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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 of their pure main components (eucalyptol, eugenol, trans-cinnamic aldehyde and thymol) was observed against the Gram-negative luminescence gene-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 by 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.

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Direct bioautography performed with luminescence gene-tagged bacteria enables almost real-time detection of antimicrobial compounds in plant extracts. This method for the detection of chamomile ( Matricaria recutita ) components with antibacterial effect against Bacillus subtilis soil bacteria was more sensitive than commonly used bioautographic visualization by staining with a tetrazolium salt. Some compounds had a strong inhibiting effect only via the bioluminescence measurement. Extraction of antibacterial components of chamomile flowers was most effective with 50% ethanol; slightly lower efficiency was achieved with acetone and methanol, and hexane was least effective. The results were confirmed by using luminescent Pseudomonas syringae pv. maculicola plant pathogen bacteria.

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Sunscreen products are meant to protect people from damaging UVA and UVB radiation. However, in some formulations the UV filters they contain can react and form many photodegradation products. Their potential toxicity has not yet been investigated. In this study effect-specific analysis has been used to evaluate the bioactivity of photodegradation products in sunscreens. HPTLC-bioluminescence coupling with the luminescent bacterium Vibrio fischeri was used. Problems in method development were because of the sensitivity of the bacteria and the wettability of HPTLC plates. A separation system using HPTLC LiChrospher plates and automated multiple development (AMD) with tert -butyl methyl ether- n -hexane was chosen. Detection was by UV in addition to Vibrio fischeri . First, biodetection was performed on pure standard solutions of the UV filters. UV filters with molecular weight >400 had no bioactivity; these included all newer UV filters (not in use before 1998). Five commercially available sunscreens with different UV filter combinations were then analyzed. They were irradiated on microscope slides with artificial light and natural sunlight and on the skin with natural sunlight. For extraction, a mixture of ethanol and acetone was used. The bioactivity which can be indicative of (cyto)toxic effects of the photodegradation products was higher than that of the corresponding UV filter. In comparison of HPLC-DAD and LC-MS with detection with Vibrio fischeri , a high signal in chemical-physical detection did not always correspond to high bioactivity, and vice versa. It was shown that biodetection with Vibrio fischeri was a suitable method for examination of photodegradation products in sunscreens, making this bioassay a useful addition to conventional analytical methods.

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In this study, thin-layer chromatography—direct bioautography (TLC—DB) was used for guiding the isolation and identification of antibacterial constituents of Thymus vulgaris L. ethanol extract. This TLC—bioassay method enables the separation and detection of active components directly on the surface of chromatographic plates. They can be identified by comparison with reference substances or using physicochemical methods, preferably spectroscopic ones (liquid chromatography—tandem mass spectrometry [LC—MS/MS], in the presented paper). The described method belongs to the effect-directed analyses (EDA). Seven bacterial strains were used as test organisms, both pathogenic and nonpathogenic, including methicillin-resistant Staphylococcus aureus as well as luminescent bacteria like Aliivibrio fischeri. Five fractions with the widest antimicrobial spectra were detected using TLC—DB, isolated by semi-preparative TLC and subjected to LC—MS/MS analyses. Finally, two bioactive components were tentatively identified, basing on their fragmentation pattern, as eriodictyol and 4,4′-dihydroxy-5,5′-diisopropyl-2,2′-dimethyl-3,6-bifenylodion.

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. 2002 50 63 73 Gellert, G. (2000): Sensitivity and significance of luminescent bacteria in chronic toxicity

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inhibitory effect of water samples on the light emission of Vibrio fischeri (Luminescent bacteria test). ISO 21338:2010, Water quality – Kinetic determination of the inhibitory effects of sediment, other solids and

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. (1997) Recombinant luminescent bacteria for measuring bioavailable arsenite and antimonite. Appl. Environ. Microbiol. 63 , 4456–4461. Virta M. Recombinant luminescent bacteria

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. [33] International Organization for Standardization, EN ISO 11348-1:2008, Water quality – determination of the inhibitory effect of water samples on the light emission of Vibrio fischeri (luminescent bacteria test) – part 1: method using

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Acta Biologica Hungarica
Authors: G. Paulovits, Nóra Kováts, A. Ács, Á. Ferincz, Anikó Kovács, B. Kakasi, Sz. Nagy, and Gy. Kiss

luminescent bacteria tests. Altern. Lab Anim. 35 , 101–110. Douay F. Rapid screening for soil ecotoxicity with a battery of luminescent bacteria tests Altern

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