The authors gratefully acknowledge funding support from the Center for Diabetes, Obesity and Metabolism and the Clinical and Translational Science Center, the Wake Forest School of Medicine, the Department of Defense funding (Grant number: W81XWH-18-1-0118), the Kermit Glenn Phillips II Chair in Cardiovascular Medicine; the National Institutes of Health funded Claude D. Pepper Older Americans Center (funded by P30AG12232); R01AG18915; R01DK114224 and the Clinical and Translational Science Center (Clinical Research Unit, funded by UL1TR001420), is also thankfully acknowledged. We also thank the volunteers for providing fecal samples, and our other lab members for their technical helps during this experiment.

CAUTION: Consult the appropriate Material Safety Data Sheets and follow the instructions and guidelines for appropriate Biosafety Level 2 (BSL-2) training. Follow all the culturing steps as per the standard biosafety rules and use a BSL-2 cabinet using aseptic conditions. Furthermore, fecal samples from different models and human subjects may have potential risk of spreading microbial borne diseases. Immediately seek medical aid in the occurrence of any injury and infection. In addition, the use of human and animal stool samples should be approved through institutional ethical committees and must compliant with protocols to use samples and subject information.
1. Preparation of Culture Media
<ol>
	<li>Preparation of the culture media, prepare nine types of stock solutions
	<ol>
		<li>Solution A (1,000 mL): Dissolve 5.4 g of sodium chloride (NaCl), 2.7 g of potassium dihydrogen phosphate (KH2PO4), 0.16 g of calcium chloride dihydrate (CaCl2&#183;2H2O), 0.12 g of magnesium chloride hexahydrate (MgCl2&#183;6H2O), 0.06 g of manganese chloride tetrahydrate (MnCl2&#183;4H2O), 0.06 g of cobaltous chloride hexahydrate (CoCl2&#183;6H2O), and 5.4 g of ammonium sulfate (NH4)2SO4, in deionized water to make total volume to 1,000 mL.</li>
		<li>Solution B (1,000 mL): Dissolve 2.7 g Potassium Hydrogen Phosphate (K2HPO4) in deionized water to make total volume to 1000 mL.</li>
		<li>Trace mineral solution (1,000 mL): Dissolve 500 mg of disodium ethylenediamine-tetraacetate dihydrate (Na2EDTA), 200 mg of ferrous sulfate heptahydrate (FeSO4&#183;7H2O), 10 mg of zinc sulfate heptahydrate (ZnSO4&#183;7H2O), 3 mg of manganese(II) chloride tetrahydrate (MnCl2&#183;4H2O), 30 mg of phosphoric acid (H3PO4), 20 mg of CoCl2&#183;6H2O, 1 mg of cupric chloride dihydrate (CuCl2&#183;2H2O), 2 mg of nickel(II) chloride hexahydrate (NiCl2&#183;6H2O) and 3 mg of sodium molybdate dihydrate (Na2MoO4&#183;2H2O) in deionized water to make total volume to 1,000 mL. 
		NOTE: This solution is light sensitive, therefore ensure to be stored in dark/black or aluminum wrapped tubes/bottles.</li>
		<li>Water soluble vitamin solution (1,000 mL): Dissolve 100 mg of thiamine hydrochloride (Thiamin-HCl), 100 mg of D-pantothenic acid, 100 mg of Niacin, 100 mg of pyridoxine, 5 mg of P-aminobenzoic acid and 0.25 mg of Vitamin B12 in deionized water to make total volume to 1,000 mL.</li>
		<li>Folate: biotin solution (1,000 mL): Dissolve 10 mg of folic acid, 2 mg of D-biotin and 100 mg of ammonium bicarbonate (NH4HCO3) in deionized water to make total volume to 1,000 mL.</li>
		<li>Riboflavin solution (1,000 mL): Dissolve 10 mg of Riboflavin in 5 mM HEPES (1.19 g/L) solution to make total volume to 1,000 mL.</li>
		<li>Hemin solution (10 mL): Dissolve 5,000 mg of Hemin in 10 mM sodium hydroxide (NaOH) (0.4 g/L) solution to make total volume to 10 mL.</li>
		<li>Short-chain fatty acid mix (10 mL): Combine 2.5 mL of N-valerate, 2.5 mL of isovalerate, 2.5 mL of isobutyrate and 2.5 mL: DL-&#945;-methylbutyrate. 
		NOTE: This solution is recommended to use in fume hood to avoid smell and fumes.</li>
		<li>Resazurin (1,000 mL): Dissolve 1 g of resazurin in deionized water and make total volume to 1,000 mL.</li>
	</ol>
	</li>
	<li>Medium used for in vitro anaerobic fermentation
	<ol>
		<li>To prepare this media, mix 330 mL of Solution A, 330 mL of Solution B, 10 mL of Trace mineral solution, 20 mL of Water soluble vitamin solution, 5 mL of Folate:biotin solution, 5 mL of Riboflavin solution; 2.5 mL of Hemin solution, 0.4 mL of Short chain fatty acid mix, 1 mL of Resazurin, 0.5 g of yeast extract, 4 g of sodium carbonate (Na2CO3), 0.5 g of Cysteine HCl-H2O, and 0.5 g of Trypticase, and add 296.1 mL of distilled water.</li>
		<li>Check the pH and ensure it is around 7.0, if not, adjust the pH with 1 N HCl or 1 N NaOH. Sterilize by vacuum filtering the media using a bottle filter under the aseptic workstation.</li>
		<li>Alternatively, mix all the components (except vitamin and hemin solutions) and autoclave at 121 &#176;C for 20 min and let it cool down to room temperature. Simultaneously, filter-sterilize vitamin and hemin solutions using 0.22 &#181;m membrane filters and add these to the autoclaved and cooled media before dispensing.</li>
	</ol>
	</li>
</ol>
2. Preparation of Anaerobic Chamber and Required Material
<ol>
