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E. coli thrives near plant roots

November 16, 2010  By Fruit & Vegetable


leafylettuceNovember 15, 2010 – E.
coli can live for weeks around the roots of produce plants and transfer to the
edible portions, but the threat can be minimized if growers don’t harvest too
soon, a Purdue University study shows.

November 15, 2010 – E.
coli
can live for weeks around the roots of produce plants and transfer to the
edible portions, but the threat can be minimized if growers don’t harvest too
soon, a Purdue University study shows.

Purdue scientists added E.
coli
to soil through manure application and water treated with manure and
showed that the bacteria can survive and are active in the rhizosphere, or the
area around the plant roots, of lettuce and radishes. E. coli eventually gets onto
the aboveground surfaces of the plants, where it can live for several weeks.
Activity in the rhizosphere was observed using a bioluminescent E. coli created
by Bruce Applegate that glows when active. Applegate, a co-author on the
project, is an associate professor in the food science and biological sciences
departments at Purdue.

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E. coli is actually quite
active in the rhizosphere. They're eating something there – probably plant
exudates,” said Ron Turco, a professor of agronomy and co-author of the study
published in the November issue of the Journal of Food Protection.

Turco said the E. coli
didn’t survive on the plants’ surfaces more than 40 days after seeds were
planted. Harvesting produce at least 40 days after planting should reduce the
possibility of contamination, but he warned that E. coli could still come from
other sources.

“In actual field
application, you pick up other things that are all around,” Turco said. “You
don’t just get the plants that are 40 days old. An animal getting loose in a
field could also contaminate plants.”

Mussie Habteselassie,
Turco’s former postdoctoral researcher and now an assistant professor of soil
microbiology at the University of Georgia’s Griffin campus, said harvesting
practices in manure-treated fields can be critical for produce crops.

“If you harvest young and
old plants together or mix them after harvesting, there is risk of
contamination of the older plants,” Habteselassie said. “If plants are uprooted
during harvest, there is also a possibility of contamination from E. coli
living in the rhizosphere.”

Producers should apply
manure to fields well in advance of planting and harvesting. Turco said a wait
of 90 to 120 days between manure application and harvesting, with a minimum of
40 days between planting and harvesting, should minimize the chance of E. coli
contamination.

Turco said he would
continue studying E. coli’s ability to survive in different situations,
including in water and processed produce.


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