Comparative Antimicrobial Efficacy of Tulsi Essential Oil and Biosynthesized Silver Nanoparticles

Amit Kumar, Anjay Dewangan, Madhu Manikpuri, Veenu Joshi*

Center for Basic Sciences, Pt. Ravishankar Shukla University, Raipur.

*Corresponding Author E-mail: vinu.jsh@gmail.com

ABSTRACT:

The increasing prevalence of antimicrobial resistance necessitates the exploration of alternative and sustainable antimicrobial agents. Ocimum tenuiflorum (Tulsi) essential oil (EO) possesses well-documented antimicrobial properties but its practical application is limited due to volatility and poor aqueous solubility. In this study, silver nanoparticles were synthesized using Tulsi EO (TEO-AgNPs) via a green synthesis approach and comparatively evaluated the antimicrobial efficacy of TEO and TEO-AgNP against selected bacteria using disk diffusion method. UV–Vis spectroscopic analysis confirmed the formation of AgNPs through the presence of a sharp peak around 410 nm. This distinct peak, free from broadening is characteristic of spherical, monodisperse nanoparticles with high colloidal stability and uniformity. The antimicrobial activity was assessed against Staphylococcus aureus, Bacillus subtilis, Escherichia coli and results demonstrated that TEO-AgNPs exhibited significantly higher antimicrobial activity than Tulsi EO, with larger zones of inhibition of 16.6 mm for E. coli, 17.3 mm for B. cereus and 15.3 mm for S. aureus. The enhanced efficacy of TEO-AgNPs is attributed to the synergistic interaction between silver ions and phytochemicals present in Tulsi. This study highlights the potential of TEO mediated AgNPs as a promising alternative antimicrobial agent for biomedical applications.

KEYWORDS: Ocimum tenuiflorum, Silver nanoparticles, Green synthesis, Antimicrobial activity, Phytochemicals.

INTRODUCTION:

Antimicrobial resistance (AMR) has been identified as a major threat to healthcare worldwide, which is primarily caused by the failure of traditional antibiotics to sufficiently control different pathogens. This situation has led to a resurgence of interest in natural antimicrobial agents and synergistic compositions that can effectively resist the resistance mechanisms. Innovative approaches not only target finding new natural antimicrobial agents but also combining them with nanotechnology in order to boost their therapeutic effects. Ocimum tenuiflorum L., commonly known as Tulsi is a plant species in the family Lamiaceae. Tulsi is an aromatic medicinal plant that is widely used in Ayurvedic medicine. The plant’s essential oil shows broad antimicrobial activity. This activity is linked to its mixed set of bioactive phytochemicals, including phenolic compounds.Item g.The main constituents include eugenol, terpenoids, camphor, and eucalyptol. These compounds are thought to limit bacterial and fungal growth by damaging microbial cell membranes, reducing enzyme function, and interfering with cellular respiration ¹.Tulsi essential oil has been reported to inhibit both Gram-positive and Gram-negative bacteria, such as Escherichia coli, but the level of inhibition varies with the concentration used and the specific organism tested ².

However, Tulsi essential oil is confronted with several practical problems such as high volatility, hydrophobicity, and low stability when used in biological environments.

These factors restrict its application in water-based systems and reduce the reliability of its bioavailability. Although EO can inhibit bacterial growth at some concentrations, it often shows lower activity than standard antibiotics, which has led to work on formulations that increase its potency and improve delivery.

Nanotechnology may address these challenges by allowing control of materials at very small scales. Silver nanoparticles (AgNPs) are widely studied in nanomaterials research because they show antimicrobial activity that differs from bulk silver. Silver nanoparticles (AgNPs) can affect microbial cells through several routes, including binding to the cell wall, damaging membrane structure, increasing reactive oxygen species (ROS) and disrupting DNA replication and normal protein activity ³. Because these treatments act on more than one biological target, bacteria are less likely to develop resistance than they are with antibiotics that act on only a single target. AgNPs have also shown increased activity against various bacteria, including pathogens that form biofilms ⁴. The present study reports a green synthesis of silver nanoparticles (AgNPs) using Ocimum tenuiflorum essential oil. The volatile bioactive phytochemicals in the oil act as both reducing and stabilizing agents, which removes the need for hazardous chemical reducing agents or surfactants.

