Healthy dogs and cats could be passing on multidrug-resistant organisms to their owners, and likewise humans could be transmitting these dangerous microbes to their pets, according to a new research.

Multidrug-resistant organisms are bacteria that resist treatment with more than one antibiotic.

"Our findings verify that the sharing of multidrug-resistant organisms between companion animals and their owners is possible," said Carolin Hackmann from Charite University Hospital Berlin, Germany.

"However, we identified only a handful of cases suggesting that neither cat nor dog ownership is an important risk factor for multidrug-resistant organism colonisation in hospital patients," he added.

The role of pets as potential reservoirs of multidrug-resistant organisms is a growing concern worldwide. Antimicrobial resistance happens when infection-causing microbes (such as bacteria, viruses or fungi) evolve to become resistant to the drug designed to kill them.

In the study, researchers wanted to find out whether pets (ie, cats and dogs) play a role in the infection of hospital patients with multidrug-resistant organisms.

They focused on the most common superbugs in hospital patients -- methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), third generation cephalosporin-resistant Enterobacterales (3GCRE) and carbapenem-resistant Enterobacterales (CRE), which are resistant to multiple antibiotics including penicillin and cephalosporins.

Between June 2019 and September 2022, nasal and rectal swabs were collected from 2,891 patients hospitalised in Charite University Hospital (1,184 patients with previous colonisation or colonisation on admission and 1,707 newly-admitted patients as controls), and from any dogs and cats that lived in their households.

Overall, 30 per cent of hospital patients tested positive for multidrug-resistant organisms. The rate of dog ownership was 11 per cent and cat ownership 9 per cent in those who tested positive for multidrug-resistant organisms.

Further, throat and stool swab samples from 400 pets were also analysed. Of these, 15 per cent of dogs and 5 per cent of cats tested positive for at least one multidrug-resistant organism.

"Although the level of sharing between hospital patients and their pets in our study is very low, carriers can shed bacteria into their environment for months, and they can be a source of infection for other more vulnerable people in hospital such as those with a weak immune system and the very young or old," Hackmann said.

However, the researchers said "this is an observational study and cannot prove that close contact with pets causes colonisation with multidrug-resistant organisms". It only suggests the possibility of co-carriage, while the direction of transfer is unclear.

The findings will be presented at this year's European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) to be held in Denmark in April.