Name: assessing the viability of a synthetic bacterial consortium on the in vitro gut host-microbe interface
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The authors gratefully acknowledge financial support from the Flanders Research Foundation to Marta Calatayud Arroyo (FWO postdoctoral fellowship-12N2815N). Emma Hernandez-Sanabria is a postdoctoral fellow supported by Flanders Innovation and Entrepreneurship (Agentschap voor Innovatie door Wetenschap en Technologie, IWT).

1. Strains and Culture Conditions
NOTE: The synthetic oral community was composed by strains commonly present in the oral microbiome3.
<ol>
	<li>Obtain the following strains from the American Type Culture Collection (ATCC): Aggregatibacter actinomycetemcomitans (ATCC 43718), Fusobacterium nucleatum (ATCC 10953), Porphyromonas gingivalis (ATCC 33277), Prevotella intermedia (ATCC 25611), Streptococcus</e...

<ol>
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U., Egli, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+and+interpretation+of+bacterial+viability+by+using+the+LIVE/DEAD+BacLight+kit+in+combination+with+flow+cytometry.">Assessment and interpretation of bacterial viability by using the LIVE/DEAD BacLight kit in combination with flow cytometry.</a> Applied and Environmental Microbiology. 73, 3283-3290 (2007).</li><li>Props, R., Monsieurs, P., Mysara, M., Clement, L., Boon, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+the+biodiversity+of+microbial+communities+by+flow+cytometry.">Measuring the biodiversity of microbial communities by flow cytometry.</a> Methods in Ecology and Evolution. 7, 1376-1385 (2016).</li><li>Yamashita, Y., Takeshita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+oral+microbiome+and+human+health.">The oral microbiome and human health.</a> Journal of Oral Science. 59, 201-206 (2017).</li><li>Wade, W. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+oral+microbiome+in+health+and+disease.">The oral microbiome in health and disease.</a> Pharmacological Research. 69, 137-143 (2013).</li><li>Yu, 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=A+resource+for+cell+line+authentication,+annotation+and+quality+control.">A resource for cell line authentication, annotation and quality control.</a> Nature. 520, 307 (2015).</li><li>Pelaseyed, T., 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=The+mucus+and+mucins+of+the+goblet+cells+and+enterocytes+provide+the+first+defense+line+of+the+gastrointestinal+tract+and+interact+with+the+immune+system.">The mucus and mucins of the goblet cells and enterocytes provide the first defense line of the gastrointestinal tract and interact with the immune system.</a> Immunological Reviews. 260, 8-20 (2014).</li><li>Bengoa, A. A., 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=Simulated+gastrointestinal+conditions+increase+adhesion+ability+of+Lactobacillus+paracasei+strains+isolated+from+kefir+to+Caco-2+cells+and+mucin.">Simulated gastrointestinal conditions increase adhesion ability of Lactobacillus paracasei strains isolated from kefir to Caco-2 cells and mucin.</a> Food Research International. 103, 462-467 (2018).</li><li>Kleiveland, C. R., et al., Verhoeckx, K., 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=.">.</a> The Impact of Food Bioactives on Health: in vitro and ex vivo models. , 197-205 (2015).</li><li>Laparra, J. 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The oral microbiome is a key element in human health as recently reported by several authors20,21. Previous findings suggest that the ingestion of saliva containing large loads of bacteria can influence the microbial ecosystem of the small intestine, which is one of the main sites for immune priming. The combination of a static upper gastrointestinal digestion model with the host interface represented by intestinal epithelial and mucus-secreting cells, served to ...

Humans cohabit with bacteria, which are present at the same number as human cells1. Hence, it is of crucial important to obtain a comprehensive understanding of the human microbiome. The oral cavity is a unique environment in that it is divided into several smaller habitats, thus containing a large variety of bacteria and biofilms in those different locations. Being an open ecosystem, some species in the mouth may be transient visitors. However, certain microorganisms colonize soon after birth and form organized biofilms2. These are found in the teeth surface above the gingival crevice, the subgingival crevice, tongue, mucosal surfaces and dental prosthetics and fillings3. Bacteria can also be present as flocs and planktonic cells in the lumen of the tooth canal, either intermixed with necrotic pulp tissue or suspended in a fluid phase.
There is active, continuous cross-talk between host cells and the resident microbiota4. Bacteria communicate within and between species, and only a small proportion of the natural colonizers can adhere to tissues, while other bacteria attach to these primary colonizers. For instance, cell-cell binding between microorganisms is key for integrating secondary colonizers into oral biofilms, and building complex networks of interacting microbial cells4. Around 70% of bacterial aggregates in a saliva sample are formed by Porphyromonas sp., Streptococcus sp., Prevotella sp., Veillonella sp., and unidentified Bacteroidetes. F. nucleatum is an intermediate colonizer in the subgingival biofilm and aggregates with the late colonizers P. gingivalis, T. denticola, and Tannerella forsythia, which are implicated in periodontitis5. In addition, Streptococcus mitis occupies both mucosal and dental habitats, while S. sanguinis and S. gordonii prefer to colonize teeth3. Thus, S. sanguinis is present in lower incisors and canines, while Actinomyces naeslundii has been found in upper anteriors6.
In addition, the indigenous microbiome plays a role in maintaining human health2. Resident microbiota participates in immune education and in preventing pathogen expansion. This colonisation resistance occurs because the native bacteria may be better adapted at attaching to surfaces, and more efficient at metabolising the available nutrients for growth. Although probiotic strains survive the gastrointestinal passage and remain active, the persistence of autochthonous bacteria swallowed from an upper location of the gastrointestinal tract has not been fully described. Thus, we subjected an artificial community, representative of the oral ecosystem, to simulated gastrointestinal transit conditions. Viability of bacterial cells was assessed using a multicompartment model resembling the gut epithelium. Current gut simulators offer suitable reproducibility in terms of analysis of the luminal microbial community7. However, bacterial adhesion and host-microbe interaction are separately addressed, as combining cell lines with microbial communities is challenging8. In contrast, we present a framework that provides potential mechanistic explanation of successful colonization events reported on the gut interface. Indeed, this model can be jointly used with a static gut model to evaluate the impact of microbial communities on host surface signalling.

