Intra-house circulation and persistence of methicillin-resistant Staphylococcus pseudintermedius in Brazil: Evidence of transmission between a dog and its family.

We investigated a case of postoperative osteomyelitis in a dog caused by methicillin-resistant Staphylococcus pseudintermedius (MRSP) at a veterinary teaching hospital in Brazil, and screened the cohabiting dog, five household members and the attending surgeon for MRSP and other methicillin-resistant staphylococci (MRS) during infection (2021) and two years later (2023). Nasal and skin swabs were cultured on oxacillin-supplemented media. Isolates were identified as MRSP by PCR and characterized by PFGE and whole-genome sequencing, including MLST, SCCmec typing, resistance gene profiling and core-genome SNP analysis. The index infection was caused by MRSP ST71-SCCmec II-III displaying multidrug resistance but amikacin susceptible; the dog was successfully treated with prolonged amikacin therapy combined with surgical revision. During infection, MRSP ST71-SCCmec II-III was recovered from the patient, four owners and the surgeon (6/8 colonized with MRSP), while the cohabiting dog carried methicillin-resistant S. epidermidis. Two years later, MRSP carriage was identified in the cohabiting dog and two owners (3/7), with co-existence of MRSP ST71-SCCmec II-III (cohabiting dog skin) and the emerging lineage ST1095-CC551-SCCmec V (cohabiting dog nares; two owners), while the patient and two other owners carried other MRS. Within each lineage, pairwise SNP distances were ≤ 8, consistent with recent transmission. Overall, this case illustrates long-term intra-household circulation and strain replacement of MRSP across dogs and humans, highlighting the importance of hygiene measures in households to reduce the risk of transmission.