	<li>Keep all the materials, solutions and tools needed for the fermentation experiment inside the anaerobic chamber at least 48 h before the start of the experiment, to ensure that any residual oxygen associated with tools and soluble oxygen in buffers/solutions is removed and all the materials are acclimatized to the set anaerobic conditions. 
	NOTE: Materials needed inside the anaerobic chamber (48 h earlier of experiment to start): (i) fermentation media; (ii) anaerobic solution (prepared according to section 4.1), (iii) vortexer, (iv) weighing balance, (v) muslin cheese cloths, (vi) scissors, (vii) funnel, (viii) 1.5, 2.0, 15, 50 mL tubes, (ix) pipettor (2, 20, 200 and 1,000 &#181;L) and compatible pipet tips, (x) gun pipet and pipets (5 and 10 mL), (xi) paper tissues, (xii) markers, (xiii) tube stands for different tubes, (xiv) waste box, (xv) O2 indicator and (xvi) 70% ethanol spray bottle (disinfectant).</li>
</ol>
3. Preparation of Tubes and Fibers
<ol>
	<li>Weight 300 mg of inulin and transfer to a 50 mL tube followed by the aseptically addition of 26 mL of fermentation media already prepared and stored in the anaerobic chamber. Prepare one blank tube for each fecal sample type and experimental tube(s) (according to the number of compounds being tested), in triplicate.</li>
	<li>Leave these tubes inside the anaerobic chamber for around 24 h to allow hydration of samples before starting the fermentation experiment. Ensure the tube temperature is 37 &#176;C at the time of inoculation, therefore bring the tubes in the incubator enclosed within the anaerobic chamber.</li>
</ol>
4. Preparation of Inoculum
<ol>
	<li>Anaerobic dilution solution (at least 48 h before fermentation experiment): Dissolve 5 g of NaCl, 2 g of glucose and 0.3 g of Cysteine-HCl in deionized water and make total volume to 1,000 mL. Autoclave and store it inside the anaerobic chamber at least 48 h before use.</li>
	<li>Fecal inoculum preparation (at the day of fermentation experiment): Weigh 5 g of fresh fecal sample in a 50 mL conical tube, add anaerobic dilution solution for a final volume of 50 mL (1:10 w/v) and vortex for 15 min or until completely homogenized. Filter the homogenized mixture through 4 layers of sterile cheesecloth (autoclaved) and use it immediately for inoculation in the tubes containing media. 
	NOTE: The fecal samples from a group of subjects can be pooled if the experimental objective is to compare the effect of a given compound/ingredient on overall healthy versus diseased fecal microbiota in general.</li>
</ol>
5. Fermentation and Sampling
<ol>
	<li>Prepare tubes according to the section 4.2 and inoculate blank/control and experimental tubes with 4 mL of diluted and filtered fecal inoculum. Incubate the inoculated tubes at 37 &#176;C inside the anaerobic chamber. Shake the tubes once every hour by inverting gently to re-suspend the fibers and inoculum.</li>
	<li>Collect samples as frequently as needed, for example, hourly to 0, 3, 6, 9 and 24 h during fermentation by taking a 2 mL aliquot sample out into a 2 mL tube from respective fermenting tubes.</li>
	<li>Measure the pH of the aliquots using a laboratory pH meter (by directly inserting the pH electrode in the sample); centrifuge the remaining sample at 14,000 x g for 10 min at 4 &#176;C. Immediately freeze the supernatant and pellet in liquid nitrogen, and after snap freezing, store the supernatant for SCFAs analysis and pellet for microbiome analysis at -80 &#176;C.</li>
</ol>
6. Short Chain Fatty Acids (SCFAs) and Lactate Quantification
NOTE: The SCFAs and lactate in the supernatant of microbiome culture can be measured exactly according to the methods detailed elsewhere13,14,15,16.
<ol>
	<li>Briefly, thaw the snap frozen supernatants obtained in section 5 from control and treatment samples on ice and carry out all further processing steps on ice. Filter the supernatant through a 0.45&#8201;&#181;m membrane filter and use the cell-free samples to measure the concentrations of SCFAs and lactate using HPLC system with DAD detector at 210&#8201;nm, equipped with an HPX-87H column. Use inject volume of 10 &#956;L for each sample and use H2SO4 (0.005&#8201;N) to elute the column at a flow rate of 0.6&#8201;mL/min at 35&#8201;&#176;C.</li>
</ol>
7. Fecal Microbiome Analysis
NOTE: Perform microbiome analysis following the methods and pipeline detailed elsewhere7,13,14,17.
<ol>
	<li>Briefly, extract genomic DNA from approximately 200&#8201;mg of fecal slurry pellets by using a fecal DNA extraction kit13.</li>
	<li>Amplify the hypervariable region of the bacterial 16S rRNA gene by using the barcoded primers as per the method described elsewhere13, using the primer sequences as described in the Earth Microbiome Project protocol18.</li>
	<li>Purify the resulting amplicons with magnetic purification beads and quantify by Picogreen or an equivalent method. Pool the purified PCR products in equal molar concentration and sequence on a sequencer13.</li>
	<li>Process the resulting sequences for de-multiplexing, quality filtering and clustering, taxonomic assignment and rarefaction, and downstream analyses by using the Quantitative Insights into Microbial Ecology (QIIME) software as per the methods described by Caporaso et al.19.</li>
</ol>