<table>
	<tbody>
		<tr>
			<td>STRAINS</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Aggregatibacter actinomycetemcomitans </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 43718</td>
			<td></td>
		</tr>
		<tr>
			<td>Fusobacterium nucleatum </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 10953</td>
			<td></td>
		</tr>
		<tr>
			<td>Porphyromonas gingivalis </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 33277</td>
			<td></td>
		</tr>
		<tr>
			<td>Prevotella intermedia </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 25611</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus mutans </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 25175</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus sobrinus </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 33478</td>
			<td></td>
		</tr>
		<tr>
			<td>Actinomyces viscosus </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 15987</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus salivarius&#160; TOVE-R</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus mitis </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 49456</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus sanguinis </td>
			<td>BCCM/LMG Bacteria Collection</td>
			<td>LMG 14657</td>
			<td></td>
		</tr>
		<tr>
			<td>Veillonella parvula </td>
			<td>Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures</td>
			<td>DSM 2007</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptococcus gordonii </td>
			<td>American Type Culture Collection</td>
			<td>ATCC 49818</td>
			<td></td>
		</tr>
		<tr>
			<td>CELL LINES</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Caco-2 cells</td>
			<td>European Collection of Authenticated Cell Cultures</td>
			<td>86010202</td>
			<td></td>
		</tr>
		<tr>
			<td>HT29-MTX cells</td>
			<td>European Collection of Authenticated Cell Cultures</td>
			<td>12040401</td>
			<td></td>
		</tr>
		<tr>
			<td>REAGENTS AND CONSUMABLES</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Brain Heart Infusion (BHI) broth</td>
			<td>Oxoid</td>
			<td>CM1135</td>
			<td></td>
		</tr>
		<tr>
			<td>Blood Agar 2</td>
			<td>Oxoid</td>
			<td>CM0055</td>
			<td>Blood Agar medium</td>
		</tr>
		<tr>
			<td>Menadione</td>
			<td>Sigma</td>
			<td>M9429</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemin</td>
			<td>Sigma</td>
			<td>H9039</td>
			<td></td>
		</tr>
		<tr>
			<td>5% sterile defibrinated horse blood</td>
			<td>E&#38;O Laboratories Ltd,</td>
			<td>P030</td>
			<td></td>
		</tr>
		<tr>
			<td>InnuPREP PCRpure Kit</td>
			<td>Analytik Jena</td>
			<td>845-KS-5010250</td>
			<td>PCR purification kit</td>
		</tr>
		<tr>
			<td>Big Dye</td>
			<td>Applied Biosystems</td>
			<td>4337454</td>
			<td>Dye for sequencing</td>
		</tr>
		<tr>
			<td>ABI Prism BigDye Terminator v3.1 cycle sequencing kit</td>
			<td>Applied Biosystems</td>
			<td>4337456</td>
			<td></td>
		</tr>
		<tr>
			<td>SYBR&#160;Green I</td>
			<td>Invitrogen</td>
			<td>S7585</td>
			<td></td>
		</tr>
		<tr>
			<td>Propidium Iodide</td>
			<td>Invitrogen</td>
			<td>P1304MP</td>
			<td></td>
		</tr>
		<tr>
			<td>T25 culture flasks uncoated, cell-culture treated, vented, sterile</td>
			<td>VWR</td>
			<td>734-2311</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA solution</td>
			<td>Sigma-Aldrich</td>
			<td>T3924-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue solution 
			0.4%, liquid, sterile-filtered</td>
			<td>Sigma-Aldrich</td>
			<td>T8154&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>14190250</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM cell culture media, with GlutaMAX and Pyruvate</td>
			<td>Life technologies</td>
			<td>31966-047</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning Transwell polyester membrane cell culture inserts</td>
			<td>Sigma-Aldrich</td>
			<td>CLS3450-24EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Mucin from porcine stomach Type II&#160;&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>M2378</td>
			<td></td>
		</tr>
		<tr>
			<td>Inactivated fetal bovine serum</td>
			<td>Greiner Bio One</td>
			<td>758093</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic-Antimycotic (100X)</td>
			<td>Gibco</td>
			<td>15240062</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X 100 for molecular biology</td>
			<td>Sigma-Aldrich</td>
			<td>T8787&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS without calcium, magnesium</td>
			<td>Gibco</td>
			<td>14190-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Pierce LDH Cytotoxicity Assay Kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>88953</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning HTS Transwell-24 well, pore size 0.4 &#181;m</td>
			<td>Corning Costar Corp</td>
			<td>3450</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuclease-free water</td>
			<td>Serva Electrophoresis</td>
			<td>28539010</td>
			<td></td>
		</tr>
		<tr>
			<td>EQUIPMENT</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Neubauer counting chamber improved</td>
			<td>Carl Roth</td>
			<td>T729.1</td>
			<td></td>
		</tr>
		<tr>
			<td>BD Accuri C6 Flow cytometer</td>
			<td>BD Biosciences</td>
			<td>653118</td>
			<td></td>
		</tr>
		<tr>
			<td>PowerLyzer 24 Homogenizer</td>
			<td>MoBio</td>
			<td>13155</td>
			<td></td>
		</tr>
		<tr>
			<td>T100 Thermal Cycler</td>
			<td>BioRad</td>
			<td>186-1096</td>
			<td></td>
		</tr>
		<tr>
			<td>Flush system</td>
			<td>Custom made</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>InnOva 4080 Incubator Shaker</td>
			<td>New Brunswick Scientific</td>
			<td>8261-30-1007</td>
			<td>Shaker for 2.10</td>
		</tr>
		<tr>
			<td>Memmert CO2 incubator</td>
			<td>Memmert GmbH &#38; Co.</td>
			<td>ICO150med</td>
			<td></td>
		</tr>
		<tr>
			<td>Millicell ERS (Electrical Resistance System)</td>
			<td>EMD Millipore, Merck KGaA</td>
			<td>MERS00002</td>
			<td></td>
		</tr>
		<tr>
			<td>Millipore Milli-Q academic, ultra pure water system</td>
			<td>Millipore, Merck KGaA</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Shaker (ROCKER 3D basic)</td>
			<td>IKA</td>
			<td>4000000</td>
			<td>Shaker for 6.10</td>
		</tr>
	</tbody>
</table>

