Antibacterial Activity of Curcuma longa (Turmeric) Ethanolic Extract Against Staphylococcus aureus and E. coli: An In Vitro Study

Abstract

Background: Antimicrobial resistance (AMR) is a growing global public health crisis that undermines the effectiveness of conventional antibiotics. Natural plant-derived compounds have received renewed attention as alternative or adjunct antimicrobial agents. Curcuma longa (turmeric), a member of the Zingiberaceae family, contains bioactive constituents, notably curcumin, flavonoids, tannins, and alkaloids, with well-documented antibacterial properties. The aim of this study is to evaluate the in vitro antibacterial activity of the ethanolic extract of Curcuma longa rhizomes against Staphylococcus aureus and E. coli. Methods: Fresh rhizomes of C. longa were sourced from Dei Dei Market, Abuja, Nigeria, and extracted by cold maceration in 90% ethanol for 72 hours. Staphylococcus aureus was isolated from a throat swab and confirmed by Mannitol Salt Agar (MSA) morphology, Gram staining, and catalase and coagulase tests. E. coli was isolated from a campus tap water sample and confirmed on Eosin Methylene Blue (EMB) Agar with positive indole and methyl red tests. Antibacterial activity was assessed by agar well diffusion on Mueller-Hinton Agar (MHA) at six extract concentrations (50, 100, 200, 400, 800, and 1000 mg/mL). Ciprofloxacin (5 µg) and Ampicillin (10 µg) served as positive controls; DMSO served as the negative control. Results: No inhibitory activity was observed at 50–200 mg/mL for either organism. At 400, 800, and 1000 mg/mL, mean zones of inhibition (ZOI) against S. aureus were 15.0, 22.0, and 27.5 mm respectively; against E. coli, ZOI were 11.5, 17.0, and 21.5 mm. Staphylococcus aureus was consistently more susceptible than E. coli at all active concentrations. At 1000 mg/mL, the extract marginally exceeded both the Ciprofloxacin (26.0 mm) and Ampicillin (21.0 mm) positive controls. Conclusion: Locally sourced Nigerian turmeric demonstrates significant, concentration-dependent antibacterial activity against both test organisms, with S. aureus being more susceptible than E. coli, consistent with the structural differences between Gram-positive and Gram-negative cell walls. These findings support C. longa as a promising natural antimicrobial candidate in the context of antimicrobial resistance.