Anti-diarrhoeal evaluation of some medicinal plants used by Zulu traditional healers

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Abstract

Aqueous and methanolic extracts of several medicinal plants, Psidium guajava (leaves), Aristea spp., Iridaceae family (stem), Bridelia micrantha (bark) and Eleutherina bulbosa (bulb), used by Zulu traditional healers were evaluated for anti-diarrhoeal activity against different experimental models of diarrhoea in rats as well as for anti-microbial activity against different pathogenic microorganisms that cause diarrhoea. The methanolic extract of P. guajava (leaves) was the only agent showing significant inhibitory activities against the growths of Salmonella spp. (two isolates), Shigella spp. (S. flexneri, S. virchow and S. dysenteriae) and enteropathogenic Escherechia coli (two isolates). The methanolic extract of B. micrantha (Bark) demonstrated weak inhibitory activities against S. flexneri and S. plesiomonas. Based on the results in experimental rat models, there were significant reductions in faecal output and frequency of droppings when plant extracts were administered compared with castor-oil treated rats. All plant extracts also significantly retarded the propulsion of charcoal meal and significantly inhibited the PGE2-induced enteropooling. The results have confirmed the effectiveness of all these Zulu medicinal plants as anti-diarrhoeal agents.

Introduction

Diarrhoea continues to be one of the leading causes of mortality and morbidity especially in children in developing countries (Black et al., 1982) including South Africa. The emergence of multiple drug resistant strains of diarrhoeagenic pathogens has made the treatment of dysentery more difficult (Munshi et al., 1987, Bennish et al., 1984). In developing countries, the majority of people living in rural areas almost exclusively use traditional medicines in treating all sorts of diseases including diarrhoea.

Due to these facts, the World Health Organization (WHO) incorporates studies of traditional medicinal practice in its diarrhoeal disease control program. Several studies have evaluated the effectiveness of some traditional medicines in treating diarrhoea in all different continents (Chowdhury et al., 1991, Ferdous et al., 1992, Ahsan et al., 1996, Rao et al., 1997, Menezes and Rao, 1998, Mukherjee et al., 1998, Zavala et al., 1998, Das et al., 1999, Offiah and Chikwendu, 1999, Rani et al., 1999, Tona et al., 1999). South Africa has a great environmental and biological (genomic) diversity compared with the rest of the world. A range of medicinal plants with anti-diarrhoeal properties has been widely used by the traditional healers of difficult tribes in South Africa. The effectiveness of many of these antidiarrhoeal traditional medicines, however, has not been scientifically evaluated. Aristea spp., Iridaceae family has been used to treat cold, flu, malaria, toothache and bruise and Eleutherina bulbosa to treat burns. However, anecdotal evidence suggests that the above two medicinal plants can also be used to treat gastro-intestinal diseases. Bridelia micrantha is also used by traditional healers for the treatment of gastro-intestinal diseases, paralysis and painful joints. Psidium guajava originally from Mexico is also widely used by local traditional healers. P. guajava is also a relatively well studied species with respect to diarrhoea (Lutterodt, 1989, Ghosh et al., 1993, Tona et al., 1999).

This study reports on the anti-diarrhoeal effects of some medicinal plants used by traditional Zulu herbalists using different experimental models in rats. It also looks at the anti-microbial activities of these medicinal plants against different pathogenic microorganisms that cause diarrhoea.

Section snippets

Preparation of plants extracts

P. guajava (leaf), Aristea spp., Iridaceae family (stem), B. micrantha (bark) and E. bulbosa (bulb) were collected from the campus of the University of Zululand, identified by A. Hutchings from the Botany Department and confirmed by the National Botanical Institute. The plant extracts were prepared as described by Lin et al. (1999). In brief, dry plant materials were extracted using distilled water in a Soxhlet extractor for 24 h. The aqueous extracts were concentrated in vacuo, at 40 °C, using

Results

The methanolic extract of P. guajava (leaves) was the only agent showing significant inhibitory activities (inhibitory zone ≥10 mm) against the growths of Salmonella spp (two isolates), Shigella spp. (S. flexneri, S. virchow and S. dysenteriae) and enteropathogenic E. coli (two isolates). (Data not shown) All aqueous, ethanol and acetone medicinal plant extracts showed no significant inhibitory activity against all tested microorganisms. The methanolic extract of B. micrantha (bark)

Discussion

The methanolic extract of P. guajava (leaves) was the only agent that showed significant inhibitory activities against the growths of some diarrhoeagenic pathogens in this study. Several studies (Lutterodt, 1989, Ghosh et al., 1993, Tona et al., 1999) have also demonstrated that P. guajava possesses antidiarrhoeal and antimicrobial activities. In addition, leaf extract of P. guajava contains anticough (Jaiarj et al., 1999), antiamoebic and antispasmodic properties (Lozoya et al., 1994, Tona et

Acknowledgements

We would like to thank the Medical Research Council (SA) and the University of Zululand for the financial support. We also would like to thank A. Hutchings from the Botany Department at the University of Zululand for the collection and the identifications of these medicinal plants.

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