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The authors have nothing to disclose.

The in vitro fecal slurry fermentation model presented here is a simple single-batch model to approximate the effects of different substrates and microbial strains (e.g., prebiotics and probiotics) on the composition of human fecal microbiota as well as its metabolic activities in terms of fecal pH and SCFAs levels. The results presented herein demonstrate that the inoculation of inulin decreases the fecal pH and significantly increases the levels of SCFAs and lactate in inulin-treated fecal specimen as compared to non-t...

The human microbiota is a complex community consisting of bacteria, archaea, viruses and eukaryotic microbes1, that inhabit the human body internally and externally. Recent evidences have established the fundamental role of the gut microbiota and the gut microbiome (the entire collection of microbes and their genes found in the human gastrointestinal tract) in various human diseases including obesity, diabetes, cardiovascular diseases, and cancer1,2,3. Additionally, the microorganisms living in our gut produce a wide spectrum of metabolites which significantly affect our health and can also contribute to the pathophysiology of several diseases as well as a variety of metabolic functions4,5. Abnormal changes (perturbations) in the composition and function of this gut microbial population are generally termed as &#34;gut dysbiosis&#34;. Dysbiosis is usually associated with an unhealthy state of the host and hence can be differentiated from the normal (homeostatic) microbial community associated with a healthy control state of the host. Specific patterns of gut microbiome dysbiosis are often found in various different diseases1,2,3,6,7.
The fermentation of undigested food, particularly the fermentable carbohydrates/fibers, by the gut microbiota not only yields energy but also produces divergent metabolites including short-chain fatty acids (SCFAs), lactate, formate, carbon dioxide, methane, hydrogen, and ethanol6. In addition, the gut microbiota also produces a number of other bioactive substances such as folate, biotin, trimethylamine-N-oxide, serotonin, tryptophan, gamma-aminobutyric acid, dopamine, norepinephrine, acetylcholine, histamine, deoxycholic acid, and 4-ethylphenyl sulfate. This occurs primarily through the utilization of intrinsic metabolic fluxes within the host-microbe niche, which contributes in several body processes, metabolic functions and epigenetic changes1,8,9,10. However, the effects of various interventions on such microbial products remain unkown or unclear due to the lack of easy, efficient and reproducible protocols. The human gut microbiota composition is an extremely complex and diverse ecosystem, and hence, many questions about its role in human health and disease pathology still remain unanswered. The effects of many common gut microbiome modulators (e.g., probiotics, prebiotics, antibiotics, fecal transplantation and infections) on the composition and metabolic functions of the intestinal microbiota remain largely elusive. In addition, the examination and validation of these effects in vivo is difficult, particularly because most of the nutrients and metabolites produced by the gut microbiota are absorbed or disposed of simultaneously and rapidly in the gut; therefore, measuring the production, amount and processing of these metabolites (e.g., SCFAs) in vivo still remains a practical challenge. Indeed, physiological models such as animals and human subjects are critical for determining the role of gut microbiome and its modulation on host health, but these may not be suitable for large-scale screening of different types of microbiome modulators due to ethical, monetary or time constraints. To this end, in vitro and/or ex vivo models, such as culturing of gut microbiota in vitro and then intervening with different microbiota modulators, can offer time- and money-saving opportunities and hence can allow for preliminary or large-scale screening of various components (such as probiotics, prebiotics, and other interventional compounds) to examine/predict their effects on the fecal microbiota diversity, composition and metabolic profiles. Studies using such in vitro and ex vivo systems of the gut microbiome may facilitate further understanding of the host-microbiome interactions that contribute to host health and disease, and could also lead to finding novel therapies that target the microbiome to ameliorate host health and prevent and treat various diseases1.
Although the in vitro gut microbiota culture systems cannot truly replicate the actual intestinal conditions, several laboratories have endeavored to develop such models, some of which have been found practicable to some extent and have been successfully used for different purposes. One of the recent gut models is the Simulator of the Human Intestinal Microbial Ecosystem, which mimics the entire human gastrointestinal tract, including the stomach, small intestine, and different regions of the colon. However, such technically complex models may not be accessible to other research facilities worldwide. Therefore, there is still a critical need for the development of new alternative models that are relatively simple, affordable and practical for laboratories studying the microbiome modulators and their effects on gut microbiota and host health. Hence, the use of an in vitro (or ex vivo) fecal microbiota culture system would be useful for studying the effects of such interventions11,12. Specifically, the effect of different prebiotics on the microbiota fermentation capacity in terms of periodic changes in the gut microbiota diversity and composition, the fecal pH, and the levels of microbial metabolites including SCFAs and lactate can be studied13. Herein, using inulin (one of the most widely studied prebiotic components) as an example of the microbiome modulator, a step-by-step protocol of this simple ex vivo microbiota batch-culture system is described to demonstrate its use to estimate the changes in the fecal microbiota and microbial metabolites following intervention with the microbiome modulators.

