Antibacterial activity and phytochemical components of leaf extract of Calpurnia aurea

Local Ethiopians use Calpurnia aurea to treat skin infections. However, there is no adequate scientific confirmation. The aim of this study was to evaluate the antibacterial activities of the crude and the fractionated extracts of C. aurea leaves against different bacterial strains. The crude extract was made by maceration. The Soxhlet extraction method was used to obtain fractional extracts. The antibacterial activity against gram positive and gram negative American Type Culture Collection (ATCC) strains was performed using the agar diffusion technique. The minimum inhibitory concentration was determined through the microtiter broth dilution method. Preliminary phytochemical screening was done using standard techniques. The largest yield was obtained from ethanol fractional extract. Except for chloroform, which provided a relatively low yield when compared to petroleum ether, increasing the polarity of the extracting solvent improved the yield. The crude extract, solvent fractions, and the positive control showed inhibitory zone diameter, while the negative control did not. When used at a concentration of 75 mg/ml, the crude extract had similar antibacterial effects as gentamicin (0.1 mg/ml) and the ethanol fraction. The 2.5 mg/ml crude ethanol extract of C. aurea suppressed the growth of Pseudomonas aeruginosa, Streptococcus pneumoniae, and Staphylococcus aureus, according to the MIC values. The extract of C. aurea was more effective in inhibiting P. aeruginosa than the other gram-negative bacteria. Fractionation enhanced the antibacterial effect of the extract. All fractionated extracts showed the highest inhibition zone diameter against S. aureus. Petroleum ether extract had the greatest inhibition zone diameter against all bacterial strains. The non-polar components were more active compared to the more polar fractions. The phytochemical components discovered in the leaves of C. aurea included alkaloids, flavonoids, saponins, and tannins. Among these, the tannin content was remarkably high. The current results could provide a rational support for the traditional use of C. aurea to treat skin infections.