Formulation, Characterization and In Vitro Evaluation of Nanotechnology-Enabled Natural Products for Enhanced Antimicrobial Activity

Abstract

Background: The increasing prevalence of antimicrobial resistance has intensified the search for alternative and complementary antimicrobial strategies based on naturally derived bioactive compounds. Medicinal plants contain diverse phytoconstituents, including phenolics, flavonoids, terpenoids and alkaloids, with established biological activity. However, the practical application of plant-derived antimicrobials may be limited by poor aqueous solubility, instability and inadequate delivery.

Objective: The present study was undertaken to formulate and characterize chitosan nanoparticle-based preparations containing selected medicinal plant extracts and to comparatively evaluate the in vitro antibacterial activity of crude extracts and their corresponding nanoformulations.

Methods: Four medicinal plants, namely Curcuma longa, Azadirachta indica, Ocimum tenuiflorum and Zingiber officinale, were selected for the study. Hydroethanolic extracts were prepared and subjected to preliminary phytochemical screening, total phenolic content and total flavonoid content determination. Each extract was separately incorporated into a standardized chitosan nanoparticle system using ionic gelation with sodium tripolyphosphate. The resulting formulations were characterized for particle size, polydispersity index, zeta potential, encapsulation efficiency, morphology and Fourier-transform infrared spectroscopy. Antibacterial activity was evaluated against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae.

Results: The hydroethanolic extraction yields ranged from 11.7% to 15.6%. O. tenuiflorum demonstrated the highest total phenolic content (91.7 ± 3.6 mg GAE/g), whereas its total flavonoid content was 67.2 ± 3.1 mg QE/g. The formulated nanoparticles exhibited particle sizes ranging from 162.7 ± 7.9 to 174.6 ± 8.9 nm, with polydispersity indices below 0.30 and positive zeta potentials ranging from +25.8 ± 2.0 to +29.2 ± 1.6 mV. Encapsulation efficiency ranged from 76.8 ± 2.8% to 82.6 ± 2.4%. The nanoformulations demonstrated lower MIC and MBC values than their corresponding crude extracts against the majority of tested organisms. The greatest reduction in MIC was observed with the C. longa and A. indica nanoformulations, particularly against S. aureus.

Conclusion: The incorporation of selected medicinal plant extracts into a chitosan nanoparticle platform resulted in nanoscale formulations with favorable physicochemical characteristics and enhanced in vitro antibacterial activity compared with corresponding crude extracts. The findings support further investigation of plant-extract-loaded chitosan nanoparticles as a potential approach for improving the functional performance of natural antimicrobial agents.