In Vitro Evaluation of Ocimum gratissimum Leaf (Scent Leaf) Extracts Against Selected Clinical Multidrug-Resistant Bacterial Isolates

Abstract

The rise in multidrug-resistant (MDR) pathogens has made the search for alternative sources of antimicrobial agents a global priority.  This study investigated the phytochemical constituents, antioxidant capacity, and antibacterial activities of aqueous and ethanol leaf extracts of O. gratissimum against selected MDR clinical bacterial isolates (Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Klebsiella pneumoniae).  Phytochemical constituents and total antioxidant capacity of O. gratissimum were determined using standard laboratory procedures.  Antibacterial activity was assessed by the agar well diffusion method at concentrations ranging from 12.5 to 200 mg/mL, while minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using broth dilution techniques.  Data were expressed as mean ± standard deviation (SD), and statistical analysis was performed using one-way analysis of variance (ANOVA) at p < 0.05.  The ethanol extract produced a higher extraction yield (17.88%) than the aqueous extract (13.66%) and contained significantly greater amounts of phytochemicals (p < 0.05) and exhibited higher antioxidant capacity (240.53 ± 3.12 µg/mL) than the aqueous extract (228.19 ± 2.84 µg/mL) (p = 0.018).  Both extracts showed concentration-dependent antibacterial activity, although the ethanolic extract produced significantly larger inhibition zones ( p < 0.001).  Both extracts had an MIC of 25 mg/mL, while the ethanolic extract exhibited MBC values between 50-100 mg/mL.  These findings support the traditional therapeutic use of the plant and suggest its potential as a natural source of antimicrobial agents.  Further studies involving advanced phytochemical characterization, toxicity evaluation, and in vivo validation are recommended to support future pharmaceutical applications.