Methicillin-resistant commensal staphylococci in healthy dogs as a potential zoonotic reservoir for community-acquired antibiotic resistance.

Beta-lactam-resistant staphylococci evolved due to widespread nosocomial antibiotic use during the twentieth century, but the last decade has seen the emergence of genotypically distinct resistant bacteria outside hospitals, such as community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). This changing epidemiology suggests that mechanisms other than direct antibiotic selection could be involved in the spread of bacterial resistance. Here we report a 17% prevalence of methicillin-resistant Staphylococcus intermedius (MRSI)-a markedly higher rate than the 0-2% reported in some other series-in a random sample of nasal swabs from healthy pet dogs in Hong Kong. In contrast, MRSA was not detected. Since the mecA mobile genetic element responsible for methicillin resistance has been shown by others to be horizontally transmissible between dogs and humans, our findings suggest that the high prevalence of this resistance vector in companion species is a legitimate concern for public health, and raise the important possibility that pet-acquired methicillin-resistant staphylococci (PA-MRS) could play a role in zoonotic mecA gene spread.