Name: thin-layer chromatographic (tlc) separations and bioassays of plant extracts to identify antimicrobial compounds
Uploaded: 2014-03-27T22:00:00
Description: Watch this Scientific Journal Video about Thin-layer Chromatographic TLC Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds at JoVE.com

We thank the late Dr. Norm Taylor, Dept. Plant and Soil Science at the University of Kentucky, for allowing us to use samples from his red clover plots for this study. This project was funded by the United States Department of Agriculture.

1. Preparation of Plant Extract
<ol>
	<li>See Kagan and Flythe10 for extraction of phenolic compounds from Trifolium pratense cv. Kenland.&#160;</li>
	<li>To extract other compounds in other plants, check the phytochemical analysis literature for plant- or metabolite-specific extraction methods (many are described), or look for protocols such as those of Khurram et al.7,8 which &#160;isolate many compounds with a wide range of polarities.</li>
</ol>
2. Prepa...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+inhibitors+of+Erwinia+carotovora+and+E.+herbicola+on+thin-layer+chromatograms.">Detection of inhibitors of Erwinia carotovora and E. herbicola on thin-layer chromatograms.</a> J. Chromatogr. 110, 193-196 (1975).</li><li>Betina, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bioautography+in+paper+and+thin-layer+chromatography+and+its+scope+in+the+antibiotic+field.">Bioautography in paper and thin-layer chromatography and its scope in the antibiotic field.</a> J. Chromatogr. A. 78, 41-51 (1973).</li><li>Weltzien, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ein+biologischer+Test+f&#252;r+fungizide+Substanzen+auf+dem+Papierchromatogramm.">Ein biologischer Test f&#252;r fungizide Substanzen auf dem Papierchromatogramm.</a> Naturwissenschaften. 45, 288-289 (1958).</li><li>Khurram, M., Khan, A. M., Hameed, A., Abbas, N., Quayum, A., Inayat, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibacterial+activities+of+Dodonaea+viscosa+using+contact+bioautography+technique.">Antibacterial activities of Dodonaea viscosa using contact bioautography technique.</a> Molecules. 14 (3), 1332-1341 (2009).</li><li>Khurram, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+anticandidal+potential+of+Quercus+baloot+Griff.+using+contact+bioautography+technique.">Evaluation of anticandidal potential of Quercus baloot Griff. using contact bioautography technique.</a> Afr. J. Pharm. Pharmacol. 5 (12), 1538-1542 (2012).</li><li>Robinson, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Organic Constituents of Higher Plants. , (1963).</li><li>Kagan, I. A., Flythe, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Factors+affecting+the+separation+and+bioactivity+of+red+clover+(Trifolium+pratense)+extracts+assayed+against+Clostridium+sticklandii,+a+ruminal+hyper+ammonia-producing+bacterium.">Factors affecting the separation and bioactivity of red clover (Trifolium pratense) extracts assayed against Clostridium sticklandii, a ruminal hyper ammonia-producing bacterium.</a> Nat. Prod. Commun. 7 (12), 1605-1608 (2012).</li><li>Mattila, P., Kumpulainen, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+free+and+total+phenolic+acids+in+plant-derived+foods+by+HPLC+with+diode-array+detection.">Determination of free and total phenolic acids in plant-derived foods by HPLC with diode-array detection.</a> J. Agric. Food Chem. 50 (13), 3660-3667 (2002).