assessing the viability of a synthetic bacterial consortium on the in vitro gut host-microbe interface

The interplay between host and microbiota has been long recognized and extensively described. The mouth is similar to other sections of the gastrointestinal tract, as resident microbiota occurs and prevents colonisation by exogenous bacteria. Indeed, more than 600 species of bacteria are found in the oral cavity, and a single individual may carry around 100 different at any time. Oral bacteria possess the ability to adhere to the various niches in the oral ecosystem, thus becoming integrated within the resident microbial communities, and favouring growth and survival. However, the flow of bacteria into the gut during swallowing has been proposed to disturb the balance of the gut microbiota. In fact, oral administration of P. gingivalis shifted bacterial composition in the ileal microflora. We used a synthetic community as a simplified representation of the natural oral ecosystem, to elucidate the survival and viability of oral bacteria subjected to simulated gastrointestinal transit conditions. Fourteen species were selected, subjected to in vitro salivary, gastric, and intestinal digestion processes, and presented to a multicompartment cell model containing Caco-2 and HT29-MTX cells to simulate the gut mucosal epithelium. This model served to unravel the impact of swallowed bacteria on cells involved in the enterohepatic circulation. Using synthetic communities allows for controllability and reproducibility. Thus, this methodology can be adapted to assess pathogen viability and subsequent inflammation-associated changes, colonization capacity of probiotic mixtures, and ultimately, potential bacterial impact on the presystemic circulation.

This protocol leads to the generation of a model suitable for elucidating the survival and viability of oral bacteria subjected to simulated gastrointestinal transit conditions. The counts of intact cells from individual strains is approximately 108 cells mL-1 prior the creation of the synthetic community, while the multispecies microcosm contained above 90% of viable cells during the establishment of the community (Figure 1A </s...

Watch this Scientific Journal Video about Assessing the Viability of a Synthetic Bacterial Consortium on the In Vitro Gut Host-microbe Interface at JoVE.com

Assessing the Viability of a Synthetic Bacterial Consortium on the In Vitro Gut Host-microbe Interface

Gut host-microbe interactions were assessed using a novel approach combining a synthetic oral community, in vitro gastrointestinal digestion, and a model of the small intestine epithelium. We present a method that can be adapted to evaluate cell invasion of pathogens and multi-species biofilms, or even to test probiotic formulations&#39; survivability.

Assessing the Viability of a Synthetic Bacterial Consortium on the In Vitro Gut Host-microbe Interface

The interplay between host and microbiota has been long recognized and extensively described. The mouth is similar to other sections of the ...

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