Bioprospecting for Effective Antibiotics from Selected Kenyan Medicinal Plants against four Clinical Salmonella Isolates

Abstract

The extracts from T. diversifolia, W. ugandesis, C. megalocarpus, C. edulis and L. cornuta plants traditionally used in treatment of typhoid fever were screened for anti-salmonella activity using disc diffusion and microdilution techniques. The results from the present study have shown that out of thirty six extracts investigated, only nine extracts from T. diversifolia and W. ugandensis showed activity against four clinical Salmonella isolates at 1000 mg/ml. The inhibition zones of 9 plant extracts ranged from 8 to 18.5 ± 0 mm. These results were comparable with those of ciprofloxacin (19.67 to 26 mm) and chloramphenicol (6.67 to 24.33 mm). The Minimum Inhibitory Concentration (MIC) of the 9 plant extracts were in the range of 0.031 to 15.63 mg/ml which compared well with ciprofloxacin (0.015 to 0.02) and chloramphenicol (0.022 to 0.03 mg/ml). The safety profiles of the 9 extracts were evaluated for acute and sub-chronic toxicity in Swiss white mice. In acute toxicity study, each extract up to 2000mg/kg given in single dose orally did not produce any toxic effect or death. In sub-chronic toxicity study, administration of 300mg/kg, 600mg/kg and 1200mg/kg to treatment groups for consecutive 28 days twice daily of the plant extracts did not produce any toxic effect or death. No gross lesions and histopathological changes were detectable between controls and the treated animals. The nine extracts that demonstrated in vitro anti-Salmonella activity were also tested for in vivo anti-salmonella activity in mice, experimentally infected with S. ser. Typhymurium ATCC 1408. In vivo studies showed that only three extracts; methanol extract of T. diversifolia leaf, ethyl acetate and hexane extracts of stem bark and root respectively of W. ugandensis were observed to have anti-salmonella activity in mice.The extracts of the two plants were fractionated by column chromatography (CC) technique and 7, 4 and 7 fractions were obtained respectively. The MICs values of the CC fractions were determined by microdilution assay. The MIC values of the fractions ranged from 1.22- 312.5µg/ml. These results were comparable with that of ciprofloxacin (1.22-19.53µg/ml). In addition, the fractions were also evaluated for their abilities to inhibit dihydrofolate reductase activity. The fractions from T. diversifolia and W. ugandensis plants showed high potency as anti-salmonella agents and deserve further investigations in this regard. Gas Chromatography- Mass Spectrometry analysis was carried out to identify compounds in the fractions and a total of thirty three known compounds were identified. For example, hexadecanoic acid, 9, 12- octadecadienoic acid (Z, Z), 1, 2-benzenedicarboxylic, 1, 4, 8-cycloudecatriene-2, 6, 6-carophylene, ß-sequiphellandrene and 3-ethenyl-3-methyl-2, 1-(1-methylethenyl) cyclohexanol were identified and their fractions demonistrated strong anti-salmonella activity. These findings demonstrate that T. diversifolia and W. ugandensis extracts exhibit appreciable amount of anti-salmonella activity and thus have great potential as a source for natural health products.