Faculty of Science

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    Purification, Bioactivity and Structure Elucidation of Mosquito Larvicidal Compunds from Mycelium of BAsidiomycete JO5444
    (Egerton University, 2009-03) Njogu, E.M.
    As malaria burden persists in most parts of the developing world, the concept of implementation of new strategies to control the disease continue to gain support. ln Kenya, mosquito population has increased to unprecedented levels as the insects are now a common sight in places they were previously not known to habit. Mosquitoes species belonging to genera Anopheles, Culex, and Aedes are the principal vectors of etiologic agents of various diseases like malaria. filariasis, Japan encephalitis (JE), dengue fever, dengue hemorrhagic fever (DHF) and yellow fever to mention just but a few. It is known that elimination of the vector is one of the most effective ways of controlling disease transmission. This takes the approach of using adulticides and larvicides. Whereas the former is well established, it has limitations like the challenges of targeting mobile adult mosquitoes and resistance of mosquitoes to insecticides. Larval control has long been an option for disease control but it has been greatly under developed and underutilized approach especially in tropical Africa where it may be of much utility than is generally appreciated. Killing mosquito larvae before they emerge as adults can reduce or eliminate the need for ground or aerial application of pCnli\.i\.i¢> l.u kill mosquitoes. During the search for new. effective and environmentally bcnignnatural larvicidal compounds. larvicidal activity of nine enriched fractions and one pure compound from mycelium of basidiomycetes serialized JO5444 were investigated. Bioactivity-guided fractionation and purification afforded one pure novel compound identified as (oxiran-2-yl)methylpentanoate by its spectral data. The LC50 and LCQQ at 24 hours of the pure compound against larvae of Ae aegypti in their late third and early fourth instars were studied and found to be l.50ppm and l.90ppm respectively. The complete structure of the purified compound was obtained from both lD and 2D NMR experiments, and analysis of the spectra obtained allowed complete 1H and BC NMR assignments. The ‘H NMR and BC NMR data for the purified compound have been provided. Fungal secondary metabolites are therefore hereby reported and proposed as a complimentary tool for control of mosquitoes and hence reduce transmission of diseases that they vector. \ vi
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    Prospecting for Antibacterial Compounds from A Basidiomycete JO5191
    (Egerton University, 2007-07) Mutambi, Emily Mbayisi
    The need for new antibacterial compounds with different modes of action to manage drug-resistant bacterial strains is urgent. The molecular basis of most antimicrobial agents is now fairly well known and thus it is now possible to develop new compounds with improved antimicrobial properties. lliougli there are several drug targets that have been idcntiticd and upon which most antil>actc|'ial agents act. there is still great need and potential to prospect from novel sources for new drug candidates. liasidioinycctes have proved to be cwellcnt producers of secondary metabolites \\‘llll vast activities. Picliniinaiy scicemiig of nude extracts from a basidiomyccte .IO5l9l, revealed strong antibacterial activity against two Urani-negative bacteria: /;'.\'1'/11'1"/1'/rm ¢‘n// and .S'rlln/um’/lu !4i'/r/Iinzu/"Imn. lhls resealcli piojettt involved the purification of the compounds using column chromatography and semi preparative lll’LC followed by structure elucidation of the compounds responsible for the observed antibacterial activity. The fungus was cultivated in 25 replicates of I litre~scale in nutrient liquid media for 22 days and crude extracts prepared from both the myccliuin and the culture filtrate immediately allcr stopping growth. The crude extracts were screened for anti- bacterial activity and the compounds purified by bioassay-guided fractionation on silica gel and reverse phase high-pressure liquid chromatography. The chemical structures of the purified compound(s) were detennined using spectroscopic techniques: infrared (IR), nuclear magnetic resonance (NMR) in conjunction Willi MS and CD and found to be flavanones. The antibacterial activities were detennined by the calculation of minimum inhibitory concentrations (MIC), which were found to be in the range 3ig/ml - l2tg/ml. agreeing considerably well with those from the literature. -
