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

Inhibition of citrus postharvest pathogens by vapor of citral and related compounds in culture

Copyright © 2003 American Chemical SocietyThe vapors of citral, its isomers geranial and neral, and its related compounds were examined for their effect on Penicillium digitatum, Penicillium italicum, and Geotrichum candidum, the major fungi responsible for postharvest spoilage of citrus. Vapor of citral and its two isomers generated from 15 μL L⁻¹ aqueous solutions in Petri dishes inhibited development of the three pathogens, with concentrations of 2-6 μL L⁻¹ also being effective against P. italicum. Vapors of citral and geranial from 15 μL L⁻¹ solutions were fungicidal to P. digitatum and G. candidum, while neral was fungicidal to G. candidum. Citral-related compounds were much less effective, with effectiveness decreasing from citronellal to citronellol and citronellic acid. R and S isomers of these three citral-related compounds generally had similar effects on the fungi tested.Erminawati Wuryatmo, Andreas Klieber, and Eileen S. Scot

Effect of method of application on antifungal efficacy of citral against postharvest spoilage fungi of citrus in culture

Three methods of challenging Penicillium digitatum, P. italicum and Geotrichum candidum with citral in culture were examined. All three species failed to grow when spores were spread on neutral Dox-yeast (NDY) agar mixed with 3000, 6000 or 15 000 μL/L citral in 400 μL/L TritonX emulsifier, but development progressed normally in the absence of citral. Mixing of spores with citral solutions of 3000–15 000 μL/L for 1 h before plating, to simulate dipping of fruit, reduced viability of P. italicum, and growth of G. candidum was completely inhibited by 6000–15 000 μL/L citral. Citral solutions of 15 000 μL/L inhibited all three species completely. Exposure of spores to citral in the volatile phase, simulating fumigation, completely prevented growth of all three fungi at headspace concentrations of 16 000–40 000 μL/L. The potential of citral in the volatile phase to control postharvest spoilage of citrus is discussed

Effect of volatile citral on the development of blue mould, green mould and sour rot on navel orange

The essential oil, citral, has potential for non-conventional control of postharvest diseases of citrus caused by Penicillium digitatum, Penicillium italicum and Geotrichum citri-aurantii. Citral in volatile phase has been shown to inhibit the three pathogens in vitro. The effect of citral applied as a fumigant on the incidence of disease on navel oranges (Citrus sinensis) was therefore studied. Fumigation of oranges with citral (20, 60 or 150 mL L−1 in absorbent pads) in a closed system, following application of conidia (20 μL of 106 conidia mL−1) to puncture wounds, delayed the onset of sour rot at room temperature by 7–10 days and at 5 °C, by 13–30 days, but had limited effect on blue and green mould. Blue and green mould developed faster on oranges wounded by puncture than by abrasion and volatile citral delayed the development of blue mould in abraded, but not punctured, oranges stored at 5 °C. Phytotoxicity symptoms were observed on the upper surface of some fruit close to or in direct contact with citral-soaked pads at concentrations of 60 and 150 mL L−1. Citral residue was not detected in the rind of fumigated oranges. Volatile citral applied at 60 mL L−1 appeared to have potential for the control of sour rot, although phytotoxicity was associated with high concentrations of volatile citral.E. Wuryatmo, A. J. Able, C. M. Ford, E. S. Scot