<table>
	<tbody>
		<tr>
			<td>Ammonium Bicarbonate (NH4HCO3)</td>
			<td>Sigma-Aldrich</td>
			<td>217255</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium Sulfate (NH4)2SO4 </td>
			<td>TGI</td>
			<td>C2388</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>Calcium Chloride Dihydrate (CaCl2&#8226;2H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>C3306</td>
			<td>Irritating</td>
		</tr>
		<tr>
			<td>Cobaltous Chloride Hexahydrate (CoCl2&#8226;6H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>255599</td>
			<td></td>
		</tr>
		<tr>
			<td>Cupric Chloride Dihydrate (CuCl2&#8226;2H2O)</td>
			<td>Acros organics</td>
			<td>2063450000</td>
			<td>Toxic, Irritating</td>
		</tr>
		<tr>
			<td>Cysteine-HCl</td>
			<td>Sigma-Aldrich</td>
			<td>C121800</td>
			<td></td>
		</tr>
		<tr>
			<td>D-biotin</td>
			<td>Sigma-Aldrich</td>
			<td>B4501</td>
			<td></td>
		</tr>
		<tr>
			<td>D-Pantothenic acid</td>
			<td>Alfa Aesar</td>
			<td>A16609</td>
			<td></td>
		</tr>
		<tr>
			<td>Disodium Ethylenediaminetetraacetate Dihydrate (Na2EDTA)</td>
			<td>Biorad</td>
			<td>1610729</td>
			<td></td>
		</tr>
		<tr>
			<td>DL-&#945;-methylbutyrate</td>
			<td>Sigma-Aldrich</td>
			<td>W271918</td>
			<td></td>
		</tr>
		<tr>
			<td>Ferrous Sulfate Heptahydrate (FeSO4&#8226;7H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>F8263</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>Folic acid</td>
			<td>Alfa Aesar</td>
			<td>J62937</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G8270</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemin</td>
			<td>Sigma-Aldrich</td>
			<td>H9039</td>
			<td></td>
		</tr>
		<tr>
			<td>Hepes</td>
			<td>Alfa Aesar</td>
			<td>A14777</td>
			<td></td>
		</tr>
		<tr>
			<td>Isobutyrate</td>
			<td>Alfa Aesar</td>
			<td>L04038</td>
			<td></td>
		</tr>
		<tr>
			<td>Isovalerate</td>
			<td>Alfa Aesar</td>
			<td>A18642</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Chloride Hexahydrate (MgCl2&#8226;6H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>M8266</td>
			<td></td>
		</tr>
		<tr>
			<td>Manganese Chloride Tetrahydrate (MnCl2&#8226;4H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>221279</td>
			<td></td>
		</tr>
		<tr>
			<td>Niacin (Nicotinic acid)</td>
			<td>Sigma-Aldrich</td>
			<td>N4126</td>
			<td></td>
		</tr>
		<tr>
			<td>Nickel(Ii) Chloride Hexahydrate (NiCl2&#8226;6H2O)</td>
			<td>Alfa Aesar</td>
			<td>A14366</td>
			<td>Toxic</td>
		</tr>
		<tr>
			<td>N-valerate</td>
			<td>Sigma-Aldrich</td>
			<td>240370</td>
			<td></td>
		</tr>
		<tr>
			<td>P-aminobenzoic acid</td>
			<td>MP China</td>
			<td>102569</td>
			<td>Toxic, Irritating</td>
		</tr>
		<tr>
			<td>Phosphoric Acid (H3PO4)</td>
			<td>Sigma-Aldrich</td>
			<td>P5811</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Dihydrogen Phosphate (KH2PO4)</td>
			<td>Sigma-Aldrich</td>
			<td>P5504</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Hydrogen Phosphate (K2HPO4)</td>
			<td>Sigma-Aldrich</td>
			<td>1551128</td>
			<td></td>
		</tr>
		<tr>
			<td>Pyridoxine</td>
			<td>Alfa Aesar</td>
			<td>A12041</td>
			<td></td>
		</tr>
		<tr>
			<td>Resazurin</td>
			<td>Sigma-Aldrich</td>
			<td>R7017</td>
			<td></td>
		</tr>
		<tr>
			<td>Riboflavin</td>
			<td>Alfa Aesar</td>
			<td>A11764</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium carbonate (Na2CO3)</td>
			<td>Sigma-Aldrich</td>
			<td>1613757</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Fisher BioReagents</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide (NaOH)</td>
			<td>Fisher Chemicals</td>
			<td>S320</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Molybdate Dihydrate (Na2MoO4&#8226;2H2O)</td>
			<td>Acros organics</td>
			<td>206375000</td>
			<td></td>
		</tr>
		<tr>
			<td>Thiamine Hydrochloride (Thiamin-HCl)</td>
			<td>Acros organics</td>
			<td>148991000</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypticase</td>
			<td>BD Biosciences</td>
			<td>211921</td>
			<td></td>
		</tr>
		<tr>
			<td>Vitamin B12</td>
			<td>Sigma-Aldrich</td>
			<td>V2876</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>Sigma-Aldrich</td>
			<td>70161</td>
			<td></td>
		</tr>
		<tr>
			<td>Zinc Sulfate Heptahydrate (ZnSO4&#8226;7H2O)</td>
			<td>Sigma-Aldrich</td>
			<td>Z0251</td>
			<td></td>
		</tr>
		<tr>
			<td>0.22 &#181;m membrane filter</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>AMPure magnetic purification beads</td>
			<td>Agencourt</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Anaerobic chamber with incubatore</td>
			<td>Forma anaerobic system, Thermo Scientific, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Bottle filter</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cheesecloth</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Illumina MiSeq sequencer</td>
			<td>Miseq reagent kit v3</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pH meter</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Qiagen PowerFecal kit</td>
			<td>Qiagen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Quantitative Insights into Microbial Ecology (QIIME) software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Qubit-3 fluorimeter</td>
			<td>InVitrogen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex</td>
			<td>Thermoscientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Waters-2695 Alliance HPLC system</td>
			<td>Waters Corporation</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

