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.
