Abstract
The acetone extract of Ochna pretoriensis was evaluated for antibacterial activity using bioautography and serial microplate dilution methods against four nosocomial bacterial pathogens namely: Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa. A bioassay-guided fractionation of the crude extract led to the isolation of two antibacter ial biflavonoids, ochnaflavone and ochnaflavone 7-O-methyl ether. Gram-negative bacteria were more sensitive to the isolated compounds than the Gram-positive bacteria (MIC values: 31.3 μg/mL for P. aeruginosa and 62.5 μg/mL for S. aureus). In addition, the isolated com pounds were assessed for their pot ential toxic effects in the MTT toxicity assay using monkey kidney vero cells and Ames genotoxicity test using Salmonella typhimurium strain TA98. LC50 values were 125.9 μg/mL for ochnaflavone and 162.0 μg/mL for ochnaflavone 7-O- methyl ether. The isolated compounds have selectivity index values r anging from 1.29 to 4.03. Selectivity index values higher than one indicate that test samples are less toxic to the host cells than to the pathogens. The biflavonoids did not have any mutagenic effects in the Salmonella/microsome assay without metabolic activation.