</li><li>Hamburger, M. O., Cordell, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+direct+bioautographic+TLC+assay+for+compounds+possessing+antibacterial+activity.">A direct bioautographic TLC assay for compounds possessing antibacterial activity.</a> J. Nat. Prod. 50 (1), 19-22 (1987).</li><li>Flythe, M., Kagan, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antimicrobial+effect+of+red+clover+(Trifolium+pratense)+phenolic+extract+on+the+ruminal+hyper+ammonia-producing+bacterium,+Clostridium+sticklandii.">Antimicrobial effect of red clover (Trifolium pratense) phenolic extract on the ruminal hyper ammonia-producing bacterium, Clostridium sticklandii.</a> Curr. Microbiol. 61, 125-131 .</li><li>Rahalison, L., Hamburger, M., Hostettmann, K., Monod, M., Frenk, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+bioautographic+agar+overlay+method+for+the+detection+of+antifungal+compounds+from+higher+plants.">A bioautographic agar overlay method for the detection of antifungal compounds from higher plants.</a> Phytochem. Anal. 2 (5), 199-203 (1991).</li><li>Chomnawang, M. T., Trinapakul, C., Gritsanapan, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+antigonococcal+activity+of+Coscinium+fenestratum+stem+extract.">In vitro antigonococcal activity of Coscinium fenestratum stem extract.</a> J. Ethnopharmacol. 122, 445-449 (2009).</li><li>Stahl, E., Kaldewey, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spurenanalyse+physiologisch+aktiver,+einfacher+Indolderivate.">Spurenanalyse physiologisch aktiver, einfacher Indolderivate.</a> Hoppe-Seyler&#8217;s Z. Physiol. Chem. 323, 182-191 .</li><li>Kagan, I. A., Hammerschmidt, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arabidopsis+ecotype+variability+in+camalexin+production+and+reaction+to+infection+by+Alternaria+brassicicola.">Arabidopsis ecotype variability in camalexin production and reaction to infection by Alternaria brassicicola.</a> J. Chem. Ecol. 28 (11), 2121-2140 (2002).</li><li>Kline, R. M., Golab, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+technique+in+developing+thin-layer+bioautographs.">A simple technique in developing thin-layer bioautographs.</a> J. Chromatogr. 18, 409-411 (1965).</li><li>Wedge, D. E., Nagle, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+2D-TLC+bioautography+method+for+the+discovery+of+novel+antifungal+agents+to+control+plant+pathogens.">A new 2D-TLC bioautography method for the discovery of novel antifungal agents to control plant pathogens.</a> J. Nat. Prod. 63 (8), 1050-1054 (2000).</li><li>Beck, A. B., Knox, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+acylated+isoflavone+glycosides+from+subterranean+clover+and+red+clover.">The acylated isoflavone glycosides from subterranean clover and red clover.</a> Aust. J. Chem. 24 (7), 1509-1518 (1971).</li><li>Kahn, R. A., Bak, S., Svendsen, I., Halkier, B. A., M&#248;ller, B. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+reconstitution+of+cytochrome+P450ox+and+in+vitro+reconstitution+of+the+entire+biosynthetic+pathway+of+the+cyanogenic+glucoside+dhurrin+from+sorghum.">Isolation and reconstitution of cytochrome P450ox and in vitro reconstitution of the entire biosynthetic pathway of the cyanogenic glucoside dhurrin from sorghum.</a> Plant Physiol. 115 (4), (1997).</li><li>Peterson, C. A., Edgington, L. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+estimation+of+the+fungicide+benomyl+using+a+bioautograph+technique.">Quantitative estimation of the fungicide benomyl using a bioautograph technique.</a> J. Agr. Food Chem. 17 (4), 898-899 (1969).</li></ol>

