Antibacterial activity of plants that are used in the treatment of heartwater in livestock and the isolation and identification of bioactive compounds from Petalidium Oblongifolium and Ipomoea adenioides

Abstract

The general antibacterial activity of Drimia delagoansis, Petalidium oblongifolium and Ipomoea adenioides was determined using selected Gram-positive and Gram-negative bacteria. Only extracts or compounds with high antibacterial activity were then tested against the causative agent of heartwater, Ehlrichia ruminantium, since the latter requires specialised culturing conditions. The crude aqueous extract of D. delagoansis had low antibacterial activity with its highest MIC against Gram-negative bacteria being 20.0 mg ml-1 while the crude methanolic extracts of P. oblongifolium and I. adenioides had their highest antibacterial activity against Gram-negative bacteria at MIC's of 5.0 and 10.0 mg ml-1 respectively. Two compounds were isolated and identified from I. adenioides and an unidentified one was isolated from P. oblongifolium. The two compounds from I. adenioides proved to be caffeic acid with MIC's of 0.8 and 1.0 mg ml-1 against Gram-positive and Gram-negative bacteria respectively; and ethyl caffeate with MIC's of 0.4 and 1.0 mg ml-1 against Gram-positive and Gram-negative bacteria respectively. Synergism between the two compounds increased the respective MIC's to 0.4 and 0.2 µg ml-1 against Gram-positive and Gram-negative bacteria. The unidentified compound isolated from P. oblongifolium had a very low MIC of 2.5 µg ml-1 against E. ruminantium.