Onopordum acaulon extracts–mediated synthesis of zinc oxide nanoparticles, evaluation of cytotoxicity, and inhibitory potential of microbial biofilm and quorum sensing

Plant extracts are used as cheap and environmentally friendly complexing and stabilizing agents for the green synthesis of nanoparticle with good properties. Zinc oxide nanoparticles were synthesized from Onopordum acaulon ethanol extract (zinc oxide nanoparticles–ethanol extract), aqueous extract (zinc oxide nanoparticles–aqueous extract), and dry plant powder (zinc nanoparticles–dry plant powder). The zinc oxide nanoparticles were characterized using ultra violet–visible spectroscopy, Fourier Transform Infrared spectroscopy, scanning electron microscopy, and X-ray diffraction which confirmed the formation of zinc oxide nanoparticles with sizes ranging from 11 to 17 nm and a Wurtzite crystalline phase. Cytotoxicity on Saccharomyces cerevisiae indicates that zinc oxide nanoparticles predominantly exhibit dose-dependent cytostatic effects with LC 50 values exceeding 60 mg mL −1 , suggesting good biocompatibility. Minimal inhibitory concentrations ranged from 0.312 to 2.5 mg mL −1 . Zinc oxide nanoparticles from ethanol extract were most active against Bacillus subtilis and Escherichia coli , zinc oxide nanoparticles from aqueous extract exhibited the best antimicrobial activity against Staphylococcus aureus and Escherichia coli , while zinc oxide nanoparticles from dry plant powder had the lowest minimal inhibitory concentration against Bacillus subtilis . Nanoparticles synthesized with aqueous extract (zinc oxide nanoparticles–aqueous extract) showed highest biofilm inhibition against Bacillus subtilis , Escherichia coli , Salmonella typhi , and Candida albicans , while against Staphylococcus aureus , biofilm, the nanoparticles from hydroethanol extract (zinc oxide nanoparticles from ethanol extract) were most active. Zinc oxide nanoparticles from dry plant powder had the lowest antimicrobial activity against Chromobacterium violaceum 12472; it exhibited the best violacein inhibition. Zinc oxide nanoparticles from ethanol extract and zinc oxide nanoparticles from aqueous extract exhibited good quorum-sensing inhibition with anti-quorum-sensing zones of 21.5 ± 1.5 and 18.7 ± 0.9 mm, respectively, at minimal inhibitory concentration which reduced to 9.5 ± 0.1 and 8.3 ± 0.5 mm at minimal inhibitory concentration/8. All zinc oxide nanoparticles showed concentration-dependent inhibition of swimming and swarming motilities against Pseudomonas aeruginosa PA01. The green-synthesized nanoparticles exhibit promising antimicrobial properties and inhibited biofilm and quorum sensing, suggesting their application in reducing microbial virulence, pathogenicity, and resistance.