Antibacterial activities of Calpurnia aurea and Ocimum lamiifolium extracts against selected gram positive and gram-negative bacteria

Abstract

Indigenous knowledge, literature reports and ethnobotanical records suggest that plants are the basis for medicines. This study was designed to examine in-vitro antibacterial activity of Calpurnia aurea (leaf, bark) and Ocimum lamiifolium (leaf, flower) collected from Wonsho and Shebedino districts of Sidama Zone, southern Ethiopia, with different solvents against three Gram negative (Escherichia coli, Salmonella typhimurium and Pseudomonas aeruginosa) and one Gram positive (Staphylococcus aureus) bacteria in 2018. The leaf and bark of Calpurnia aurea and leaf and flower of Ocimum lamiifolium were dried, powdered and extracted with 80% acetone, ethanol, methanol and distilled water. Disc diffusion method was used for the antibacterial assay and measuring the zone of inhibition and minimum inhibition concentration (MIC) was determined by broth macrodilution method. The highest percentage yield of crude bioactive agents, i.e., 36.9% was obtained from Ocimum lamiifolium leaf with methanol as a solvent, while the lowest yield 12.6% was obtained from Calpurnia aurea bark with acetone extract. All crude extracts from the different plant parts showed antibacterial activity. Accordingly, Calpurnia aurea bark with methanol extract exhibited the highest antibacterial activity 22.64±0.95 (mm) against S. aureus which was comparable to standard antibiotic disc Ciprofloxacin with inhibition zone of 24.00 ±0.19 (mm), while the lowest inhibition of 6.12±0.41 (mm) was recorded from Ocimum lamiifolium flower with water crude extract against P. aeruginosa. The MIC of 3.13mg/ml was observed from methanol crude extract of bark of Calpurina aurea on S. aurea. Crude bark extract of Methanol showed the highest antibacterial activity. The studies revealed that antibacterial activity of the crude extracts from the different parts of the plant were variable when extracted by different solvents, however, possesses good antimicrobial activity which support the traditional use of the plant in the treatment of bacterial infections under study. Finally, to support the traditional users, scientific verification on phytochemical analysis and toxicity test should be carried out to confirm users’ safety.