Antibacterial and anti-biofilm effects of microwave-assisted biologically synthesized zinc nanoparticles

The present study aimed to investigate the antibacterial and anti-biofilm potential of the non-oxidized form of zinc nanoparticles (Zn NPs) prepared by a ‘green approach’ using the Lavandula vera extract with microwave irradiation. After synthesis of Zn NPs, the microdilution and disk diffusion methods was applied for antimicrobial evaluation followed by anti-biofilm activity measurement using crystal violet colorimetric assay procedure. The obtained results demonstrated the production of spherical Zn NPs within the size range of 30-80 nanometers. The measured minimum inhibitory concentration of the Zn NPs and ZnSO4 against the biofilm-producing and clinically isolated pathogens of Staphylococcus aureus, Pseudomonas aeruginosa, and Proteus mirabilis was estimated to be more than 2560 µg/ml. In addition, a non-significant increase (P>0.05) was observed in the antibacterial activity against methicillin-resistant S. aureus after the addition of the Zn NPs (500 µg/disk) to the antibiotic discs containing tobramycin, erythromycin, tetracycline, azithromycin, and kanamycin compared to ZnSO4. On the other hand, the Zn NPs significantly decreased the biofilm formation of P. mirabilis compared to P. aeruginosa (P<0.05). Biofilm formation by S. aureus also reduced to 68.3±2.1% in the presence of the Zn NPs (640 µg/ml), which was considered significant compared to P. mirabilis and P. aeruginosa at the same concentration (P<0.05). To sum up, the biofilm inhibitory activity of Zn NPs at higher concentrations than 160 µg/ml against S. aureus and P. mirabilis was more significant compared to the inhibitory effects of ZnSO4. However, further investigations are required in order to determine the antibacterial and anti-biofilm mechanism of Zn NPs.