an in vitro batch-culture model to estimate the effects of interventional regimens on human fecal microbiota

The emerging role of the gut microbiome in several human diseases demands a breakthrough of new tools, techniques and technologies. Such improvements are needed to decipher the utilization of microbiome modulators for human health benefits. However, the large-scale screening and optimization of modulators to validate microbiome modulation and predict related health benefits may be practically difficult due to the need for large number of animals and/or human subjects. To this end, in vitro or ex vivo models can facilitate preliminary screening of microbiome modulators. Herein, it is optimized and demonstrated an ex vivo fecal microbiota culture system that can be used for examining the effects of various interventions of gut microbiome modulators including probiotics, prebiotics and other food ingredients, aside from nutraceuticals and drugs, on the diversity and composition of the human gut microbiota. Inulin, one of the most widely studied prebiotic compounds and microbiome modulators, is used as an example here to examine its effect on the healthy fecal microbiota composition and its metabolic activities, such as fecal pH and the fecal levels of organic acids including lactate and short-chain fatty acids (SCFAs). The protocol may be useful for studies aimed at estimating the effects of different interventions of modulators on fecal microbiota profiles and at predicting their health impacts.

The protocol is used to demonstrate the effect of a specific prebiotic (i.e., inulin on the microbiota composition and metabolic activities in terms of changes in the fecal pH and the concentration of lactate and SCFAs in the feces of healthy human subjects over different time-points following treatment with inulin). The fecal pH, the fecal levels of lactate and SCFAs (Figure 1), and the microbiota composition (Figure 2 and <stro...

Watch this Scientific Journal Video about An In Vitro Batch-culture Model to Estimate the Effects of Interventional Regimens on Human Fecal Microbiota at JoVE.com

An In Vitro Batch-culture Model to Estimate the Effects of Interventional Regimens on Human Fecal Microbiota

This protocol describes an in vitro batch-culture fermentation system of human fecal microbiota, using inulin (a well-known prebiotic and one of the most widely studied microbiota modulators) to demonstrate the use of this system in estimating effects of specific interventions on fecal microbiota composition and metabolic activities.

The emerging role of the gut microbiome in several human diseases demands a breakthrough of new tools, techniques and technologies. Such improvements are ...

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Research

JoVE Journal

Immunology and Infection

9.4K Views.  Wake Forest School of Medicine. This protocol describes an in vitro batch-culture fermentation system of human fecal microbiota, using inulin (a well-known prebiotic and one of the most widely studied microbiota modulators) to demonstrate the use of this system in estimating effects of specific interventions on fecal microbiota composition and metabolic activities.

Video: An In Vitro Batch-culture Model to Estimate the Effects of Interventional Regimens on Human Fecal Microbiota

Human In Vitro Suppression as Screening Tool for the Recognition of an Early State of Immune Imbalance

Regulatory T cells (Tregs) are critical mediators of immune tolerance to self-antigens. In addition, they are crucial regulators of the immune response following an infection. Despite efforts to identify unique surface marker on Tregs, the only unique feature is their ability to suppress the proliferation and function of effector T cells. While it is clear that only in vitro assays can be used in assessing human Treg function, this becomes problematic when assessing the results from cross-sectional studies where healthy cells and cells isolated from subjects with autoimmune diseases (like Type 1 Diabetes-T1D) need to be compared. There is a great variability among laboratories in the number and type of responder T cells, nature and strength of stimulation, Treg:responder ratios and the number and type of antigen-presenting cells (APC) used in human in vitro suppression assays. This variability makes comparison between studies measuring Treg function difficult. The Treg field needs a standardized suppression assay that will work well with both healthy subjects and those with autoimmune diseases. We have developed an in vitro suppression assay that shows very little intra-assay variability in the stimulation of T cells isolated from healthy volunteers compared to subjects with underlying autoimmune destruction of pancreatic &beta;-cells. The main goal of this piece is to describe an in vitro human suppression assay that allows comparison between different subject groups. Additionally, this assay has the potential to delineate a small loss in nTreg function and anticipate further loss in the future, thus identifying subjects who could benefit from preventive immunomodulatory therapy1. Below, we provide thorough description of the steps involved in this procedure. We hope to contribute to the standardization of the in vitro suppression assay used to measure Treg function. In addition, we offer this assay as a tool to recognize an early state of immune imbalance and a potential functional biomarker for T1D.

