Isolation and characterisation of antimicrobial compounds from Antizoma angustifolia

Abstract

Infectious diseases are responsible for more than 17 million deaths per year worldwide, most of which are associated with bacterial infections. The increase in antibiotic resistance is thought to be a contributing factor to this problem. It is thus clear that more antimicrobials with different mechanisms of action are needed to help alleviate the problem. Isolation of antimicrobial compounds from plants could contribute towards solving this problem as they may have different mechanisms of action than the antimicrobial agents currently in use. The aim of the study was to identify a specific plant with antimicrobial activity and to isolate and characterise the compounds responsible for this activity. Eight plants, namely Antizoma angustifolia, Carpobrotus acinaciformis, Delosperma herbeum, Melianthus comosus, Physalis viscosa, Rhus pyroides, Zanthoxylum capensis and Ziziphus mucronata were selected for screening. Soxhlet extraction was used to prepare extracts of the different morphological parts of each plant using petroleum ether, dichloromethane, ethyl acetate and ethanol successively. These plant extracts were screened for antimicrobial activity against a range of micro-organisms using disc diffusion and microplate methods. The extracts showed variable activity with the dichloromethane extract of Antizoma angustifolia leaves showing the most promising activity. The leaf extracts (dichloromethane, ethyl acetate and ethanol) of Antizoma angustifolia were subjected to activity-guided fractionation using column chromatography. This lead to the isolation of bulbocapnine and dicentrine from the dichloromethane extract and the isolation of crotsparine from the dichloromethane, ethyl acetate and ethanol extracts. The compounds were identified by spectroscopic techniques. These compounds were evaluated for antimicrobial activity using the microplate method and crotsparine showed weak activity. Although the activity of crotsparine was not very high, it might still be useful as a lead compound in the development of antimicrobial drug development. The biological activity of these compounds does however confirm the fact that the diverse chemistry of plants is still a very important source of novel biologically active and lead compounds. The biological activity of the compounds isolated from Antizoma angustifolia could justify its ethnopharmacological uses.