Antibiotic-resistant E. coli is more likely to be spread by people failing to wash their hands after going to the toilet than undercooked meat or other food, according to new research from a consortium including the University of East Anglia.

E. coli has become considerably more antibiotic resistant over the past 20 years both in humans and animals. Particularly important are strains with “Extended Spectrum Beta-Lactamases.” These are enzymes that destroy many important penicillin and cephalosporin antibiotics. Many strains with ESBLs often have other key resistances too. But until now, it has not been known whether antibiotic-resistant E. coli that cause bloodstream infections are picked up via the food chain, or passed from person to person.

To answer this question, scientists sequenced the genomes of resistant E. coli from multiple sources across the United Kingdom -- including from human bloodstream infections, human feces, human sewage, animal slurry and meat including beef, pork and chicken, and fruit and salad.

Their report in The Lancet Infectious Diseases reveals that antibiotic-resistant ‘superbug’ strains of E. coli from human blood, feces and sewage samples were similar to one another. Strain ‘ST131’ dominated among ESBL-E. coli from all these human sample types.

Resistant E. coli strains from meat, principally chicken, cattle and animal slurry were largely different to those infecting humans. ST131 was scarcely seen. Instead, strains ST23, 117 and ST602 dominated. In short, there was little crossover of ESBL-E. coli from animals to humans.

“E. coli bacteria normally live in the intestines of healthy people and animals. Most varieties are harmless or cause brief diarrhea,” says lead author and professor David Livermore, from UEA’s Norwich Medical School. “But E. coli is also the most common cause of blood poisoning, with over 40,000 cases each year in England alone. And around 10% of these cases are caused by highly resistant strains with ESBLs. Infections caused by ESBL-E. coli bacteria are difficult to treat. And they are becoming more common in both the community and hospitals. Mortality rates among people infected with these superbug strains are double those of people infected with strains that're susceptible to treatment.”

ESBL-E. coli can be found in food animals too but, until now, the extent of transmission from these sources to humans has been uncertain, with the role of the food chain debated.

“We wanted to find out how these superbugs are spread - and whether there is a cross-over from the food chain to humans,” Livermore says.

The team compared ESBL-E. coli from infected human blood samples with those from human feces, sewage, food, dairy farm slurry and animals across five UK regions - London, East Anglia, Northwest England, Scotland and Wales. The ESBL-E .coli infected blood samples came from NHS laboratories. Food studied included beef, pork, chicken, fruit and salad.

“We looked at more than 20,000 fecal samples and around 9% were positive for ESBL-E. coli across the regions, except for in London, where the carriage rate was almost double - at 17%. We found ESBL-E. coli in 65% of retail chicken samples - ranging from just over 40% in Scotland to over 80% in Northwest England. But the strains of resistant E. coli, were almost entirely different from the types found in human feces, sewage and bloodstream infections,” Livermore says. “Only a very few beef and pork samples tested positive, and we didn’t detect ESBL-E. coli at all in 400 fruit and vegetable samples - many of which were imported to the UK.

“In short, what the results show is that there are human-adapted strains of ESBL-E. coli, principally ST131, which dwell in the gut and which occasionally - usually via UTIs - go on to cause serious infections. And that there are animal strains of ESBL-E. coli. But - and critically - there’s little crossover between strains from humans, chickens and cattle. The great majority of strains of ESBL-E. coli causing human infections aren’t coming from eating chicken, or anything else in the food chain.

“Rather - and unpalatably - the likeliest route of transmission for ESBL-E. coli is directly from human to human, with fecal particles from one person reaching the mouth of another. We need to carry on cooking chicken well and never to alternately handle raw meat and salad. There are plenty of important food-poisoning bacteria, including other strains of E. coli, that do go down the food chain. But here - in the case of ESBL-E. coli - it’s much more important to wash your hands after going to the toilet.”

“And it’s particularly important to have good hygiene in care homes, as the most of the severe E. coli infections occur among the elderly,” says professor Neil Woodford of Public Health England. “In order to tackle antibiotic resistance, we not only need to drive down inappropriate prescribing, but reduce infections in the first place. In order to limit serious, antibiotic resistant E. coli bloodstream infections, we must focus on thorough hand washing and good infection control, as well as the effective management of urinary tract infections.

“Prudent use of antibiotics is essential in both animals and humans. Antibiotics are a finite resource. We need them to continue to work when we get sick. We are committed to reducing infections in both the community and in healthcare settings, and are working with front-line NHS staff, NHS England, NHS Improvement and the Department of Health and Social Care to do this.”

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