The University of Vermont has received a $500,000 three-year grant from the Food and Drug Administration to determine how long E. coli will survive in soil after raw manure and a spray containing benign forms of the bacteria are applied to it.  

The results of the research trials, which began last week, will help inform an important revision of a proposed produce safety rule in the Food Safety Modernization Act, the most sweeping reform of food safety regulation in over 70 years. 

The 2011 law was prompted by a spate of deadly incidents involving hamburger and spinach contaminated with a rare pathogenic form of the E. coli bacterium, O157:H7. Initially it called for a nine-month waiting period before crops fertilized with raw manure, which can contain E. coli, although very rarely the dangerous type, could be sold.

But during the public comment period that preceded the law’s implementation and in field hearings held across the country, including in Vermont, growers complained that a nine-month wait would all but eliminate their ability to bring produce to market during a growing season. 

In response, FDA, working in partnership with the USDA Agriculture Research Service, is conducting trials at five sites around the country to determine the die-off rate of E. coli, and will revise its rules on what constitutes a safe waiting period based on the results.  

The UVM trial is the only one taking place in the Northeast and will be used to determine E. coli die off rates in cold climates and in northeastern soils.  

Principal investigators on the UVM grant are Deb Neher, chair of the Plant and Soil Science Department, a soil ecologist who studies the microbiology of compost, and Nutrition and Food Sciences professor Cathy Donnelly, an expert in the microbiology of food safety.

“The concerns expressed in Vermont at the field hearings were loud and clear,” said Donnelly. The nine month waiting period “would significantly impact their bottom line. The reaction was basically, ‘Forget it; we’re not able to grow any crops with that kind of constraint.’ We see our role as helping make this a data-driven decision.”  

Vermont Sen. Patrick Leahy and his staff organized the Vermont field hearings.

Neher and Donnelly have set up their test fields on UVM land roughly an acre in size on either side of Spear Street in South Burlington near Wheelock Farm.

The experimental design of the research calls for three treatments: raw manure applied to the top of the soil, raw manure tilled into the soil and a cocktail of three E. coli varieties sprayed into the soil. The E. coli in the spray and the manure, which is analyzed before it is applied, are all benign but serve as effective surrogates for the deadly strain of the bacterium. 

Following a set schedule all the test sites adhere to, the researchers will test soil samples frequently in the early weeks of the project and less frequently as time goes on. "The idea is to create a die-off chart to see what the persistence is," Neher said. 

Donnelly and Neher will reapply manure, as farmer do, along with the three E. coli cocktail, in the spring and then plant spinach and other leafy greens. They’ll continue to monitor both soil and plants, which can “uptake”  E. coli into their stems and leaves. The experiment, which follows the same experimental design at all the FDA sites, will be repeated for two more years so results can take into account variability in weather.   

The FDA has said it will wait for five to 10 years to gather and analyze evidence from the test sties before setting new rules on the wait period. At other sites, which have begun their experimental trials, E. coli appear to die off within weeks of the raw manure being applied.  

A final Vermont field hearing will be held Nov. 17 at Vermont Law School. Learn more on the Vermont Agency of Agriculture, Food and Markets website.