Evaluation of extracts of the root of Landolphia owerrience for antibacterial activity

Ethanolic and aqueous (cold and hot) extracts of Landolphia owerrience root parts (whole-root, root-bark and root-wood) were tested for activity against ten bacterial strains using agar-well diffusion and macro-broth dilution methods, respectively. The ethanolic extracts of the whole-root and root-wood were active against 100 and 80% of the test organisms, respectively. Ethanolic and aqueous extracts of the root-bark were moderately active while the aqueous (cold and hot) extracts of the root-wood exhibited little or no activity. Out of the nine extracts prepared, 66.7% were active against Staphylococcus aureus ATCC 12600, 55.6% variously against each of Pseudomonas aeruginosa ATCC 10145 and local clinical isolates of P. aeruginosa, S. aureus, Escherichia coli and Salmonella typhi, 44.4% against Proteus sp., 33.3% against Bacillus subtilis ATCC 6051 and 22.2% against E. coli ATCC 11775. The agar-well-determined MIC values for the ethanolic whole-root extract (0.78-50 mg/ml) were higher (indicating lower activity) than the corresponding macro-broth-determined values (0.39-50 mg/ml) probably because of slow diffusion rates of the active constituents of the extract in agar. On the other hand, the differences could be due to the effects of DMSO used to dissolve the ethanolic extracts in the agar-well diffusion tests. Similar discrepancies in the MIC values detectable with the two test methods were apparent in the root-wood extract and the control drug, Gentamycin, except that in the latter the agar-well-determined MIC values (0.125-8.0 microg/ml) were lower than the macro-broth-determined values (0.125-64 microg/ml). The strong activity of the ethanolic extracts against known etiologic agents of diseases traditionally treated with L. owerrience root of similar preparations provides scientific justification for the use of the herb in ethnomedical practice in Nigeria.