In vitro activity of robenidine analogue NCL195 against methicillin-resistant Staphylococcus pseudintermedius

The rise of difficult-to-treat infections among companion animals, particularly the increasing incidence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) in dogs poses significant challenges for effective treatment options in veterinary practice. In this study, we demonstrate that the novel robenidine analog NCL195 exhibits antibacterial activity against MRSP isolates collected from dogs, achieving uniform minimal inhibitory concentrations of 1 μg/mL across all 160 isolates from multiple clinical cases and representing diverse sequence types. NCL195 acts by disrupting the bacterial cell membrane potential; no resistant mutants emerged during prolonged serial passage experiments, and transmission electron microscopy showed marked changes to the cell membrane of NCL195-treated MRSP compared to untreated controls. Furthermore, NCL195 showed minimal lysis of dog and sheep red blood cells and moderate toxicity to mammalian cell lines. These results highlight NCL195 as a promising candidate for further development as a novel antimicrobial agent to address the urgent need for effective treatments against MRSP infections in veterinary medicine.IMPORTANCEThe rise of difficult-to-treat infections among companion animals, particularly the increasing incidence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) in dogs, poses significant challenges for effective treatment options in veterinary practice. Here, we show that NCL195, a member of a novel class of pyrimidine compounds, exhibits antibacterial activity against 160 MRSP isolates collected from dogs from multiple clinical cases. Additionally, no resistant mutants developed during prolonged serial passage experiments, and NCL195 showed low lysis of dog and sheep red blood cells. Developing NCL195 as an "animal-only" drug promotes the "responsibility" and "refinement" principles of antimicrobial stewardship.