416 Article Info Article history Received 3 August 2021 Revised 20 September 2021 Accepted 21 September 2021 Published Online 30 December 2021 Keywords Ocimum Basil Agar well-diffusion Antibacterial activity Antifungal activity HPLC fingerprinting Effective microbiocidal activity of Ocimum sanctum L. and Ocimum gratissimum L. extracts Nasrin Rahman, Basanta Kumar Borah  , Tankeswar Nath, Swapnali Hazarika*, Sushil Singh and Akhil Ranjan Baruah Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat-785013, Assam, India *Chemical Engineering Group, CSIR-North East Institute of Science and Technology, Jorhat-785006, Assam, India Abstract Innovation of effective antimicrobial agents in terms of resistance against various pathogenic microorganisms is a universal challenge for the pathologists and researchers, leading to improvement of innovative technologies that have great potential and efficacy. With this intention, we investigated and compared the antimicrobial activities of leaf extracts of Ocimum sanctum L. and Ocimum gratissimum L. against few bacteria, such as Escherichia coli, Agrobacterium tumefaciens and Bacillus megaterium, and fungi such as Fusarium oxysporum and F. solani . Methanol, petroleum ether, n- hexane as well as water were used to prepare the extracts; the antimicrobial activities were tested using the well-diffusion method. As expected, irrespective of the solvent, the highest concentration (100%) of the extract generally showed the highest efficacy with the largest zones of inhibition of the three bacterial and two fungal species. Among the solvents, overall, the methanolic extract was the most effective (showing the largest zones of inhibition) against bacteria; but the solvents did not show any difference in their activity between the two fungal species. Meanwhile, the most susceptible bacterial species against both the species of tulsi was A. tumefaciens, and the most susceptible fungal species was F. oxysporum. The extracts of O. gratissimum showed relatively higher antimicrobial activity against both bacteria and fungi; this finding correlated with the higher vigour, stronger aroma and higher eugenol content of this species of tulsi. HPLC-fingerprinting of them showed different patterns that correlated with their antimicrobial activities. Copyright © 2021 Ukaaz Publications. All rights reserved. Email: ukaaz@yahoo.com; Website: www.ukaazpublications.com Annals of Phytomedicine 10(2): 416-425, 2021 Annals of Phytomedicine: An International Journal http://www.ukaazpublications.com/publications/index.php Print ISSN : 2278-9839 Online ISSN : 2393-9885 DOI: http://dx.doi.org/10.21276/ap.2021.10.2.55 Corresponding author: Dr. Basanta Kumar Borah Assistant Professor, Department of Agricultural Biotechnology, Assam Agricultural University, Jorhat-785013, Assam, India E-mail: basanta.k.borah@aau.ac.in Tel.: +91-8011050299 Original Article : Open Access 1. Introduction Ocimum is a versatile aromatic genus and is considered as the most sacred plant in the Indian subcontinent. The plant also contains economically important essential oils, and is one of the most important medicinal herbs used in several traditional medicinal systems. The Ocimum species, popular as Basil, is one of the largest genera of the Lamiaceae family (Sajjadi, 2006) with nearly 160 species. It is native to the tropical and subtropical Asia, Africa, and Central and South America (Darrah, 1974). India is home to nine and the North East India to four species of the plant (Kalita and Khan, 2013). Because of the great diversity of the genus, its members are placed under two categories, viz., the Basilicum and the Sanctum group. The Basilicum group includes O. canum, O. basilicum, O. americanum and O. kilimandsacharium; and the Sanctum group includes O. sanctum, O. gratissimum, O. viride, O. sauve and O. micranthum. Commonly known medicinal species include O. sanctum (Krishna tulsi), O. gratissimum (Ram tulsi), O. canum (Dulal tulsi), O. bascilicum (Ban tulsi), O. kilimandsachricum, O. americanum, O. camphora and O. micranthum (Kalita and Khan, 2013; Atal and Kapur, 1989). In Assam, two types of Ocimum are mostly cultivated; the Ram tulsi (O. gratissimum) possessing green leaves, and the Krishna tulsi (O. sanctum) bearing purple leaves. The genus, Ocimum, is an important source of medicine, and contains a wide range of essential oils and other products. The essential oils are rich in phenolics, and are responsible for its aroma and biological activity (Sajjadi, 2006). Eugenol (l-hydroxy-2-methoxy-4-allylben- zene) is an active constituent present in O. sanctum which largely controls the therapeutic potentials of the plant (Singh and Kumar, 2010). O. gratissimum exhibited antifungal activity against dermato- phytes, imperfect filamentous fungi and pathogenic yeasts (Koba et al., 2009), and also against Aspergillus repens, Curvularia lunata and Fusarium moniliforme (Amadi et al., 2010). The medicinal properties exhibited by the Ocimum spp. include adaptogenic, metabolic, antibacterial, antifungal, immunomodulatory, analgesic, antiulcer, anti-inflammatory, antioxidant, antistress, antiarthritic, antiasthmatic, radioprotective, antioxidant, antifertility, anticancer, anticonvulsant, antidiabetic, antihyperlipidemic, memory enhancer and neuroprotective activity (Kadian and Parle, 2012; Jamshidi and Cohen, 2017). Methanolic extracts of O. sanctum revealed its antibacterial activity against pathogens such as Enterococcus faecalis, Enterobacter cloacae, Escherichia coli, Proteus vulgaris, Klebsiella pneumoniae, Staphylococcus aureus and S. saprophyticus (Tantry et al., 2016). Hexane and ethanolic extract of O. sanctum also showed antimicrobial activity against S. aureus, E. coli and Klebsiella spp. (Bansavatar et al., 2015). Camphor, eucalyptol and eugenol present in O. tenuiflorum show antimicrobial activity against S. aureus,