Antibiotic-Resistant Infections in Dogs

PetMD Editorial
Nov 1, 2012
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Methicillin-Resistant Staph aureus (MRSA) Infection in Dogs

Some strains of the Staphylococcus aureus bacteria are resistant to standard antibiotics. When the organism is resistant to methicillin and other beta-lactam types of antibiotics, they are referred to as methicillin-resistant Staph aureus, or MRSA.

Staphylococcus aureus, also called Staph aureus or S. aureus, is a specific type of bacteria. It is commonly encountered and normally does not cause illness unless a person or pet becomes ill or injured, in which case the bacteria can become opportunistic and cause an infection.

People can be carriers of Staph aureus and may be otherwise perfectly healthy. This is referred to as colonization. Though dogs are not normally colonized with Staph aureus, if your dog is exposed to a person that is colonized or who has an active infection, your dog can become infected or colonized as well.

Symptoms and Types of MRSA

  • Main symptoms are:
    • Fever
    • Discharge from a wound (even a wound that looks small can be severely infected, as the infection can go deep rather than wide)
    • Skin lesion(s)
    • Skin swelling
    • Slow to heal wound(s)
  • MRSA infections in dogs most commonly involve skin and other soft tissues. They can result in skin infections and abscesses.
  • MRSA may also cause post-operative infections of surgical wounds and secondary infections of wounds originating from other causes.
  • More rarely, MRSA can also infect the dog’s urinary tract, ears, eyes and joints.

Causes of MRSA

Dogs kept as pets can become colonized or infected by MRSA organisms through exposure to colonized or infected people. Risk factors that may increase the chance of MRSA infections include previous surgery, hospitalization, and/or antibiotic use. Therapy pets, particularly those used in hospital visitation programs, may also be at increased risk.

When exposed to an MRSA organism, your dog may be colonized, in which case the MRSA bacteria may be present in your dog's nose or anal region. Colonized dogs are considered to be carriers of the disease and are often asymptomatic, appearing perfectly healthy. 

Alternatively, your dog may also become infected, particularly if he has pre-existing wounds. Dog can be both colonized and infected simultaneously under the right circumstances.

Most dog are exposed to MRSA infections through human contact. However, once colonized or infected, your dog can potentially pass the disease to other animals, as well as to people.

Diagnosis of MRSA

Diagnosis is usually accomplished through a bacterial culture. Samples for culture may be collected by swabbing the nose or anal region of a suspected carrier, or by culturing an infected wound directly, if present. By definition, if a Staph aureus organism that is resistant to methicillin is isolated, a diagnosis of MRSA is established. In reality, oxacillin (an antibiotic closely related to methicillin) is the antibiotic used to test for susceptibility. Staph aureus organisms that are resistant to oxacillin are considered to be MRSA.

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