Assessment of In vitro Antibacterial Activity and Cytotoxicity Effect of Nigella sativa Oil

Background: Methicillin resistance is a serious health concern since it has spread among Staphylococcus aureus and coagulase‑negative Staphylococci (CoNS) that are frequent community and nosocomial pathogens worldwide. Methicillin‑resistant strains are often resistant to other classes of antibiotics, making their treatment difficult. Nigella sativa oil is known to be active against Gram‑positive cocci, yet its in vitro cytotoxicity is rarely investigated, is a proper and powerful candidate for treatment of methicillin‑resistant isolates. Objectives: The aim of this study is to evaluate the in vitro antibacterial activity and cytotoxicity effect of N. sativa oil. Materials and Methods: The minimal inhibitory concentrations (MICs) of N. sativa oil were determined by broth microdilution method against four different American Type Culture Collection strains, 45 clinical isolates of methicillin‑resistant S. aureus (MRSA), and 77 methicillin‑resistant CoNS (MRCoNS). The effects of different dilutions (0.25 μg/mL, 0.5 μg/mL, and 1 μg/mL) of N. sativa oil on the proliferation of gingival fibroblasts were evaluated. Results: The MIC values of N. sativa oil against clinical isolates of Staphylococci were between <0.25 µg/mL and 1.0 µg/mL. Compared to the control group, there was no cytotoxic effect on the proliferation of the gingival fibroblasts. Conclusion: In the present study, the oil of N. sativa was very active against MRSA and MRCoNS and had no in vitro cytotoxicity at relevant concentrations. These findings emphasize that there is a requirement for further clinical trials on N. sativa oil for “safe” medical management of infections caused by methicillin‑resistant Staphylococci.