We would like to thank Dr. Hiroshi Miyazaki, Dr. Scott Henderson, Dr. Todd Kitten, Dr. Justin Hutcherson, Dr. Catherine Jauregui, and Collin R. Berry. This work was supported by NIH NIDCR grants R01DE016124, R01DE018039, and R01DE023304 to J.P. Lewis.
Microscopy was performed at the VCU Department of Anatomy and Neurobiology Microscopy Facility, supported, in part, with funding from NIH-NINDS Center core grant (5P30NS047463).

The following protocols will describe methods for culturing and studying the invasion by the anaerobic species, P. gingivalis; however, these protocols may be used for a number of anaerobic pathogens. Although HUVECs are used, this protocol may be used for other eukaryotic cells both immune and non-immune.
1. Anaerobic Chamber Use and Maintenance
Note: P. gingivalis is an anaerobe sensitive to normal levels of oxygen encountered in ambient air. A controlled anaerobic environment is vital for the cultivation of P. gingivalis.
<ol>
	<li>Here, maintain an artificial atmosphere designated as mixed anaerobic gas (80% N2, 10% H2, 10% CO2) in a vinyl anaerobic chamber (Figure 1A). Use an airlock (Figure 1B) for transferring items from the laboratory environment to the anaerobic chamber. The airlock operates manually, twice purging with N2 gas before introducing the mixed anaerobic gas.</li>
	<li>Use a hydrogen sulfide removal column (Figure 1C) for maintenance-free removal of the undesirable hydrogen sulfide. Place a dehumidifier within the chamber to remove H2O created by the catalyst and to avoid aerosols that facilitate the spread of contamination. 
	Note: Hydrogen sulfide is a natural metabolic byproduct of many anaerobic bacteria and its accumulation is toxic to bacteria and can result in damage to electronics and decrease the lifetime of a catalyst.</li>
	<li>Use a fan box to circulate the chamber&#8217;s atmosphere through a palladium catalyst, which removes oxygen in the presence of hydrogen (Figure 1D). 
	Note: A recirculating atmospheric (HEPA) filter removes airborne contaminants with a size of 0.22&#160;&#181;m or larger.</li>
	<li>Culture anaerobic bacteria in a 37 &#176;C incubator that is located inside of the anaerobic chamber. Use standard aseptic techniques when working inside the anaerobic chamber.</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/53408/53408fig1.jpg" /> 
Figure 1. Anaerobic vinyl chamber and its components. (A) A vinyl anaerobic chamber sealed completely from atmospheric oxygen provides workspace for two individuals at a time (32 in x 78 in). It contains an incubator set at 37 &#176;C (back middle). (B) An airlock is used for the transfer of items from the lab environment to the anaerobic chamber. Pictured is an automatic airlock operated through a controller that can be programmed to automatically perform the vacuum and purge procedures needed to create an anaerobic environment. (C) A Hydrogen Sulfide Removal Column provides maintenance-free high capacity removal of undesirable hydrogen sulfide. (D) Two catalyst fan boxes are placed throughout the anaerobic chamber to help circulate the chamber&#8217;s atmosphere through palladium catalyst, which, in the presence of hydrogen, removes oxygen. The anaerobic chamber is set up according to manufacturer&#8217;s instructions. <a href="https://www.jove.com/files/ftp_upload/53408/53408fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Preparation of Anaerobic Bacteria
Note: P. gingivalis is aerotolerant and can be stored in aerobic conditions but it will not grow in the presence of oxygen at levels higher than 6%17,18. An anaerobic chamber is necessary for the proper cultivation of P. gingivalis and other anaerobic species (Figure 1). Proper training and education on anaerobic chamber use is required before working with microanaerobes19.
<ol>
