Clinically overt infections with methicillin-resistant Staphylococcus aureus in animals in New Zealand:: A pilot study

AIM: To describe clinically overt infections with methicillin-resistant Staphylococcus aureus (MRSA) in animals in New Zealand, characterise clinical isolates, and track their sources. METHODS: MRSA isolates identified in 2005 and 2006 by a veterinary diagnostic laboratory were referred to Massey University for confirmation and characterisation. Clinical information was extracted from the laboratory records or obtained from referring clinicians. RESULTS: Seven MRSA isolates from animals and contact persons were characterised. All the isolates belonged to the British epidemic MRSA 15 strain (EMRSA-15). Three EMRSA-15 were isolated from post-operative infections in two dogs. An EMRSA-15 indistinguishable from the isolate recovered from one dog was isolated from the anterior nares of a healthy hospital staff member involved in the care of the animal, suggesting nosocomial transmission. Other EMRSA-15 isolates of uncertain clinical significance were isolated from the femoral head of a cat, and from a sample of cow's milk. All EMRSA-15 isolates were resistant to ciprofloxacin, and four were resistant to erythromycin; the latter four isolates also exhibited inducible resistance to clindamycin. CONCLUSIONS: MRSA can cause clinically overt and difficult-to-treat infections in animals in New Zealand. The rapid emergence of EMRSA-15 as the dominant MRSA strain in humans has resulted in infection spillover to animals. CLINICAL RELEVANCE: Little is known about the incidence of clinically overt infections with MRSA in animals. The cases described here illustrate the complexities involved in the pharmacological management of EMRSA-15 infections, which is compounded by the universal resistance to beta-lactams, and by the strain's fluoroquinolone resistance and frequent inducible resistance to clindamycin. Such complexities indicate there is a need to develop specific empirical antimicrobial treatment strategies and antibiotic susceptibility testing protocols in countries where EMRSA-15 is dominant.