Antimicrobial Activity of Annatto (Bixa orellana) Extract

Abstract

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 used in our study.

Key Words:

• Annatto
• Bixa orellana
• Bixaceae
• antibacterial effect
• Staphylococcus aureus
• Bacillus subtilis
• Streptococcus faecalis