A study of 600 healthy pet dogs has found a strong link between the canines being fed raw meat, and pooping out Escherichia coli baceria that is resistant to the broad spectrum antibiotic ciprofloxacin.

In other words, dangerous and difficult-to-kill bacteria could be making its way between humans and farm animals through raw meat that's fed to dogs. That's an alarming finding, say the researchers from the University of Bristol in the UK.

"Our aim was not to focus on raw dog food, but to investigate what might make a dog more likely to excrete resistant E. coli in its feces," says genetic epidemiologist Jordan Sealey, from the University of Bristol.

"Our study found a very strong association between excreting ciprofloxacin-resistant E. coli and feeding dogs a raw food diet."

Based on poop analysis and surveys filled out by the dog owners – covering diet, other animal companions, and walking and playing environments – it was only eating raw meat that showed up as a significant risk factor in the excretion of antibiotic-resistant E. coli.

What's more, the E. coli strains most commonly identified in rural dogs matched those also found in cattle. In urban areas, dogs were more likely to have strains found in humans, suggesting a more complicated mix of infection routes.

The researchers urged owners to consider putting their pets on non-raw food diets, and for livestock owners to take steps to reduce the use of antibiotics on farms where dog food is sourced, a practice that encourages antibiotic resistance.

"Individual measures to reduce the risk of resistant bacteria being excreted by dogs include changing to a non-raw food diet or sourcing good quality raw meat that can be cooked, and then cooking it," says Sealey.

"Most raw food sold for consumption by dogs is not of a quality that can be cooked, and can cause a serious health hazard to dogs if cooked."

E. coli form part of a healthy gut microbiome in humans and animals. While most strains are harmless, some can cause problems, particularly in people with weakened immune systems. When infections do occur, especially in tissues such as blood, they can be life-threatening, demanding urgent treatment with antibiotics.

If the E. coli isn't affected by antibiotics such as ciprofloxacin, then the infections become more difficult to treat, and combating that means a better understanding of how the health of humans, animals, and the environment are linked, the researchers say.

"Stricter limits should be set on the numbers of bacteria allowed in meat that is sold to be eaten uncooked than in meat sold to be cooked prior to eating," says molecular bacteriologist Matthew Avison from the University of Bristol.

The research has been published in One Health.