The deadly strain of E.coli can mostly be found in cows, however they show no signs of the disease.

Deadly strain can mostly be found in cows

A superbug study by the University of Edinburgh has revealed how a strain of E.coli become a potentially fatal infection.

Published in the journal Microbial Genomics, the study reveals how E.coli 0157 became deadly in the UK around 30 years ago when it acquired a powerful toxin. 

The finding helps to explain why severe outbreaks of food poisoning began in the 1980s.

The majority of E.coli strains are harmless and live in the guts of humans and animals without causing illness.  However, E.coli 0157 produces molecules called shiga-toxins, which are linked to more serious infections in humans.

In the study, researchers decoded over a thousand samples of E.coli 0157 collected from humans and animals over the last 30 years.

Their analysis showed that the ancestor of E.coli 0157 has been in existence for more than 175 years. They found that the majority of the ancestor strains carry only stx1 but some strains began to acquire stx2a around 60 years ago.

The dangerous strains of E.coli 0157 that have caused most illness in people in the UK acquired stx2a around three decades ago when outbreaks of severe food poisoning began to appear.

The deadly strain can mostly be found in cows, although they show no signs of the disease. However, animals that are infected with strains that produce stx2a excrete higher levels of dangerous bacteria in their manure. This encourages the spread of infection between animals and increases the chance of the bacteria being passed to humans.

Commenting on the study, Professor David Gally from the University of Edinburgh’s Roslin Institute said: “Thankfully, dangerous E. coli outbreaks remain relatively rare. Our research underlines the need to study the genetic code of strains that cause infections in humans and those present in farmed animals.

“Good hygiene practices – both with food and when out enjoying the countryside – can help to minimise the risk of these and other severe infections.  Our work endeavours to understand how these toxic strains persist in cattle and the best ways to prevent them spreading to us.”