Felis ISSN 2398-2950

Meticillin-resistant Staphylococcus aureus

Synonym(s): MRSA; meticillin-resistant S.aureus, MR-S. aureus

Contributor(s): Susan Dawson, Melissa Kennedy, Anette Loeffler




  • Genus: Staphylococcus.
  • Family: Micrococcaceae.
  • Species: aureus.
  • Antimicrobial-resistance: carries additional genetic marker mecA for methicillin-resistance and broad β-lactam resistance.


  • Gk: staphyle - bunch of grapes; coccus - grain or berry; Latin: aureus - golden.
  • Meticillin (INN; international non-proprietory name) or Methicillin (USAN; United States adopted names): semisynthetic penicillin introduced for clinical use in 1959 but no longer manufactured today. Marker for broad β-lactam antibiotic resistance.

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Clinical Effects



  • See under 'Distribution'.


  • Skin and mucosae of healthy animals.
  • Adhere to skin squames and hair.
  • Environmental contamination through squames and hair shed by the host.
  • May inhabit the gastrointestinal tract.
  • Preferred niche: nostrils.
  • Humans (nostrils and throat) are the preferred host for MRSA isolates most commonly.


  • Reproduction by binary fission.


  • Direct and indirect transmission.
  • In human hospitals, most important route via hand contact.
  • Endogenous infection (opportunistic infection by commensal strains).
  • Transmission between pets and in-contact people in both directions but human-to-pet considered original direction as isolates typically human-healthcare associated strains ("reverse zoonosis").

Pathological effects

  • MRSA infections show the same pathology as those due to meticillin-susceptible S. aureus and other Staphlococcus spp.
  • Typicaly skin and ear infections, traumatic and post-surgical wound infections, often associated with implants, suture material and biofilm.
  • Other organs can be involved in infection (eg urinary tract, respiratory tract) as for other staphylococci.
  • No known lasting immunity after recovery.
  • Severe, life-threatening soft tissue infections reported in people with toxin-producing PVL-positive MRSA (currently rare in pets).

Other Host Effects

  • Same as for other Staphylococcus spp and as for meticillin-susceptible S. aureus.
  • MRSA can colonize skin and mucous membranes of healthy animals and predispose to subsequent (endogenous) MRSA infection.
  • Has host-preference but is not host-specific, ie can contaminate or colonize non-preferred host species and cause infection in immune-compromised individuals (opportunistic).


Control via chemotherapies

  • All MRSA strains are resistant to all penicillins, most cephalosporins and carbapenems.
  • Topical antibacterial therapy should be used whenever appropriate (surface and superficial skin, wound and ear infections).
  • 2-4% chlorhexidine Chlorhexidine preparations and/or fusidic acid Fusidic acid containing creams have good efficacy if owner and pet are compliant.
  • Individual isolates can be susceptible to tetracyclines, lincomycin, potentiated sulfonamide.
  • Antibacterial choice must always be based on sensitivity testing.
  • Prognosis can be good depending on prognosis of underlying primary problem that led to infection.


  • None commercially available.