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    Polymorphism of Attachin D Gene in Glossina pallidipes Tsetse Fly Populations of Nguruman and Busia-Teso, Kenya
    (Egerton University, 2011-03) Mayoke, Abraham
    Tsetse flies (Glassina spp) that spread African trypanosomes express Attacin, an immune system protein, during trypanosome infection. The actual mechanism of protection by Attacin proteins in trypanosome-infected Glossina pallidipes is unknown. The objectives for this study was to assess polymorphism of Attacin gene in natural G. pallidzpes populations isolated from Nguruman and Busia-Teso regions of Kenya (regions with different disease transmission levels and genetic diversity of tsetse flies) and correlate polymorphism of the gene to trypanosome infection in G. pallidzpes from the study regions. Biconical traps and suitable attractants were used to lure and capture the G. pallidipes flies. Midguts were dissected from the captured flies and preserved in Trizol reagent. Trypanosome parasitemia in the salivary glands of the flies were determined through standard microscopy. PCR of Attacin D (AttD) gene was conducted on Genomic DNA (extracted from carcasses), and the product sequenced using automated sequencer. Trypanosome infections in the rnidgut tissues were detected by microscopy and their presence confirmed via nested RT-PCR using trypanosome species specific primers. A total of 586 non-teneral and l5l teneral G. pallidipes were sampled fiom Nguruman. In Busia ~ Teso, 17 and 16 non-teneral and teneral G. palidipes were sampled. A homologue of G. m. morsitans Attacin D in G. pallidzpes was successfully identified fiom a region of 484 base pairs. Most polymorphism were mutations, deletions and substitutions but with predominance of mutation in coding sites. Two types of AttD were revealed, a conserved region and several introns in all individual flies’ sequences in position 170 to 180. Attacin D polymorphism in G. pallidzpes from Nguruman and Busia-Teso were predominant downstream from position 199 to position 298. Microcopy examination revealed putative presence of trypanosome in midgut and proboscis of two flies, one each from Nguruman and Busia~Teso, while PCR results revealed putative infections in two and four flies from respective towns. Putative G. pallidipes Attacin D homologous were identified only in G. m. morsitans and in Aedes aegypti among insect vectors of pathogens in Glossina, Aedes and Rhodnius genera. Interproscan analyses did not reveal any differences in domain architecture among the putative G. pallidipes attacin D sequences. The observed differences in polymorphism of Atttacin D populations in Ngururnan and Busia-Teso may be responsible for the differences in Trypanosomiasis incidences in the two towns. vi
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    Genetic Diversity and Relationship of African Sheep-A Y Chromosome Perspective
    (Egerton University, 2007-01) Ouna, Benard Aswani
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    Human Exposure to Lead in Selected Areas in Olkalou and Nairobi, Kenya
    (Egerton University, 2007-09) Kimani, G. Njoroge
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    Mathematical Models Applicable in Business Investments
    (Egerton university, 2004-10) Manyanga, David Ondiek
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    Milk Fat Changes in Accelerated Shelf Life Testing of Ready-To-Fry Chapati
    (Egerton university, 2004-04) Chitsaka, Grace Mwangome
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    Model-Based Assessment of Trends for some Communicable Diseases in Kenya
    (Egerton university, 1999-10) Kiprotich, James Rutto
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    Optimal Harvesting in Matrix Population Models
    (Egerton university, 1993-12) Oguna, Bernard Omolo
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    The Local Field and Orientational Order Parameter in Nematic and Smectic Liquid Crystals
    (Egerton University, 1995) Mukhebi, Lutta Abraham Michael.
