By Dr Linda Vogelnest
What are the implications of MRSP?
What does culture of MRSP from a skin surface swab or ear swab mean? Nothing unless cytology supports infection and consistent lesions are present: MRSP (Methicillin-resistant Staph.
pseudintermedius) may be part of the normal flora on dog and cat skin and in ear canals.
• MRSP on culture from skin AND neuts + intracellular cocci on cytology or histology confirms MRSP pyoderma
• MRSP on culture from an inflamed/irritated ear AND numerous bacterial cocci on cytology confirms MRSP otitis
• MRSP culture alone does not confirm disease: concurrent cytology (for superficial lesions) or histopathology (for deep nodular lesions) is ESSENTIAL to assess any disease role
Where did the MRSP come from?
There has been very quick spread of relatively few clones of MRSP worldwide in recent years. A recent Australian study evaluating culture of staph found 12% of Staph pseud cultured were MRSP. Similarly, as for other normal bacterial flora, dogs share their bacteria when interacting (e.g. dog parks, vet hospitals, friend’s houses). There is a higher risk of MRSP colonisation if dogs have been at a vet hospital, or on systemic antibiotics recently.
What are the implications of MRSP on culture for our veterinary patients?
MRSP is not more likely to cause disease than non-resistant Staph psuedintermedius (MSSP) i.e. it is not more pathogenic – but it is more difficult to treat when infection does occur.
• Superficial skin infections – often less problematic as topical antiseptics (chlorhex 4% solution BID) are effective.
Management of the underlying disease to limit recurrence is essential. For atopic patients, with recurrent pyoderma, regular skin barrier treatments, topical antiseptics +/- cyclosporin are often helpful.
• Deep infections (e.g. deep pyoderma, cellulitis, internal infections) are much more challenging as MRSP are often multidrug resistant.
Culture and sensitivity testing is essential to guide therapy:
MRSP will be resistant to all B-lactams (cephalexin, amoxyclav, cevofecin), and MRSP species in Australia are usually resistant to clindamycin, fluoroquinolones, and chloramphenicol; some may be sensitive to doxycycline or trimethoprim sulfur, and some are only sensitive to rifampicin or potentially amikacin (both have significant risk of severe side effects). After a positive MRSP culture, this patient, and optimally other pets in this household, will need C&S testing to guide use of systemic antibiotics for skin infections every time OR only be treated with topical therapy. Later cultures may
reveal infection due to MSSP or MRSP: MRSP colonisation is not necessarily permanent!
What are the implications of MRSP on culture for owners?
MRSP are bacteria mainly adapted to live on dog’s skin, and do not thrive on human skin. Staph aureus (SA) is the common skin staph in humans. MSSA and MRSA infections are rare in animals. MSSP or MRSP infections are very rare in humans; most typically seen in immune-compromised people. Older people with poor circulation and lower eg ulcers may be more at risk. If infection occurs – as in dogs – it is more difficult to treat. Regular antimicrobial shampoos (e.g. chlorhexidine 2-3% twice weekly) for culture positive dogs, and daily chlorhexidine 4% solution on any lesions, will help limit potential contagion of MRSP from patients to other pets or humans.
What are the implications of MRSP on culture for the vet hospital?
MRSP will occur in a subset of our dog (and cat) patients. When associated with surface skin infections, there will be increased numbers of bacteria and greater potential for contagion. Patients with known MRSP infections should be barrier-nursed: they have contagion potential, particularly when hospitalised. The more problematic group are dogs with pyoderma before we know this is due to MRSP (i.e. at the initial consult): there is potential to share their MRSP with other patients in the waiting room and/or consult room.
Good hospital hygiene is the key to reducing risk: always clean consult tables, and also clean floors when contaminated with hair and/or scale, between every patient – step one is to remove any physical material (hair, scale etc) and step two is to disinfect (alcohol e.g. metho is quickest for consult tables; bleach is good for floors – 0.1% = 1ml of 6% household bleach per 60ml of water). Good hand hygiene between every patient is an important routine: removing any physical material with soap and water first (only needed if material present), followed by disinfection (alcohol gels). Do you do this between every patient.