Detection of antibacterial activity of essential oil components by TLC-bioautography using luminescent bacteria

The aim of the present study was the chemical characterization of some medically relevant essential oils (tea tree, clove, cinnamon bark, thyme and eucalyptus) and the investigation of antibacterial effect of the components of these oils by use of a direct bioautographic method. Thin layer chromatography (TLC) was combined with biological detection in this process. The chemical composition of the oils was determined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Eucalyptol (84.2%) was the main component of the essential oil of eucalyptus, eugenol (83.7%) of clove oil, and trans-cinnamic aldehyde (73.2%), thymol (49.9%) and terpinen-4-ol (45.8%) of cinnamon bark, thyme and tea tree oils, respectively. Antibacterial activity of the separated components of these oils, as well as their pure main components (eucalyptol, eugenol, trans-cinnamic aldehyde and thymol) was observed against the Gram-negative luminescence tagged plant pathogenic bacterium Pseudomonas syringae pv. maculicola (Psmlux) and the Gram-negative, naturally luminescent marine bacterium Vibrio fischeri. On the whole, the antibacterial activity of the essential oils could be related to their main components, but the minor constituents may be involved in this process. Trans-cinnamic aldehyde and eugenol were the most active compounds in TLC-bioautography. The sensitivity of TLC-bioautographic method can be improved with using luminescent test bacteria. This method is more cost-effective and provides more reliable results in comparison with conventional microbiological methods, e.g. disc-diffusion technique

Antibacterial activity of essential oils on Xanthomonas vesicatoria and control of bacterial spot in tomato

The objective of this work was to evaluate the effects of plant essential oils (EOs) on the growth of Xanthomonas vesicatoria, on bacterial morphology and ultrastructure, and on the severity of tomato bacterial spot. EOs from citronella, clove, cinnamon, lemongrass, eucalyptus, thyme, and tea tree were evaluated in vitro at concentrations of 0.1, 1.0, 10, and 100% in 1.0% powdered milk. The effect of EOs, at 0.1%, on the severity of tomato bacterial spot was evaluated in tomato seedlings under greenhouse conditions. The effects of citronella, lemongrass, clove, and tea tree EOs, at 0.1%, on X. vesicatoria cells were evaluated by transmission electron microscopy. All EOs showed direct toxic effect on the bacteria at a 10%-concentration in vitro. Under greenhouse conditions, the EOs of clove, citronella, tea tree, and lemongrass reduced disease severity. EOs of clove and tea tree, and streptomycin sulfate promoted loss of electron-dense material and alterations in the cytoplasm, whereas EO of tea tree promoted cytoplasm vacuolation, and those of citronella, lemongrass, clove, and tea tree caused damage to the bacterial cell wall. The EOs at a concentration of 0.1% reduce the severity of the disease

A study on antimicrobial activity and chemical compositions of essential oils from flowers of Lavandula Angutifolia and Salvia Officinalis

Abstract: Chemical composition and antimicrobial effects on E.coli and S.aureus of essential oils from Lavandula angustifolia and Salvia officinalis were studied. Disk diffusion method was conducted to evaluate the zone of microbial growth inhibition at 1, 1:2, 1:8 and 1:16 dilutions of the essential oils at four stages of zero (fresh oil), 1, 2 and 3 months post-extraction. The antimicrobial effect was also studied against 10^7/ml, 10^6/ml and 10^5/ml concentrations of microbial cells to find out Minimal Inhiitory Concentration (MIC) and Minimal Bactricidal Concentration (MBC). The essential oils were bactericidal against both the micro organisms. Comparatively, Gram negative bacterium. E.coli, was readily affected by the essential oil of Lavandula angustifolia and S.aureus was redily affected by the essential oil of Salvia officinalis. Chemical composition of the essential oils were analyzed by Gas. Chromatography and Mass Spectrometry (GC and GC/MS). Twelve common chemical compounds of ?-Humulene, ?-pinene, ?-pinene, ?-Thujene, 1,8-Camphene, Camphor, Cis-?-ocimene, Linalool, P-Cymene and Terpinene-4-ol were found at various concentrations in both the oils, most of which were monoterpenes. Major components of essential oil of Salvia officinalis were ?-pinene (16%), Berneol (9.4%), Glubulol (9.3%), ?-Humulene (8.4%), ?-Thujene (6.4), ?-Pinene (5.5%), Camphene (5%), and those of Lavandula angustifolia were Linalol (36.9%), 1,8-Cineole (16%), ?-Orneol (11.5%), Camphor (4.2%) and Terpinene-4-ol (4.19%). It seems that monoterpenes give antibacterial property to the essential oils. Keywords: Lavandula angutifolia, Salvia officinalis, Antimicrobial, Essential oil