Antibacterial effects of stem bark and wood extracts of African medicinal plants Terminalia laxiflora and Terminalia brownii

Terminalia laxiflora and Terminalia brownii are used in African traditional medicine for treatment of infectious diseases and their symptoms, such as venereal diseases, cough, inflammations, eye diseases and skin disorders (1). T. laxiflora has not been studied before for antibacterial activity, and to the best of our knowledge there exists only one earlier study on antibacterial effects of T. brownii (2). Because of this we have evaluated these plant species for their potential as sources of antibacterial agents.

Extracts of stem wood and bark of T. laxiflora and T. brownii, obtained using sequential extraction and solvent partition, were investigated for their antibacterial activities against the human pathogenic Staphylococcus epidermidis, Staphylococcus aureus, Micrococcus luteus and Pseudomonas aeruginosa. The aqueous and ethyl acetate extracts of all the investigated plants gave in general the best antimicrobial effects, with the exception of a chloroform extract of T. laxiflora stem wood, which gave outstanding effects against P. aeruginosa (Figure 1). Ethyl acetate extracts of the stem bark of T. laxiflora gave MIC values of 39 µg/ml against P. aerginosa, and were more effective than gentamycin (MIC 62 µg/ml) against this bacterial strain. Promising MIC values of 156, 312 and 625 µg/ml of an ethyl acetate extract of the stem wood of T. laxiflora were recorded against P. aeruginosa, M. luteus and S. aureus, respectively. Low MIC values of 156 µg/ml were also recorded for ethyl acetate and aqueous extracts of the stem wood of T. brownii against M. luteus.

Fig. 1: Antibacterial effects of stem bark and wood extracts of T. laxiflora and T. Brownii T.L.w, T laxiflora stem wood; T.L.b, T laxiflora stem bark; T.b.w, T brownii stem wood; T.b.b, T brownii stem bark: CHCl₃, chloroform extract; EtOAc, ethyl acetate extract; aqueous, aqueous extract; amp, ampicillin; gent, gentamicin; tetra, tetracycline; pen, penicillin; M.l. Micrococcus luteus; S.a, Staphylococcus aureus; P.a, Pseudomonas aeruginosa; S.e, Staphylococcus epidermidis. Results as diameter of inhibition zones in mm (n = 4).

References:

[1] Neuwinger, H.D., 2000. African traditional medicine. Press Stuttgart, Germany.

[2] Mbwambo, Z. H. et al, 2007. Complementary and Alternative Medicine 7 (9), 1 – 5.