Escherichia coli Contamination of Vegetables Grown in Soils Fertilized with Noncomposted Bovine Manure: Garden-Scale Studies

Abstract

In this study we tested the validity of the National Organic Program (NOP) requirement for a >120-day interval between application of noncomposted manure and harvesting of vegetables grown in manure-fertilized soil. Noncomposted bovine manure was applied to 9.3-m 2 plots at three Wisconsin sites (loamy sand, silt loam, and silty clay loam) prior to spring and summer planting of carrots, radishes, and lettuce. Soil and washed (30 s under running tap water) vegetables were analyzed for indigenous Escherichia coli. Within 90 days, the level of E. coli in manure-fertilized soil generally decreased by about 3 log CFU/g from initial levels of 4.2 to 4.4 log CFU/g. Low levels of E. coli generally persisted in manure-fertilized soil for more than 100 days and were detected in enriched soil from all three sites 132 to 168 days after manure application. For carrots and lettuce, at least one enrichment-negative sample was obtained <100 days after manure application for 63 and 88% of the treatments, respectively. The current >120-day limit provided an even greater likelihood of not detecting E. coli on carrots (>1 enrichment-negative result for 100% of the treatments). The rapid maturation of radishes prevented conclusive evaluation of a 100-or 120-day application-to-harvest interval. The absolute absence of E. coli from vegetables harvested from manure-fertilized Wisconsin soils may not be ensured solely by adherence to the NOP >120-day limit. Unless pathogens are far better at colonizing vegetables than indigenous E. coli strains are, it appears that the risk of contamination for vegetables grown in Wisconsin soils would be elevated only slightly by reducing the NOP requirement to >100 days.

Microbiological quality of organic vegetables produced in soil treated with different types of manure and mineral fertilizer

“…Internalization of bacteria in seedlings is more likely in hydroponic systems than in soil (25,62), but internalization and transport throughout the plant can still occur in the latter growth medium (57). Collectively, the literature on bacterial colonization of plants and internalization suggests that the critical time for preventing vegetable contamination with manure fertilizer may be at the time of planting (28).…”

Hygienic-sanitary quality of vegetables and evaluation of treatments for the elimination of indigenous E. coli and E. coli O157:H7 from the surface of leaves of lettuce (Lactuca sativa L.)

“…Bolton et al (1999) detected E. coli O157: H7 in soil 99 days after a fecal suspension containing this organism was applied to grassland. In the study by Ingham et al (2004), when no manure was applied, bird and/ or mammal recontamination was the cause of the apparent persistence of indigenous E. coli in manure-fertilized soils. According to the authors, the results of the manure-fertilized soil analyses suggested that the application of non-composted bovine manure sufficiently in advance of vegetable harvesting would present little additional risk beyond that associated with nonfertilized soil.…”

“…According to Ingham et al (2004), bovine manure is a well-known source of food-borne pathogenic bacteria and using it without prior treatment to destroy pathogens increases the likelihood of contaminating vegetables grown in manure-fertilized soils. Composting is an accepted manure pathogen reduction treatment, and compostgenerated heat is believed to eliminate pathogenic bacteria (INGHAM et al, 2004).…”

Escherichia coli Contamination of Lettuce Grown in Soils Amended with Animal Slurry

“…Pathogens persist in manure for a variable length of time, depending on the storage conditions, e.g., in stacked heaps or slurry tanks, which affect heat development, a main determinant of pathogen survival (5,20,22,26,39). When fresh or inadequately stored manure is used to fertilize vegetable crops, the pathogens present contaminate the soil, where their survival can vary from a few days to several months (29,30). Consequently, lettuce seedlings planted in animal slurry-amended soil are exposed to persistent pathogens either through roots embedded in the contaminated soil or via splash onto the leaf surface during irrigation or rain events.…”