Staphylococcus spp.
Staphylococci are gram-positive cocci frequently found as commensals on the skin and mucous membranes of mammals and birds. They may also act as opportunistic pathogens, particularly in animals with predisposing conditions, resulting in localised and invasive disease. More than 40 species are described, which are broadly divided into coagulase-positive and coagulase- negative organisms, with the former more commonly associated with infection than the latter. 3 Staphylococci display different host specificities, although cross-species transmission is common. Staphylococcus pseudintermedius • Staphylococcus pseudintermedius is a common organism colonising cutaneous and mucocutaneous surfaces in dogs and cats. Like other coagulase-positive staphylococci, colonisation is more commonly seen at mucocutaneous surfaces rather than skin. Staphylococcus pseudintermedius is more frequently isolated from dogs than cats, where S. felis is more common. Staphylococcus pseudintermedius colonisation or infection is uncommon in humans. • Carriage rates of S. pseudintermedius in healthy dogs in Australia have been reported from 85.5% (rural Victoria) 4 to 46.2% (remote NSW) 5 , and are similar to those from other countries. Carriage rates are highest in the nose, mouth and perineum. 6 In cats, carriage rates of 8.8% (remote NSW) have been reported. 5 Carriage is not typically associated with clinical signs, however opportunistic infections may occur, particularly cutaneous infections where it is the predominant pathogen in over 90% of cases of pyoderma. 7 • Methicillin-resistance in S. pseudintermedius is a more recent phenomenon than in S. aureus, with the first reports in Australian dogs in 2014. 8 Methicillin-resistant S. pseudintermedius (MRSP) isolates have however been identified in archived samples in Australia dating back to 1999 (USYD archives, J. Norris, unpublished data). MRSP isolates are frequently resistant to a broad range of antimicrobials, including fluoroquinolones. As with S. aureus, resistance to beta-lactam antimicrobials in S. pseudintermedius is usually due to the presence of the mecA gene (which encodes penicillin-binding protein 2a [PBP2a]). • Prevalence of MRSP varies depending on study population and methods. MRSP carriage in dogs in Queensland is reported as 8.7% versus 0% in cats. 9 A study from Sydney reported a similar finding, with MRSP carriage in 7% of client owned dogs, 8% of dogs owned by veterinary personnel, and 0% of cats. 10 Studies in remote Indigenous communities failed to identify MRSP in sampled dogs and cats, likely associated with limited access to veterinary care and use of antimicrobials in these communities. 5,11 • Carriage of MRSP is not associated with clinical signs, however opportunistic infections may result in disease. In Australia, 11.8% of S. pseudintermedius submissions from clinical infections were MRSP, with resistant isolates most commonly associated
with skin and soft-tissue infections and surgical site infections. 12 Overseas it is reported that up to 65% of S. pseudintermedius pyoderma cases are methicillin-resistant. 13 • Transmission of MRSP from colonised or infected companion animals to humans has been reported but it is thought to be uncommon, with carriage in humans relatively short lived. 14 • Staphylococcus pseudintermedius has been reported in up to 4% of owners of healthy dogs or cats based upon nasal swabbing, with carriage associated with rare or infrequent hand washing after handling pets. 15 • Infection with S. pseudintermedius in humans is rare, most commonly involving local infection of bite wounds. More severe manifestations including bacteraemia, endocarditis, pneumonia, brain abscesses, and otitis have been rarely reported. 16
Perineum-rectum 52% (28-72%)
Nose 31% (16-64%)
Mouth 57% (42-74%)
Groin 23% (16-38%)
Estimated carriage rates of Staphylococcus pseudintermedius at different body sites in dogs. Ranges are indicated in parentheses for each site Adapted from Bannoehr et al (2012). 6
Staphylococcus pseudintermedius is the most common pathogen associated with canine pyoderma
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10 Companion Animal Zoonoses Guidelines
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