In vitro antibacterial potential of solvent fractions of aqueous and ethanolic leaf extracts of vernonia colorata against selected human pathogenic bacteria

Abstract

Vernonia colorata has been used in traditional medicine for the treatment of diseases related to certain bacteria. Crude leaf extracts of the plant have also been reported to contain antibacterial agents in previous in vitro studies. Fractionation of crude solvent extracts may lead to isolation and subsequent characterization of the active compound(s). In the current research, crude aqueous and ethanolic leaf extracts of V. colorata were evaluated for antibacterial activity against five human pathogenic bacteria. The crude extracts were further fractionated by solvent-solvent partitioning using petroleum ether, chloroform and diethyl ether. The various fractions were tested against selected bacteria using the agar-well diffusion method. Crude ethanolic extract showed MIC ranging between 5-6 mg/ml while aqueous extract showed MIC between 6-7.5 mg/ml. All fractions from the aqueous extract at 10 mg/ml did not show zone of inhibition against the bacteria tested. However, the chloroform fraction of the ethanolic extract showed activity only against S. aureus at 10 mg/ml with zone of inhibition of 15.00 ± 0.20 mm. The antibacterial activity of the chloroform fraction of the ethanolic extract was significant in comparison with control (P < 0.05). The results suggested that the crude ethanolic leaf extract of V. colorata possess superior antibacterial activity as compared with aqueous extract. The result further suggests that chloroform fraction of the ethanolic leaf extract possesses antibacterial activity hence turn out to be a good candidate for further isolation and characterization of antibacterial agents.