TEO is composed of terpenoids, phenylpropanoids and phenolic compounds including eugenol, methyl eugenol, linalool and -caryophyllene which would play dual roles in reducing silver ions (Ag⁺) to metallic silver nanoparticles through the bioreduction-cum-stabilizing agents. The resulting eco-friendly synthesized AgNPs are biocompatible, stable and exhibit enhanced antimicrobial activity, which make them potential candidates for biomedical and pharmaceutical applications.

Several recent studies have reported successful Tulsi-mediated AgNP synthesis with potent antibacterial action against waterborne pathogens (E. coli, Salmonella typhi, Vibrio cholerae), common nosocomial organisms (MRSA, ESBL-producing Klebsiella pneumoniae) and clinical isolates involved in mastitis ⁵.

Relative to the essential oil alone, silver nanoparticles synthesized with Tulsi essential oil show stronger antimicrobial activity, which may stem from synergy between silver ions and phytochemical residues. Together, these effects improve dispersion in water-based systems, increase contact with microbial cells and support the sustained release of active agents. Engineered AgNPs may inhibit microbial biofilm formation and efflux pump activity, processes that support the survival of resistant strains ⁶.
Although the field has advanced very fast, there are still some gaps like very few comparative studies that assess the antimicrobial activity of Tulsi essential oil against the same oil in nanoparticle form have been reported. These comparisons help assess the strengths, weaknesses, and likely uses of each formulation, especially for treating drug-resistant infections and for developing new antimicrobial therapies.

This study therefore aims to systematically compare the antimicrobial efficacy of Tulsi essential oil and Tulsi EO-mediated AgNPs against three different bacteria and assessing zones of inhibition to provide a comprehensive evaluation of their relative strengths and potential clinical utility.

MATERIALS AND METHODS:

Fresh leaves of Ocimum tenuiflorum were collected, washed, air-dried and subjected to hydrodistillation using a clevenger apparatus to extract essential oil (Fig 1). The oil was stored at 4°C until further use.

Fig 1: Extraction of Tulsi crude essential oil by hydrodistillation

For the preparation of silver nanoparticles (AgNPs) essential oil was mixed with distilled water to form an aqueous extract. To this mixture, 1mM AgNO₃ solution was added dropwise with constant stirring. This step was followed by addition of 0.1 M NaOH which resulted in a visible change in color to black, indicating the formation of AgNPs ⁷. The mixture was incubated at 50°C for 30–40 minutes to allow complete reduction of silver ions. The AgNPs synthesized was separated from the reaction mixture by centrifugation at 6000 rpm for 10 min (Fig 2). Further, characterization was done using UV–Vis spectroscopy.

Three bacterial strains Staphylococcus aureus (MTCC 3160), Escherichia coli (MTCC 1687) and Bacillus cereus (McR 3) were selected for the study. Twenty-four hour old bacterial cultures were spread on Muller-Hinton agar using sterile swab. To each inoculated MH plate, disc of antibiotic streptomycin (30mg/ml), crude essential oil and Tulsi EO-AgNPs were placed. The obtained zone of inhibition after incubation at 37 °C for 24h was estimated and interpreted.

RESULTS AND DISCUSSION:

UV–Vis absorption spectrum of the synthesized Tulsi EO-AgNPs showed a characteristic Sharp peak around 410nm with absorbance increasing from about 0.047at 320nm to a maximum of 0.183 at 410nm, then gradually decreasing to 0.005 (Fig3).

