Rosemary essential oil nanoparticles enhance antimicrobial activity and induce bacterial DNA disruption

Abstract The current work aimed to formulate Rosemary essential oil nanoparticles (Ros-ES-NPs) and evaluate their antimicrobial effect in comparison with free oil (Ros- ES). Physicochemical characterization was performed using Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering, zeta potential analysis, transmission electron microscop y (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The cytotoxic activity of Ros-ES-NPs on human lung fibroblast cell line (Wi-38) was examined in comparison with Ros- ES using MTT assay. Ros-ES exhibited dose-dependent cytotoxicity, with an IC 50 of approximately 6.06 mg/ml on Wi-38. In contrast, the Ros-ES-NPs not only showed no toxicity but actually appeared to increase cell viability (up to ≈ 136%) possibly due to high metabolic actvity. The antimicrobial activity of Ros-ES and Ros-ES-NPs was evaluated against three isolates of Multidrug-Resistant Bacteria, comprising two Gram-negative isolates ( Shigella flexneri and Klebsiella pneumoniae ) and one Gram-positive isolate ( Streptococcus pneumoniae ), alongside C andida albicans as the fungal pathogen. Ros-ES-NPs showed a significant antimicrobial efficacy against all isolates under study where, at 25 mg/ml, Ros-ES inhibited K. pneumoniae and Shigella flexneri by 55.16 ± 0.09% and 76.47 ± 1.16%, respectively, whereas Ros-ES-NPs showed inhibition rates of 95.66 ± 9.74% and 87.13 ± 2.63%, respectively. Against Streptococcus pneumoniae , at 25 mg/ml, Ros-ES inhibited by 68.75 ± 0.60%, while Ros-ES-NPs exhibited a higher inhibition rate of 80.73 ± 5.6%. In case of C. albicans , Ros-Es showed a higher inhibition (81.85 ± 0.54) than Ros-Es-NPs (60.39 ± 5.69). Rosemary essential oil nano-formulation significantly enhances antibacterial efficacy while improving biocompatibility and inducing pronounced microbial DNA damage.