Plants are essential to maintaining the ecological dynamics of ecosystems. Furthermore, they offer numerous substances with potential healing properties [1, 2]. Medicinal plant extracts and essential oils are factories of valued natural bioactive compounds widely evaluated/used in the food, pharmaceutical, nutraceutical, and cosmetic industries due to their fragrance, flavor, and therapeutic abilities [3–6]. Terpenes and their oxygenated derivatives, benzoids, and phenylpropanoids are volatile, complex mixtures of essential oils [4, 7]. Generally, essential oils are often two or three compound mixtures in high quantities (> 20–95%); these are the major constituents, while others can be present only in very small amounts.
Free radicals like reactive oxygen species (ROS) are formed in redox processes, which are the leading cause of degenerative diseases like stroke, rheumatoid arthritis, diabetes, inflammation, aging, cancer, and neurological disorders in the human body [2, 8]. ROS have been connected with lipid oxidation, peroxidation, and DNA mutations of proteins [9]. Any substance that can remove ROS is called an antioxidant. Due to their resonance stabilization effect, phenolic compounds can effectively scavenge free radicals [10]. Interest in the finding of new plant-based drugs with antioxidant properties has grown in modern times.
Nowadays, bacterial infections are on the rise. As with the use of antibiotics in bacterial treatment, the percentage of therapeutic drug failures is increasing due to the development of resistance in microbial strains. Notwithstanding medical advances in infectious diseases, chemotherapy and immunization remain serious health concerns [11]. The resistance of microorganisms towards medicines used as antimicrobial drugs imposes the necessity to investigate new medicines with potential antimicrobial action [12]. Further studies have focused on essential oils extracted from plants that contain various volatile bioactive constituents that can act as therapeutics in humans [6, 7].
Aedes aegypti L. is responsible for transmitting arboviruses that cause diseases such as yellow fever, dengue, chikungunya, and zika in tropical regions [13–15]. Rapid urbanization, a lack of infrastructure, and poor sanitation are ideal circumstances for the spread of this female Aedes aegypti mosquito, which is resistant to pesticides and commercialized repellents [13, 15]. Furthermore, the drawbacks of chemical pesticides, such as pollutants and harm to non-target species, have limited their widespread usage [16]. Therefore, it is necessary to develop alternative pesticides with high efficacy, minimal environmental harm, and low toxicity to humans for controlling mosquitoes. Currently, mosquito control programs focus more on eradicating mosquito larvae with plant-based agents [17]. In this context, essential oils extracted from plants have garnered much attention as possible sources of mosquito repellents and larvicides [18].
The genus Ocimum (Basil) comprises 160 species and is the major species in the Lamiaceae globally. Ocimum is called "the king of herbs" due to the presence of enormous applications in traditional medicine, pharmaceuticals, and the cosmetic industry [19, 20]. Several species of Ocimum, such as O. basilicum, O. gratissimum, O. tenuiflorum, O. americanum, O. kilimandscharicum, and O. micranthum, are cultivated for the isolation of high-value fragrance, flavor, and medicinal properties [21]. Ocimum has traditionally been used to treat a variety of ailments, including rheumatism, epilepsy, paralysis, diarrhea, sunstroke, influenza, high fever, gonorrhea, abdominal pains, mental illness, colds, and coughs, as well as having antipyretic, anti-emetic, stomatic, antihelmintic, and antimalarial activity [22]. Furthermore, Ocimum leaves have been investigated as a food and flavoring agent due to their aromatic properties [23]. Its essential oils and aromatic fragrance have numerous therapeutic potentials, especially antimicrobials, antioxidants, insecticidal, and nematocidal properties [24]. Interestingly, Ocimum essential oils were documented as rich in terpenoids and phenylpropanoids such as methyl cinnamate, linalool, thymol, camphor, citrol, eugenol, and geraniol, which are important active constituents that are variable and influenced by environmental factors [23–25].
Ocimum basilicum L. is an aromatic herb and main commercial crop with numerous biological uses [26]. This plant is used as a supplement in the perfume, pharmaceutical, food, aromatherapy, and cosmetic industries as its main constituent [27]. Essential oils and aromatic leaves have been used in plant-based healthcare since ancient times in traditional systems of medicine [28]. Ocimum basilicum is an aromatic fragrance distinguished by its chemotypes, especially methyl chavicol-rich, linalool-rich, eugenol-rich, methyl eugenol-rich, and methyl cinnamate-rich, which were documented in India [23]. Earlier studies have reported that essential oil extracted from O. basilicum exhibited potential antimicrobial, fungicidal, antioxidant, antiviral, anti-proliferative, anti-inflammatory, antispasmodic, and sedative properties [29].
Another renowned species of Ocimum is Ocimum americanum L. (syn. O. canum Sims.), which is commonly spread through India and tropical Africa. It is also known as "hairy basil. Preparations achieved from its aerial parts are repetitively used in folk remedies to treat insomnia and anxiety [30]. In Nigeria, O. americanum leaf decoction or infusion is used to control fever, coughs, colds, piles, and diabetes[31]. In Yoruba tribals, O. americanum is used to prepare soup due to its aroma and flavor [32]. O. americanum acetone extract inhibited neurotoxins that caused brain damage in rats [33]. With these regards, the current work was conducted to determine the chemical profile of the essential oils extracted from O. basilicum and O. americanum leaves and to investigate their antibacterial, antioxidant, and anti-mosquito larvacidal properties.