Antimicrobial activity and toxicity of extracts from the bark and leaves of South African indigenous Meliaceae against selected pathogens

Species of the family Meliaceae in traditional medicine are well documented. This study evaluated the antimicrobial efficacy and toxicity of aqueous, methanolic and dichloromethane leaf and bark extracts of South African Meliaceae against selected pathogens. The species sampled represent four of the seven indigenous genera and seven of the 14 indigenous species. Antimicrobial activity was evaluated using the micro-plate dilution assay and the toxicity potential was determined using the brine shrimp lethality assay. About 69% of the extracts investigated showed moderate (0.25— 0.50 mg/ml) activities against the oral pathogens (Streptococcus mutans ATCC 25,175 and Fusobacterium nucleatum ATCC 25,586) tested. Pseudomonas aeruginosa and S. mutans was recorded as the most susceptible pathogens to the extracts. The antimicrobial activity of the extracts from Ekebergia pterophylla, Nymania capensis and Turraea obtusifolia (here documented for the first time) demonstrated varied activity depending on the pathogen. The aqueous extracts showed no antimicrobial activity with some exceptions against Streptococcus mutans (ATCC 25,175), where Ekebergia capensis and Trichilia dregeana exhibited noteworthy activity (0.13 mg/ml). In the brine shrimp assay, all DCM extracts of the studied parts of the plant species demonstrated minimal to no toxicity levels. The results obtained have lent credence to folkloric usage of some of the South African species of Meliaceae for anti-infective purposes including traditional uses against oral pathogens.