Abstract:
Background: Antimicrobial resistance (AMR) poses a major and growing threat to infectious disease management, particularly given the rising prevalence of drug-resistant Staphylococcus aureus (S. aureus). Methicillin-resistant S. aureus (MRSA) is especially challenging because it is less susceptible to commonly used β-lactam antibiotics. The search for novel antimicrobial resources has therefore intensified, with medicinal plants receiving renewed scientific interest because of their chemically diverse bioactive constituents. Azadirachta indica (A. indica), known as neem, is a plant widely used in traditional medicine and is rich in secondary metabolites with potential antimicrobial properties. This study investigated the phytochemical composition and antimicrobial activity of aqueous and 70% ethanolic A. indica leaf extracts against MRSA and methicillin-susceptible S. aureus (MSSA) and further examined the extract-ampicillin interactions.
Methods: Fresh A. indica leaves were washed, shade-dried, pulverized, and separately macerated in distilled water and 70% ethanol for 72 hours at a 1:5 (w/v) ratio. Standard qualitative phytochemical assays were used to detect alkaloids, saponins, steroids, tannins, flavonoids, and glycosides. Antimicrobial activity was assessed using the agar well-diffusion method against MRSA and MSSA at graded extract concentrations, with ampicillin and penicillin serving as antibiotic controls. Sequential extract-ampicillin treatments were additionally evaluated to investigate changes in antimicrobial activity following combined exposure.
Results: Both aqueous and 70% ethanolic extracts contained saponins and steroids. Tannins and Flavonoids were detected in the aqueous extract, whereas alkaloids were detected exclusively in the 70% ethanolic extract; glycosides were absent from both extracts. At 200mg/mL, the 70% ethanolic extract exhibited stronger activity against MRSA, producing an inhibition zone of 19.10 ± 0.82 mm, compared with 16.67 ± 1.53 mm for the aqueous extract. Against MSSA, the aqueous extract produced a slightly larger inhibition zone (19.67 ± 1.70 mm) than the 70% ethanolic extract (19.33 ± 1.53 mm). In the sequential combination experiment, the aqueous extract demonstrated a progressive increase in inhibition from 16.0 mm at 50 mg/mL to 30.0 mm at 200 mg/mL under the tested treatment sequence. The 70% ethanolic extract produced comparatively variable inhibition zones ranging from 14.5 mm to 23.0 mm. Addition of ampicillin to the extract treatment did not consistently produce a greater inhibition response, with inhibition declining to 16.0 mm and subsequently 11.0 mm at higher sequential ampicillin exposures, indicating a complex extractantibiotic interaction.
Conclusion: A. indica leaf extracts demonstrated measurable and concentration-responsive antimicrobial activity against S. aureus, with extraction solvent influencing both phytochemical composition and antimicrobial performance. The stronger activity of the 70% ethanolic extract against MRSA and the pronounced activity of the aqueous extract against MSSA indicate the potential importance of solvent-dependent phytochemical profiles in targeting different bacterial phenotypes. Notably, the aqueous extract reached an inhibition zone of 30.0 mm during sequential treatment, whereas addition of ampicillin did not consistently enhance antimicrobial activity. These findings identify A. indica as a promising source of plant-derived antimicrobial compounds while emphasizing the need for MIC/MBC, checkerboard synergy, and mechanistic studies to determine whether specific A. indica constituents can safely and reproducibly modulate antibiotic activity against resistant pathogens
Biography:
Basilide Naga is a Biochemistry graduate and early researcher from Ghana with research interests spanning antimicrobial discovery, infectious diseases, biotechnology, and sustainable biomedical innovation. He holds a BSc in Biochemistry from the University of Technology and Applied Sciences (UTAS), where his undergraduate research investigated the “evaluation of the antibacterial activity of 70% ethanolic and aqueous extracts of Azadirachta indica leaf, stem, and root against the prevalence of bacterial infections in northern Ghana". He currently serves as a Teaching Assistant and Research Assistant, with an interest in translating biological resources and emerging technologies into practical solutions for global health challenges. His broader research interests include antimicrobial resistance, medical chemistry, pharmacodynamics, pharmacokinetics, bioprocessing, microbial biotechnology, and One Health.
