Exploring the molecular basis of potassium usnate activity against Staphylococcus warneri persistence and resistance through protein interaction networks and molecular docking

Mastitis remains a major cause of antimicrobial use in dairy herds, contributing to the spread of antimicrobial resistance (AMR). Staphylococcus warneri has emerged as a recurrent pathogen associated with persistent and resistant infections in goats. To explore potential alternative agents, this study integrated in vitro assays with in silico modeling to evaluate the antimicrobial activity of usnic acid (UA) and potassium usnate (KU) against S. warneri isolates from clinical mastitis. Two strains with documented enrofloxacin persistence were characterized in vitro and analyzed using protein–protein interaction (PPI) network modeling and molecular docking (MD). KU displayed higher predicted affinity to persistence- and resistance-associated protein targets than UA. Prominent protein families included ABC transporters (ABC_tran and ATP-Binding_Cassette) related to resistance, and MenD_MenH_VitK_biosynth, Metallo-β-lactamase_sf, and HipB-associated domains linked to persistence. Functional PPI networks highlighted biologically relevant clusters centered on NorB, VraR, SrrB, ArlR, CodY, SarA, BcrA, and MazF. KU binds with higher affinity than reference antibiotics to key resistance (BcrA, TcaR) and persistence (GTP pyrophosphokinase, glycerol kinase) targets. These findings suggest that KU may interfere with essential bacterial survival pathways, supporting its potential as a potent natural antibacterial agent for combating resistant and persistent infections and supporting its continued investigation as a natural product–derived candidate for combating AMR in veterinary infections.