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

Overview and Clinical Importance

Methicillin-resistant Staphylococcus aureus (MRSA) is an important zoonotic pathogen that has emerged as a significant concern in veterinary medicine. While S. aureus is primarily a human-adapted pathogen, cats can become colonized or infected, serving as potential reservoirs for transmission between humans and animals. Understanding MRSA in cats is critical for the NAVLE because it encompasses antimicrobial resistance concepts, zoonotic disease management, and appropriate infection control practices.

MRSA carries the mecA gene (or less commonly mecC), which encodes an altered penicillin-binding protein (PBP2a or PBP2') with reduced affinity for beta-lactam antibiotics. This confers resistance to all penicillins, cephalosporins, and carbapenems, making treatment challenging and culture and sensitivity testing essential.

Etiology and Pathophysiology

The Organism

Staphylococcus aureus is a Gram-positive, catalase-positive, coagulase-positive coccus that typically forms grape-like clusters on Gram stain. It is a commensal organism in humans, found in the nasal passages of approximately 20-30% of the population. In contrast, S. aureus is not host-adapted to cats, meaning feline colonization typically originates from human sources.