What causes MRSA?


We’ve all heard of it, but what actually causes MRSA? Vet Roberta Baxter explains…

“It doesn’t feel like that long ago that I was at university, but when I was, the treatment of bacterial diseases was markedly different from what it is today. For a start, the range of antibiotics were effective against the conditions we were fighting, and with new classes of antibiotics coming forward, we had an armoury to tackle even the nastiest of diseases.

“Of course, I knew that resistance to antibiotics could occur, and it was something we saw from time to time, but it was rare in those days to isolate bacteria that were difficult to treat.

“These days, resistant bugs are becoming more common, and treating them is ever more difficult. This has huge implications, not only for the health of our pets, but also for us — resistant skin bacteria can be transmitted from our pets to us and back again. Even if they don’t immediately cause disease, they can become a problem if they are transmitted to anyone with immune-suppressive diseases, or anyone who undergoes surgical treatment.”

What is MRSA?

“MRSA or MRSP (methicillin resistant Staphylococcus aureus and Staphylococcus pseudintermedius) are resistant strains of skin bacteria which are present on normal skin and don’t usually cause problems, but can be pathogenic (disease-causing) if they get into wounds. They are easily passed from dog to dog, and to their humans, often with no symptoms whatsoever.

“However, resistance in skin bacteria means that patients undergoing operations are at risk, as are those who get skin wounds. If these bugs get deep into the tissues, there is a risk of infection which “is unresponsive to normal antibiotics. This can mean potentially fatal infections, particularly in the very young, the very old, or those with suppressed immune systems due to other diseases.

“Certain combinations of antibacterials can be effective in some cases. However, the antibiotics which work tend to be ones that have restricted use and should be avoided as much as possible, to try to prevent further resistance developing, and in some cases, have to be used at high levels with potential side effects.”

How to avoid MRSA

“When trying to avoid these resistant infections, the first step is to try to swab all skin infections or infected wounds which occur, and to culture bacteria in urinary and respiratory infections. This is so we can precisely identify the bacteria involved, and can use appropriate antibiotics that will rapidly kill them. This avoids using courses of failed antibiotics which contribute to the future development of resistant bugs.

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“At present, most infections are only swabbed or cultured if they fail to respond to initial antibacterial treatment, due to cost and time issues, but I think that in the long term, we will all have to use laboratories much more frequently to identify bacteria.

“Humans are often swabbed for these bugs before undergoing surgical procedures, so that they can be treated prior to surgery to avoid infection, and the time may come when routine swabbing is also advised for pets in our animal hospitals.

“Some doctors have regular swabs, and we should consider whether this may be advisable for vets carrying out certain surgeries as well. Another step is that we should all avoid using antibiotics when they’re not necessary. We and our pets lived without antibiotics a century ago, and many infections resolve with cleaning and topical treatment.

“Vets should not prescribe antibiotics for infections which are likely to resolve without them, however much some of their clients want them to.

“Finally, one of the problems which contributes to resistant bacterial development is compliance failure. This is the term which refers to the times when owners forget to give part of an antibiotic course, or fail to finish a course of antibiotics, perhaps because they perceive that the infection is better and there is no further need. Studies show that this is very common.

“However, incomplete courses of antibiotics select for resistant bacteria, and lead to an increase in the chance of a dog carrying bacteria with resistance. This means that owners should try to follow their vet’s advice precisely.

“Other issues contributing to the development of resistant bacteria include the use of antibiotics in food animals (although this is much reduced these days, and is being dealt with), and the availability of certain medicines online from countries with less stringent prescribing laws. I’d strongly advise owners to refrain from buying such products, and to always seek their vet’s advice when dealing with infections.”