Tracking E. coli at ARS

Posted 5/5/22

NATIONWIDE — When a foodborne illness outbreak happens, tracking the source down is critical.

Scientists with the USDA’s Agricultural Research Service (ARS) have a plan: they are …

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Tracking E. coli at ARS

Posted

NATIONWIDE — When a foodborne illness outbreak happens, tracking the source down is critical.

Scientists with the USDA’s Agricultural Research Service (ARS) have a plan: they are studying the DNA of a specific population of this bacterium and can see how it gradually evolves within its natural environment. E. coli O157:H7 is associated with foodborne illness. Food contaminated with this bacterium can cause serious illness, hospitalizations and even death.

The findings from scientists at the U.S. Meat Animal Research Center (USMARC) at Clay Center, Neb., equip outbreak investigators with information on specific elements of the bacterium’s DNA that can narrow where to look for the outbreak source.

As these bacteria are found naturally in the intestines of cattle, the team of scientists analyzed samples collected from the Center’s closed cattle feedlot from 1997 to 2019 and studied the genomes (the organism’s genetic composition) of various strains, or subtypes, of E. coli O157:H7 found in these samples.

“The USMARC feedlot has been closed to any introduction of cattle,” said Maggie Weinroth, a computational biologist, “except those raised in the center. This means that the E. coli strains have not been influenced by cattle from other locations for 23 years, allowing us to focus on changes in the bacteria genomes as they evolved over those years.˝

The scientists identified four unique clades within the specific bacteria population they studied. (Clades are a group of organisms that share specific characteristics.) Even though all clades shared a portion of their genetic composition, each clade also contained unique elements that can be shared, called mobile elements.

“We noticed that bacteria were able to exchange mobile elements in their genome over time,” said research microbiologist Jim Bono. “Some of these elements stayed in all strains and became part of the core sequence of that specific bacterium’s DNA. Interpretation of these mobile elements’ role during an outbreak investigation can help identify relatedness between human and environmental isolates of this bacteria.”

Results from this and future studies will continue to build information for rapid, more accurate traceback responses during outbreak investigations.

The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. For more information, visit ars.usda.gov.

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