Antimicrobial activity of selected plants used in Ethnomedicine in South-Western Nigeria

Nine plants [Aframomum melegueta K. Schum. (Zingiberaceae), Alstonia boonei De Wild. (Apocynaceae), Annona senegalensis Pers. (Annonaceae), Bixa orellana L. (Bixaceae), Cassia podocarpa Guill. & Perr. (Leguminosae), Combretum racemosum P. Beauv. (Combretaceae), Gardenia ternifolia Schum & Thonn. (Rubiaceae), Heliotropium indicum L. (Boraginaceae) and Mucuna pruriens (Linn) DC (Leguminosae)] are used in herbal remedy to treat diarrhoea, dysentery and skin diseases [1].

The methanolic extracts of the plants were evaluated for in vitro antimicrobial activity at concentrations ranging from 25–125mg/ml using the agar diffusion method to validate the ethnobotanical uses of the plants and compare activities.

The root of Combretum and the Annona stem bark showed significant activity against the local and standard strains of Staphyloccocus aureus (MIC 25–50mg/ml) and Shigella dysenterae (MIC 25–50mg/ml) while the root of Combretum was also active against Escherichia coli (MIC 25mg/ml) and Salmonella paratyphi (MIC 25mg/ml).

Aframomum root, Cassia root and Heliotropium whole plant were active against Salmonella paratyphi, S. aureus and E. coli respectively (MIC 100mg/ml). Alstonia bark, Bixa fruit, Gardenia and Mucuna root showed no antimicrobial activity.

None of the plant extracts exhibited activity comparable to the reference compound tetracycline.

However, Combretum afforded greater antimicrobial activity than Annona, Aframomum, Cassia and Heliotropium. S. aureus was most susceptible to the plant extracts.

References: [1] Burkill, H.M. (1994). Royal Botanic Gardens. Surrey. [2] Bauer, A. et al. (1966) Amer. J. Clin. Path. 45: 493–496.