Biosynthesis of Ag and Cu NPs by secondary metabolites of usnic acid and thymol with biological macromolecules aggregation and antibacterial activities against multi drug resistant (MDR) bacteria.

Thymol and usnic acid as the important secondary metabolites of respectively Artemisia haussknechtii and Protoparmeliopsis muralis were used for reduction and stabilizing of AgNO and CuSO in metal nanoparticles (MNPs) biosynthesis process. Antibacterial effects of prepared Ag-thymol (ATNPs), Ag-usnic acid (AUNPs), Cu-thymol (CTNPs), and Cu-usnic acid (CUNPs) on multi drug resistant (MDR) bacteria including methicillin-resistant Staphylococcus aureus (MRSA) (gram positive), Acinetobacter baumannii (A52), and Klebsiella pneumonia (K38) (gram negative) were compared with thymol, usnic acid, AgNO, CuSO, and tetracycline. Results of this study showed higher antibacterial activities of usnic acid, CUNPs, and CTNPs with MIC/MBC values (20, 40, and 40 μg/mL, respectively) than ATNPs and AUNPs against MRSA bacteria. Leakage of macromolecules involving nucleic acids and proteins from bacteria under stress of MNPs, thymol, and usnic acid proved significant antibacterial activities of usnic acid, and Cu NPs. In addition, SEM images illustrated different patterns of aggregation in biofilms resulted from interactions of these antibacterial agents with bacterial macromolecules. Totally, this investigation illustrated new green method of Ag and Cu NPs biosynthesis with suitable antibacterial properties.