theresa, Micallef Shirley A, Sharma Manan, Millner Patricia D, Buchanan Robert L
Department of Nutrition and Food Science, University of Maryland, College Park, Maryland, USA.
Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland, USA.
Appl Environ Microbiol. 2016 Jun 13;82(13):3746-3753. doi: 10.1128/AEM.00052-16. Print 2016 Jul 1.
The California Leafy Green Products Handler Marketing Agreement (LGMA) requires leafy green crops within 9 m of the edge of a flooded field not be harvested due to potential contamination (California Leafy Green Products Handler Marketing Board, Commodity Specific Flood Safety Guidelines for the Production and Harvest of Lettuce and Leafy Greens, 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.
This 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.
《加利福尼亚绿叶蔬菜产品处理商营销协议》（LGMA）规定，由于存在潜在污染风险，距离被洪水淹没田地边缘9米以内的绿叶蔬菜作物不得采收（加利福尼亚绿叶蔬菜产品处理商营销委员会，《生菜和绿叶蔬菜生产与采收特定商品洪水安全指南》，2012年）。此外，先前被洪水淹没的土壤在60天内不应重新种植。在本研究中，评估了LGMA指标对美国中大西洋地区农场的适用性。在马里兰州贝尔茨维尔一块坡度为-5%的土地上建立的菠菜种植床上端，用含有6 log CFU/ml大肠杆菌的水淹没，以模拟细菌在土壤中移动的最坏情况。通过最大可能数（MPN）分析，在长达63天的时间里，测定距离洪水边缘9米范围内土壤和叶组织中的大肠杆菌流行情况。在春季试验中，1天内在9米处迅速检测到大肠杆菌，秋季试验中3天内检测到，但14天后在洪水区域外的植物上未检测到大肠杆菌。在两次试验的第63天，洪水区域土壤中的大肠杆菌数量秋季高于春季。回归分析预测，洪水区域内大肠杆菌数量减少3-log MPN/g（干重）所需的时间在春季符合LGMA的60天指导方针，但在秋季需要90天。总体而言，数据表明当前指南应进行修订，以纳入对可能促进细菌移动和存活的田间和天气条件的考虑。
本研究追踪了大肠杆菌从洪水穿过土壤水平面的移动情况以及远处绿叶蔬菜产品受污染的可能性。本研究的目的是探讨《加利福尼亚绿叶蔬菜产品处理商营销协议》中关于洪水事件后绿叶蔬菜作物采收建议的有效性。这些建议基于农业设备的转弯半径，但未考虑水中病原体通过土壤的潜在地下移动。本研究表明，可能需要进一步考虑田间坡度、温度和额外降雨事件，以提供适当的指南，防止采收被洪水中肠道病原体污染的绿叶蔬菜作物。本研究可用于为种植者提供洪水事件后良好采收实践的综合建议框架。
