Phytochemical analysis and antibacterial activities of various leaf extracts of Ocimum gratissimum and Newbouldia laevis

Leaves of Ocimum gratissimum and Newbouldia laevis were subjected to cold maceration in ethanol, ethyl acetate, and water for 24 hours. The extracts which on phytochemical screening showed the presence of alkaloids, flavonoids, saponins, tannins, glycosides, and phenols, were tested for antimicrobial activities. Various concentrations of the plant extracts (200, 100, and 50 mg/ml) were assayed for antibacterial activity using the agar well diffusion method. Two Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and four Gram-negative (Escherichia coli, Klebsiella aerogenes, Salmonella typhi, and Pseudomonas aeruginosa) bacteria were used for the study. The ethanol extract of O. gratissimum showed the highest zone of inhibition against E. coli with 18mm at 200mg/ml concentration, followed by ethyl acetate and aqueous extracts with 15 mm and 8 mm, respectively. Ethanol extract of N. laevis displayed the best activities against E.coli and S. aureus with both displaying inhibition zones of 10 mm, followed by 8.5mm against S. typhi. The aqueous extract had the best activity against K. aerogenes (9.5 mm), followed by S. aureus (5 mm). The zones of inhibition against the test organisms decreased with decreasing concentration of the plant extracts. Overall, the ethanol extracts displayed the best activity, while the aqueous extracts had the least activity. The results obtained showed that leaf extracts of the two plants have broad-spectrum activities, and could serve as potential sources for the development of useful natural antibacterial agents.