Superbug study reveals how E. coli strain acquired deadly powers

September 22, 2015, University of Edinburgh
Escherichia coli. Credit: Rocky Mountain Laboratories, NIAID, NIH

A strain of E. coli became a potentially fatal infection in the UK around 30 years ago, when it acquired a powerful toxin, a gene study has revealed.

The discovery helps to explain outbreaks of severe food poisoning that began in the 1980s.

Scientists say their findings show that E. coli O157 is continuing to evolve and should be monitored closely.

Most strains of E. coli are harmless and live in the guts of people and animals without causing illness.

E. coli O157 strains can produce molecules called shiga-toxins, which are linked to more serious human infections.

The strains that are responsible for the majority of serious illness in people in the UK produce two types of shiga-toxin - stx1 and stx2a.

A team of researchers - including scientists at Public Health England and the University of Edinburgh - decoded the genetic sequences of more than a thousand samples of E. coli O157 collected from and animals over the past 30 years.

Their analysis reveals that the ancestor of E. coli O157 has been around for more than 175 years.

They found that most of the ancestor strains carry only stx1 but some strains began to acquire stx2a around 60 years ago. The dangerous strains of E. coli O157 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.

Some more recent infections are being caused by E. coli O157 strains that carry only stx2a. Early evidence suggests that these strains may be even more dangerous than those to date.

Cows are the main reservoir of E. coli O157, though they show no signs of the disease. Animals that are infected with strains that produce stx2a excrete higher levels of dangerous bacteria in their manure. This helps to spread infection between animals and increases the chances of the bacteria being passed to people.

The research was conducted by the University of Edinburgh, Public Health England, Animal Laboratories and Plant Health Agency, the Scottish E. coli Reference Laboratory, Scotland's Rural College and the University of East Anglia. Continuing work in this area is being supported by the Food Standards Agency and Food Standards Scotland. The study is published in the Microbiology Society's journal Microbial Genomics.

Professor David Gally, of 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 persist in cattle and the best ways to prevent them spreading to us."

Explore further: E. coli more virulent when accompanied by beneficial bacteria

Related Stories

E. coli more virulent when accompanied by beneficial bacteria

September 17, 2015

Scientists wonder why some people get so sick and even die after being infected by the foodborne pathogen E.coli O157:H7, while others experience much milder symptoms and recover relatively quickly. Now Penn State's College ...

Horizontal gene transfer in E. coli

May 19, 2015

Escherichia coli O104 is an emergent disease-causing bacterium various strains of which are becoming increasingly well known and troublesome. The pathogen causes bloody diarrhea as well as and potentially fatal kidney damage, ...

U.S. E. coli O157 outbreaks mainly due to food

July 20, 2015

(HealthDay)—Outbreaks of Shiga toxin-producing bacterium Escherichia coli O157 infection are mainly caused by food, especially beef and leafy vegetables, according to a study published in the August issue of the U.S. Centers ...

E. coli gets a boost from lettuce disease

July 31, 2015

Escherichia coli O157:H7, a bacterium that causes foodborne illness in humans, is more likely to contaminate lettuce when downy mildew is already present, according to U.S. Department of Agriculture (USDA) scientists.

Recommended for you


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.