Combretum apiculatum (Combretaceae): Antibacterial testing of extracts from the leaves and seeds

Combretum apiculatum (red bush willow) is a small to medium-sized deciduous tree which occurs in various savanna regions. Traditional healers use a steam bath from leaf decoctions to treat abdominal disorders and microbial infections. They also treat inflammation that causes headache and toothache, and conjunctivitis. The objective of this study is the screening of sequential dichloromethane (DCM) and methanol extracts from the leaves, and the methanol extract from the seeds of Combretum apiculatum against the E. faecalis, K. pneumoniae, and C. neoformans bacterial strains, and the subsequent isolation, purification, and characterization of any active compound.

A sample of powdered leaves (80 g) was extracted sequentially with DCM and MeOH, yielding 13.4 g and 40.1 g of extract, respectively. A sample of the methanol extract (35 g) was suspended in water and partitioned with heptane (Hept), ethyl acetate (EtOAc), and water saturated with butanol (BuOH). The seeds were extracted with methanol to yield 20.3 g of crude extract. The seed extract (17 g) was suspended in water and partitioned with heptane, ethyl acetate, and water saturated with butanol.

All of the 11 samples exhibited a noteworthy antimycobacterial effect on at least one of the bacterial strains, with four samples showing activity against all three bacterial strains. Minimum inhibitory concentrations were determined using the INT micro-well method (NCCLS, 2003) [Table 1].

Tab. 1: MIC values expressed in mg/mL

Sample	Diluent	Concentration	E. faecalis ATCC 29212	K. pneumoniae ATCC 13883	C. neoformans ATCC 90112
Seeds MeOH extract	Acet	32 mg/ml	0.13	0.25	Insufficient
Seeds Hept	Acet	5 mg/ml	1.25	0.63	0.48
Seeds EtOAc	Acet	5 mg/ml	0.94	0.32	0.03
Seeds BuOH	Acet	5 mg/ml	> 1.25	0.48	0.02
Seeds H2O	Acet	5 mg/ml	> 1.25	1.25	0.04
Leaves DCM extract	Acet	32 mg/ml	1.00	> 8.00	0.50
Leaves MeOH extract	DMSO	32 mg/ml	2.00	4.00	1.00
Leaves Hept	Acet	5 mg/ml	> 1.25	> 1.25	0.08
Leaves EtOAc	Acet	5 mg/ml	0.63	0.63	0.32
Leaves BuOH	Acet	5 mg/ml	> 1.25	0.32	0.04
Leaves H2O	Acet	5 mg/ml	0.63	0.63	0.32