Scientists at the U.S. Department of Agriculture recently discovered key gene and chemical interactions that allow toxic Escherichia coli (commonly known as E. coli or O157:H7) bacteria to colonize in the guts of cattle.  According to their research, the bovines not only host but can also shed the deadly human pathogen.

Many E. coli O157:H7 outbreaks have been associated with contaminated meat products and cross contamination of produce crops.  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 the cattle as well as the environment.

Researchers at the USDA Agricultural Research Service (ARS) and animal scientist Thomas S. Edrington reported on how the E. coli bacteria are aware of a key chemical that plays a critical role in allowing the bacteria to colonize in cattle’s gastrointestinal (GI) tracts.  

Edrington and the ARS Food and Feed Safety Research Unit, based out of College Station, Texas, published the study in the Proceedings of the National Academy of Science. The study was conducted at the University of Idaho campus in Moscow, Idaho. Working with the ARS scientists were several researchers from other universities.  Prof. Vanessa Sperandio of the Dallas-based University of Texas Southwestern Medical Center headed the project.

In order to grow, E. coli express genes differently based on their current environment, such as having a cattle host, inside the cattle rumen, or even at the end of the cattle GI tract.  Researchers aimed to gain a better understanding of when, why and how these bacteria colonize, which could lead to practical applications in the future, Edrington explained.

Researchers showed that the “quorum sensing” chemicals produced by other bacteria, called acyl-homoserine lactones (AHLs), are present within the bovine rumen but absent in other areas of the cattle GI tract.  AHLs are important because E. coli harbor a regulator, called SdiA, which senses these AHLs and then prompts the E. coli to attach and colonize.

According to the USDA, limiting the production of the SdiA chemical, or blocking bacterial reception of AHLs, may eventually lead to new strategies for keeping E. coli from attaching inside the animal host.

The ARS office is one of the USDA’s principal intramural scientific research agencies.  This research project was done in accordance with USDA’s goal of ensuring food safety.