	<li>Equilibrate all liquid media and plates to anaerobic conditions for at least 12 hr prior to experimentation to remove residual oxygen.</li>
	<li>Transfer P. gingivalis from -80 &#176;C freezer to anaerobic chamber, let thaw.</li>
	<li>Streak P. gingivalis on trypticase soy blood agar plates (TSA II with 5% sheep blood). Wrap plates in parafilm and store at 37 &#176;C in an anaerobic incubator for 4-7 days.</li>
	<li>Inoculate P. gingivalis into 3 ml brain heart infusion (BHI) broth supplemented with hemin and menadione, an enriched non-selective liquid media for the isolation and culture of anaerobic and fastidious microorganisms, using sterile loops. 
	Note: For long-term storage, mix bacterial cultures prepared in BHI with glycerol or DMSO (10-20% final concentration) and place in a -80 &#176;C freezer.</li>
	<li>Prepare a starter culture of P. gingivalis by making a 1:10 dilution and allowing bacteria to grow until mid-log phase.</li>
</ol>
Note: The optical density of the bacterial suspension is determined and the bacterial concentration for each strain to be examined is adjusted. For P. gingivalis a suspension at OD660 of 0.7 corresponds to mid-log phase and ~7 x 108 cells/ml. Growth conditions described in the protocol above are specific for P. gingivalis and may need to be adapted for other bacterial strains.
3. Endothelial Cell Culture
Note: Purchase pooled primary HUVECs and culture in basal medium containing vascular endothelial growth factors (VEGF) at 37 &#176;C in 5% CO2 according to manufacturer&#39;s instructions.
<ol>
	<li>Seed HUVECs in T-75 flasks at 2.5 x 105 cells/flask in 15 ml VEGF media. 
	Note: Check viability via a 1:1 dilution with 4.0% trypan blue. Cells with a compromised membrane will retain trypan blue, healthy cells with intact membranes will appear white when viewed under a binocular light microscope. Count 100 cells, ensure that over 80% of the cells are viable20.</li>
	<li>Replace media every 2 days with pre-warmed fresh VEGF media until cells reach ~80% confluency.</li>
	<li>Wash cells once with pre-warmed PBS. Liberate cells from the T75 flask by incubating with 2 ml trypsin-EDTA (0.25%) for 5 min followed by 2 ml trypsin neutralizing solution.</li>
	<li>Collect suspended HUVECs in a 50 ml conical tube. Wash out any extra cells from T-75 flasks with PBS and transfer to 50 ml conical tubes.</li>
	<li>Centrifuge cells at 200 x g for 10 min.</li>
	<li>Remove supernatant, suspend cell pellet in 10 ml pre-warmed VEGF media.</li>
	<li>Determine cell concentration using a hemocytometer or similar cell counting device.</li>
	<li>Calculate amount of cell suspension to add to either 6-well plate (400,000/well) or 12-well plate with coverslips (50,000/well). HUVECs will be ready for experimentation the next day.</li>
</ol>
4. Survival Assay Invasion/Interaction (Plating)
Note: When performing this assay, prepare two 6-well plates of endothelial cells seeded at 400,000 cells/well. One plate will be used to assess bacteria attached to and internalized by host cells. The other plate will account for intracellular bacteria. The 6-well plate allows for triplicates of two samples to be performed in one experiment. For an outline of this protocol please refer to the survival assay flowchart (Figure 2).
<ol>
	<li>Prepare anaerobic bacteria as described above (see section 1) until they reach mid-log growth (OD660 0.5-0.7).</li>
	<li>Centrifuge bacteria at 5,000 x g for 10 min. 
	Note: If centrifuge is outside anaerobic chamber, carry bacterial samples in a tightly sealed 15 ml tube, wrap the cap with parafilm to prevent oxygen leakage.</li>
	<li>Place pelleted P. gingivalis back in chamber, discard supernatant. Wash with PBS, pellet bacteria again before resuspending in VEGF media. Prepare suspensions for all bacterial strains to be tested at OD660 of 0.7 which corresponds to mid-log phase (~7 x 108 cells/ml). The bacteria are now ready for infection.</li>
