Comparative Assessment of Antibacterial Activity of Secondary Metabolites from Three Medicinal Plants: Ocimum sanctum, Azadirachta indica and Mentha arvensis

Author Name: *Anushree Srivastava
Author Email: anushree.srivastava02@gmail.com

Abstract

Indiscriminate use of antibiotics has ensued into pathogen resistance, therefore, it is essential to discover the natural alternatives to combat the infectious diseases caused by these bacteria, and one scientific approach is to examine the antibacterial activities of the secondary compounds from medicinal plants that are considered to have significant prophylactic properties from centuries. In the present study, three medicinal plants: Ocimum sanctum, Azadirachta indica and Mentha arvensis, have been selected for the extraction of secondary metabolites to perform a comparative evaluation of their antibacterial activities, using Agar-well diffusion method, against three bacterial strains: Bacillus larvae, Actinomyces bovis and Staphylococcus aureus, which have been isolated from soil and identified by Gram staining and biochemical tests. Secondary phytochemicals extracted from Mentha arvensis demonstrated the most profound activity against Staphylococcus aureus and Actinomyces bovis, which indicates that it can be a potential counteractive against these pathogenic bacteria and facilitate the discovery novel. It can be used as a natural antibacterial agent that can combat the serious issue of growing multi-drug resistance among microorganisms.

Keywords:

Antibacterial activity, Medicinal Plants, Secondary Metabolites

Introduction

Emergence of multi-drug resistance in human and animal pathogenic bacteria as well as undesirable side effects of certain antibiotics has triggered immense interest in the search for new antimicrobial drugs of plant origin. Because of the side effects and resistance that pathogenic microorganism build against antibiotics, many scientist have recently paid attention to extracts and biologically active compounds isolated from plant species used in herbal medicines [1]. Every medicinal herb contains a number of active constituents felicitating its manifold curative activity. All of this plethora of compounds with myriad of activities can be roped into animal human system for the same properties. This belief should be the logic of medicinal plants [2] Secondary metabolites are nonnutritive plant chemicals that are synthesized to protect the plant from adverse circumstances such as microbial or parasitic attack or harsh weather conditions. A single plant may produce an arsenal of protective chemicals in response to their lack of motility as well as their stresses and interactions with their environment [3, 4]. Secondary metabolites are separated into nitrogen compounds (alkaloids, non-protein amino acids, amines, alcamides, cyanogenic glycosides and glucosinolates) and non-nitrogen compounds (monoterpenes, diterpenes, triterpenes, tetraterpenes, sesquiterpenes, saponins, flavonoids, steroids and coumarins) [5] . Although plants produce these chemicals to protect themselves, research provides evidence that they can treat humans against infections[6] An important characteristic of plant extracts and their components is their hydrophobicity, which enable them to partition the lipids of the bacterial cell membrane and mitochondria, disturbing the cell structures and rendering them more permeable [7].
The stem and leaves of Ocimum sanctum (tulsi) or holy basil contain a variety of constituents that may have biological activity, including saponins, flavonoids, triterpenoids, and tannins [8]. In addition, the following phenolic actives have been identified, which exhibit antioxidant and anti-inflammatory activities: Rosmarinic acid, propanoic acid, apigenin, isothymusin and isothymonin. Two water-soluble flavonoids: [9] Orientin and Vicenin, have shown to provide protection against radiation-induced chromosomal damage in human blood lymphocytes [10] Leaves of Azadirachta indica (neem) and its constituents have demonstrated antioxidant, immune modulatory, anti-inflammatory, antiulcer, anti-mutagenic and anti-carcinogenic properties [11]. Most of these beneficial characteristics were attributed to the presence of phenolic compounds [12]. The leaves of Mentha arvensis, (mint or podeena) the common edible aromatic herb, have been described to possess various medicinal properties including antimicrobial properties [13, 14]. It yields essential oil menthol, a monoterpene, which exert, through their rapid evaporation, slightly anaesthetic, and anodyne local effect [15, 16]. Menthol’s ability to chemically trigger the cold-sensitive TRPM8 receptors in the skin is responsible for the well-known cooling sensation it provokes when inhaled, eaten, or applied to the skin.
There has been a revival of interest in herbal medicines. This is due to increased awareness of the limited ability of synthetic pharmaceutical products to control major diseases and the need to discover new molecular structures as lead compounds from the plant kingdom. Plants are the basic source of knowledge of modern medicine. The basic molecular and active structures for synthetic fields are provided by rich natural sources.

Conclusion

In the present time when multi-drug resistant pathogens are constantly growing and can cause serious clinical implications in the future, scientific exploration on secondary phytochemicals which are naturally oriented to protect plants and contain significant prophylactic properties is the need of the hour, requires discovery of novel and natural antibiotics of plant origin, and which is the hypothesis behind the present study. Results of the present comparative assessment validate M. arvensis as a most promising antibacterial agent against A. aureus and A. bovis, whereas, O. sanctum is on the second place and A. indica is comparatively weaker in its potential to inhibit all three tested pathogens. In conclusion, M. arvensis, due to its profound antibacterial activity, can be used to discover bioactive natural products that may serve as leads for the development of new pharmaceuticals that address hitherto unmet therapeutic needs.

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