Chemical composition and antimicrobial activity of the essential oil of Ocimum gratissimum L. growing in Eastern Kenya

Hydro-distilled volatile oils from the leaves of Ocimum gratissimum L. (Lamiaceae) from Meru district in Eastern Kenya were analysed by gas chromatography-mass spectrometry (GC-MS) and also evaluatedfor antimicrobial activity. The oil was dominated by monoterpens which accounted for 92.48%. This monoterpene fraction was characterized by a high percentage of eugenol (68.8%). The other major monoterpenes were methyl eugenol (13.21%), cis-ocimene (7.47%), trans-ocimene (0.94%), -pinene (1.10%) and camphor (0.95%). The sesquiterpenes present in fairly good amounts were germacrene D(4.25%) and trans-caryophyllene (1.69%). The minor  sesquiterpenes were -farnesene (0.85%) and -bisabolene (0.74%). The antimicrobial activities of the essential oils were evaluated against both Gram positive (Staphylococcus aureus, Bacillus spp.) and Gram negative (Escherichia coli, Pseudomonasaeruginosae, Salmonella typhi, Klebisiella pneumoniae, Proteus mirabilis) bacteria and a pathogenic fungus Candida albicans. The oil had pronounced antibacterial and antifungal activities on all themicrobes

Phytochemical constituents and antimicrobial activity of leaf extracts of three Amaranthus plant species

This study investigated the phytochemical constituents and antimicrobial activity of hexane, ethyl acetate, dichloromethane and methanol leave extracts of Amaranthus hybridus, Amaranthus spinosus and Amaranthus caudatus. The microorganisms assayed for antimicrobial activity were: the grampositive Staphylococcus aureus and Bacillus spp, the gram-negative Escherichia coli, Salmonella typhi, Pseudomonas aeruginosae, Proteus mirabillis and Klebsiella pneumoniae and a pathogenic fungus Candida albicans. The leave extracts showed a broad spectrum anti-bacterial activity but resistance to the fungus. Commonly encountered phytochemical constituents in the leaf extracts of the three Amaranthus species included flavonoids, steroids, terpenoids and cardiac glycosides. The minimum inhibitory concentration (MIC) exhibited by A. spinosus extracts against the Salm. typhi was 129 mg/ml. The MIC exhibited by A. hybridus extracts against the tested organisms ranged between 200 and 755 mg/ml whereas that of A. caudatus was between 162.2 and 665 mg/ml. The antimicrobial properties of these plants which have been used by mankind for centuries without any signs of toxicity can be used in the traditional herbal medicines which play a very important role in primary care systems in the developing world and are becoming increasingly popular in the developed world

Chemical composition and larvicidal activity of essential oil of Lippia kituiensis against larvae of Rhipicephalus appendiculatus

This study evaluated the larvicidal activity of essential oil of Lippia kituiensis leaves against larvae of Rhipicephalus appendiculatus. The oil was obtained by hydro-distillation of fresh leaves and analysed using Gas Chromatography-Mass Spectrometry (GC-MS). Analysis showed that sesquiterpenes were dominant (56.57%), followed by monoterpenes (36.36%), diterpenes (2.59%) and others (5.19%). Major sesquiterpenes were germacrene D, β-bourbonene, gamma cadinene and 2-isopropyl-5-methyl-9-methylene-bicycle (4.4.0)dec-1-ene. Major monoterpenes were (1S, 4S)-(-)-camphor, trans-sabinene hydrate, gamma-terpinene, dl-limonene, alpha-terpinolene, l-Phellandrene, beta-Myrcene, sabinene, camphene, alpha-pinene, 4-terpineol, 4-methyl-1-(1-methylethyl)-3-cyclohexen-1-ol, 14.29 borneol (=endo-borneol), camphore, and neo-alloocimene. At 6, 12, 24, and 48 hrs after larval treatment, the oil showed activity against R. appendiculatus larvae with LC50in mg/ml of 3.26(3.14-3.38), 3.21(3.08-3.32), 3.15(3.03-3.26), 3.09(2.97-3.20) while LC90in mg/ml were 4.15 (3.95-4.45), 4.03 (3.85-4.30), 3.94 (3.77-4.19), 3.86 (3.69-4.09) respectively. Results of one way ANOVA (Analysis of Variance) showed there was no significant difference in activity of the oil against the larvae, between 6, 12, 24 and 48 hrs in all the concentrations used P = 0.97, 95% confidence. The findings indicatedthat essential oil of L. kituiensis possessed larvicidal properties and can be used to control tick larvae.Keywords: Rhipicephalus appendiculatus; essential oils; acaricidal activity, ticks