Human In Vitro Suppression as Screening Tool for the Recognition of an Early State of Immune Imbalance

Tregs are potent suppressors of the immune system. There is a lack of unique surface markers to define them, hence, definitions of Tregs are primarily functional. Here we describe an optimized in vitro assay capable of identifying immune imbalance in subjects at risk to develop T1D.

Regulatory T cells (Tregs) are critical mediators of immune tolerance to self-antigens. In addition, they are crucial regulators of the immune response ...

An In vitro Model to Study Heterogeneity of Human Macrophage Differentiation and Polarization

Monocyte-derived macrophages represent an important cell type of the innate immune system. Mouse models studying macrophage biology suffer from the phenotypic and functional differences between murine and human monocyte-derived macrophages. Therefore, we here describe an in vitro model to generate and study primary human macrophages. Briefly, after density gradient centrifugation of peripheral blood drawn from a forearm vein, monocytes are isolated from peripheral blood mononuclear cells using negative magnetic bead isolation. These monocytes are then cultured for six days under specific conditions to induce different types of macrophage differentiation or polarization. The model is easy to use and circumvents the problems caused by species-specific differences between mouse and man. Furthermore, it is closer to the in vivo conditions than the use of immortalized cell lines. In conclusion, the model described here is suitable to study macrophage biology, identify disease mechanisms and novel therapeutic targets. Even though not fully replacing experiments with animals or human tissues obtained post mortem, the model described here allows identification and validation of disease mechanisms and therapeutic targets that may be highly relevant to various human diseases.

An In vitro Model to Study Heterogeneity of Human Macrophage Differentiation and Polarization

Monocyte-derived macrophages are important cells of the innate immune system. Here, we describe an easy to use in vitro model to generate these cells. Using gradient centrifugation, negative bead isolation and specific cell culture conditions, monocyte-derived macrophages can be generated for phenotypic and functional studies.

Monocyte-derived macrophages represent an important cell type of the innate immune system. Mouse models studying macrophage biology suffer from the ...

An In vitro Model to Study Immune Responses of Human Peripheral Blood Mononuclear Cells to Human Respiratory Syncytial Virus Infection

Human respiratory syncytial virus (HRSV) infections present a broad spectrum of disease severity, ranging from mild infections to life-threatening bronchiolitis. An important part of the pathogenesis of severe disease is an enhanced immune response leading to immunopathology.	Here, we describe a protocol used to investigate the immune response of human immune cells to an HRSV infection. First, we describe methods used for culturing, purification and quantification of HRSV. Subsequently, we describe a human in vitro model in which peripheral blood mononuclear cells (PBMCs) are stimulated with live HRSV. This model system can be used to study multiple parameters that may contribute to disease severity, including the innate and adaptive immune response. These responses can be measured at the transcriptional and translational level. Moreover, viral infection of cells can easily be measured using flow cytometry. Taken together, stimulation of PBMC with live HRSV provides a fast and reproducible model system to examine mechanisms involved in HRSV-induced disease.

An In vitro Model to Study Immune Responses of Human Peripheral Blood Mononuclear Cells to Human Respiratory Syncytial Virus Infection

Human respiratory syncytial virus (HRSV) can cause severe bronchiolitis in young infants. Part of the pathogenesis of severe HRSV disease is caused by the host immune response. Stimulation of primary human immune cells with HRSV provides a fast and reproducible model system to study activation of inflammatory pathways and infection.

Human respiratory syncytial  virus (HRSV) infections present a broad spectrum of disease severity, ranging  from mild infections to life-threatening ...

Investigating the Effects of Probiotics on Pneumococcal Colonization Using an In Vitro Adherence Assay

Adherence of Streptococcus pneumoniae (the pneumococcus) to the epithelial lining of the nasopharynx can result in colonization and is considered a prerequisite for pneumococcal infections such as pneumonia and otitis media. In vitro adherence assays can be used to study the attachment of pneumococci to epithelial cell monolayers and to investigate potential interventions, such as the use of probiotics, to inhibit pneumococcal&#160;colonization.&#160;The protocol described here is used to investigate the effects of the probiotic Streptococcus salivarius on the adherence of pneumococci to the human epithelial cell line CCL-23 (sometimes referred to as HEp-2 cells). The assay involves three main steps: 1) preparation of epithelial and bacterial cells, 2) addition of bacteria to epithelial cell monolayers, and 3) detection of adherent pneumococci by viable counts (serial dilution and plating) or quantitative real-time PCR (qPCR). This technique is relatively straightforward and does not require specialized equipment other than a tissue culture setup. The assay can be used to test other probiotic species and/or potential inhibitors of pneumococcal colonization and can be easily modified to address other scientific questions regarding pneumococcal adherence and invasion.

