ABSTRACT
Acinetobacter baumannii (Ab) is developing resistance to a variety of common antibiotics. and become multidrug resistant, extreme drug resistant, and pan drug resistant pathogens, requiring the identification of new antibiotics as well as the identification of new plant compounds capable of acting against Ab. Recent research has revealed MDR Ab co-infections with COVID-19,, raising alarm bells. Since its isolation, Usnic acid has been investigated for a variety of pharmacological activities, including antioxidant, antitumor, antibacterial, antifungal, antiviral, antiprotozoal, and insecticidal. Many Plant-derived drugs show promising activity as new antimicrobial agents against multidrug resistant (MDR) strains. There is insufficient data to support the antibacterial activity of (+)-UA against MDR Acinetobacter baumannii.. In the present study, we evaluated the antimicrobial activity of naturally occurring compound (+) usnic acid (UA) against MDR Ab. We determined the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC), time-kill assay in twenty multidrug resistant Acinetobacter baumannii clinical isolates collected from two different centers. Results revealed promising activity of (+)-UA with MIC concentration of 512–1024 µg/mL and MBC 2048 –4096 µg/mL. The MBC/MIC index indicated that the compound was bactericidal. The time-kill assay revealed a gradual decrease in the log10 value of the bacteria. Since there is a limited research available on the activity of usnic acid against MDR Acinetobacter baumannii, present study fills the gap.