Can cats help with antibiotic-resistant bacteria?

The over-use of antibiotic drugs has led to the evolution of so-called 'superbugsp such as a type of staph infection called MRSA (Methicillin-resistant Staphylococcus aureus). This infectious bacterium can cause problems if it infects the lungs or bloodstream, because it is so hard to treat.

It has been estimated that almost 2% of people have MRSA on their skin, but this does not often cause problems because the human skin and gut are colonized by hundreds of different species of bacteria and these act as a barrier that prevent harmful bacteria from establishing a foothold or entering the body.

Other animals, including cats, have the same type of bacterial protection. Cats have the same problem with staph infection as humans and they also have to battle with an antibiotic-resistant strain. With cats this strain is Staphylococcus pseudintermedius or MRSP. Like MRSA in humans, the MRSP bacterium is widespread, in fact even more so, since about 50% of cats and dogs have it. With our pets the problem is often seen in the form of stubbornly persistent skin or ear infections. However, despite the fact that the bacterium is so prevalent in cats, they get MRSP infections less often than humans get MRSA. Why is that?

It seems that the answer lies in the cat's natural defences. Scientists from the University of California San Diego School of Medicine have recently shown that one of the other skin bacterial species found on cats is particularly good at repelling antibiotic-resistant Staphylococcus pseudintermedius.

Richard Gallo (Professor and chair of the Department of Dermatology at UC San Diego School of Medicine) and his colleagues carried out a series of experiments to determine what makes healthy cats resistant to MRSP. They grew S. pseudintermedius in the laboratory in the presence of bacteria collected from healthy cats and dogs.

They found that bacteria extracted from healthy animals produced something that inhibited the growth of S. pseudintermedius, and indeed killed many of the MRSP bacteria.

"Our health absolutely depends on these 'good' bacteria," said Gallo. "They rely on our healthy skin to live, and in return some of them protect us from 'bad' bacteria. But if we get sick, 'bad' bacteria can take advantage of our weakened defenses and cause infection."

The researchers then screened a collection of diverse staphylococcus species from 26 domestic dogs and cats to find which ones worked best against MRSP. They found that one bacterium in particular, known as S. felis, was very good at inhibiting the growth of MRSP. This unique strain (S. felis C4) inhibited not only MRSP, but also many other bacterial pathogens. Further analysis showed that S. felis C4 secretes chemicals that inhibit the growth of several drug-resistant pathogens by disrupting the cell membrane and inhibiting its functions. Although S. felis is a common bacteria found in the skin of cats, it hadn't been much studied.

Once the scientists had determined the effectiveness of S. felis in petri dishes, they wanted to see if S. felis could also provide protection to live animals, (an approach known as bacteriotherapy). Bacteriotherapy is the intentional use of bacteria or bacterial products to treat illness. This approach has been previously used with different bacteria, particularly the use of probiotics and fecal matter transplants.

In this case the team exposed mice to the most common form of MRSP and then added either S. felis or its bacterial extract to the same site on the mouse's skin. The skin of treated animals showed a reduction in scaling and redness when compared with animals that had no treatment. There were also fewer MRSP bacteria left on the mouse skin after treatment with S. felis C4.

"The potency of this species is extreme," said Gallo. "It is strongly capable of killing pathogens, in part because it attacks them from many sides - a strategy known as 'polypharmacy.' This makes it particularly attractive as a therapeutic."

So what's next? Gallo and his colleagues want to start a clinical trial to confirm whether S. felis can be used to treat MRSP infections in dogs. MRSP is an important emerging zoonotic pathogen (zoonotic pathogens can infect different species including humans) that causes severe skin infections, not only in cats and dogs but also in rare cases in humans. There is no specific treatment available at present.

Journal Reference:
Alan M O'Neill, Kate A Worthing, Nikhil Kulkarni, Fengwu Li, Teruaki Nakatsuji, Dominic McGrosso, Robert H Mills, Gayathri Kalla, Joyce Y Cheng, Jacqueline M Norris, Kit Pogliano, Joe Pogliano, David J Gonzalez, Richard L Gallo. Antimicrobials from a feline commensal bacterium inhibit skin infection by drug-resistant S. pseudintermedius. eLife (2021); article

Note: This information is for guidance only. It is not intended to replace consultation with a licensed veterynary practitioner.

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