	<li>Transfer 6-well plates containing HUVECs from tissue culture incubator into anaerobic chamber. Remove media and wash three times with anaerobic PBS. Add 2 ml of anaerobic VEGF media to each well and place the plates at 37 &#176;C in the anaerobic incubator for 20 min to equilibrate the temperature for infection. 
	Note: Plate bacteria on blood agar plates to ensure the ones used for infection are homogenous and not contaminated upon infection.</li>
	<li>Infect host cells with bacteria at a multiplicity of infection (MOI bacteria: host) of 100:1. 
	Note: HUVEC cell number is determined by performing a trypan exclusion test on a single well before infection. Bacterial cell number is determined via optical density (e.g., OD of 0.5 = 5 x 108 cells/ml). Bacterial concentration is adjusted to proper MOI based on HUVECs concentration21.</li>
	<li>Place 6-well plates with infected HUVECs into anaerobic incubator and allow bacteria to interact with host cells for 30 min.</li>
	<li>Prepare saponin in BHI (1.0% w/v) inside the anaerobic chamber and filter through a 0.2 &#181;m filter.</li>
	<li>Survival of both attached and internalized bacteria.
	<ol>
		<li>Remove plates from the incubator, aspirate media, wash three times with anaerobic PBS and add 2 ml filtered 1.0% saponin (prepared as described in step 4.8). Incubate for 15 min to allow host cell lysis.</li>
		<li>Scrape bottom of each well with cell scraper. Collect the cell mixture from each well and make a 1:1 dilution in BHI.</li>
		<li>Proceed to make serial dilutions of the sample. Depending on bacterial species and concentration, adjust serial dilutions. Start with 1:100 or 1:1,000 dilutions.</li>
		<li>Plate 200 &#181;l of desired dilution on blood agar plates. Wrap the plates in parafilm and place in the anaerobic incubator at 37 &#176;C.</li>
		<li>Following seven days of incubation at 37 &#176;C, remove the plates and count colony forming units (CFUs) using a light box to manually count colonies. 
		Note: CFUs are enumerated. For larger quantities of CFUs, images may be taken and computer software can be used to facilitate the enumeration of CFUs.</li>
	</ol>
	</li>
	<li>Survival of internalized bacteria.
	<ol>
		<li>Remove plates from the incubator. Wash three times with anaerobic PBS and add 2 ml VEGF media with supplemented antibiotic (300 &#181;g/ml of gentamicin and 400 &#181;g/ml of metronidazole).</li>
		<li>Incubate for 1 hr. Be sure to test the antibiotics so they are 100% effective at killing the desired bacterial strain and make sure that they do not penetrate host cells22,23.</li>
		<li>Aspirate media, add 2 ml of filtered 1.0% saponin. Incubate for 15 min to allow host cell lysis.</li>
		<li>Scrape bottom of each well with cell scraper. Collect the cell mixture from each well and make 1:1 dilution in BHI.</li>
		<li>Prepare serial dilutions of the sample (1:100, 1:1,000).</li>
		<li>Plate 200 &#181;l of desired dilution on blood agar plates. Wrap plates in parafilm and place in anaerobic incubator.</li>
		<li>After seven days of incubation at 37 &#176;C remove plates and count CFUs.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 2" src="/files/ftp_upload/53408/53408fig2.jpg" /> 
Figure 2. Schematic representation of a protocol used for survival of anaerobic bacteria with eukaryotic cells. Both assays for a total bacterial survival and survival of internalized bacteria can be performed at the same time. <a href="https://www.jove.com/files/ftp_upload/53408/53408fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Internalization of Bacteria into Host Cells (Fluorescent Microscopy)