Investigating the Effects of Probiotics on Pneumococcal Colonization Using an In Vitro Adherence Assay

In vitro adherence assays can be used to study the attachment of Streptococcus pneumoniae to epithelial cell monolayers and to investigate potential interventions such as the use of probiotics for inhibiting pneumococcal colonization.

Adherence of Streptococcus pneumoniae (the pneumococcus) to the epithelial lining of the nasopharynx can result in colonization and is considered a ...

An In Vitro Model for Measuring Immune Responses to Malaria in the Context of HIV Co-infection

Malaria and HIV co-infection is a growing health priority. However, most research on malaria or HIV currently focuses on each infection individually. Although understanding the disease dynamics for each of these pathogens independently is vital, it is also important that the interactions between these pathogens are investigated and understood. 
We have developed a versatile in vitro model of HIV-malaria co-infection to study host immune responses to malaria in the context of HIV infection. Our model allows the study of secreted factors in cellular supernatants, cell surface and intracellular protein markers, as well as RNA expression levels. The experimental design and methods used limit variability and promote data reliability and reproducibility. 
All pathogens used in this model are natural human pathogens (Plasmodium falciparum and HIV-1), and all infected cells are naturally infected and used fresh. We use human erythrocytes parasitized with P. falciparum and maintained in continuous in vitro culture. We obtain freshly isolated peripheral blood mononuclear cells from chronically HIV-infected volunteers. Every condition used has an appropriate control (P. falciparum parasitized vs. normal erythrocytes), and every HIV-infected donor has an HIV uninfected control, from which cells are harvested on the same day. This model provides a realistic environment to study the interactions between malaria parasites and human immune cells in the context of HIV infection.

An In Vitro Model for Measuring Immune Responses to Malaria in the Context of HIV Co-infection

Human co-infection is difficult to replicate in vitro. However, human malaria parasites can readily be cultured in vitro, as can freshly isolated human peripheral blood mononuclear cells naturally infected with HIV. This provides an excellent model for studying early immune responses to malaria parasites in the context of HIV co-infection.

Malaria and HIV co-infection is a growing health priority. However, most research on malaria or HIV currently focuses on each infection individually. ...

Visualizing the Effects of Sputum on Biofilm Development Using a Chambered Coverglass Model

Biofilms consist of groups of bacteria encased in a self-secreted matrix. They play an important role in industrial contamination as well as in the development and persistence of many health related infections. One of the most well described and studied biofilms in human disease occurs in chronic pulmonary infection of cystic fibrosis patients. When studying biofilms in the context of the host, many factors can impact biofilm formation and development. In order to identify how host factors may affect biofilm formation and development, we used a static chambered coverglass method to grow biofilms in the presence of host-derived factors in the form of sputum supernatants. Bacteria are seeded into chambers and exposed to sputum filtrates. Following 48 hr of growth, biofilms are stained with a commercial biofilm viability kit prior to confocal microscopy and analysis. Following image acquisition, biofilm properties can be assessed using different software platforms. This method allows us to visualize key properties of biofilm growth in presence of different substances including antibiotics.

This protocol describes the visualization of biofilm development following exposure to host-factors using a slide chamber model. This model allows for direct visualization of biofilm development as well as analysis of biofilm parameters using computer software programs.

Biofilms consist of groups of bacteria encased in a self-secreted matrix. They play an important role in industrial contamination as well as in the ...

Analysis of Lymphocyte Extravasation Using an In Vitro Model of the Human Blood-brain Barrier

Lymphocyte extravasation into the central nervous system (CNS) is critical for immune surveillance. Disease-related alterations of lymphocyte extravasation might result in pathophysiological changes in the CNS. Thus, investigation of lymphocyte migration into the CNS is important to understand inflammatory CNS diseases and to develop new therapy approaches. Here we present an in vitro model of the human blood-brain barrier to study lymphocyte extravasation. Human brain microvascular endothelial cells (HBMEC) are confluently grown on a porous polyethylene terephthalate transwell insert to mimic the endothelium of the blood-brain barrier. Barrier function is validated by zonula occludens immunohistochemistry, transendothelial electrical resistance (TEER) measurements as well as analysis of evans blue permeation. This model allows investigation of the diapedesis of rare lymphocyte subsets such as CD56brightCD16dim/- NK cells. Furthermore, the effects of other cells, cytokines and chemokines, disease-related alterations, and distinct treatment regimens on the migratory capacity of lymphocytes can be studied. Finally, the impact of inflammatory stimuli as well as different treatment regimens on the endothelial barrier can be analyzed.

Analysis of Lymphocyte Extravasation Using an In Vitro Model of the Human Blood-brain Barrier

Here, we describe a human blood-brain barrier model enabling to investigate lymphocyte transmigration into the central nervous system in vitro.

Lymphocyte extravasation into the central nervous system (CNS) is critical for immune surveillance. Disease-related alterations of lymphocyte ...

