An organic extract of Annatto (Bixa orellana) leaves obtained in 95% ethanol was examined for in vitro antifungal and antibacterial activity using the agar diffusion and tube dilution methods. The extract (5 mg/ml) produced antimicrobial action in agar diffusion assays against standard strains of Gram-positive bacteria including Bacillus subtilis, Staphylococcus aureus, and Streptococcus faecalis while exerting only slight action against Escherichia coli, Serratia marcescens, Candida utilis, and Aspergillus niger. The zones of inhibition obtained against the susceptible bacteria were 15-17 mm while those obtained in assays with Chloramphenicol and phenol positive controls were 12-18 mm and 10-28 mm, respectively. The minimum inhibitory concentration (MIC) of the extract was 4-16 mg/ml while its bactericidal action (MBC) was exerted at higher doses (16-64 mg/ml). The extract therefore, appears to possess a narrow spectrum of antimicrobial activity, being effective against only the Gram-positive bacteria us...

The aggregation of nanoparticles has been shown to significantly reduce the activity of nanomaterials, resulting in inferior performance. As an alternative to the use of traditional capping agents, stabilization of unstable nanoparticles with water-dispersible and biocompatible carriers is a promising strategy. A bioinspired coating strategy was developed and the hybrid nanoparticles displayed excellent colloidal stability that significantly improved antibacterial activity when silver nanoparticles (AgNPs) were used as a model. Cellulose nanocrystals (CNCs) were first modified with dopamine, followed by in situ generation and anchoring of AgNPs on the surface of CNCs through the reduction of silver ions by polydopamine coated CNCs. The results indicated that the dispersion stability of AgNPs was significantly enhanced by the CNC, which in turn resulted in more than fourfold increase in antibacterial activity based on antibacterial studies using Escherichia coli and Bacillus subtilis.