A tracheostomy tube was placed as part of the treatment of an 18-month-old castrated male golden retriever admitted to an intensive care unit (ICU). Methicillin-resistant Staphylococcus aureus (MRSA) was isolated from the tube via routine bacterial culture 10 days later. Methicillin resistance marks the presence of the mecA gene, which encodes synthesis of an altered penicillin-binding protein that has a low affinity for b-lactam antimicrobials. MRSA strains are therefore resistant to all penicillins and cephalosporins, and treatment can be further complicated because of their resistance to other classes of antimicrobials. It was impossible to prove conclusively that the MRSA cultured in this case originated within the ICU because animals were not screened when admitted. Like methicillin-susceptible S aureus, MRSA can be found in the nasal passages or intestinal tract of a small percentage of clinically normal animals. All animals in the ICU during the defined outbreak period were screened, and MRSA was isolated from 6 of 26 animals (23%). Indirect contact and personnel-borne transmission were noted by the authors as the most likely means of transmission. Infection-control measures, including active surveillance of all animals, barrier precautions (gloves and gowns), and hand hygiene were implemented to help control the apparent outbreak. MRSA colonization decreased rapidly afterward, suggesting that they may have affected the spread and ultimate control of the MRSA.

COMMENTARY: As the bond between people and pets becomes closer, transmission of bacteria between people and pets in the same environment is inevitable, and incidents such as in this report will most likely increase. Research in the UK has revealed that 12% to 18% of veterinary staff were carriers of MRSA, leading to concern about transmission to the pets in their care. As resistance increases in veterinary pathogens, culture of common conditions, such as pyoderma, will become essential. However, the fact that in other studies significantly more resistant isolates were recovered from feral cats as compared with domesticated cats indicates that there is more to the story than simple transmission between people and pets in the same household.

Cluster of methicillin-resistant Staphylococcus aureus colonization in a small animal intensive care unit. Weese JS, Faires M, Rousseau J, et al. JAVMA 231:1361-1364, 2007.