In vitro antibacterial activities of crude ethanolic extract of Vernonia amygdalina (Asteraceae) and Ocimum gratissimum (Lamiaceae) and their combined effect on some bacterial isolates from sputum

Medicinal plants especially Vernonia amygdalina and Ocimum gratissimum are used as herbal remedies for infections and in some cases they are concocted together for their additive effect. This study, therefore investigated the antibacterial activity of the ethanolic leaf extract of both plants, alone and in combination on three microorganisms (Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris) obtained from clinical isolate of sputum. The clinical isolates were identified and characterized using standard biochemical tests while the antibiotic sensitivity test was done using disc diffusion method. The ethanolic crude extract of Vernonia amygdalina and Ocimum gratissimum were also subjected to in vitro antibacterial test using Agar disc diffusion method while the combined antibacterial effect of both plants was done using agar strip diffusion method. Phytochemical tests using standard methods revealed the presence of flavonoids, alkaloids, saponins, tannins, cardiac glycosides and anthraquinones etc. Both of the plants had antibacterial effect which is represented by the inhibition zone diameter having a concentration-dependent relationship. At a concentration of 100 mg/ml, the highest inhibition zone diameter (13.66 ± 0.66 mm) and (12.86 ± 0.08 mm) were obtained for V. amygdalina and O. gratissimum respectively against Escherichia coli. The combined effect of the two plants however showed loss of antibacterial effect. The MIC of both plants were 25 mg/ml for V. amygdalina and O. gratissimum respectively. This study validates the use of the extracts of these plants for respiratory tract infection but their combined effect could be antagonistic and should therefore be discouraged because of loss of antibacterial activity.