This protocol describes a simple method for separating an extract into subsets of compounds and assaying those subsets by contact bioautography.&#160;The method is quite similar to one used by Chomnawang et al.15 to screen for plant metabolites inhibitory to gonorrhea-causing bacteria. The type of bioautography employed to screen for antimicrobial plant compounds depends on many factors, including the test microorganism, the laboratory setup, and the preferences of the person(s) performing the bioassa...

Assaying for antimicrobial compounds in plants requires separating the components of a plant extract, exposing a test microorganism to those components, and determining whether the microorganism&#8217;s growth is inhibited by any of the compounds. Separations by paper or thin-layer chromatography (PC or TLC) are convenient because many compounds can be separated on a planar surface.&#160;Separation is based on polarity, with some compounds binding tightly to the adsorbent (cellulose in the case of PC, and a variety of adsorbents in the case of TLC) and migrating less than others1. Figure 1 provides an example of the relative positions of polar and nonpolar phenolic compounds after separation on a silica TLC plate.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/51411/51411fig1highres.jpg" src="/files/ftp_upload/51411/51411fig1.jpg" /> 
Figure 1. Diagram illustrating distributions of compounds of different polarities after separation on a silica thin-layer chromatographic (TLC) plate.&#160;Phenolic compounds of red clover (Trifolium pratense L.) are used as an example.&#160;Polar compounds, such as clovamide, have a strong affinity for a polar adsorbent like silica and remain near the origin (OR), while less polar compounds, such as the three isoflavones near the solvent front (SF), partition more readily into the solvents (which are less polar than silica unless water, acids, or bases are included) and migrate farther up the plate.
After separation of an extract on a TLC plate, test microorganisms can be exposed to all compounds on the plate, thus speeding the identification of the active components of an extract2.&#160;If a fungal or bacterial culture is exposed to the chromatogram, microbial growth will occur everywhere except over areas with growth-inhibitory compounds. Zones of inhibition then can be visualized by observing the contrast between mycelial growth and the growth-free areas if fungi have been applied3&#160;or by spraying with compounds that change color when reduced or hydrolyzed by living cells4.&#160;Although the use of paper or thin-layer chromatograms for antimicrobial assays was first applied to antibiotics5 and fungicides3,6, plant extracts are now frequently screened for antimicrobial compounds with this method, often referred to as bioautography.&#160;The protocols described herein apply to bioautography of thin-layer chromatograms.&#160;TLC is widely used because it is relatively rapid and can be performed on different adsorbents (e.g. silica, starch, alumina), as well as providing good resolution and sensitivity1.
Plant extracts can be prepared for TLC in many ways.&#160;Common methods include extracting plant material in alcohol-water mixtures such as 80% ethanol7,8, possibly with the addition of acid or base9. Following an extraction in such solvents, which contain some water and are possibly acidic or basic, extracts must be concentrated so that they can be applied to TLC plates in a minimal volume.&#160;The concentration of alcohol-water extracts can be achieved by partitioning with water-immiscible organic solvents8&#160;or with a mixture of such solvents, such as ethyl acetate-ethyl ether (1:1, v/v)10,11. Different plant metabolites are extracted into different organic solvents, depending on their polarities.&#160;To ensure that plant organic acids or bases are extracted into organic solvents at this stage, the pH of an alcohol-water extract can be raised or lowered with a water-soluble acid or base to convert dissociated analytes into their nondissociated forms, which are then soluble in neutral organic solvents9. The organic phase can then be evaporated under reduced pressure or under nitrogen&#160;and adjusted to the desired volume for TLC.&#160;The pH of the extract is unlikely to be lethal to bioassay microorganisms due to the partitioning of analytes into neutral solvents, small final volume, and evaporation of the extract on the TLC plate prior to separation.
Both fungi and bacteria are employed as test microorganisms in bioautography of plant extracts2.&#160;Spores of some fungi, such as Cladosporium cucumerinum, germinate on TLC plates (apart from areas with inhibitory compounds) if sprayed onto plates in a nutrient solution and incubated in a moist environment for several days3.&#160;The dark mycelium of C. cucumerinum on noninhibitory zones provides a sharp contrast to zones free of mycelial growth.&#160;Although bacteria have been applied to thin-layer chromatography (TLC) plates in the same manner4,12, bacteria are also poured over TLC plate surfaces in agar overlays13,14.&#160;Yeast, such as Candida albicans, can be applied in agar overlays as well14.&#160;Alternatively, TLC plates can be placed face down onto agar inoculated with bacteria10,15 or yeast8, a method known as contact bioautography2.
We describe a method for contact bioautography to screen for antimicrobial phenolic compounds from red clover (Trifolium pratense cv. Kenland).&#160;The test microorganism is Clostridium sticklandii, a ruminal hyper ammonia-producing bacterium (HAB) and obligate anaerobe.&#160;Although the separations used do not resolve all components of the extract, they facilitate identification of zones of antimicrobial activity, thus narrowing the pool of possible antimicrobial compounds. The protocol utilizes standard procedures for TLC1. The protocol also describes some of the techniques required for culturing obligate anaerobes for such an assay, a usage of contact bioautography15&#160;and a visualization method with a tetrazolium salt, which stains living cells2,4.