Liquid and vapour-phase antifungal activities of selected essential oils against candida albicans: microscopic observations and chemical characterization of cymbopogon citratus

<p>Abstract</p> <p>Background</p> <p>Use of essential oils for controlling <it>Candida albicans </it>growth has gained significance due to the resistance acquired by pathogens towards a number of widely-used drugs. The aim of this study was to test the antifungal activity of selected essential oils against <it>Candida albicans </it>in liquid and vapour phase and to determine the chemical composition and mechanism of action of most potent essential oil.</p> <p>Methods</p> <p>Minimum Inhibitory concentration (MIC) of different essential oils in liquid phase, assayed through agar plate dilution, broth dilution & 96-well micro plate dilution method and vapour phase activity evaluated through disc volatilization method. Reduction of <it>C. albicans </it>cells with vapour exposure was estimated by kill time assay. Morphological alteration in treated/untreated <it>C. albicans </it>cells was observed by the Scanning electron microscopy (SEM)/Atomic force microscopy (AFM) and chemical analysis of the strongest antifungal agent/essential oil has been done by GC, GC-MS.</p> <p>Results</p> <p>Lemon grass (<it>Cymbopogon citratus</it>) essential oil exhibited the strongest antifungal effect followed by mentha (<it>Mentha piperita</it>) and eucalyptus (<it>Eucalyptus globulus</it>) essential oil. The MIC of lemon grass essential oil in liquid phase (288 mg/l) was significantly higher than that in the vapour phase (32.7 mg/l) and a 4 h exposure was sufficient to cause 100% loss in viability of <it>C. albicans </it>cells. SEM/AFM of <it>C. albicans </it>cells treated with lemon grass essential oil at MIC level in liquid and vapour phase showed prominent shrinkage and partial degradation, respectively, confirming higher efficacy of vapour phase. GC-MS analysis revealed that lemon grass essential oil was dominated by oxygenated monoterpenes (78.2%); α-citral or geranial (36.2%) and β-citral or neral (26.5%), monoterpene hydrocarbons (7.9%) and sesquiterpene hydrocarbons (3.8%).</p> <p>Conclusion</p> <p>Lemon grass essential oil is highly effective in vapour phase against <it>C. albicans</it>, leading to deleterious morphological changes in cellular structures and cell surface alterations.</p

Larvicidal effects of endophytic and basidiomycete fungus extracts on Aedes and Anopheles larvae (Diptera, Culicidae)

Introduction In vitro bioassays were performed to access the larvicidal activity of crude extracts from the endophytic fungus Pestalotiopsis virgulata (Melanconiales, Amphisphaeriaceae) and the saprophytic fungus Pycnoporus sanguineus (Basidiomycetes, Polyporaceae) against the mosquitoes Aedes aegypti and Anopheles nuneztovari. Methods The extracts were tested at concentrations of 100, 200, 300, 400 and 500ppm. Ethyl acetate mycelia (EAM) extracts and liquid culture media (LCM) from Pe. virgulata and Py. sanguineus were tested against third instar larvae of Ae. aegypti and An. nuneztovari. Results The larvicidal activity of the EAM extracts from Pe. virgulata against Ae. aegypti had an LC50=101.8ppm, and the extract from the basidiomycete fungus Py. sanguineus had an LC50=156.8ppm against the Ae. aegypti larvae. The Pe. virgulata extract had an LC50=16.3ppm against the An. nuneztovari larvae, and the Py. sanguineus extract had an LC50=87.2ppm against these larvae. Conclusions These results highlight the larvicidal effect of EAM extracts from the endophyte Pe. virgulata against the two larval mosquitoes tested. Thus, Pe. virgulata and Py. sanguineus have the potential for the production of bioactive substances against larvae of these two tropical disease vectors, with An. nuneztovari being more susceptible to these extracts

Chemical composition and antifungal activity of Piper capense oil against mycotoxigenic Aspergillus, Fusarium and Penicillium species

