Comparative Antibacterial Activity of Azadirachta indica (Neem) and Curcuma longa (Turmeric) Hydroalcoholic Extracts Against Common Clinical Isolates: An In Vitro Study

Abstract

Background: The relentless global rise of antimicrobial resistance (AMR) has renewed scientific interest in medicinal plants as reservoirs of novel antibacterial compounds. In South India, Azadirachta indica (neem) and Curcuma longa (turmeric) are deeply embedded in traditional medicine, yet head-to-head comparisons of their antibacterial potency against contemporary clinical isolates are scarce.

Objective: To compare the in vitro antibacterial activity of hydroalcoholic extracts of neem leaf and turmeric rhizome against five common clinical bacterial isolates, and to relate activity to phenolic and flavonoid content.

Methods: In this in vitro experimental study, hydroalcoholic (ethanol–water) extracts were prepared from neem leaf and turmeric rhizome. Antibacterial activity was assessed by agar well diffusion at 25, 50 and 100 mg/mL in triplicate against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterococcus faecalis, with a standard antibiotic as positive control and solvent as negative control. Minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations were determined by broth microdilution. Total phenolic (TPC) and total flavonoid (TFC) contents were quantified. Data were analysed using mean ± SD, independent t-test and one-way ANOVA (p < 0.05).

Results: Both extracts showed concentration-dependent activity. The overall mean zone of inhibition was significantly larger for neem (15.44 ± 4.65 mm) than turmeric (13.13 ± 4.32 mm) (Welch t = 2.44, p = 0.017), while both were far exceeded by the positive control (24.03 mm) and negligible for solvent (0.42 mm). At 100 mg/mL, zones ranged 20.4–21.8 mm (neem) and 17.4–18.9 mm (turmeric), with no significant inter-species difference (neem F = 1.28, p = 0.34; turmeric F = 1.47, p = 0.28). MIC/MBC patterns were organism-dependent: turmeric was more potent against E. coli, whereas neem was more potent against P. aeruginosa and E. faecalis. Neem contained higher TPC (165.91 vs 148.54 mg GAE/g) and TFC (74.84 vs 57.79 mg QE/g).

Conclusion: Both hydroalcoholic extracts exhibited meaningful, dose-dependent antibacterial activity against Gram-positive and Gram-negative clinical isolates, with neem generally superior—plausibly linked to its higher phenolic/flavonoid content. These low-cost screening findings support the traditional South Indian use of neem and turmeric and their potential relevance amid escalating AMR.