African Journal of Traditional, Complementary and Alternative Medicines African Ethnomedicines Network ISSN: 0189-6016 Vol. 5, Num. 1, 2008, pp. 51-55

African Journal of Traditional, Complimentary and Alternative Medicines, Vol.5, No. 1, 2008, pg. 51-55

Research Paper

ANTIMICROBIAL ACTIVITY OF SOME MEDICINAL PLANTS USED BY HERBALISTS IN EASTERN PROVINCE, KENYA

*Kareru P. G¹., Gachanja A. N¹., Keriko J M¹., Kenji G. M².

¹Department of Chemistry, ²Department of Food Science and Post-Harvest Technology, Jomo Kenyatta University of Agriculture and Technology, P.O. BOX 62000 - 00200, Nairobi, Kenya. *Email: pgkareru@yahoo.com

Code Number: tc08009

The aqueous extracts from medicinal plants commonly used by herbalists in Mbeere, and Embu districts of Eastern province, Kenya, were tested for their inhibitory activity against three selected strains of bacteria. All the selected plant extracts (infusions: 1.0g sample in 100 ml water) investigated showed activity against Escherichia coli with inhibition zone diameters ranging from 5.8 – 18.0 mm. Terminalia brownii gave the largest inhibition zones against E. coli and Staphylococcus aureus. Vernonia lasiopus and Tithonia diversifolia were inactive to S. aureus and Bacillus subtilis, respectively. Eighteen and sixteen plants showed sensitivity of greater than 10 mm against S. aureus and B. subtilis, respectively. All control discs gave zones of inhibition of 12 - 24 mm, which were larger than those of the extracts. The present study validated the use of the selected medicinal plants by the herbalists in the treatment of bacterial ailments caused by the strains of bacteria investigated. Medicinal plants used for non-bacterial diseases also exhibited sensitivity towards bacterial strains tested. This implied they could be used as multi-purpose medicinal plants.

Key words: Terminalia brownii, inhibition zone, aqueous extract, Escherichia coli, Kenya

Microbial infections pose a health problem throughout the World, and plants are a possible source of antimicrobial agents (Burapadaja & Bunchoo, 1995: Adenisa et al., 2000). Medicinal plants contain active principles which can be used as an alternative to cheap and effective herbal drugs against common bacterial infections. Embu and Mbeere districts of Eastern Province, Kenya, are endowed with a wide variety of indigenous medicinal plants. These plants are used by the local herbalists for treatment of a number of diseases, both bacterial and non-bacterial type and are distributed in various plant families: Papilionaceae, Labiate, Verbenaceae and Compositae, among others. Table 1 summarizes the traditional uses of some plants used by the Mbeere and Embu herbalists (Kareru et al., 2007). There was need, therefore, to assess the antimicrobial activities of these plants. Scientific proof and clinical validation of herbal formulations can be achieved by various methods: chemical standardization, biological assays, animal models and clinical trials. Thus, antimicrobial assays (Moleyar et al., 1992; Cebo et al., 1999; Moses et al., 2006; Millogo-Kone et al., 2002), cytotoxicity (Alluri et al., 2005), antiprotozoal, (Camacho et al., 2003), and anthelmintic (Abebe et al., 2000; Dawo et al., 2001; Wasswa et al., 2006) activities have been used for validation of plant extracts. However, validation should go hand in hand with regulation and evaluation of herbal treatments to avoid the administration of dangerous concoctions.

In the present investigation, some medicinal plants traditionally used by the Mbeere and Embu herbalists of Eastern Province, Kenya, were tested against three strains of bacteria and are reported. The results validated use of the medicinal plants by the herbalists.

Table 1: Ethnomedicinal uses of selected Medicinal Plants (Kareru et al., 2007)

Materials and Methods

The plants were collected in Mbeere and Embu districts of Eastern Province, Kenya, in the dry season. A plant taxonomist authenticated the medicinal plant specimens. Plants specimens used for bacterial and non-bacterial infections were sampled. Collected samples were given voucher specimen numbers and deposited with the Botany Department of Jomo Kenyatta University of Agriculture and Technology.

