Deep fungal skin infections in dogs being treated with immunosuppressant therapy pose a clinical challenge, balancing effective antifungal therapy with a sufficient immune function to control the infection whilst maintaining good control over the original disease. This case report describes the clinical presentation, diagnosis, and outcome of a dog with a concurrent deep fungal infection of the skin with two rare fungi, Purpureocillium sodanum and Alternaria rosae, and this is the first time this agents has been described in veterinary medicine. Challenges included fungal infections at multiple sites and drug–drug interactions between necessary immunosuppressive therapy and antifungals. Persistent lesions and limited therapeutic success emphasise the need for clinicians’ awareness, early diagnosis, individualised case management, and advances in immunosuppressive protocols.

Background: Methicillin-resistant Staphylococcus pseudintermedius (MRSP) represents an emerging challenge in veterinary dermatology. Commercially available ozonated oils promise antibacterial activity, but their efficacy under physiologically relevant conditions remains unexplored. Objective: We aimed to evaluate the efficacy of commercial ozonated olive oil product (800 mEq O₂/kg) against MRSP using an established in vitro model and a newly presented ex vivo canine skin model. Materials and Methods: In vitro susceptibility testing determined minimum inhibitory concentrations (MIC) and time–kill kinetics. Subsequently, canine skin samples were mounted in Franz diffusion cells, inoculated with MRSP (~10⁶ colony-forming units [CFU]), and treated for 8 h with ozonated or placebo olive oil. Bacterial viability was assessed by quantitative culture and histopathology. Results: In vitro testing demonstrated antibacterial activity for ozonated oil (MIC < 20% v/v) compared to placebo oil (90% v/v), with ozonation-specific bactericidal effects. However, ex vivo testing showed no MRSP reduction for either oil versus untreated controls, with bacterial localization in superficial dermis unchanged. Conclusions: Despite in vitro activity, this ozonated olive oil failed to reduce MRSP in ex vivo skin, revealing that tissue barriers prevent antibacterial delivery. These findings demonstrate that in vitro screening cannot predict topical efficacy and emphasize the necessity of tissue-based validation before clinical use.