Note: P. gingivalis is labeled with 2&#39;,7&#39;-Bis-(2-Carboxyethyl)-5-(and-6)-Carboxyfluorescein, Acetoxymethyl Ester (BCECF-AM). BCECF-AM is a non-fluorescent membrane-permeable dye; its conversion to fluorescein BCECF via the action of intracellular esterases can indicate cell viability. P. gingivalis is labeled with the BCECF-AM dye and then used to infect eukaryotic cells. Following infection, cells are fixed and labeled with DAPI and TRITC-phalloidin. The DAPI stain used to stain the eukaryotic cell nucleus will also label bacterial cell nucleus, which provides a counter-measure to identify non-viable bacteria that cannot metabolically cleave BCECF-AM. Host cells are highlighted with TRITC-phalloidin, a red actin dye.
<ol>
	<li>Autoclave coverslips. Aseptically add coverslips to 12-well plates before seeding endothelial cells at 5 x 104 cells/well. (Prepared day before experiment)</li>
	<li>Have endothelial cells prepared on 18 mm (#1.5 thickness) circular coverslips in 12-well plates as described above.</li>
	<li>Prepare anaerobic bacteria grown to mid-log phase (OD660 = 0.5-0.7) as described in section 1.</li>
	<li>Wash bacteria 2x with anaerobic PBS by centrifuging at 5,000 x g and suspending pellet in PBS at 5-7 x 108 cells/ml.</li>
	<li>Add 20 &#181;l of 0.2 mM BCECF-AM to 2 ml of bacterial suspension (5-7 x 108 cells/ml) to a final concentration of BCECF-AM of 2 &#181;M.</li>
	<li>Incubate at 37 &#176;C for 30 min in the dark.</li>
	<li>Transfer plates with endothelial cells seeded on 18 mm (#1.5 thickness) circular coverslips from tissue culture incubator into the anaerobic chamber. Wash with PBS and exchange with anaerobic VEGF media. 
	Note: Verify that HUVECs are healthy under a light microscope. HUVECS should be ~80% confluent, morphology should be comparable to the manufacturers.</li>
	<li>Centrifuge labeled bacteria at 5,000 x g for 10 min to remove residual BCECF-AM dye. Suspend in 2 ml anaerobic VEGF media.</li>
	<li>Infect host cells with labeled bacteria at MOI of 100:1 (bacteria: host).</li>
	<li>Incubate in anaerobic chamber at 37 &#176;C for 30 min.</li>
	<li>After infection wash cells with PBS three times and fix in freshly prepared 4.0% paraformaldehyde for 10 min. 
	Note: After fixing cells, experiment can be conducted outside of the anaerobic chamber.</li>
	<li>Wash coverslips with PBS three times.</li>
	<li>Add 1 ml of 0.2% Triton X-100 for 10 min.</li>
	<li>Wash coverslips with PBS three times.</li>
	<li>Add 50 &#181;l of TRITC phalloidin (50 &#181;g/ml) to coverslips for 45 min.</li>
	<li>Wash coverslips three times, remove from the 12-well plate and place on a slide with soft-set mounting medium containing DAPI. Seal the sides with nail polish. 
	Note: Slides may be stored for a couple months in the dark. Avoid light exposure to prevent photo-bleaching.</li>
	<li>View slides using a confocal microscope.
	<ol>
		<li>Here, use a 34 channel spectral system (32-channel array detector and two side PMT detectors, plus a transmitted light detector) configured around an AxioObserver (inverted) stand with a motorized XY stage. The system has five lasers: blue diode (405 nm), multi-line Argon (458, 488, 514 nm), green diode (561 nm), red HeNe (633 nm) and a 440 nm pulsed laser. Equip a Fluorescence Lifetime Imaging system with 2 hybrid GaAsP detectors (for FRET-FLIM).</li>
		<li>Detect fluorescence from DAPI and TRITC in one channel using a dual-band filter with excitation wavelengths of 340-380 nm and 540-560 nm, and an emission filter of 435-485 nm and 570-590 nm respectively. Detect fluorescence from BCECF-AM using a filter with excitation wavelength of 440-500 nm and an emission filter of 510-590 nm. 
		Note: Controls for BCECF-AM should be done on every bacterial strain being studied to ensure proper labeling of viable bacteria. First validate that nonviable bacteria are DAPI-positive and BCECF-negative. Second, ensure that live bacteria can metabolize BCECF-AM into fluorescein BCECF. Variable concentrations of the bacteria or BCECF-AM dye may need to be tested for optimal labeling.</li>
	</ol>
	</li>
</ol>

