What is ‘methicillin resistance’ (e.g., MRSA)?

Both humans and animals normally carry and are routinely exposed to staphylococcal bacteria without harmful effects. Dogs and cats normally have Staphylococcus pseudintermedius on their skin, while people and some horses tend to have Staphylococcus aureus. Some Staphylococcus bacteria have acquired a trait (usually after repeated antibiotic exposure) called ‘methicillin resistance’ making them resistant to commonly used antibiotics, hence more difficult to treat. When veterinary patients have been exposed to multiple courses of antibiotics, when ‘standard’ antibiotics fail to improve signs of bacterial infection, or when deep forms of bacterial infections are present, dermatologists will perform a culture of the patient’s skin sores to identify the type of bacterial infection and to determine if ‘methicillin resistant’ bacteria are present. The results of the skin culture allow the dermatologist to select the most appropriate antibiotic for the infection at hand. When ‘methicillin resistance’ is conferred to Staphylococcus aureus and Staphylococcus pseudintermedius the acronyms ‘MRSA’ and ‘MRSPi’ are used, respectively. Although not common, MRSPi is more prevalent in companion animals than people. Similarly, MRSA occurs more often in people (and occasionally horses) than in dogs and cats. While transfer of bacteria from human-to-pet or pet-to-human has been reported, this is not a common occurrence. Nevertheless, following are some simple guidelines that may help limit the spread of methicillin-resistant staphylococcal bacteria that could possibly cause health problems in humans and unaffected pets. Please keep in mind, Staphylococcus aureus (and thus MRSA) primarily causes bacterial infections in people, while Staphylococcus pseudintermedius (and thus MRSPi) is predominantly a bacterial pathogen of dogs and cats.


  • Keep young children and immunocompromised people (cancer patients, HIV/AIDS, patients receiving immunosuppressive drugs) away from the affected pet. When this is not feasible, make sure these individuals wash their hands after touching the affected pet.
  • Completely finish antibiotics as prescribed to your pet and return for follow-up examinations. If topical treatments were prescribed, use them as recommended remembering to wash your hands after administration.
  • Underlying medical or surgical conditions responsible for the bacterial infection must be sought and managed for ultimate infection resolution (and prevention of relapse).
  • Wash hands and/or use alcohol-based hand sanitizers after handling the affected pet and his/her bowls, cage, and toys. Additionally, wash your hands before and after trips to the restroom. Remember everything your elders taught you about washing your hands (e.g., wash your hands before food preparation, use soap, avoid splatter, gently scrub all surfaces of your hands during the time it takes you to sing “Happy Birthday to You” twice, dry your hands off).
  • Regularly pick up stool (dogs) or scoop litterbox (cats) of the affected pet and dispose of it in the trash can.
  • Wear gloves when topically treating the affected pet’s wounds.
  • Keep open draining wounds of the affected pet covered.
  • Keep personal wounds covered and protected.
  • Do not allow the affected pet to lick the face or wounds of people.
  • Do not share the same bed as the affected pet.
  • Do not share towels or linens with the affected pet.
  • Wash and heat dry affected pet’s bedding/laundry separate from human clothing and linens.
  • Do not allow the affected pet to serve as a “therapy animal” in human health care facilities.
  • In an attempt to limit the spread of infection, try to avoid pet daycare and public dog parks until the affected pet is cleared of the infection.
  • Consult with your personal physician if you develop skin lesions/sores (e.g., pimples, boils, swellings) or have concerns about your personal health.

To find out more about MRSA and MRSPi, please download the MRSA Information Brochure or visit the Worms & Germs Blog .