Abstract
Background:
Pyoderma is a common dermatological condition in dogs caused by various bacteria that are typically part of the normal microbiota. Staphylococcus pseudintermedius and Proteus mirabilis are opportunistic pathogens frequently encountered in canines, producing multiple virulence factors with the potential to cause life-threatening infections.

Case description:
We report the case of a 5-year-old dog that presented with skin lesions that generalized to a life-threatening condition. The initial treatment with corticosteroids, anti-parasitic medications, and antibiotics was ineffective. P. mirabilis was isolated as a sole agent and treated according to the antibiogram with no effect. In subsequent microbiological testing, methicillin-resistant and multidrug-resistant (MDR) S. pseudintermedius was identified as a coagent using mass spectrometry. The dog died a little over two months after the first symptoms with clinical signs of septic shock. This case demonstrates the severe complications caused by canine pyoderma and the challenges in the diagnosis and treatment of a mixed enterobacterial/staphylococcal infection. Furthermore, it highlights the significance of evaluating antibiotic susceptibility and the necessity for repeated microbiological sampling when the patient’s condition worsens, despite the results presented.

Conclusion:
The empirical administration of corticosteroids and beta-lactams is inappropriate in skin lesions with unclear etiology because corticosteroids may enhance the progression of the infection, whereas beta-lactams are inactive in canine staphylococci in most cases.

Key words: Dog; Methicillin-resistant Staphylococcus pseudintermedius; Proteus mirabilis; Pyoderma.