Biofilm inhibitory activity of Usnic acid and potassium usnate against Klebsiella pneumoniae, Acinetobacter baumannii, and MRSA in ventilator-associated pneumonia

Biofilm-associated infections contribute to the persistence of ventilator-associated pneumonia (VAP) and reduce the effectiveness of antimicrobial therapy. This study evaluated the antimicrobial and anti-biofilm activities of usnic acid and its water-soluble potassium salt, potassium usnate, against multidrug-resistant, biofilm-forming pathogens associated with VAP, including Staphylococcus aureus , Klebsiella pneumoniae , and Acinetobacter baumannii . Antimicrobial, anti-biofilm, molecular docking, network pharmacology, and poly(lactic-co-glycolic acid) (PLGA) coating studies were performed to investigate antimicrobial efficacy, identify potential biofilm-associated targets, and assess sustained local drug delivery. Both compounds inhibited planktonic bacterial growth and significantly reduced biofilm formation, with potassium usnate exhibiting antimicrobial activity comparable to polymyxin B. Usnic acid reduced biofilm biomass by approximately 93% in S. aureus , ~ 85% in K. pneumoniae , and ~ 80% in A. baumannii . Network pharmacology analysis identified conserved biofilm-associated regulatory proteins across the three pathogens, while molecular docking predicted favourable binding of usnic acid to the respective protein targets, providing possible mechanistic context for the experimental findings. Potassium usnate was successfully incorporated into PLGA coatings without compromising coating integrity. The coatings exhibited an initial burst release followed by sustained release over seven days, and coating eluates demonstrated antibacterial activity throughout the release period. Overall, potassium usnate incorporated into PLGA coatings exhibited controlled in vitro release and antibacterial activity in eluate assays. These findings support further investigation of potassium usnate-loaded PLGA coatings as a localized antimicrobial delivery strategy for device-associated infections. The integration of microbiological evaluation with computational analyses provides mechanistic support for the development of potassium usnate-loaded PLGA coatings as a potential strategy to reduce biofilm-associated infections on indwelling medical devices.