Researchers have looked at why dangerous forms of E. coli keep appearing in cattle.

While E. coli bacteria are a known cause of food poisoning, a wide variety of strains exist, many of them are harmless and can be found in the intestines of humans. However, ingestion of harmful strains on contaminated food can lead to illness, vomiting, diarrhea and death.

Shiga toxin (Stx)-producing E. coli (STEC) and enteropathogenic E. coli (EPEC) are major foodborne pathogens that can cause hemolytic uremic syndrome (HUS) and diarrhea, respectively. Cattle are thought to be the primary reservoir of STEC and EPEC. Stxs are divided into two major groups, Stx1 and Stx2.

Adapt to environment

A study, published in the Genome Research journal, on genetic differences and similarities in E. coli bacteria from cattle and humans, indicates that features causing food poisoning may continuously be emerging in bacteria from cattle so they can better adapt to their environment.

Yoshitoshi Ogura, associate professor at Kyushu University’s department of bacteriology, who led the research, said to develop effective preventive measures, there needs to be a deep understanding of the source and living conditions of the bacteria.

“Although cattle have long been thought to be a main source of E. coli that cause food poisoning, why dangerous forms would keep appearing in cattle has been unclear,” the report says.

Ogura’s group, with researchers in the United States, Japan, France and Belgium, investigated the genetics of E. coli bacteria collected from cattle and humans in 21 countries from six continents. A total of 575 bovine and 362 human commensal E. coli were analyzed.

Way for E. coli to protect itself
based on genetic features of the bacteria, the researchers could generally separate the different strains of E. coli into two groups, with one primarily consisting of bacteria collected from humans and the other of those from cattle.

Applying the same analysis to clinically obtained E. coli known to cause illness, the team found that most strains causing intestinal problems belonged to the group associated with cattle.

Many of the samples from cattle showed features similar to those causing food poisoning, such as production of Shiga toxin. While these signs generally appear not to cause illness in cattle, their prevalence in investigated samples suggests that such characteristics are beneficial for life in a cattle’s intestine.

“As long as there is pressure to maintain or strengthen these illness-producing characteristics to better adapt to living in a cattle’s intestine, new variants of E. coli that cause food poisoning are likely to continue appearing,” said Ogura.

The locus of enterocyte effacement (LEE)-encoded type 3 secretion system (T3SS) is the major virulence determinant of EPEC and is also possessed by major STECs.

In the data set, the bovine-associated lineage mainly consisted of strains belonging to phylogroups B1 and A and the human-associated lineage mostly of B2 and D strains.

Researchers speculated that such characteristics may help E. coli protect itself from bacteria-eating organisms in cattle intestines, but more work is needed to identify the exact reason.