A quarter of chicken samples from major supermarket chains were found to contain antibiotic resistant E.coli, according to a study.
The superbug was discovered in packs of meat sold from Tesco, Sainsbury's, Asda, Aldi, Waitrose, the Co-op and Morrisons.
Scientists tested products such as diced breast meat, whole roasting chickens, and packets of legs, thighs and drumsticks, and detected E.coli in 22 of 92 samples, the Daily Mail reported.
The study, commissioned by campaign group Save Our Antibiotics, found 24% of chicken samples tested positive for ESBL E.coli, which is resistant to certain types of antibiotics used in medicine.
Half (51%) of all chicken and pork samples were resistant to the antibiotic trimethoprim, which is used to treat lower urinary-tract infections.
The University of Cambridge's Dr Mark Holmes, who conducted the study, told the Daily Mail: "The levels of resistant E.coli that we have found are worrying. Every time someone falls ill, instead of just getting a food poisoning bug, they might also be getting a bug that is antibiotic resistant.
"I am concerned that insufficient resources are being put into the surveillance of antibiotic resistance in farm animals and retail meat. These results highlight the need for improvements in antibiotic stewardship in veterinary medicine."
A Co-op spokesperson told ITV News: "Animal welfare and food safety are priorities for our business.
"We don’t allow the use of antibiotics in any of our meat and poultry, unless there is written approval of a vet to help treat a specific health issue with an animal, and their use as a preventive measure is not permitted."
Andrew Opie, director of food and sustainability policy at the British Retail Consortium, told ITV News that retailers have been "very clear" with customers and suppliers that antibiotics must be used responsibly.
Last year, a report commissioned by the government warned that agricultural use of antibiotics is increasing resistance, and leading to new superbugs.
Symptoms of E.coli normally include a fever, which leads to sickness and diarrhoea.
Washing hands after contact with possible sources such as raw food can reduce the risk of infection.
ITV News contacted all of the named supermarkets for comment.