<table border="0" cellpadding="0" cellspacing="0" width="739">
	<tbody>
		<tr>
			<td>Silica F254 TLC plates, aluminum-backed, 0.2 mm thickness, 20 &#215; 20 cm</td>
			<td>EMD Chemicals&#160;</td>
			<td>5554/7</td>
			<td>These plates are coated with silica that contains an indicator fluorescing at 254 nm.&#160; Compounds absorbing at that wavelength appear dark on a fluorescent green background.&#160; Alternative sources include Analtech, Selecto Scientific, Fluka.&#160; Adsorbents other than silica may be needed.&#160; Plastic-backed plates may be suitable, depending on the solvents to be used.&#160;&#160;</td>
		</tr>
		<tr>
			<td>Sharp, heavy-duty scissors&#160;</td>
			<td>any sewing supply company</td>
			<td>similar to Fiskars&#160; 175800-1002</td>
			<td>For cutting TLC plates.&#160; A paper cutter with a sharp blade can be used as well.&#160; Do not inhale silica dust.</td>
		</tr>
		<tr>
			<td>Drying oven at 100 &#176;C (mechanical convection)</td>
			<td>Thermo Scientific</td>
			<td>PR305225M</td>
			<td>Quincy Lab, Inc, Chicago, IL (www.quincylab.com); Cascade Technical Sciences, Hillsboro, OR (www.cascadetek.com)</td>
		</tr>
		<tr>
			<td>TLC chamber</td>
			<td>Kimble Chase&#160;</td>
			<td>416180-0000</td>
			<td>Alternative sources:&#160; Aldrich. Pyrex beakers or preserving jars can be used for small plates (i.e. 5 &#215; 10 cm).&#160; Cover with aluminum foil (jar lids may contain material extractable by solvent vapors).</td>
		</tr>
		<tr>
			<td>50-&#181;L syringe with flat needle tip</td>
			<td>Hamilton</td>
			<td>80965</td>
			<td>For loading amounts of standard or sample exceeding 5-10 &#181;L.&#160; Alternative sources are equivalent.</td>
		</tr>
		<tr>
			<td>micropipets</td>
			<td>Drummond</td>
			<td>2-000-001</td>
			<td>For loading small amounts of standards or samples.&#160; Alternative sources:&#160; VWR.&#160; Also, Pasteur pipets can be stretched to a thinner diameter with a butane torch.&#160;&#160;</td>
		</tr>
		<tr>
			<td>Filter paper (#1 grade)</td>
			<td>Whatman</td>
			<td>1001 917</td>
			<td>Serves as a chamber wick.&#160; Other grades of filter paper are OK.&#160; This size can be trimmed for the chambers holding 20 &#215; 20 cm plates.&#160;&#160;&#160;&#160;</td>
		</tr>
		<tr>
			<td>Beaker tongs</td>
			<td>Fisher Scientific</td>
			<td>15-186</td>
			<td>For putting plates in and out of a large TLC chamber.&#160; Alternate sources: VWR&#160;</td>
		</tr>
		<tr>
			<td>Flat-edge forceps&#160;</td>
			<td>Fisher Scientific</td>
			<td>10-275</td>
			<td>For putting plates in and out of a small chamber.&#160;&#160; Alternate sources: VWR&#160;</td>
		</tr>
		<tr>
			<td>Small portable UV lamp with 4-Watt or 6-Watt bulbs for short- and long-wave UV light illumination (254 and 365 nm, respectively)</td>
			<td>Ultraviolet Products&#160;</td>
			<td>95-0271-01</td>
			<td>Alternate sources: Spectronics Corporation (www.spectroline.net)</td>
		</tr>
		<tr>
			<td>Viewing cabinet for use with hand-held UV lamp</td>
			<td>Ultraviolet Products&#160;</td>
			<td>Chromato-Vue C-10E</td>
			<td>UV-active bands are more easily circled if plates can be set in here.&#160; Alternate sources: Spectronics Corporation.&#160;</td>
		</tr>
		<tr>
			<td>Photodocumentation system with overhead UV lamp and visible lamp</td>
			<td>Kodak&#160;</td>
			<td>Gel Logic 200</td>
			<td>&#160;Alternate sources: Ultraviolet Products (www.uvp.com).&#160; See protocol for homemade alternative.</td>
		</tr>
		<tr>
			<td>Anaerobic Chamber, Type A, Vinyl</td>
			<td>Coy&#160;</td>
			<td>7150000</td>
			<td>This chamber is appropriate for anaerobic bacteria, like Clostridium sticklandii, as described. &#160;However, growth conditions must be tailored to organism used in the assay.&#160; A biosafety cabinet and other precautions should be taken if pathogenic organisms are used. Alternate sources: Anaerobe Systems, BioRad, Plas Labs, others&#160;</td>
