Evaluation of antibacterial and cytotoxic activity of Artemisia nilagirica and Murraya koenigii leaf extracts against mycobacteria and macrophages

BACKGROUND Artemisia nilagirica (Asteraceae) and Murraya koenigii (Rutaceae) are widely distributed in eastern region of India. Leaves of Artemisia nilagirica plant are used to treat cold and cough by the local tribal population in east India. Murraya koenigii is an edible plant previously reported to have an antibacterial activity. Pathogenic strains of mycobacteria are resistant to most of the conventional antibiotics. Therefore, it is imperative to identify novel antimycobacterial molecules to treat mycobacterial infection. METHODS In this study, ethanol, petroleum ether and water extracts of Artemisia nilagirica and Murraya koenigii were tested for antibacterial activity against Mycobacterium smegmatis and Mycobacterium bovis BCG in synergy with first line anti-tuberculosis (TB) drugs, and for cytotoxic activities on mouse macrophage RAW264.7 cells. Antibacterial activity was determined by colony forming unit (CFU) assay. Intracellular survival assay was performed by infecting RAW264.7 cells with M. smegmatis before and after treatment with plant extracts. Cytotoxity was checked by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay. Genotoxicity was studied by DAPI staining and COMET assay using mouse macrophage RAW264.7 cell line. Cell apoptosis was checked by Annexin-V/FITC dual staining method. Reactive oxygen species and nitric oxide production was checked by DCFH staining and Griess reagent, respectively. RESULTS Ethanol extracts of A. nilagirica (IC50 300 μg/ml) and M. koenigii (IC50 400 μg/ml) were found to be more effective against Mycobacterium smegmatis as compared to petroleum ether and water extracts. M. koenigii extract showed maximum activity against M. bovis BCG in combination with a first line anti-TB drug rifampicin. M. koenigii leaf extract also exerted more cytototoxic (IC50 20 μg/ml), genotoxic and apoptosis in mouse macrophage RAW 264.7 cell line. Treatment of mouse macrophages with A. nilagirica extract increased intracellular killing of M. smegmatis by inducing production of reactive oxygen species and nitric oxide. CONCLUSIONS Ethanol extracts of A. nilagirica and M. koenigii were found to be more effective against mycobacteria. As compared to A. nilagirica, M. koenigii ethanol extract exhibited significant synergistic antibacterial activity against M. smegmatis and M. bovis BCG in combination with anti-tuberculosis drug rifampicin, and also showed increased cytotoxicity, DNA damage and apoptosis in mouse macrophages.