Note for Pet Owners:

This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

MSRA is a potential Zoonosis and so precautions must be taken to prevent cross-infection from animals to people and vice-versa.

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MRSA stands for methicillin-resistant Staphylococcus aureus. Bacterial resistance to antibiotics has been recognised for over 60 years, and the ability of organisms including Staphylococci to develop resistance to new-generation antibiotics is well known. Of particular importance to humans is the emergence of strains of MRSA that have developed multiple resistance to antibiotics, and which can cause devastating disease and death in susceptible patients

The bacterium Staphylococcus aureus is a normal commensal inhabitant of the skin, nasal cavity and pharynx, and isolation of it from swabs taken from these areas does NOT necessarily mean that an animal is showing clinical signs of disease. The reported frequency of occurrence of Staphylococcus aureus isolated from normal dogs and cats varies from  less than 10%  to 40% of cats and  90% of dogs (Krogh & Kristensen 1976).

However, Staphylococcus aureus infections, including MRSA and multiple-resistant strains, do occur in dogs and cats. It is not clear to what extent humans are the primary reservoir source for infection transfer to dogs and cats, or to what extent dogs and cats act as reservoirs of infection for susceptible people. In one review of the subject  (Duquette and Nuttall 2004) humans were cited as being the most common source of infection for dogs and cats. 

The reported isolation rate of methacillin-resistance Staphylococcus aureus from normal dogs and cats also varies from 93/6519 (1.42%) in domestic animals (Rich and Roberts 2004), to 3/148 (2.03%) cats (Lilenbaum et al 1998).

The occurrence of methicillin-resistant strains of Staphylococci (not just S.aureus) increases in the presence of disease, and in one study 15/40 dogs with recurrent pyoderma were infected with methicillin-resistant bacteria (Frank et al 2003). In another study 23/25 methacillin-resistant Staphylococci (9 of which were MRSA) isolated from dog wounds or skin lesions possessed the mecA gene, which has been linked to methicillin-resistance in human infections.

In one study,  5/5 patients with MRSA infected wounds that were tested grew MRSA positive cultures when they had a swab taken from their nasopharynx (Boag et al 2004)

Breed Occurrence And Other Factors
There is no reported breed predisposition to develop MRSA infections, however they are associated with :

  • Wound infections (including post-elective surgery)
  • Hospitalisation
  • The use of immunosuppressant drugs

The relative importance of these factors, and the significance of human or pet contact with Hospital premises is unclear.

Wound infections, including post-operative wound infections are the most common manifestation of MRSA infections in dogs and cats and account for over 66% of all reports so far :

Study Total Number of MRSA Cases Number Isolated From Wound Infections (%)
Boag et al (2004) 14 11 (78.6%)
North Carolina State University, Duquette & Nuttall (2004) 3 2 (66.7%)
Rich and Roberts (2004) 93 71 (76.3%)
Tomlin et al (1999) 11 11 (100%)
University of Liverpool, Duquette & Nuttall (2004) 4 4 (100%)

Veterinary Staff Considerations
Veterinary staff should consider themselves to be potential carriers of MRSA, and take suitable precautions to prevent transmission of this potential pathogen to their patients. 

Susceptible members of staff should consider themselves at risk of contracting MRSA from their patients, and take precautions to prevent such cross-infection

Strict hygiene controls should be employed on veterinary premises, especially in surgical areas with respect to instrumentation sterilisation and handling, and wound management to minimise the risk of post-operative wound infection. 

Unnecessary  intimate contact between veterinary staff and patients which might facilitate the transfer of bacteria from skin or nasal cavities should be discouraged.

The rational use of antibiotics is important to minimise the risk of further drug resistance developing.


Culture and Sensitivity 

The diagnosis of MRSA infections needs to be carried out in an experienced laboratory and care needs to be taken when interpreting results. For example, specific broth or agar plate culture techniques are preferred to Kirby-Baur disc techniques because of different specificities and sensitivities, and the latter techniques over-estimate methicillin resistance.

During sample collection and investigation care MUST be taken to avoid :

  • contamination of swabs from non-diseased areas of the patient known to carry MRSA organisms eg skin, upper respiratory tract, AND 
  • contamination from humans who may be carrying the organism.


PCR is used to identify the presence of the mecA gene.


Patients infected with MRSA can be treated with alternative antibiotics, based upon culture and sensitivity findings. For example , one case of joint infection following elective cranial cruciate repair was successfully treated by surgically inserting an absorbable gentamicin-impregnanted sponge (Owen MR et al 2004) 

Zoonosis Considerations
Several reports have demonstrated that Staphylococcus aureus infections can be transferred from pets to humans (Simoons-Smit et al 2000, Bradshaw 2003), and these would suggest that humans could acquire MRSA infections from their pets and vice versa. 

There are also reports of transmission of MRSA from animals to humans. A cat was implicated as a reservoir of MRSA for the re-infection of humans in a geriatric ward (Scott et al 1998) and carrier dogs have been implicated as a reservoir for the infection of people in  family homes (Cefai et al 1994; Manian 2003)


Boag A, Loeffler A, and Lloyd DH. Methicillin-resistant Staphylococcus aureus isolates from companion animals. Veterinary Record (2004) 154: 411

Bradshaw SE . Endocarditis due to Staphylococcus aureus after a minor dog bite. Southern Medical Journal (2003) 96: 407-9

Cefai C , Ashurst S and Owens C. Human carriage of methicillin-resistant Staphylococcus aureus linked with pet dog. Lancet (1994) 344:539-540

Duquette RA and Nutall TJ. Methicillin-resistant Staphylococcus aureus in dogs and cats : an emerging problem ?. Journal of Small Animal Practice (2004) 45:591-7

Manian FA. Asymptomatic nasal carriage of mupirocin-resistant methicillin-resistant Staphylococcus aureus in a pet dog associated with MRSA infection in household contacts. Clinical Infectious Disease (2003) 36: E26-E28

Owen MR, Moores AP and Coe RJ. Management of MRSA septic arthritis in a dog using a gentamicin-impregnated collagen sponge . Journal of Small Animal Practice (2004) 45: 609-612

Rich M and Roberts L . Methicillin-resistant Staphylococcus aureus isolates from companion animals. Veterinary Record (2004) 154: 310.

Scott GM et al. Cross-infection between animals and man : possible feline transmission of Staphylococcus aureus infections in humans ? Journal of Hospital Infection (1998) 12:29-34

Simoons-Smit AM et al. Transmission of Staphylococcus aureus between humans and domestic animals in a household. European Journal of Clinical Microbiology and Infectious Diseases (2000) 19: 150-2

Tomlin J et al. Methicillin-resistant Staphylococcus aureus infections in 11 dogs. Veterinary Record (2004) 144: 60-64


Updated October 2013