Hydro-distilled essential oil from Piper capense (L. f.) growing in Kenya was analyzed by gas chromatography mass spectrometry (GC-MS) and evaluated for antifungal activity. The oil was dominated by sesquiterpene hydrocarbons (43.9%) with δ-cadinene (16.82%), b-bisabolene (5.65%) and bicyclogermacrene (3.30%). There was appreciable quantity of monoterpene hydrocarbons (30.64%) including b-pinene (7.24%) and α-phellandrene (4.76%). Arylpropanoids (8.64%) was found in reasonable quantity having myristicin (4.26%) as its major constituent. A total of ten, fourteen and sixteen mycotoxigenic species of Aspergillus, Fusarium and Penicillium respectively were assayed. The oil showed strong antifungal activity against these fungi with Minimum Inhibition Concentration (MIC) ranging from 33.1 to 265 mg/ml. These results show that the oil has antifungal activities against fungi that are producers of poisonous mycotoxins found in foods and therefore can be used in food preservation systems to inhibit the growth of moulds and retard subsequent mycotoxin production.Keywords: Essential oil, inhibition zone, moulds, mycotoxigenic fungi

Aloe plant extracts as alternative larvicides for mosquito control

The larvicidal activity of extracts from Aloe turkanensis, Aloe ngongensis and Aloe fibrosa against the common malaria vector, Anopheles gambie, was determined. Ground Aloe leaves from the three plants were sequentially extracted with hexane, ethyl acetate, chloroform, acetone and methanol. Only the ethyl acetate extract of A. turkanensis, hexane, ethyl acetate, acetone, chloroform and methanolextracts of A. ngongensis and the hexane, acetone and methanol extracts of A. fibrosa showed activity. A series of concentrations of the extracts ranging from 0.05-2 mg/ml (0.005-0.2% w/v) were testedagainst third instar larvae and their percentage mortalities, LC50 values determined. The ethyl acetate soluble extract of A. turkanensis showed very high larvicidal activity where 100% mortality wasachieved at a concentration of 0.2 mg/ml and it had an LC50 of 0.11 mg/ml. All the extracts of A. ngongensis showed larvicidal activity to A. gambie larvae, but at higher concentration showing LC50´sof 0.84 (0.55 – 1.27), 1.14 (0.72 – 2.28), 0.98 (0.78 – 1.27), 1.08 (0.90 – 1.28), 2.0 (1.85 – 2.36) for the hexane, ethyl acetate, chloroform, acetone and methanol, respectively. The three active fractions of A. fibrosa had very close LC50´s ranging from 1.76 – 1.90 mg/ml. Thin layer chromatographic analysis (TLC) showed the presence of chromones and anthrones in the chloroform and ethyl acetate extracts. Application of these extracts to larval habitats may lead to promising results in malaria and mosquito management programmes

Field grain losses and insect pest management practices in subsistence agriculture: Farmers' perceptions

A farm survey was conducted in subsistence farming communities to document the major grain crops, insect pests, indigenous pest control methods (PCM) and farmer perceptions of grain losses associated with identifiable pest species and perceived efficacies of the PCMs. Maize, beans and sorghum were identified as the major staple food crops, with the major pests being cutworm, stem borers, aphids, beanfly, pod borers, armyworms and termites. Statistical analyses revealed that the level of crop yield losses was dependent upon the area cropped, total yield and respondents' background. There was, however, a negative correlation between crop yield loss due to insect pests and the efficacy of PCM applied. Farmers lost, on average, 24.75% of their crop to insect pests with high value crops suffering the greatest insect pest attack in terms of species diversity and magnitude of damage incurred. The occurrence of field insect pests varied from season to season with most species reportedly occurring during the long rains. Most (72.6%) farmers never applied any PCM against all the insect pests of food crops. The use of synthetic pesticides and alternatives accounted for less than 10%. Seventy one percent of the respondents crops, with the major pests being cutworm, stem borers, aphids, beanfly, pod borers, armyworms and termites. Statistical analyses revealed that the level of crop yield losses was dependent upon the area cropped, total yield and respondents' background. There was, however, a negative correlation between crop yield loss due to insect pests and the efficacy of PCM applied. Farmers lost, on average, 24.75% of their crop to insect pests with high value crops suffering the greatest insect pest attack in terms of species diversity and magnitude of damage incurred. The occurrence of field insect pests varied from season to season with most species reportedly occurring during the long rains. Most (72.6%) farmers never applied any PCM against all the insect pests of food crops. The use of synthetic pesticides and alternatives accounted for less than 10%. Seventy one percent of the respondents reported that the efficacy of the PCMs applied was unknown. Some of the indigenous PCMs reportedly used included crude powders and aqueous extracts of local botanical plants such as Tobacco, Tephrosia, and Basil. The study recommends that bioassay-guided investigations be instituted to develop and rationalise the use of identified PCM strategies compatible with the target user domains.Keywords: Farmer perceptions yield loss, indigenous pest control Journal of Agriculture, Science and Technology Vol. 8 (1) 2006: pp. 24-4