		</tr>
		<tr>
			<td>Tetrazolium red</td>
			<td>Sigma-Aldrich</td>
			<td>T8877</td>
			<td>Alternate sources: MP Biomedicals, Santa Cruz Biotechnology, Alfa Aesar</td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Ingredients for HAB media</td>
		</tr>
		<tr>
			<td>Pyridoxamine &#183; 2 HCl</td>
			<td>Sigma-Aldrich</td>
			<td>P9380</td>
			<td>For this and for all the other reagents in this table, alternative sources are equivalent.</td>
		</tr>
		<tr>
			<td>Riboflavin</td>
			<td>Sigma-Aldrich</td>
			<td>R4500</td>
			<td></td>
		</tr>
		<tr>
			<td>Thiamine HCl</td>
			<td>Sigma-Aldrich</td>
			<td>T3902</td>
			<td></td>
		</tr>
		<tr>
			<td>Nicotinamide</td>
			<td>Sigma-Aldrich</td>
			<td>N3376</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium D-Pantothenate</td>
			<td>Sigma-Aldrich</td>
			<td>C8731</td>
			<td></td>
		</tr>
		<tr>
			<td>Lipoic Acid&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>T5625</td>
			<td></td>
		</tr>
		<tr>
			<td>p-Aminobenzoic acid&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>A9878</td>
			<td></td>
		</tr>
		<tr>
			<td>Folic acid</td>
			<td>Sigma-Aldrich</td>
			<td>F8798</td>
			<td></td>
		</tr>
		<tr>
			<td>Biotin</td>
			<td>Sigma-Aldrich</td>
			<td>B4639</td>
			<td></td>
		</tr>
		<tr>
			<td>Cobalamine&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>C3607</td>
			<td></td>
		</tr>
		<tr>
			<td>Pyridoxal HCl</td>
			<td>Sigma-Aldrich</td>
			<td>P9130</td>
			<td></td>
		</tr>
		<tr>
			<td>Pyridoxine</td>
			<td>Sigma-Aldrich</td>
			<td>P5669</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Sigma-Aldrich</td>
			<td>&#160;E6758</td>
			<td></td>
		</tr>
		<tr>
			<td>Iron sulfate &#183; 7 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>&#160;F8263</td>
			<td></td>
		</tr>
		<tr>
			<td>Zinc sulfate &#183; 7 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>Z0251</td>
			<td></td>
		</tr>
		<tr>
			<td>Manganese chloride &#183; 4 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>M8054</td>
			<td></td>
		</tr>
		<tr>
			<td>Boric acid</td>
			<td>Sigma-Aldrich</td>
			<td>B6768</td>
			<td></td>
		</tr>
		<tr>
			<td>Cobalt chloride &#183; 6 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>&#160;C8661</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper chloride &#183; 2 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>459097</td>
			<td></td>
		</tr>
		<tr>
			<td>Nickel chloride &#183; 6 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>203866</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium molybdate &#183; 2 H2O</td>
			<td>Sigma-Aldrich</td>
			<td>331058</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;Trypticase (Pancreatic digest of casein)</td>
			<td>Thermo Fisher</td>
			<td>B11921</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic anhydrous</td>
			<td>Thermo Fisher</td>
			<td>P284</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium carbonate &#183; H2O&#160;</td>
			<td>Thermo Fisher</td>
			<td>S636</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Thermo Fisher</td>
			<td>50841063</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium sulfate &#183; 6 H2O</td>
			<td>Thermo Fisher</td>
			<td>7791-18-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride &#183; 2 H2O</td>
			<td>Thermo Fisher</td>
			<td>BP510</td>
			<td></td>
		</tr>
		<tr>
			<td>Cysteine HCl</td>
			<td>Thermo Fisher</td>
			<td>19464780</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate dibasic anhydrous</td>
			<td>Thermo Fisher</td>
			<td>P290</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Thermo Fisher</td>
			<td>BP358</td>
			<td></td>
		</tr>
	</tbody>
</table>

