Antimicrobial and Phytochemical Evaluation of Nyctanthes arbor-tristis Linn. Leaf Extracts in Various Solvents against Pathogenic Microbial Strains: An In-vitro Study

Introduction: Antimicrobial Resistance (AMR) poses a growing global health challenge by reducing the effectiveness of conventional antibiotics against a wide range of pathogenic microorganisms. In this context, medicinal plants are increasingly being explored as alternative sources of bioactive compounds with antimicrobial potential. Nyctanthes arbor-tristis Linn., a traditionally used medicinal plant, holds promise due to its diverse phytochemical composition. Aim: To evaluate the in-vitro antimicrobial activity and phytochemical profile of N. arbor-tristis leaf extracts obtained using various solvents and to assess their efficacy against selected pathogenic microbial strains. Materials and Methods: This in-vitro study was conducted at the Shri Guru Ram Rai (SGRR) University campus, Dehradun, Uttarakhand, India, between June 2021 and September 2024. The study investigated the antimicrobial properties, chemical constituents and qualitative phytochemical composition of N. arbor-tristis extracts. Leaves were subjected to Soxhlet extraction using five solvents: water, methanol, acetone, chloroform and ethyl acetate. Antimicrobial activity was tested against Salmonella enterica serovar Newport {Microbial Type Culture Collection (MTCC) 3225}, Escherichia coli (MTCC 723), Staphylococcus aureus subsp. aureus (MTCC 740), and Candida albicans (MTCC 3017) using the well diffusion method. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were also determined at different concentrations. Phytochemical screening was performed to detect secondary metabolites. Following the antimicrobial susceptibility tests, the MIC was determined to identify the lowest concentration inhibiting microbial growth. Data were presented in tables and graphs, with p-values calculated using appropriate statistical tests. A p-value of <0.05 was considered statistically significant. Results: Methanolic extracts exhibited the highest antimicrobial activity across all tested pathogens, with the largest Zones Of Inhibition (ZOI) observed against Salmonella Newport (23.6±0.57 mm at 0.5 mg/100 µL and 24.6±0.57 mm at 1 mg/100 µL). Aqueous extracts showed the highest yield but were the least effective, particularly against Candida albicans, which showed no inhibition zone. Phytochemical analysis revealed the presence of alkaloids, flavonoids, tannins, glycosides, steroids, terpenoids and saponins, while anthraquinones and phlobatannins were absent. Methanol and acetone extracts demonstrated the richest phytochemical diversity. Conclusion: The study demonstrated that N. arbor-tristis methanolic leaf extract possesses significant antimicrobial activity, correlating with its rich phytochemical content. These findings support the potential of this plant as a natural source of antimicrobial agents, particularly in the context of rising antibiotic resistance.