In vitro evidence of synergism for plant part combinations of Croton gratissimus (Euphorbiaceae) used in African traditional healing

Croton gratissimus Burch. var gratissimus is a tree traditionally used medicinally to treat abdominal and uterine disorders, inflammation and swelling, fevers, coughs, colds and inflammation of the lungs. The hydro-distilled leaf essential oil, extracts of bark, root and leaf are comparatively assessed with results indicating higher efficacies for extracts than the oils. Croton gratissimus is one of many plants used in African traditional healing in combination i.e. roots and leaves are combined and used in therapeutic regimens. The root, leaf and bark extracts were investigated singularly and combined in various ratios to establish possible interaction. The minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) results indicated variable efficacies for the plant combinations, the greatest of which was noted for C. neoformans in the root and leaf combination (MIC 0.4mg/mL and FIC of 0.4). Further combination studies were thereafter conducted on varying ratios of root and leaf extracts based on the traditional usage of the plant. Isobolograms indicated greatest synergy for Bacillus cereus and Cryptococcus neoformans.