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    The Ecology of Benthic Communities in a Tropical Mangrove Forests at Gazi Bay, Kenya
    (Egerton University, 2008-04) Kubasu,Kizito Masinde
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    Analysis of Selected Toxic Heavy Metals and Pesticide Residues in Catha Edulis from Selected Regions in Meru County, Kenya
    (Egerton University, 2024-09) Oyugi, Albert Morang’a
    Heavy metal and pesticide pollutions on environmental matrices and their potential human toxicity have attracted considerable attention worldwide in recent years. The desire to increase food production to satisfy the ever rising population has resulted in the use of potentially toxic pesticides and fertilisers. The application of these chemicals in modern farming technologies is a source for potentially toxic heavy metals and pesticide residue levels in human consumables such as foodstuffs, which may ultimately trigger adverse health effects. Accordingly, this study focused on the concentration profiles of cadmium (Cd), lead (Pb), chromium (Cr), iron (Fe), nickel (Ni), and copper (Cu) and pesticide residues in 11 khat (Catha edulis) samples randomly sourced from 11 farms within regions of Meru County, Kenya. These analyses are meant to evaluate any associated human health risks through comparison with the World Health Organisation/ Food and Agriculture Organisation (WHO/FAO) safe limits. Human health risk assessment was done using target hazard quotient (THQ) and health index (HI). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis gave results of heavy metal concentrations (mg/kg) in dry khat samples as follows; Cd (7.81 ± 1.56), Cr (15.98 ± 2.22) and Pb (32.35 ± 9.95), indicating all was above the acceptable WHO/FAO limits. The levels of Ni, Cu and Fe heavy metals were below permissible limits and may benefit important human biological functions. The Pb and Cd THQ values and the HI of all investigated heavy metals in the khat samples exceeded the threshold value of 1.0. This suggests that the excessive consumption of Meru khat-based products, poses a potential health risk to the consumers. Besides, the gas chromatograph-mass spectrometry (GC-MS) results showed the detection and identification of pyrethroid and organophosphate pesticides representing 54.5% pesticide contamination prevalence rate of the sample size. The Ultraviolet-Visible (UV-Vis) quantification results revealed that acephate and cypermethrin residue levels in khat samples were below maximum residue limits (MRLs) thus, there is no acephate and cypermethrin pesticide contamination reported from this study. Consequently, Meru khat farmers should regularly be educated on safe post-harvest practices to protect consumers. Therefore, the results of this work are important in sensitizing khat farmers that the use of agro-chemicals should significantly be minimized or avoided on farms and encourage on alternative farming practices that do not potentially increase potentially toxic heavy metals and residues in khat. Regular monitoring and evaluation of pesticide residues and heavy metals in khat products is necessary to ensure public and environmental health.
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    Secondary Metabolites from Juniperus Procera with Activity against Selected Maize and Bean Pathogens
    (Egerton University, 2024-09) Nduati, Teresia Wangui
    Maize (Zea mays) and beans (Phaseolus vulgaris L.) are important food crops in Kenya however, these crops have registered a decline in yields which is partly due to attack by fungal and bacterial pathogens. These pathogens are currently managed by use of synthetic pesticides, whose long term and widespread use has led to negative impacts which has endangered the environment in general. Extracts from Juniperus procera have been used as traditional medicine in treatment of various human pathogens. Scientific research has also proved efficacy of its various secondary metabolites towards human pathogens but minimal research has been done on their activity towards phytopathogens. This study, therefore, aimed at isolating secondary metabolites from the bark and leaves of J. procera with activity against three important plant pathogens; Xanthomonas axonopodis pv. phaseoli and Pseudomonas savastanoi pv. phaseolicola whose host is common bean and a maize pathogen Fusarium graminearum. The leaf and bark samples were collected from Mount Elgon National Park Forest, dried under shade and ground into a fine powder. Solvent extraction method was used to extract secondary metabolites from the powdered plant material whereby the powder was first soaked in methanol, filtered and solvent evaporated to obtain methanol extract. The methanol extract was suspended in water and partitioned between hexane and ethyl acetate to obtain ethyl acetate, hexane and aqueous extracts. The ethyl acetate extracts were purified using various chromatographic techniques. The pure compounds were analysed using 1D and 2D NMR and their masses determined using mass spectrometry. A flavonoid was isolated from the bark; epicatechin (12) while a biflavonoid and a diterpenoid were isolated from the leaf; podocarpusflavone A (13) and juniperolide (14) respectively. Disc agar diffusion assay was used to test the extracts and pure compounds against the three phytopathogens. Crude extracts were more active against the bacterial pathogens than the semi-pure fractions. For example, methanol and aqueous crude extracts from leaf had highest inhibition zones of 18.0 and 17.3 mm respectively against P. savastanoi pv. phaseolicola. Compound 12 had the highest inhibition zone of 21 mm against P. savastanoi pv. phaseolicola. Both compound 13 and 14 registered inhibition zones of 8 mm against P. savastanoi pv. phaseolicola. The extracts and the pure compounds did not show activity towards F. graminearum. It can therefore, be concluded that this medicinal plant can be a source of compounds to be used in control of important plant bacterial pathogens.