Authors have nothing to disclose.

All the above methods can be used to design specific assays to assess the interaction of anaerobic bacteria with eukaryotic cells. However, there are several considerations to successfully perform the experiments. First are the microbial strains to be used in a study.
It is crucial in the comparison of two strains with both the survival assay as well as by microscopy analysis that they are at similar growth phases and attain similar cell concentrations as any differences in the above can influ...

Anaerobic bacteria colonize almost all surfaces of the human body. Although predominant in the flora of the intestinal and genitourinary tracts where oxygen concentrations are low, they also exist at high levels on the skin, mouth, nose, and throat1. Anaerobic bacteria are a common cause of endogenous infections and are frequently isolated from diseased sites. However, because of their fastidious nature, anaerobes can be difficult to isolate and culture. Studies involving anaerobic bacteria must be done under restricted conditions. Modern anaerobic-culture techniques allow researchers to mimic the anaerobic settings required to study many anaerobic laboratory strains or even clinical isolates2,3.
Pathogenic anaerobic bacteria have developed a dynamic relationship and co-evolution with the host cells in which they reside. Most anaerobes are susceptible to killing by the host immune response before reaching infectious levels. However, some pathogenic bacteria have developed mechanisms to escape from or subvert the host immune response. They accomplish this goal through mechanisms such as evasion of immune recognition, neutralization of immune mediators, alteration of cell-mediated immunity, invasion of host cells, and alteration of immune signaling4. Porphyromonas gingivalis, a Gram-negative anaerobe implicated in both oral and extraoral diseases, is one example of a highly adapted bacterial pathogen capable of causing pathogenic changes in the host5-7.
Pockets of biofilm plaque accrued in deep crevices formed between the teeth and gingival mucosal tissue can harbor anaerobic bacteria that are protected from atmospheric oxygen8. These periodontal pockets serve as a niche for various anaerobic pathogens, such as P. gingivalis9. P. gingivalis is a keystone pathogen that is capable of remodeling the oral microbial community in ways that promote development and progression of periodontal diseases10. It produces a large number of virulence factors that are active against a broad spectrum of host proteins and provides mechanisms for evasion of host defenses11. It is also capable of invading epithelial, endothelial, fibroblastic, and periodontal ligament cells in vitro12-14 and in vivo15. By effectively invading host cells, P. gingivalis can escape host immunity. Effective invasion of host cells not only allows the bacterium to escape host defenses but also serves as a reservoir for future re-infection as well as alters the host cell. Studies of the molecular mechanisms involved in adhesion and internalization of the bacterium by host cells are needed. Research in several laboratories is focused on understanding the molecular events associated with internalization of P. gingivalis by the host cells as well as the mechanisms used to suppress and hijack the immune response and survive the hostile host defense mechanisms.
There are many assays capable of identifying and characterizing pathogens that are capable of invading host cells. However, in vitro studies with anaerobic pathogens pose many experimental problems for the researcher mainly because it is difficult to perform studies that rely on bulky instruments in the absence of oxygen. This is compounded by the fact that eukaryotic cells require oxygen to grow and thus must be prepared separately in tissue culture incubators. One way to avoid such obstacles would be to perform the studies under atmospheric oxygen, but that would make growth of anaerobic bacteria impossible. Another method would be to use heat-killed bacteria to infect and study host-cell interactions. However, differences exist between heat-killed and viable bacteria that diminish the relevancy of the host-pathogen interaction16. It is central to study viable bacteria with unaltered expression interacting with host cells; therefore, methods for culturing P. gingivalis in an anaerobic setting are given. Also, two simple cost-effective protocols are demonstrated for assessing the ability of P. gingivalis to be internalized by human umbilical vein endothelial cells (HUVECs). The first protocol is based on the popular antibiotic protection assay. Although the assay is straightforward, considerations when using anaerobic microorganisms are given. The second protocol requires the use of a fluorescent scanning microscope to visualize interacting and internalized P. gingivalis. Each assay has its limitations and advantages that will be discussed to provide the researcher an outline for studying the invasiveness of anaerobic bacteria. Although the current manuscript studies P. gingivalis and HUVECs, these protocols can be used for many other anaerobic bacteria as well as for other types of host cells.

<table><tbody><tr><td>Vinyl Anaerobic Chamber-Type B</td><td>Coy Laboratory Products</td><td></td><td>Model 2000 incubator&amp;nbsp;</td></tr><tr><td>TSA II Trypticase Soy Agar with 5% Sheep Blood</td><td>BBL</td><td>221261</td><td></td></tr><tr><td>Human Umbilical Vein Endothelial Cells 10-donor Pool</td><td>LifeLine Technology</td><td>FC-0044</td><td></td></tr><tr><td>VascuLife VEGF Medium Complete Kit</td><td>LifeLine Technology</td><td>LL-0003</td><td></td></tr><tr><td>TrypKit</td><td>LifeLine</td><td>LL-0013</td><td></td></tr><tr><td>Saponin</td><td>Riedel-de Haen</td><td>16109</td><td></td></tr><tr><td>Gentamicin Sulfate Salt</td><td>Sigma-Aldrich</td><td>G-1264</td><td></td></tr><tr><td>Metronidazole</td><td>Sigma-Aldrich</td><td>M-3761</td><td></td></tr><tr><td>BCECF-AM</td><td>LifeTechnologies</td><td>B1150</td><td></td></tr><tr><td>TRITC Phalloidin&amp;nbsp;</td><td>Sigma-Aldrich</td><td>P1951</td><td></td></tr><tr><td>18 mm Circular Coverslips</td><td>Electron Microscopy Sciences</td><td>72222-01</td><td></td></tr><tr><td>VectaShield Mounting Medium with DAPI</td><td>Vector Laboratories</td><td>H-1200</td><td></td></tr></tbody></table>

porphyromonas gingivalis as a model organism for assessing interaction of anaerobic bacteria with host cells

