Chemical compositions, antioxidant, antimicrobial, and mosquito larvicidal activity of Ocimum americanum L. and Ocimum basilicum L. leaf essential oils

Background: Ocimum americanum L. and Ocimum basilicum L. are highly valued aromatic medicinal plants. The leaves of O. basilicum and O. americanum are widely used as spices in traditional cuisine. Its essential oil is extensively used in the food, cosmetic, and pharmaceutical industries. The purpose of this study is to investigate the main chemical profile of O. americanum and O. basilicum leaf essential oils and to assess their effects on antibacterial, antioxidant, and larvicidal properties. Methods: : Essential oils were extracted from the leaves of O. basilicum and O. americanum using steam distillation in a Clevenger-type apparatus. The chemical constituents of the essential oils (EO) were analyzed by gas chromatography-mass spectrometry (GC-MS). DPPH, FRAP, and metal chelating techniques were used to assess the free radical scavenging ability of the oils. The extracted oil was also tested for its antibacterial activities by a disc-diffusion test and the broth microdilution method. Furthermore, the mosquito larvicidal activity was tested using standard protocols. Results: : Camphor (33.869%), limonene (7.215%), longifolene (6.727%), caryophyllene (5.500%), and isoledene (5.472%) were identified as the five major compounds in O. americanum leaf essential oil. The essential oil yield was 0.4%, and citral (19.557%), estragole (18.582%), linalool (17.605%), and camphor (9.224%) were the major compounds found among the 37 chemical constituents identified in O. basilicum oil. O. basilicum exhibited more potent antioxidant activity in DPPH, FRAP, and ABTS tests than O. americanum . The zones of inhibition and MIC of the oils in the microdilution and disc diffusion methods were 8.00±0.19 to 26.43±2.19 mm and 3.12 – 100 μg/mL, respectively. At 400 ppm, O. basilicum and O. americanum demonstrated larvicidal activity with mortality ratios of 73.60±0.89 and 78.00±1.00%, respectively. Furthermore, after 30 min of exposure, the larval death rate was 73.60±0.89 and 78.00±1.00% for O. americanum and O. basilicum respectively. Conclusions: : These findings revealed that essential oils extracted from the leaves of O. basilicum and O. americanum exhibited reasonable antioxidant, antibacterial, and mosquito larvicidal potentials that can be used as alternative medicine in treating human health and larvicidal mosquito control.