Each year, humans produce about 100,000 tons of antibiotics – about half the weight of a freighter passing through the ocean, enough to save millions of lives each year from infections that were once death sentences.
But the bulk goes to livestock, which are dosed to ward off diseases in crowded conditions or to speed growth. This means that we have created the perfect conditions for bacteria to learn to overcome our defences. Currently, about 35,000 people die from antibiotic-resistant bacteria in the United States annually, and the United Nations estimates that the annual number could reach millions by 2050 because we lose our ability to treat dormant diseases now.
And perhaps these powerful microbes enter our homes through a previously unknown side door: pets. Two new studies from Portuguese research teams presented at a European Conference on Infectious Diseases have found that raw dog food, at least as sold in Europe, harbors multidrug-resistant bacteria, and that dogs may be able to pass on this resistance to the bacteria in their owners.
In the Pet Food Study, researchers tested 55 different samples of four types of dog food: wet, dry, processed, and raw. They were looking for Enterococcia genus of bacteria that live in animal guts and sewage (two types common in humans are E. faecalis And the E. Stool), and can cause anything from urinary tract infections to meningitis if they find their way to the right parts of the body.
Enterococci It is also remarkably resistant to common antibiotics, including penicillin. Of the 30 samples tested positive for the bacteria, more than 40 percent were resistant to eight different antibiotics.
According to a press release, some of the multidrug-resistant strains were “identical to bacteria isolated from hospital patients in the UK, Germany and the Netherlands,” as well as strains from British farm animals.
Even more alarming, 23 percent were resistant to linezolid, an antibiotic that has been saved as a precursor for treating multidrug-resistant infections. Oddly enough, linezolid is not used to treat animals, it is mostly intended to treat tuberculosis and MRSA in humans. However, this isn’t the first study to find resistance to the drug of last resort in cattle, and a study last year out of China suggested that the trait might be the result of some form of transient immunity to another common antibiotic.
But the resistance has centered on raw pet food, all of which contain some multidrug-resistant bacteria. Resistance appeared in more than 10 percent of wet foods, and it was not seen at all in other species. This isn’t the first time that raw pet food has been found to harbor this bacteria; In 2017, a team in the Netherlands found that cats who ate raw food were more likely to shed drug-resistant bacteria.
Now, based on these studies, it appears that raw dog food – essentially frozen ground meat – is more popular in Europe than in the United States. And we can’t know if the same bacteria would show up in the ocean far away. But according to most accounts from veterinarians, raw food is growing in popularity in the United States — often interpreted as a pet-focused branch of natural food and antiquity trends — and, like much pet food, it comes from traditionally farmed meat.
The problem is not limited to pets or their owners, because bacteria and other single-celled microorganisms have a very peculiar way of evolving: they can pass beneficial genes to each other, not only within species, but across them. A 2017 study found that bacteria shed by Dutch cats are at risk of passing on their drug resistance to their entire environment.
The second Portuguese team found something similar: In a study of 126 pet owners and 102 cats and dogs, eight dogs were infected with bacteria that confer resistance to another antibiotic, colistin. So did four people. (Cats have never carried drug-resistant bacteria.)
In two families, both the owner and the dog had the resistant breed. In one of them, the researchers reported, the dog appeared to have passed the gene on to its owner. The danger, they say, is that dogs can act as a reservoir of genes — although at the moment it’s rare enough that you probably don’t have to worry about your dog’s microbiome.
One author recommended: “Dog owners should wash their hands with soap and water immediately after eating pet food and after picking up feces.” But we really hope you know that already.