The efficacy and safety of nine South African medicinal plants in controlling Bacillus anthracis Sterne vaccine strain

Abstract

BackgroundAnthrax 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.ResultsThe 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).ConclusionsThe 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.

Potency and selectivity indices of acetone leaf extracts of nine selected South African trees against six opportunistic Enterobacteriaceae isolates from commercial chicken eggs

“… NA Not applicable, AJ Alexander Jambalang, * 0.004 The SI and TAA values of the extracts was calculated from the cytotoxicity and percentage yield of the extracts results published in Elisha et al [ 12 ] Numbers in bold font MIC < 0.1 mg/ml …”

“…Maesa lanceolata and E. croceum extracts had high total antibacterial activity against S. maltophilia with TAA = 1390 and 1125 ml/g respectively due to their low MIC values and high percentage extract yield, but they were judged as unsuitable for further investigation due their high cytotoxicity (Table 1 ). Maesa lanceolata extracts have high efficiency against Bacillus anthracis and may be a potential disinfectant, especially in poor communities where disinfectants are not readily available or affordable [ 12 ]. In the same manner, the potential of the extracts as decontaminants or disinfectants in hatcheries could be explored.…”

“…In this study, we determined the potency, efficacy and selectivity acetone leaf extracts of nine South African trees with high activity against Escherichia coli based on the unpublished PhD thesis of Dr E Pauw [ 11 ] against six Gram-negative enteric pathogens isolated from commercial eggs, sold in the Gauteng Province of South Africa. The activity of these extracts have also been examined against Bacillus anthracis [ 12 ].…”

Pittosporum viridiflorum Sims (Pittosporaceae): A review on a useful medicinal plant native to South Africa and tropical Africa

“…assay with LC 50 values greater than 1 mg/ml, and was recommended for further exploration (Otang et al, 2013 (positive control) = 9.02 µg/ml (Otang et al, 2014). Again, the leaf acetone extract collected in Gauteng South Africa was slightly toxic against the monkey kidney Vero cell line with an IC 50 value of 54.6 µg/ml, however, the toxicity was lower than that of doxorubicin (positive control) = 8.3 µg/ml (Elisha et al, 2016). The inconsistencies of the toxicity of P.…”

“…When new and old leaves as well as twigs (50% MeOH extracts) of P. viridiflorum collected in KwaZulu-Natal, South Africa were tested for their antimicrobial potential, they did not show noteworthy inhibition against Staphylococcus aureus and Pseudomonas aeruginosa with MIC values ranging from 1.56 to ˃6.25 mg/ml, however both extracts were reported to have noteworthy antifungal activity against Candida albicans with MIC values of 0.78 and 0.91 mg/ml(Amoo et al, 2013). Leaf acetone extracts collected in Gauteng, South Africa showed good antibacterial activity against Bacillus anthracis Sterne strain with an MIC value of 0.04 mg/ml(Elisha et al, 2016). The ethnopharmacological use of P. viridiflorum against gastrointestinal and respiratory tract infections is ascribed to its antimicrobial activity towards both Gram-positive and Gram-negative bacterial strains associated with such ailments, however in vivo studies are needed to confirm this assertion.Although P. viridiflorum is known in TM for treating tuberculosis, there are no pharmacological studies that have been done to verify this property.…”