Evaluation of Antibacterial Efficacy of Ocimum gratissimum n-Hexane Extract against Staphylococcus aureus

Abstract

Background: Ocimum gratissimum is a medicinal plant widely used in traditional medicine for the treatment of various infections due to its antimicrobial properties. Aim: This study evaluated the antibacterial activity of n-hexane leaf extract of Ocimum gratissimum against Staphylococcus aureus. Methodology: The plant leaves were collected, air-dried, and ground into powder before extraction using n-hexane as the solvent (50 g in 250 mL). The extract obtained was concentrated and subsequently dissolved using Dimethyl Sulfoxide to obtain a uniform solution. The antibacterial activity of the extract was determined using the agar well diffusion method with a 0.5 McFarland standard (~1.5 × 10⁸ CFU/mL), 6 mm wells, 100 μL per well, and incubation at 37℃ for 24 hours. MIC was determined by broth dilution from 100% to 6.25%, and MBC was assessed by subculture. Results: The n-hexane leaf extract of Ocimum gratissimum exhibited concentration-dependent antibacterial activity against Staphylococcus aureus, with zones of inhibition of 12-22 mm. In broth dilution, no turbidity was observed at 100% and 50% concentrations, while turbidity was observed at 25%, 12.5%, and 6.25%; hence, the MIC was 50%. For MBC determination, only concentrations up to 50% were subcultured because the extract volume at 100% concentration was insufficient. Growth was observed at 50%; hence, the MBC was not achieved within the tested range (MBC >50%), indicating bacteriostatic activity at ≤50%. Conclusion: These findings indicate that Ocimum gratissimum possesses preliminary in vitro antibacterial activity against Staphylococcus aureus and may serve as a candidate for the development of plant-based antimicrobial agents against antibiotic-resistant pathogens.