If you’ve ever had a conversation about food safety, it’s likely that E. coli, salmonella, and listeria have come up in the conversation. Couple those pathogens with terms like “antibiotic-resistance,” and you have the culprits behind some of the most headline-grabbing news reports people see. You’ll also hear media repeating the steps for proper food preparation.
New research out of England’s University of East Anglia may change the way we think about at least a portion of that. A report published in The Lancet Infectious Diseases points to the fact that poor toilet hygiene is a significantly greater risk for antibiotic-resistant E. coli than is undercooked chicken and other food.
E. coli is a Jekyll and Hyde organism. We all harmlessly carry it in our gut, as do animals. However, some E. coli strains cause food poisoning whereas others cause urinary tract infections and infections after gut surgery. At worst, these develop into bacteraemias — bloodstream infections.
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” (ESBLs). 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 UK — including from human bloodstream infections, human feces, human sewerage, animal slurry, meat including beef, pork and chicken, and fruit and salad.
Their report reveals that antibiotic-resistant “superbug” strains of E. coli from human blood, feces, and sewerage 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.
“Infections caused by ESBL-E. coli bacteria are difficult to treat,” said lead author Prof David Livermore, from UEA’s Norwich Medical School. “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 are widespread in retail chicken meat and 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 found ESBL-E. coli in 65 percent of retail chicken samples — ranging from just over 40 percent in Scotland to over 80 per cent in Northwest England,” Livermore said. “But the strains of resistant E. coli, were almost entirely different from the types found in human faeces, sewage, and bloodstream infections. 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,” he continued, “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 faecal 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.”