A superbug that could be untreatable is being passed on by dogs to their owners through dog baskets or sharing a bed.
Scientists are warning of a nightmare scenario where humans pick up the bug which is known to create resistance to life-saving drugs.
The mcr-1 gene was first reported in China in 2015 and is resistant to colistin, an antibiotic used to defeat bacterial infections which other drugs can not tackle.
Experts have warned for years that overuse of colistin, especially on meat-producing animals, risks the rise of mutant genes that could make the drug useless.
Now a study has found that the mcr-1 gene is being passed on from dogs to humans.
A team at the University of Lisbon took fecal samples from 126 healthy people living with 102 cats and dogs in 80 households across two years up to February 2020.
Eight of the dogs and four of the humans were found to have bacteria, including mcr-1.
In two of the households where dogs had tissue infections, the mcr-1 gene was found in both the dog and owner.
Analysis suggests the gene was passed from the dogs to the owners. However, it is possible for people to pass on the gene to their dogs.
The scientists believe the mcr-1 gene is being passed on via humans sharing a bed with their dog.
The gene lives in the gut and is moved via microscopic particles of feces. This means dog baskets are also a place where humans can pick up the gene.
The study was presented at the European Congress of Clinical Microbiology and Infectious Diseases conference this weekend.
Dr Juliana Menezes, who led the research, said: “If bacteria resistant to all drugs acquire this resistance gene, they would become untreatable, and that’s a scenario we must avoid at all costs.
“We know that the overuse of antibiotics drives resistance and it is vital that they are used responsibly, not just in medicine but also in veterinary medicine and in farming.”
The gene is carried by multiple species, but scientists are worried about domestic dogs carrying it because they are in close contact with humans.
The study comes amid a growing crisis of resistance to drugs that is estimated to have killed 700,000 people a year around the world.
Forecasts suggest drugs no longer working could kill 10 million people per year by 2050 unless action is taken.
A separate study has revealed how raw dog food is a major source of bacteria that is resistant to antibiotics.
University of Porto researchers analysed a range dog food and found that 54 per cent contained the bacteria Enterococci. 40 per cent of those cases were resistant to a range of strong antibiotics.