"We were able to find transmission of pathogens happening across 400 feet," Thakur said of the earlier project. "What did we learn - maybe the 400-foot distance isn't enough. Maybe there's a way we can possibly reduce the distance because not every farm can afford 400 feet."
The previous study examined pathogen transmission at NCSU's Piedmont Research Station as well as on three small-scale farms in North Carolina and two in Tennessee. The current project will be conducted exclusively at the Piedmont Research Station to give them more control over the experiment. Using the university's facility, a 2,500-acre working farm, also allows the researchers to collect enough produce samples to develop a substantial dataset.
They began by planting a 100-foot-by-160-foot vegetative buffer zone between each animal operation (chicken house and dairy unit) and the adjacent produce field. Each vegetative buffer zone has five different layers, based on plant height, and includes poplar, loblolly pipe, shrubs and different types of grasses. Depending on the season, each produce field is planted with lettuce or tomatoes.
Throughout the growing season, researchers will collect produce samples and assay them for the presence of STEC and Salmonella. They also will sample the vegetative buffer zones as well as the manure from the chicken house and dairy unit and test them for STEC and Salmonella.
Later this year, Thakur said they plan to remove each vegetative buffer zone in phases, collecting samples along the way to gauge its impact on reducing pathogen transmission between the animal operations and the produce field.
The researchers are taking testing a step further and using whole genome sequencing to identify the pathogen strains present in each sample. This will allow them to determine whether any of the pathogen strains found in the animal manure became airborne and were trapped by the buffer or transmitted to the produce.
"There are different strains from different sources," Thakur said, adding they've identified 30 strains of Salmonella just from the cattle and chickens. "This is where we have to look to see if it's the same strain or a different strain when we compare samples. Then I think it will become clearer.
"Further, it's evident that when soil is contaminated, we have few tools to remediate the presence of these pathogens, and transmission may be occurring directly from soil to produce instead of from the animal operations. Our research indicates there is a significant need for soil remediation tools that farmers can implement in addition to reducing transmission by implementing a vegetative buffer zone."
Although the researchers still have more crops to plant and sample, Thakur said he's hopeful they can develop a viable and economical system that will help these small-scale operations reduce the risk of airborne transmission of pathogens from animals to nearby produce. If the research is successful, he said the results should be applicable to farms of all sizes.
"Our hope is it will reduce the contamination, but we have to understand that we cannot absolutely prevent it," he said. "But this could also help us better use the land that is available to us."
