Methicillin Resistant Staphylococcus Aureus Infections in Animals

Methicillin resistant Staphylococcus aureus (MRSA) infections are becoming more prevalent over the past few years1. These infections are important because the bacteria have acquired resistance to many of the common antibiotics. As such, they are very hard to treat and therefore present serious challenges for clinicians with infected patients.

I have personal experience with the struggle to treat MRSA infections. About a year ago I treated a Great Dane for a bite wound on its foot. Treatment was initiated with routine wound care and antibiotic therapy. After a week of treatment however the patient’s wound still wasn’t healing and his lameness was getting worse. I radiographed the foot and found a broken bone which I thought was probably the reason that the wound wasn’t healing. At that time I did send a culture specimen to a reference lab so that I would know if any bacteria were also growing in the wound. When the culture results came back I was dismayed to find that the wound was also infected with MRSA. At this point I completely understood why it had been such a challenge to treat his wound, not only was the foot broken but it was also infected with a very problematic bacteria.

After evaluating all of the relevant clinical findings I decide referral was the best option and I therefore referred him to Oregon State University’s teaching hospital. His wound was surgically debrided at the referral hospital and after extended care, was able to make a full recovery. If your pet has a non-healing wound, I suggest that ask your veterinarian if culture would be an option, so that you can determine if they are infected with a resistant bacterium such as MRSA. The positive culture results in connection with the radiograph were the two critical pieces of information I needed to recommend the appropriate course of action for this patient.

In addition to wounds, dogs that have MRSA infections can have skin infections, bone infections, ear infections, abscesses, or infected surgical incisions2. In one study 17-40% of Staphylococcus infections in dogs where MRSA infections and most of these were most likely contracted from an infected human2.

MRSA bacteria can infect both humans and animals and can be spread back and forth between both species. MRSA are either acquired in a hospital situation called a nosocomial infection or from outside of the hospital, called a community acquired infection2. In this case his MRSA infection was community acquired.

Another area in which your veterinarian can help you is with culturing clinically normal dogs and cats which reside in the home with a human patient infected with MRSA. I recently received a call from an owner whose husband was struggling with a MRSA infection. She was wondering if their female Labrador was harboring the bacteria and was a source of infection for her husband. In response to her query I collected culture specimens and sent them to the same lab that had cultured the MRSA from my patient. Fortunately her dog was negative; giving some peace of mind that her husband’s infection was not a result of the bacteria transmitting back and forth between him and the dog.

Any other questions you may have about MRSA infections can be answered by your veterinarian. Not all of your pet’s infections need to be cultured, but don’t hesitate to ask your veterinarian if culture is right for your pet, especially if it has been frustrating to treat. If you have a family member infected with MRSA you should request that you veterinarian submit samples from your dogs and cats to determine if they are contributing to the problem.

1. Veterinary Medicine November 2011 Vol. 106 No. 11

2. DIAGNOSTIC UPDATE IDEXX Reference Laboratories; March 2009 #103

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