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The main volatile compounds from three medicinal plants belonging to Lamiaceae family were screened for their biological properties. The plants were Salvia officinalis, Thymus vulgaris, and Mentha × piperita containing as the main volatile constituents thujone, thymol, and menthol, respectively. The applied chromatographic system was silica gel developed with toluene-ethyl acetate (93:7). Thin-layer chromatography — direct bioautography (TLC-DB) against Escherichia coli and Bacillus subtilis was used for detection of antibacterial activity of the plant extracts and essential oils. The bioautographic fingerprints were compared with the fingerprints obtained after derivatization with anisaldehyde.

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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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Thin-layer chromatography—direct bioautography (TLC—DB) followed by liquid chromatography—tandem mass spectrometry (LC—MS/MS) was used for screening and tentative identification of the antibacterial constituents of Salvia officinalis L. ethanol extract. Seven bacterial strains were used as test organisms, both pathogenic and nonpathogenic, that is, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Staphylococcus epidermidis, Micrococcus luteus, Bacillus subtilis, luminescence gene-tagged Pseudomonas syringae pv. maculicola, and naturally luminescent marine bacterium Aliivibrio fischeri. Eight fractions with the widest antimicrobial spectrum were detected using TLC—DB, isolated by semi-preparative TLC, and subjected to LC—MS/MS analyses. Finally, five bioactive components were tentatively identified, based on their fragmentation pattern, such as salvigenin, cirsimaritin, rosmanol, carnosic acid, and 12-O-methyl carnosic acid.

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Commercially available hop pellets of different origins were extracted by use of ethanol and water, chromatographed on silica layers by use of nonaqueous eluents, chemically derivatized and observed in ultraviolet (UV) light for the localization of component bands. The plates were developed in optimized systems, and direct bioautographic method by use of Bacillus subtilis and Escherichia coli strains was applied for the examination of the antimicrobial activities of hop components. The method enables for the identification of bactericidal/bacteriostatic components in the extracts of different polarities and shows differences in the composition of extracts from various varieties from an antimicrobial point of view.

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Summary

Schizonepeta annua (Pall.) Schischk. is an endemic annual plant from the Lamiaceae family and it has been employed to cure tracheitis in traditional herbal medicine. Its essential oil exhibited a strong antimicrobial and antioxidative effect. Next, high-performance thin-layer chromatography-bioautography was applied for investigation of the bioactive compounds of S. annua, and gas chromatography-quadrupole time-of-flight mass spectrometry was used to perform subsequent targeted identification of compounds. Three active components were characterized, and two of them were tentatively identified as thymol and carvacrol. S. annua has the potential to be a good alternative for synthetic disinfectants and antioxidants.

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Fluoroquinolones are a relatively new group of synthetic antibiotics (chemotherapeutics) widely used both in human and animal treatment. Because veterinary enrofloxacin and its main metabolite ciprofloxacin, a widely used human antibiotic, can be present as residues in milk, there is a need for methods for their separation and determination. Matrix solid-phase dispersion (MSPD) on a siliceous sorbent was used for isolation and concentration of enrofloxacin and ciprofloxacin residues from cows’ milk. This preseparation method was combined with high-performance liquid chromatography and with thin-layer chromatography-direct bioautography. Mean recoveries were calculated for different levels of the antibiotics in milk. The results revealed that thin-layer chromatography-direct bioautography can be used for the screening of enrofloxacin and ciprofloxacin at the maximum residue level stipulated for milk by the European Union.

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The antibacterial effect of the components of clary sage (Salvia sclarea L.) and spearmint (Mentha spicata L. var. crispa (Bentham) Danert) was investigated by means of high-performance thin-layer chromatography-direct bioautography against the Gram-positive soil bacterium Bacillus subtilis (Bs) and Gram-negative bacteria such as a pepper pathogen Xanthomonas euvesicatoria (Xe), a luminescence gene-tagged Arabidopsis pathogen Pseudomonas syringae pv. maculicola (Psm) and a luminescent marine Aliivibrio fischeri (Af). Sclareol, linalool, and linalyl acetate were identified as active components of clary sage and carvone as the antibacterial substance in spearmint. Sclareol inhibited all tested bacteria, linalool and carvone showed antibacterial effect against all Gram-negative strains tested, while linalyl acetate only against Xe and Af. Some minor components of the clary sage essential oil also gave a zone of inhibition when tested on Gram-negative bacterium strains.

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In this study, the antibacterial profiling of the ethanolic leaf extract of greater burdock (Arctium lappa L.) is demonstrated, applying thin-layer chromatography (TLC) coupled bioassays against the Gram-positive soil bacterium Bacillus subtilis and the Gram-negative pepper pathogen Pseudomonas syringae pv. maculicola. The main active component was isolated by eluting from the adsorbent bed and subjected to a targeted characterization by high-performance liquid chromatography–diode array detection–electrospray ionisation–mass spectrometry. The identification of the germacranolide sesquiterpene lactone onopordopicrin was based on its retardation factor, bioactivity in TLC-based methods, and retention tim as well as ultraviolet (UV) and mass spectra, compared to those of the reference substance isolated earlier in our laboratory from Onopordum acanthium leaf.

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