Antimicrobial Activity of Neem and Bitter Gourd Extract Combinations Against Urban Respiratory Isolates

Authors

  • Isaac Emmanuel Omara Stellenbosch University, South Africa Author
  • Nabil Husni University of Melbourne, Australia Author
  • Alissia Hui Monash University, Australia Author

Keywords:

Azadirachta indica, Momordica charantia, respiratory isolates, antimicrobial activity, synergy, plant extracts

Abstract

Background: Urban bioaerosols can carry opportunistic bacteria and fungi, while increasing antimicrobial resistance complicates treatment of respiratory infections.

Objective: To determine the concentration-dependent antimicrobial activity of aqueous neem and bitter-gourd extracts alone and in combination against respiratory isolates.

Methods: Sixty non-duplicate bacterial and fungal isolates representing Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Candida albicans and Aspergillus species were tested. Minimum inhibitory concentrations were determined by broth microdilution. Checkerboard assays evaluated extract combinations, and time-kill experiments were performed for isolates showing the strongest interaction.

Results: Neem extract showed greater activity against Gram-positive bacteria, whereas bitter-gourd extract produced modest inhibition across both bacterial and fungal groups. The combination reduced median inhibitory concentrations by one dilution for S. aureus and C. albicans. Fractional inhibitory concentration indices indicated synergy in 28% of S. aureus isolates and 22% of C. albicans isolates, with no antagonism observed. Time-kill analysis demonstrated a 2.1-log10 reduction in viable S. aureus at 12 hours for the combination compared with 0.9-log10 and 0.7-log10 for neem and bitter gourd alone. Activity against P. aeruginosa remained limited.

Conclusion: Aqueous neem and bitter-gourd extracts displayed organism-specific and concentration-dependent antimicrobial effects, with partial synergistic activity against selected respiratory isolates. The findings justify chemical fractionation and toxicology testing but do not support clinical use without standardisation and controlled human evidence.

Publication format: research abstract. No full-text manuscript accompanies this record.

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Published

2026-10-01

Issue

Vol. 1 No. 1 (2026): October 2026 — Inaugural Issue

Section

Research Papers

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Copyright (c) 2026 Farhan Kabir, Brian Otieno

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