School of Pure and Applied Sciences
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Item ANTIBACTERIAL EFFICACY AND SAFETY OF SELECTED KENYAN MEDICINAL PLANTS(Kenyatta University, 2013-06) Abiba, Alfred OgaoMany disease-causing organisms have become resistant to conventional antibiotics. The toxicity and side effects of conventional drugs have also become increasingly unmanageable, while their costs are prohibitive. It has therefore become necessary to continue searching for alternative medicines to treat such diseases. The possibility of developing pharmaceutical industries using local raw materials should be looked into critically so that the cost of drugs can be affordable to the local people. This study involved screening of various medicinal plants commonly used by herbal medicine practitioners for bioactive compounds against bacteria. Standard bioassay methods were employed throughout this study. They included preliminary screening bioassay against human pathogenic bacteria strains using Agar Disc Diffusion method, Minimum Inhibitory Concentration (MICs), Minimum Bactericidal Concentration (MBCs), Time kill kinetics, phytochemical determination methods and one dose in vivo toxicity tests using mice. Hexane, dichloromethane, acetone and methanol extracts of ten (10) medicinal plants: Dichrostachyus. cinerea, Combretum molle, Euclea divinorum, Ficus sur, and other five plants were screened by preliminary bioassay against nine (9) human pathogenic bacteria strains (E. coli, ATCC 25922 S. aureus ATCC 85923, Pseudomonas aeruginosa NCTC 10662, Escherichia coli, Shigella flexinery, Pseudomonas aeruginosa, Staphlococcus aureus, Shigella dysenteriae and Klebsiella hospital isolates) using agar disc diffusion method. Acetone, methanol extracts of D. cinerea and C. molle showed remarkable inhibitory activity against all nine human pathogenic bacteria. Acetone and dichloromethane of E. divinorum and F. sur showed activity against all human pathogenic bacteria except P. aeruginosa and klebsiella. All extracts of six (6) plants were inactive against the test human pathogenic bacteria. MICs of acetone and methanol extracts of the four (4) plants D. cinerea, C. molle, and dichloromethane and acetone extracts of E. divinorum and F. sur were active against the test bacteria. MIC results showed that acetone and methanol extracts of D. cinerea, and C. molle gave very good low MICs ranges (0.3-2.5mg/ml), dichloromethane and acetone extracts of E. divinorum and F. sur gave MICs ranging between 7.5-100mg/ml. MBCs of acetone and methanol extracts of D. cinerea, and C. molle were as low as 0.3mg/ml while the highest being 5mg/ml. Phytochemical determination showed that both methanolic and acetone extracts of D. cinerea and C. molle contained alkaloids, tannins, steroids and triterpenoids, flavone glycones, anthrocyanins and reducing sugar. Kill kinetics studies of the bioactive organic extracts on the tested bacteria indicated that acetone extracts of D. cinerea, acetone extracts of C. molle, methanol extracts of C. molle, methanol extracts of D. cinerea at 4, 6 and 8mg/ml against Staphylococcus aureus ATCC 85923, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa NCTC 10662, displayed dose and time dependent rapid kinetics of the bacterial killing. Because the toxicity of a drug to the bystander host cells could render it unsuitable for therapeutic purposes, the toxicity of the active plant extracts against the tested bacteria was assessed. The reduced growth rate, organ weights, white and red blood cells counts, plus increased levels of biochemicals in the serum in plant extract treated animals relative to that of the controls, indicate that these extracts contained constituents with toxic effects on them. Such constituents include some of the phytochemicals present in these extracts. The mineral content may also cause toxicity but this was not the case with the measured minerals since their levels were below the recommended daily allowance except for potassium which was 67 to 141 times the recommended daily allowance.Item Enhancing Tripartite Symbiosis between Soybean, Bradyrhizobia and Arbuscular Mycorrhizal Fungiunder Contrasting Farm Management Practices in Tharaka-Nithi County-Kenya(Kenyatta University, 2021-05) Gitonga, Nicholas MawiraOrganic farming is gaining popularity as agronomically and environmentally sound soil management strategy with the potential to enhance soil microbial diversity and fertility, environmental quality and sustainable crop production. However, the role of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) in organic farming systems is poorly understood. Field experiments were carried out to evaluate the effects of organic farming and bradyrhizobia inoculation on soybean nodulation, AMF root colonization, growth, production and yield quality. Greenhouse and laboratory experiments sought to determine the effects of bradyrhizobia and/or AMF inoculation and dual inoculation in promoting root colonization and nodulation, determine soil mycorrhizal inoculum potential (MIP), evaluate the abundance and effectiveness of native bradyrhizobia and determine the morphological and genetic diversity of native bradyrhizobia isolates under different farm management practices. Field experimental treatments included native bradyrhizobia, commercial Bradyrhizobiun japonicum, a mixture of native and commercial Bradyrhizobium japonicum and control. Promiscuous soybeans varieties SB 19 and SC squire as well as non-promiscuous Gazelle were used as test plants. All field experiments were carried out in split-split plot design. In the greenhouse, AMF and bradyrhizobia were inoculated and dual inoculated on SC squire soybeans. The AMF inoculants used were Funneliformis mosseae and Rhizophagus irregularis while bacteria involved commercial bradyrhizobia and native bradyrhizobia. Greenhouse experiments were set out using completely randomized design. The native bradyrhizobia were isolated and characterized. Deoxyribonucleic acid (DNA) from nodule isolates was extracted using Gene Jet DNA extraction kit. Polymerase chain reaction (PCR) targeting 16S rDNA gene was carried out using universal primers P5-R and P3-F. Polymerase chain reaction product purification and sequencing was carried out in MacrogenNetherlands. Sequencing was done using the same primers. Non molecular data obtained was analyzed using analysis of variance (ANOVA). Means that were significantly different at p< 0.05 were separated using Tukey’s HSD test. Field experiment results demonstrated significant improvement of soybean nodule dry weight (NDW), shoot dry weight (SDW) and seed dry weight (SEDW) due to inoculation. Bradyrhizobia inoculation increased soybean seed yields by between 29-59% of its potential yield. Remarkably, organic farming significantly (p=0.001) out-performed conventional systems in SDW, NDW, SEDW and AMF root colonization. Moreover, seed nutrient significantly differed in organic and conventional farming where, seed nitrogen, phosphorus, potassium and organic carbon were higher in organic farming. Soybean varieties differed significantly on SDW, NDW and SEDW, where SC squire performed better compared to SB 19 and Gazelle. Greenhouse results showed bradyrhizobia and AMF dual inoculation significantly enhanced AMF root colonization, NDW and SDW compared with individual bradyrhizobia, AMF or control. Moreover, organic farming significantly (p=0.001) increased SDW, NDW and AMF root colonization compared to conventional farming. Organic farming had a significant effect (p = 0.001) on soil MIP. Based on molecular analysis, isolates were bradyrhizobia and matched with Bradyrhizobium japonicum among other species. There was little or no genetic differentiation of isolates with the highest molecular variation (91.12%) within the populations and 8.88 % among populations. The results demonstrate the importance of organic farming and dual inoculation in sustainable crop production. The highly potential native bradyrhizobia isolates (GRPc and GRPk) and exotic AMF should be xix popularized and commercially ultilized by farmers to alleviate declining soil fertility and increase food production with minimum expenses.Collection Collection Collection