Anaerobic bacteria far outnumber aerobes in many human niches such as the gut, mouth, and vagina. Furthermore, anaerobic infections are common and frequently of indigenous origin. The ability of some anaerobic pathogens to invade human cells gives them adaptive measures to escape innate immunity as well as to modulate host cell behavior. However, ensuring that the anaerobic bacteria are live during experimental investigation of the events may pose challenges. Porphyromonas gingivalis, a Gram-negative anaerobe, is capable of invading a variety of eukaryotic non-phagocytic cells. This article outlines how to successfully culture and assess the ability of P. gingivalis to invade human umbilical vein endothelial cells (HUVECs). Two protocols were developed: one to measure bacteria that can successfully invade and survive within the host, and the other to visualize bacteria interacting with host cells. These techniques necessitate the use of an anaerobic chamber to supply P. gingivalis with an anaerobic environment for optimal growth.
The first protocol is based on the antibiotic protection assay, which is largely used to study the invasion of host cells by bacteria. However, the antibiotic protection assay is limited; only intracellular bacteria that are culturable following antibiotic treatment and host cell lysis are measured. To assess all bacteria interacting with host cells, both live and dead, we developed a protocol that uses fluorescent microscopy to examine host-pathogen interaction. Bacteria are fluorescently labeled with 2&#39;,7&#39;-Bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) and used to infect eukaryotic cells under anaerobic conditions. Following fixing with paraformaldehyde and permeabilization with 0.2% Triton X-100, host cells are labeled with TRITC phalloidin and DAPI to label the cell cytoskeleton and nucleus, respectively. Multiple images taken at different focal points (Z-stack) are obtained for temporal-spatial visualization of bacteria. Methods used in this study can be applied to any cultivable anaerobe and any eukaryotic cell type.

Protocols outlined above were used in studying host-pathogen interaction between P. gingivalis and endothelial cells. P. gingivalis W83 and a P. gingivalis V3150 carrying a deletion of PG0228 were used in the study. The PG0228 is predicted to encode a protein that may alter the levels of RNA and proteins, which may ultimately affect interaction of P. gingivalis with host cells. To investigate the effect of PG0228 on P. gingivalis&#8217;s ability to interact with host cells, th...

Watch this Scientific Journal Video about Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells at JoVE.com

Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

This article presents two protocols: one to measure anaerobic bacteria that can successfully invade and survive within the host, and the other to visualize anaerobic bacteria interacting with host cells. This study can be applied to any cultivable anaerobe and any eukaryotic cell type.

Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

Anaerobic bacteria far outnumber aerobes in many human niches such as the gut, mouth, and vagina. Furthermore, anaerobic infections are common and ...

porphyromonas-gingivalis-as-model-organism-for-assessing-interaction

Research

JoVE Journal

Immunology and Infection

26.2K Views.  Virginia Commonwealth University. This article presents two protocols: one to measure anaerobic bacteria that can successfully invade and survive within the host, and the other to visualize anaerobic bacteria interacting with host cells. This study can be applied to any cultivable anaerobe and any eukaryotic cell type. 

Video: Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

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.

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.

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

Biochemistry

A Mouse Model for Pathogen-induced Chronic Inflammation at Local and Systemic Sites

Chronic inflammation is a major driver of pathological tissue damage and a unifying characteristic of many chronic diseases in humans including neoplastic, autoimmune, and chronic inflammatory diseases. Emerging evidence implicates pathogen-induced chronic inflammation in the development and progression of chronic diseases with a wide variety of clinical manifestations. Due to the complex and multifactorial etiology of chronic disease, designing experiments for proof of causality and the establishment of mechanistic links is nearly impossible in humans. An advantage of using animal models is that both genetic and environmental factors that may influence the course of a particular disease can be controlled. Thus, designing relevant animal models of infection represents a key step in identifying host and pathogen specific mechanisms that contribute to chronic inflammation.
Here we describe a mouse model of pathogen-induced chronic inflammation at local and systemic sites following infection with the oral pathogen Porphyromonas gingivalis, a bacterium closely associated with human periodontal disease. Oral infection of specific-pathogen free mice induces a local inflammatory response resulting in destruction of tooth supporting alveolar bone, a hallmark of periodontal disease. In an established mouse model of atherosclerosis, infection with P. gingivalis accelerates inflammatory plaque deposition within the aortic sinus and innominate artery, accompanied by activation of the vascular endothelium, an increased immune cell infiltrate, and elevated expression of inflammatory mediators within lesions. We detail methodologies for the assessment of inflammation at local and systemic sites. The use of transgenic mice and defined bacterial mutants makes this model particularly suitable for identifying both host and microbial factors involved in the initiation, progression, and outcome of disease. Additionally, the model can be used to screen for novel therapeutic strategies, including vaccination and pharmacological intervention.

Animal models have proven to be invaluable tools in defining host and pathogen specific mechanisms that contribute to the development of chronic inflammation. Here we describe a mouse model of oral infection with the human pathogen Porphyromonas gingivalis and detail methodologies to assess the progression of inflammation at local and systemic sites.

Chronic inflammation is a major driver of pathological tissue damage and a unifying characteristic of many chronic diseases in humans including ...

