BACKGROUND : Anthrax is a zoonotic disease caused by Bacillus anthracis, a Gram-positive spore-forming bacterium.
The presence of the bacteria and the toxins in the blood of infected hosts trigger a cascade of pathological events
leading to death. Nine medicinal plants with good activities against other bacteria were selected to determine their
in vitro antibacterial activity against Bacillus anthracis Sterne strain. The cytotoxicity of the extracts on Vero kidney
cells was also determined.
RESULTS : The minimum inhibitory concentration (MIC) values of the extracts against Bacillus anthracis Sterne strain
ranged from 0.02 to 0.31 mg/ml. Excellent MIC values were observed for the following plant species: Maesa
lanceolata (0.02 mg/ml), Bolusanthus speciosus, Hypericum roeperianum, Morus mesozygia (0.04 mg/ml) and
Pittosporum viridiflorum (0.08 mg/ml). The total antibacterial activity of the extracts ranged from 92 to 5562 ml/g.
Total activity presents the volume to which the extract from 1 g of plant material can be diluted and still inhibit
microbial growth. Maesa lanceolata and Hypericum roeperianum had the highest total activity with values of 5562
and 2999 ml/g respectively. The extracts of Calpurnia aurea had the lowest total activity (92 ml/g). The cytotoxicity
determined on Vero cells indicated that most of the extracts were relatively non-toxic compared to doxorubicin
(LC50 8.3 ± 1.76 μg/ml), except for the extracts of Maesa lanceolata, Elaeodendron croceum and Calpurnia aurea with
LC50 values at 2.38 ± 0.25, 5.20 ± 0.24 and 13 ± 2.26 μg/ml respectively. The selectivity index (SI) ranged from 0.02 to
1.66. Hypericum roeperianum had the best selectivity index, (SI = 1.66) and Elaeodendron croceum had lowest value
(SI = 0.02).
CONCLUSIONS : The crude acetone extracts of the selected plant species had promising antibacterial activity against
Bacillus anthracis. Maesa lanceolata extracts could be useful as a disinfectant and Hypericum roeperianum could be
useful to protect animals based on its high total activity and selectivity index. Further investigation of these plant
extracts may lead to the development of new therapeutic agents to protect humans or animals against anthrax.