The collected plants’ parts were dried in the shade, chopped, and ground to a fine powder. A hot water infusion (1.0 g powder in 100 ml hot water) was used for the tests. The filtered infusions were diluted five times with distilled water prior to use.

Isolates of three bacteria species were obtained from a medical research centre and the required suspension of bacteria was prepared equivalent to McFarland standard 1 (1 x 10⁸ CFUs/ml) in 0.85% NaCl (aq) and adjusted by the standard plate count method (Black, 1996). Six-millimeter sterile paper discs were dipped into the aqueous sample extracts. The discs were then placed on cultured pathogenic bacteria on agar plates, and incubated at 37 º C. The inhibition zone diameters of bacteria growth were measured after 24 hours. The sensitivity of Escherichia coli, Staphylococcus aureus and Bacillus subtilis to the 26 infusions were determined in triplicate. This was repeated using commercial discs of tetracycline (100 µg), streptomycin (25 µg), sulphamethoxazole (200 µg), cotrimoxazole (25 µg) and gentamicin (10 µg) as positive controls.

The results are presented in Tables 2 and 3.

In a previous study, the herbalists were known to treat bacterial infections such as diarrhea, gonorrhea, pneumonia, stomach pains, and typhoid with forty-two medicinal plants. The latter diseases were among those reported in the local hospital morbidity data (Kareru et al., 2007) and treatable by the herbalists. In the present research, the plants investigated were distributed in sixteen plant families: five from Papilionaceae; three in each case from Labiate and Mimosaceae; two each from Verbenaceae and Compositae, and one each from eleven other plant families (Table 1). The most potent plant extracts against the microorganisms tested were from Combretaceae, Santalaceae, and Verbenaceae families respectively, and the least potent was from Compositae family. However, one of the least potent plants (Vernonia lasiopus O. Hoffm.) from the Compositae family was traditionally used for non-bacterial infections. In addition, eight other medicinal plants used by the herbalists for non-bacterial conditions were active against the strains of bacteria tested. This implied that some plants could be used as multi-purpose medicinal plants, that is, for bacterial and non-bacterial infections.

Table 2 summarizes the sensitivities of aqueous medicinal plant extracts against E. coli, S. aureus and B. subtilis. All the plant infusions were active against the test organisms (inhibition zone diameter 5.8 – 18.0 mm), except Vernonia lasiopus and Tithonia diversifolia extracts which were not sensitive to Staphylococcus aureus and Bacillus subtilis respectively. Terminalia brownii extracts gave the highest sensitivities to E.coli and S. aureus, respectively. Among all the plants tested, Vitex strickeri gave the smallest inhibition diameter against E. coli (5.8 mm), but relatively larger towards S. aureus. All control discs gave zones of inhibition of 12-24 mm, which were higher or comparable to those of the plant extracts.

In conclusion, all the medicinal plants investigated were effective against bacterial strains tested except two plants Vernonia lasiopus and Tithonia diversifolia, which were not sensitive to S. aureus and B. subtilis. This validated the use of the plants in the treatment of bacterial diseases by the herbalists. Some medicinal plants used for non-bacterial infections also exhibited activity to the strains of bacteria tested.

Table 2: Inhibition Zone Diameters (mm) of plant aqueous extracts

Table 3: Inhibition zone diameters (mm) of control drugs (antibiotics)

We would like to thank the African Institute for Capacity Development (AICAD) and Jomo Kenyatta University of Agriculture Technology (JKUAT) for funding this research. We thank Muthanga of Botany Department JKUAT, for providing bacteria isolates and carrying out bioassays, and Geoffrey Mungai of the East African Herbarium for identifying medicinal plants.

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