Robust Ligature-Induced Model of Murine Periodontitis for the Evaluation of Oral Neutrophils

The main advantages of studying the pathophysiology of periodontal disease utilizing murine models are the reduced cost of animals, array of genetically modified strains, the vast number of analyses that can be performed on harvested soft and hard tissues. However, many of these systems are subject to procedural criticisms. As an alternative, the ligature-induced model of periodontal disease, driven by the localized development and retention of a dysbiotic oral microbiome, can be employed, which is rapidly induced and relatively reliable. Unfortunately, the variants of ligature-induced murine periodontitis protocol are isolated to focal regions of the periodontium and subject to premature avulsion of the installed ligature. This minimizes the amount of tissue available for subsequent analyses and increases the number of animals required for study. This protocol describes the precise manipulations required to place extended molar ligatures with improved retention and usage of a novel rinse technique to recover oral neutrophils in mice with an alternative approach that mitigates the aforementioned technical challenges.

This article presents a protocol for establishing a ligature-induced model of murine periodontitis involving multiple maxillary molars, resulting in larger areas of the involved gingival tissue and bone for subsequent analysis as well as reduced animal usage. A technique to assess oral neutrophils in a manner analogous to human subjects is also described.

The main advantages of studying the pathophysiology of periodontal disease utilizing murine models are the reduced cost of animals, array of genetically ...

Models of Murine Vaginal Colonization by Anaerobically Grown Bacteria

The mammalian vagina can be colonized by many bacterial taxa. The human vaginal microbiome is often dominated by Lactobacillus species, but one-in-four women experience bacterial vaginosis, in which a low level of lactobacilli is accompanied by an overgrowth of diverse anaerobic bacteria. This condition has been associated with many health complications, including risks to reproductive and sexual health. While there is growing evidence showing the complex nature of microbial interactions in human vaginal health, the individual roles of these different anaerobic bacteria are not fully understood. This is complicated by the lack of adequate models to study anaerobically grown vaginal bacteria. Mouse models allow us to investigate the biology and virulence of these organisms in vivo. Other mouse models of vaginal bacterial inoculation have previously been described. Here, we describe methods for the inoculation of anaerobically grown bacteria and their viable recovery in conventionally raised C57Bl/6 mice. A new, less stressful procedural method for vaginal inoculation and washing is also described. Inoculation and viable recovery of Gardnerella are outlined in detail, and strategies for additional anaerobes such as Prevotella bivia and Fusobacterium nucleatum are discussed.

The protocol presents a mouse model of vaginal colonization with anaerobically cultured human vaginal bacteria. We focus on Gardnerella vaginalis,&#160;while including suggestions for Prevotella bivia and Fusobacterium nucleatum. This protocol can also be used as a guide for vaginal inoculations and viable recovery of other anaerobically grown bacteria.

The mammalian vagina can be colonized by many bacterial taxa. The human vaginal microbiome is often dominated by Lactobacillus species, but one-in-four ...

Organotypic Tissue Model Systems for Investigating Host-Pathogen Interactions In Vitro

Recapitulating the host-pathogen interface at the epithelial or mucosal barrier in vitro remains a challenging prospect for infection biologists. While in-house grown 2D epithelial monolayers lack true representation of the in vivo situation, commercially available tissue models are often overlooked due to their cost and practicality. However, with careful planning, such models provide reproducible platforms for a vast array of different applications. Here, we report the use of epithelial models that can be utilized for a wide variety of experimental purposes to investigate host-pathogen interactions in various ecological niches, such as the oral cavity, skin, and vaginal mucosa. From simple planktonic cells to complex biofilm co-culture, epithelial models are used to assess microbial adherence and invasion, and to evaluate the host response at a transcriptional and/or protein level, with scope for more detailed profiling using different omics approaches. Furthermore, these biological systems can be used as more accurate test beds for evaluating conventional and novel antimicrobial activity in a complex host-pathogen microenvironment in vitro. The protocols described herein document how models are handled upon arrival and prepared in the laboratory for co-culture stimulation with biofilm communities. The methods detail how experimental outputs are achieved from the model systems, including the processing of tissue, the co-culture setup, and data generation. These experiments include host gene expression through single- and multiplex qPCR analyses and inflammatory protein detection using ELISAs. In conclusion, epithelial models provide useful in vitro systems for preclinical investigatory studies into simple or complex host-pathogen interactions.

The present protocol outlines the application of organotypic tissue models for investigating host-pathogen interactions in vitro. Specifically, the model system described uses a multi-layered oral epithelium exposed to microorganisms associated with biofilms (dental plaque) within the context of oral health versus disease.

Recapitulating the host-pathogen interface at the epithelial or mucosal barrier in vitro remains a challenging prospect for infection biologists. While ...