The results of antibacterial activity study indicates that TEO exhibits moderate antibacterial activity with average inhibition zones of 12.0mm (range 11.6–13.3mm) against B. cereus and 13.3mm (range 11–17mm) against E. coli and 13.3 mm for S. aureus (Table 1, Fig 4). These results align with earlier studies reporting moderate to strong activity of O. tenuiflorum essential oil (Yamani et al., 2016). Similar studies on O. basilicum and O. sanctum essential oils have shown slightly higher zones (20+mm) for E. coli ⁸. Overall, the observation indicates that the TEO exhibits a clear antibacterial effect against the three bacterial strains.

Fig 3: UV–Visible absorption spectrum of TEOs-AgNPs

Table 1: The average diameter of zone of inhibition (mm) produces by TEO

Measurement of inhibition zone (mm)
*B. cereus*	Plates	TEO	Streptomycin
	A	11.6mm	28.6mm
	B	12.3mm	28.3mm
	C	13.3mm	32.3mm
	average	12mm	29.3mm
*E.coli*	Plates	TEO	Streptomycin
	A	12mm	26mm
	B	17mm	26mm
	C	11mm	27mm
	average	13.3mm	26.3mm
S.aureus	Plates	TEO	Streptomycin
	A	12.3mm	26.3 mm
	B	17.6mm	26.6 mm
	C	11.3mm	32.3 mm
	average	13.3 mm	27 mm

TEO contains bioactive compounds like eugenol and methyl eugenol, which are known to possess antimicrobial properties⁹, but the relatively lower concentrations of these compounds or their volatility may limit their efficacy. For these reasons, TEO may be better suited as a natural antimicrobial supplement or as an adjuvant, rather than as a standalone therapeutic agent. To improve practical use, methods like increasing the concentration, combining agents that act synergistically, or developing advanced formulations such as nanoemulsions and encapsulated delivery systems can be used ^{10, 11}.These methods may improve the oil’s stability, bioavailability, and antimicrobial activity in clinical and industrial settings. Further, the results of antibacterial activity study of TEO- AgNPs showed moderate bactericidal activity along with average inhibition zones of 16.6mm for E.coli, 17.3mm for B. cereus and 15.3mm for S. aureus which are higher than the TEO activity (Fig 5, Table 2). These results align with previous studies reporting green-synthesized AgNPs producing inhibition zones between 12–20mm against both Gram-positive and Gram-negative bacteria^11,12. Slightly higher activity against B. cereus is consistent with literature, possibly due to differences in cell wall structure. On comparison with crude essential oil, synthesized silver nanoparticle shows higher antibacterial activity against the selected bacterial strains. The findings support the potential use of TEO-AgNPs as effective antimicrobial agents, while TEO may be useful in mild infections or in synergy with other agents. The green synthesis approach is eco-friendly, scalable and avoids toxic chemicals, making it suitable for biomedical and pharmaceutical applications.

Table 2: The average diameter of zone of inhibition (mm) produced by TEO-AgNP

Measurement of antibacterial inhibition zone (mm)
Plate	*E. coli*	*B. cereus*	*S. aureus*
A	20mm	18mm	16mm
B	15mm	18mm	15mm
C	15mm	16mm	15mm
Average	16.6mm	17.3mm	15.3mm

The enhanced antimicrobial activity of Tulsi-mediated AgNPs can be attributed to increased surface area for microbial interaction, synergistic effect of silver ions and phytochemicals, ability to penetrate microbial cell walls and induction of oxidative stress in pathogens. In contrast, Tulsi EO alone exhibited moderate activity but was limited by volatility and solubility issues. The nanoparticle formulation improved stability and bioavailability.

CONCLUSION:

This study demonstrates that Tulsi EO-mediated silver nanoparticles exhibit higher antimicrobial activity compared to Tulsi essential oil alone. The green synthesis approach is eco-friendly, cost-effective and scalable. Tulsi EO-AgNPs hold great potential for applications in wound dressings, medical coatings and food packaging.

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Received on 13.09.2025 Revised on 23.11.2025

Accepted on 08.01.2026 Published on 10.02.2026

Available online from February 16, 2026

Research J. Pharmacy and Technology. 2026;19(2):979-983.

DOI: 10.52711/0974-360X.2026.00138

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