Other countermeasures

  • For known MRSA patients: barrier nursing:
  • Outpatients should be booked in for last appointment of the day.
  • Waiting and walking in the practice should be minimized.
  • Rigorous hand hygiene (frequent and thorough).
  • Cleaning and disinfection of practice environment after every patient.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Morris D O, Loeffler A, Davis M F et al (2017) Recommendations for approaches to meticillin-resistant staphylococcal infections of small animals: diagnosis, therapeutic considerations and preventative measures: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Vet Dermatol 28 (3), 304-e69 PubMed.
  • Harrison E M, Weinert L A, Holden M T et al (2014) A shared population of epidemic methicillin-resistant Staphylococcus aureus 15 circulates in humans and companion animals. mBio (3), e00985-13 PubMed.
  • Singh A, Walker M, Rousseau J et al (2013) Methicillin-resistant staphylococcal contamination of clothing worn by personnel in a veterinary teaching hospital. Vet Surg 42 (6), 643-648 PubMed.
  • McCarthy A J, Lindsay J A, Loeffler A (2012) Are all meticillin-resistant Staphylococcus aureus (MRSA) equal in all hosts? Epidemiological and genetic comparison between animal and human MRSA. Vet Dermatol 23 (4), 267-75, e53-54 PubMed.
  • Walther B, Hermes J, Cuny C et al (2012) Sharing more than friendship--nasal colonization with coagulase-positive staphylococci (CPS) and co-habitation aspects of dogs and their owners. PLoS One (4), e35197 PubMed.
  • García-Álvarez L, Holden M T, Lindsay H et al (2011) Meticillin-resistant Staphylococcus aureus with a novel mecA homologue in human and bovine populations in the UK and Denmark: a descriptive study. Lancet Infect Dis 11 (8), 595-603 PubMed.
  • Loeffler A, Pfeiffer D U, Lloyd D H et al (2010) Meticillin-resistant Staphylococcus aureus carriage in UK veterinary staff and owners of infected pets: new risk groups. J Hosp Infect 74 (3), 282-288 PubMed.
  • Loeffler A, Lloyd D H (2010) Companion animals: a reservoir for methicillin-resistant Staphylococcus aureus in the community? Epidemiol Infect 138 (5), 595-605 PubMed.
  • Loeffler A, Pfeiffer D U, Lindsay J A et al (2010) Lack of transmission of methicillin-resistant Staphylococcus aureus (MRSA) between apparently healthy dogs in a rescue kennel. Vet Microbiol 141 (1-2), 178-181 PubMed.
  • Soares Magalhães R J, Loeffler A, Lindsay J et al (2010) Risk factors for methicillin-resistant Staphylococcus aureus (MRSA) infection in dogs and cats: a case-control study. Vet Res 41 (5), 55 PubMed.
  • Weese J S, Dick H, Willey B M et al (2006) Suspected transmission of methicillin-resistant Stapylococcus aureus between domestic pets and humans in veterinary clinics and in the household. Vet Microbiol 115 (1-3), 148-155 PubMed.
  • Rankin S, Roberts S, O'Shea K et al (2005) Panton valentine leukocidin (PVL) toxin positive MRSA strains isolated from companion animals. Vet Microbiol 108 (1-2), 145-148 PubMed.
  • van Duijkeren E, Wolfhagen M J, Heck M E et al (2005) Transmission of a Panton-Valentine leucocidin-positive, methicillin-resistant Staphylococcus aureus strain between humans and a dog. J Clin Microbiol 43 (12), 6209-6211 PubMed.
  • Duquette R A & Nuttall T J (2004) Methicillin-resistant Staphylococcus aureus in dogs and cats: an emerging problem? JSAP 45 (12), 591-597 PubMed.
  • Owen M R, Moores A P & Coe R J (2004) Management of MRSA septic arthritis in a dog using a gentamicin-impregnated collagen sponge. JSAP 45 (12), 609-612 PubMed.
  • van Duijkeren E, Wolfhagen M J, Box A T et al (2004) Human-to-dog transmission of Methicillin-resistant Staphylococcus aureus. Emerg Infect Dis 10 (12), 2235-2237 PubMed.
  • Manian F A (2003) Asymptomatic nasal carrriage of mupirocin-resistant, methicillin-resistant Staphylococcus aureus (MRSA) in a pet dog associated with MRSA infection in household contacts. Clin Infect Dis 36 (2), e26-28 PubMed.
  • Seguin J C, Walker R D, Caron J P et al (1999) Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal-transmission. J Clin Microbiol 37 (5), 1459-1463 PubMed.
  • Tomlin J, Pead M J, Lloyd D H et al (1999) Methicillin-resistant Staphylococcus aureus infections in 11 dogs. Vet Rec 144 (3), 60-64 PubMed.
  • Cefai C, Ashurst S & Owens C (1994) Human carriage of methicillin-resistant Staphylococcus aureus linked with pet dog. Lancet 344 (8921), 539-540 PubMed.