Antimicrobial properties of extracts from Euclea crispa subsp. crispa (Ebenaceae) towards human pathogens

Abstract

Leaf samples of Euclea crispa subsp. crispa were collected in the Bloemfontein area of the Free State Province as part of a project to screen South African plants for their antimicrobial potential. Crude extracts were obtained with a 95% methanol solution and the aqueous fraction remaining after methanol was removed by distillation, was bioassayed in vitro for its potential to inhibit the growth of eleven human pathogenic bacteria and two human pathogenic fungi. Of all the plant extracts tested, the E. crispa crude leaf extract showed the most promising antimicrobial activity against human pathogenic bacteria and fungi. Subsequently, the crude extract was fractionated by means of liquid-liquid extraction using four different organic solvents in order of increasing polarity. Most of the antibacterial activity was observed in the more polar ethyl acetate fraction. No particular trend of inhibition was observed between the Gram-negative and Grampositive bacteria. Neither the crude extract nor the semipurified fractions inhibited the growth of Haemophilus influenzae, Klebsiella pneumoniae and Streptococcus pneumoniae. The growth of the other eight human pathogenic bacteria was inhibited to different degrees. Both the crude extract as well as all the semi-purified fractions inhibited the growth of two human pathogenic test fungi.