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

Prenyltransferases (PT) are a group of enzymes that catalyze chain elongation of allylic diphosphate using isopentenyl diphosphate (IPP) via multiple condensation reactions. DHDDS (dehydrodolichyl diphosphate synthase) is a eukaryotic long-chain cis-PT (forming cis double bonds from the condensation reaction) that catalyzes chain elongation of farnesyl diphosphate (FPP, an allylic diphosphate) via multiple condensations with isopentenyl diphosphate (IPP). DHDDS is of biomedical importance, as a non-conservative mutation (K42E) in the enzyme results in retinitis pigmentosa, ultimately leading to blindness. Therefore, the present protocol was developed in order to acquire large quantities of purified DHDDS, suitable for mechanistic studies. Here, the usage of protein fusion, optimized culture conditions and codon-optimization were used to allow the overexpression and purification of functionally active human DHDDS in E. coli. The described protocol is simple, cost-effective and time sparing. The homology of cis-PT among different species suggests that this protocol may be applied for other eukaryotic cis-PT as well, such as those involved in natural rubber synthesis.

Overexpression and Purification of Human Cis-prenyltransferase in Escherichia coli

A simple protocol for overexpression and purification of codon-optimized, human cis-prenyltransferase, under non-denaturing conditions, from Escherichia coli, is described, along with an enzymatic activity assay. This protocol can be generalized for production of other cis- prenyltransferase proteins in quantity and quality suitable for mechanistic studies.

Prenyltransferases (PT) are a group of enzymes that catalyze chain elongation of allylic diphosphate using isopentenyl diphosphate (IPP) via multiple ...

Effects of Taste Signaling Protein Abolishment on Gut Inflammation in an Inflammatory Bowel Disease Mouse Model

Inflammatory bowel disease (IBD) is one of the immune-related gastrointestinal disorders, including ulcerative colitis and Crohn's disease, that affects the life quality of millions of people worldwide. IBD symptoms include abdominal pain, diarrhea, and rectal bleeding, which may result from the interactions among gut microbiota, food components, intestinal epithelial cells, and immune cells. It is of particular importance to assess how each key gene expressed in intestinal epithelial and immune cells affects inflammation in the colon. G protein-coupled taste receptors, including G protein subunit &#945;-gustducin and other signaling proteins, have been found in the intestines. Here, we use &#945;-gustducin as a representative and describe a dextran sulfate sodium (DSS)-induced IBD model to evaluate the effect of gustatory gene mutations on gut mucosal immunity and inflammation. This method combines gene knockout technology with the chemically induced IBD model, and thus can be applied to assess the outcome of gustatory gene nullification as well as other genes that may exuberate or dampen the DSS-induced immune response in the colon. Mutant mice are administered with DSS for a certain period during which their body weight, stool, and rectal bleeding are monitored and recorded. At different timepoints during administration, some mice are euthanized, then the sizes and weights of their spleens and colons are measured and gut tissues are collected and processed for histological and gene expression analyses. The data show that the &#945;-gustducin knockout results in excessive weight loss, diarrhea, intestinal bleeding, tissue damage, and inflammation vs. wild-type mice. Since the severity of induced inflammation is affected by mouse strains, housing environment, and diet, optimization of DSS concentration and administration duration in a pilot experiment is particularly important. By adjusting these factors, this method can be applied to assess both anti- and pro-inflammatory effects.

Here we present a protocol to investigate the effect of the nullification of gustation-related genes on immune responses in a dextran sulfate sodium (DSS)-induced inflammatory bowel disease (IBD) mouse model.

Inflammatory bowel disease (IBD) is one of the immune-related gastrointestinal disorders, including ulcerative colitis and Crohn's disease, that affects ...

Analysis of Interactions between Endobiotics and Human Gut Microbiota Using In Vitro Bath Fermentation Systems

Human intestinal microorganisms have recently become an important target of research in promoting human health and preventing diseases. Consequently, investigations of interactions between endobiotics (e.g., drugs and prebiotics) and gut microbiota have become an important research topic. However, in vivo experiments with human volunteers are not ideal for such studies due to bioethics and economic constraints. As a result, animal models have been used to evaluate these interactions in vivo. Nevertheless, animal model studies are still limited by bioethics considerations, in addition to differing compositions and diversities of microbiota in animals vs. humans. An alternative research strategy is the use of batch fermentation experiments that allow evaluation of the interactions between endobiotics and gut microbiota in vitro. To evaluate this strategy, bifidobacterial (Bif) exopolysaccharides (EPS) were used as a representative xenobiotic. Then, the interactions between Bif EPS and human gut microbiota were investigated using several methods such as thin-layer chromatography (TLC), bacterial community compositional analysis with 16S rRNA gene high-throughput sequencing, and gas chromatography of short-chain fatty acids (SCFAs). Presented here is a protocol to investigate the interactions between endobiotics and human gut microbiota using in vitro batch fermentation systems. Importantly, this protocol can also be modified to investigate general interactions between other endobiotics and gut microbiota.

Described here is a protocol to investigate the interactions between endobiotics and human gut microbiota using in vitro batch fermentation systems.

Human intestinal microorganisms have recently become an important target of research in promoting human health and preventing diseases. Consequently, ...