thin-layer chromatographic (tlc) separations and bioassays of plant extracts to identify antimicrobial compounds

A common screen for plant antimicrobial compounds consists of separating plant extracts by paper or thin-layer chromatography (PC or TLC), exposing the chromatograms to microbial suspensions (e.g. fungi or bacteria in broth or agar), allowing time for the microbes to grow in a humid environment, and visualizing zones with no microbial growth.&#160;The effectiveness of this screening method, known as bioautography, depends on both the quality of the chromatographic separation and the care taken with microbial culture conditions.&#160;This paper describes standard protocols for TLC and contact bioautography&#160;with a novel application to amino acid-fermenting bacteria. The extract is separated on flexible (aluminum-backed) silica TLC plates, and bands are visualized under ultraviolet (UV) light.&#160;Zones are cut out and incubated face down onto agar inoculated with the test microorganism.&#160;Inhibitory bands are visualized by staining the agar plates with tetrazolium red.&#160;The method is applied to the separation of red clover (Trifolium pratense cv. Kenland) phenolic compounds and their screening for activity against Clostridium sticklandii, a hyper ammonia-producing bacterium (HAB) that is native to the bovine rumen.&#160;The TLC methods apply to many types of plant extracts&#160;and other bacterial species (aerobic or anaerobic), as well as fungi, can be used as test organisms if culture conditions are modified to fit the growth requirements of the species.

Representative silica TLC separations of red clover (Trifolium pratense cv. Kenland) extracts, containing phenolic compounds, are shown in Figure 2. Separation of red clover extract in ethyl acetate-hexane (9:1, v/v), over 8.5 cm, resulted in five bands, one incompletely resolved from the origin (Figure 2A). However, Figure 2B demonstrates that about twice as many bands were revealed when a different sample of red clover extract (from the same cultivar, but grow...

Watch this Scientific Journal Video about Thin-layer Chromatographic TLC Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds at JoVE.com

Thin-layer Chromatographic TLC Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds

Methods are described for thin-layer chromatographic (TLC) separation of plant extracts and contact bioautography to identify antibacterial metabolites. The methods are applied to the screening of red clover phenolic compounds inhibiting hyper&#160;ammonia-producing bacteria (HAB) native to the bovine rumen.

Thin-layer Chromatographic (TLC) Separations and Bioassays of Plant Extracts to Identify Antimicrobial Compounds

A common screen for plant antimicrobial compounds consists of separating plant extracts by paper or thin-layer chromatography (PC or TLC), exposing the ...

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Chemistry

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