In 2022, a batch of chicken and duck embryos that died before hatching arrived at a veterinary lab in China for testing.
Buried in their brain tissue, researchers found Acinetobacter baumannii – a pathogen labelled ‘Priority 1′ by the World Health Organization’. It’s best known for tearing through hospital ICUs due to its resistance to even last-resort antibiotics.
It’s also more recently starting to become recognized as being zoonotic: capable of moving between animals and people.
It’s long been thought that livestock may play a role in spreading drug resistance in superbugs.
But, interestingly, the specific strains of bacteria isolated from the poultry weren’t actually resistant to much of anything.
When comparing this genetic data to that found in humans and companion animals such as cats and dogs, the researchers from Nanjing Agricultural University, Wuhu Institute of Technology, and Nanjing University of Chinese Medicine in China found that the real concern turned up somewhere closer to home.
Researchers pulled together genetic data on 509 A. baumannii samples collected from animals in 17 countries, spanning 33 species – everything from white storks in Poland (which, oddly, make up a vast proportion of the animal samples on record) to cats, dogs, and horses in veterinary clinics across Europe.
Combined with thousands of human clinical samples from the same regions, plus the new poultry data, the picture that emerged wasn’t reassuring for pet owners.
“A. baumannii isolated from animals can be divided into two groups: a high antimicrobial resistance (AMR) group dominated by hosts such as horses, cats, and dogs and a low AMR group dominated by hosts such as livestock, poultry, and wildlife,” the researchers, led by Xiangkuan Zheng at Nanjing Agricultural University, wrote in the journal Applied and Environmental Microbiology.
Using a classification system that groups related A. baumannii strains into “international clones” – the same lineages behind hospital outbreaks worldwide – the team found that several of these clones, including one called ST25, turned up again and again in companion animals.
ST25 alone was found in nine different animal species, mostly cats, dogs, and horses.
Bacteria from cats, dogs, and horses turned out to be genetically almost indistinguishable from strains infecting people in hospitals nearby, with genome similarity scores above 99 percent, and in some cases over 99.5 percent.
Livestock, poultry, and wild animals, by contrast, carried strains that were far more distant relatives – typically just 97 to 98 percent similar to the human strains.
“Our study suggests that A. baumannii has a higher potential of intertransmission between companion animals and humans compared to livestock, poultry, and wildlife,” write the researchers. “This elevated potential may be related to the close contact of companion animals with humans.”
Cats and dogs even carried resistance genes that livestock never should. Isolates from companion animals turned up two genes that make bacteria resistant to carbapenems – the antibiotics doctors reach for when nothing else works, and which are off-limits in livestock farming altogether. Those same resistance genes turned up in precisely zero of the livestock, poultry, or wildlife samples.
None of this means your dog or cat has given you a hospital infection, or ever will.
Let’s be clear: there’s no direct evidence here of the bacterium actually jumping from a specific pet to a specific person, just a genetic paper trail suggesting the opportunity is there, and has been for a while.
Last year, the American Society for Microbiology (AMR) published an article exploring the emerging link between antibiotic-resistant bacteria in pets and humans – which specifically flagged the need for more species specific pathogen sampling to help further understand the picture moving forward.
While this latest study gives us more important clues, there’s still a long way to go.
What happens next is more sampling – of paws, feathers, hooves, and the humans standing next to them – to work out how often, and how easily, this hospital regular slips between species.
Related: Ancient Killer Is Rapidly Gaining Resistance to Antibiotics, Study Warns
The research has been published in Applied and Environmental Microbiology.
This article was fact-checked by Kate Mallord and edited by Kate Mallord. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
