Canine Methicillin-Resistant Staphylococcus aureus (MRSA) – NAVLE Study Guide

Overview and Clinical Importance

Methicillin-resistant Staphylococcus aureus (MRSA) is a strain of Staphylococcus aureus bacteria that has developed resistance to beta-lactam antibiotics, including methicillin, penicillins, and cephalosporins. While S. aureus is primarily a human-adapted pathogen, it can colonize and infect dogs, representing an important zoonotic concern from a One Health perspective.

In dogs, MRSA infections most commonly manifest as skin and soft tissue infections, including pyoderma, surgical site infections, and wound infections. Dogs typically acquire MRSA from human sources, particularly healthcare workers or household members who carry the organism. Understanding MRSA in veterinary medicine is critical for the NAVLE as it encompasses antimicrobial resistance concepts, zoonotic disease principles, and dermatologic management.

Etiology and Epidemiology

Bacterial Characteristics

Staphylococcus aureus is a Gram-positive, coagulase-positive coccus that typically appears in grape-like clusters on Gram stain. It is primarily adapted to human hosts and is commonly found in the nasal passages and skin of approximately 30% of the human population. In dogs and cats, S. aureus is not part of the normal flora; instead, Staphylococcus pseudintermedius is the predominant commensal staphylococcal species.