Comparisons between strains show little crossover between ESBL-E coli in meat and in humans.
Extended-spectrum β-lactamase-producing Escherichia coli (ESBL-E coli) strains demonstrate antibiotic resistance due to ESBL enzymes targeting many penicillin and cephalosporin antibiotics. This makes preventing ESBL-E coli infections from occurring in the first place a target for efforts to preserve antibiotic efficacy.
It was not previously known whether ESBL-E coli was acquired via the food chain or passed from person to person. Now, a new report in The Lancet Infectious Diseases suggests that poor post-toilet hygiene and infection prevention measures are more likely to spread ESBL-E coli than food products.
Investigators in the United Kingdom (UK), where ESBL-E coli is responsible for more than 5000 cases of bacteremias annually, used selective media to detect ESBL-E coli in routinely submitted samples of human feces between August 1, 2013, and December 15, 2014. The team also collected samples from sewage, farm slurry, and retail foodstuffs in East Anglia, London, northwest England, Scotland, and Wales. The recovered isolates were sequenced and compared with 293 bloodstream and 83 veterinary surveillance ESBL-E coli isolates from the same regions.
Foods studied included beef, pork, chicken, fruit, and salad. It was discovered that antibiotic resistant ESBL-E coli strains from meat—primarily chicken, cattle, and animal slurry—were largely different from those infecting humans.
A total of 2157 out of 20,243 human feces samples contained ESBL-E coli. ESBL-E coli were also found in retail chicken (104 of 159 meat samples) but were not commonly found in other meats and absent entirely from plant-based foods.
Most human bacteremias with ESBL-E coli involve human-associated sequence types (STs), particularly ST131 and, indeed, that type dominated among ESBL-E coli from human blood (188 out of 293 isolates), feces (128 of 360), and sewage (14 of 65). ST38 and ST648 were also widespread throughout, and CTX-M-15 was the predominant ESBL in these lineages.
In contrast, STs 602, 23, and 117 with CTX-M-1 ESBL dominated food and veterinary isolates (68 of 218). Only 2 ST131 organisms were recovered. ST10 occurred in both humans and animals, appearing in 11 of 51 cattle and 15 of 360 human fecal isolates, but human and animal S10 isolates were diverse in serotype.
Altogether, these findings show that ST131 was rarely seen in the food supply, thus little potential for crossover of ESBL-E coli from animals to humans. Lead author David Livermore, PhD, University of East Anglia Norwich Medical School, said that “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.”
Livermore also noted that it is still important to continue practicing hygienic food preparation, as well as infection prevention in animal husbandry, and pointed out that there are “plenty of important food-poisoning bacteria, including other strains of E coli,” but that in the case of ESBL-E coli human toilet hygiene, infection control, and effective management of urinary tract infections were all key.
“Better potential control points are prevention of transmission by good post-toilet hygiene (eg, in care homes) and prevention of severe infection through good patient care and rapid effective treatment of initial uncomplicated urinary tract infections, which precipitate most of the bacteremias,” the authors concluded. “Vaccines might also be a future solution.”
Research from Denmark has identified potential antibiotic cocktails which could counteract antibiotic resistance in in ESBL-E coli that has led to urinary tract infections, but prevention through hygienic measures such as ensuring proper hand washing. Livermore said that good post-toilet hygiene is particularly important to practice in care homes, given the severity of E-coli infections that occur in the elderly.