WASHINGTON – Key gene and chemical interactions that allowEscherichia coli (E. coli)O157:H7 bacteria to colonize the gut of cattle have been discovered by a U.S. Department of Agriculture (U.S.D.A.) scientist and his colleagues. The animals not only host, but can shed the deadly human pathogen.

ManyE. coliO157:H7 outbreaks have been associated with contaminated meat products and cross-contamination of produce crops, writes U.S.D.A.’s Rosalie Marion Bliss. Because the bacteria do not cause cattle to show clinical symptoms of illness, and due to other unknown variables, they can be hard to detect within cattle and the environment.

The researchers, including USDA Agricultural Research Service (A.R.S.) animal scientist Thomas Edrington, reported how theE. coli sense a key chemical that plays a critical role in allowing the bacteria to colonize inside the cattle's gastrointestinal (G.I.) tract. A.R.S. is U.S.D.A.'s principal intramural scientific research agency. This research supports the U.S.D.A. priority of ensuring food safety.

Edrington is with the A.R.S. Food and Feed Safety Research Unit in College Station, Texas. The study, published in the Proceedings of the National Academy of Sciences, was conducted at the University of Idaho, Moscow, Idaho, campus. It involved researchers from several universities and was headed by Vanessa Sperandio, who is with the University of Texas Southwestern Medical Center, in Dallas.

E. coliexpress genes differently based on their environment, such as outside the cattle host, inside the cattle rumen, or even at the end of the cattle GI tract in order to proliferate. Having a better understanding of when, why and how these bacteria colonize could lead to practical applications in the future, according to Edrington.

Researchers showed that "quorum sensing" chemicals called acyl-homoserine lactones (A.H.L.s), which are produced by other bacteria, are present within the bovine rumen but absent in other areas of the cattle G.I. tract. A.H.L.s are important becauseE. coli harbor a regulator, called SdiA, which senses these A.H.L.s and then prompts theE. colito attach and colonize.

Limiting production of the SdiA chemical, or blocking bacterial reception of the A.H.L.s, may eventually lead to new strategies for keepingE. colifrom attaching inside the animal.