Antimicrobial activity and phytochemical screening of Antidesma venosum root and stem bark ethanolic extracts

Abstract

Antidesma venosum E. Mey. ex Tull root and stem bark ethanol extracts and their dichloromethane, petroleum ether and methanol fractions exhibited strong antibacterial activity against 5 Gram positive bacteria including Sta- phylococcus aureus (ATCC25923), Bacillus anthracis (NCTC10073), Bacillus subtilis (clinical isolate), Streptococcus faecalis (clinical isolate) and Bacillus cerius (clinical isolate) with MICs ranging from 0.0195 to 0.7812 mg/ml. The crude ethanol extracts of both the stem bark and roots were inactive against Gram negative bacteria except for Pseudomonas aeruginosa (ATCC 29953) against which they both exhibited weak activity MIC 1.25 and 5.0 mg/ml, respectively, Escherichia coli (ATCC 25922) and Klebsiella pneumoniae (ATCC 700603) which gave MICs between 2.50-5.00 mg/ml. The Petroleum ether and dichloromethane fractions of the root ethanol extract showed weak activity against almost all the Gram negative bacteria with MICs between 2.5 and 5.0 mg/ml. Whereas the crude extracts did not show antifungal activity, the petroleum ether and dichloromethane fractions of both the root and stem bark ethanol extracts showed weak activity against Candida albicans (ATCC 90028) and Cryptococcus neo- formans (clinical isolate), MIC 2.5-5.0 mg/ml. The extracts of the stem bark and roots exhibited mild to moderate toxicity against brine shrimp larvae with LC50 ranging between 25.56-40.93 µg/ml for the stem bark and 62.97- 80.26 µg/ml for the root ethanol extract. Phytochemical screening revealed the presence of terpenoids, tannins and steroids in both the root and stem bark extracts. These results show promising activity against Gram positive bacteria, especially by the petroleum ether and dichloromethane fractions of the roots and thus support the popular use of this plant for the treatment of conditions associated with bacterial infections such as cut wounds, chest infections and some types of diarrhoea. Further studies are ongoing to identify the active compounds.