Annual Research & Review in Biology

Aims: This study was carried out to evaluate the antibacterial activity of aqueous and ethanol leaf extracts of Ocimum gratissimum and Carica papaya against selected clinical isolates of Gram-negative bacteria and to also determine the phytochemical constituents of the plants.
Methodology: Extraction of plant leaves was carried using the cold maceration method and preliminary antimicrobial screening of the extracts was done using the disc diffusion method. The minimum inhibitory concentrations (MICs) of the plant extracts against test organisms were determined using the broth dilution technique. The minimum bactericidal concentrations (MBCs) were also determined.
Results: Phytochemical analyses of leaf extracts of both plants revealed the presence of tannins, alkaloids, saponins and anthraquinones. Antibacterial activity was recorded at concentrations ranging from 12.5-50 µg/mL. At 50 µg/mL, the aqueous and ethanol extracts of O. gratissimum showed best activity against E. coli and S. typhi respectively. Also, the aqueous and ethanol extracts of C. papaya recorded good activity against E. coli. The minimum inhibitory concentrations (MICs) of the aqueous extract of C. papaya against test isolates ranged from 12.5-25 µg/mL and that of the ethanol extract ranged from 25-50 µg/mL. O. gratissimum recorded MICs that ranged from 12.5-25 µg/mL for the aqueous extract, and 25 µg/mL for the ethanol extract. The minimum bactericidal concentrations (MBCs) of C. papaya ranged from 25-50 µg/mL for the aqueous extracts and 50 µg/mL for the ethanol extract; and that of O. gratissimum ranged from 12.5-25 µg/mL for the aqueous extract, and 25−50 µg/mL for the ethanol extracts.
Conclusion: This study shows that C. papaya and O. gratissimum leaves have antibacterial activity and supports the traditional use of these plants as medicines.