Establishing Stable Binary Cultures of Symbiotic Saccharibacteria from the Oral Cavity

Many bacterial species cannot be cultured in the laboratory using standard methods, posing a significant barrier to studying the majority of microbial diversity on earth. Novel approaches are required to culture these uncultured bacteria so that investigators can effectively study their physiology and lifestyle using the powerful tools available in the laboratory. The Candidate Phyla Radiation (CPR) is one of the largest groups of uncultivated bacteria, comprising ~15% of the living diversity on earth. The first isolate of this group was a member of the Saccharibacteria phylum, 'Nanosynbacter lyticus' strain TM7x. TM7x is an unusually small bacterium that lives as a symbiont in direct contact with a bacterial host, Schaalia odontolytica, strain XH001. Taking advantage of the unusually small cell size and its lifestyle as a symbiotic organism, we developed a protocol to rapidly culture Saccharibacteria from dental plaque. This protocol will show how to filter a suspension of dental plaque through a 0.2 &#181;m filter, then concentrate the collected Saccharibacteria cells and infect a culture of host organisms. The resulting coculture can be passaged as any normal bacterial culture and infection is confirmed by PCR. The resulting binary culture can be maintained in the laboratory and used for future experiments. While contamination is a possibility, the binary culture can be purified by either further filtering and reinfection of host, or by plating the binary culture and screening for infected colonies. We hope this protocol can be expanded to other sample types and environments, leading to the cultivation of many more species in the CPR.

We demonstrate a method for isolating difficult-to-grow members of the novel bacterial phylum, Saccharibacteria, by filtering dental plaque and co-culturing with host bacteria.

Many bacterial species cannot be cultured in the laboratory using standard methods, posing a significant barrier to studying the majority of microbial ...

Biology

Measuring the Migration and Biofilm Formation of Various Bacteria

As microbes that thrive in the host body primarily have adaptive abilities that facilitate their survival, methods for classifying and identifying their nature would be beneficial in facilitating their characterization. Currently, most studies focus only on one specific characterization method; however, the isolation and identification of microorganisms from the host is a continuous process and usually requires several combinatorial characterization methods. Herein, we describe methods of identifying the microbial biofilm-forming ability, the microbial respiration state, and their chemotaxis behavior. The methods are used to identify five microbes, three of which were isolated from the bone tissue of Sprague-Dawley (SD) rats (Corynebacterium stationis, Staphylococcus cohnii subsp. urealyticus, and Enterococcus faecalis) and two from the American Type Culture Collection (ATCC)-Staphylococcus aureus ATCC 25923&#160;and Enterococcus faecalis V583. The microbes isolated from the SD rat bone tissue include the gram-positive microbes. These microbes have adapted to thrive under stressful and nutrient-limiting environments within the bone matrix. This article aims to provide the readers with the specific know-how of determining the nature and behavior of the isolated microbes within a laboratory setting.

Here, we present a practical method for the isolation and identification of microorganisms within the host. In this way, the physicochemical properties of microorganisms and possible ways of living in the host are clearly described.

As microbes that thrive in the host body primarily have adaptive abilities that facilitate their survival, methods for classifying and identifying their ...

Anti-Infective Efficacy in Cystic Fibrosis with Aggregate Biofilm Models

Cystic Fibrosis Aggregate Biofilm Model to Study Infection-relevant Gene Expression

Standard pre-clinical testing methods for novel antimicrobial therapeutics used to treat chronic lung infections in people with cystic fibrosis do not reflect the environmental conditions of the hostile lung niche. Current reductionist testing conditions can lead to the progression of compounds along a preclinical pipeline without evidence of their activity under cystic fibrosis lung niche-appropriate conditions. Several approaches used to study traditional antimicrobials may not be suitable for antibiotic alternatives, including anti-virulence therapeutics like anti-quorum sensing agents and siderophore inhibitors. This protocol documents an aggregate biofilm model of Pseudomonas aeruginosa to compare resistance and infection-relevant gene expression in single-species and multi-species cultures (Staphylococcus aureus and Candida albicans), examining colony-forming unit (CFU) reductions and changes in gene expression, using algD as an exemplar. The model was optimized for small, static volumes of bacterial cultures to allow the study of novel compounds in the discovery phase of the drug development pipeline, where compound quantities may be limited. Single-species P. aeruginosa biofilms were formed in Synthetic Cystic Fibrosis Medium 2 (SCFM2) for 24 h before treatment with meropenem at different concentrations (1, 16, and 256 &#181;g/mL) for a further 24 h. Polymicrobial biofilms were established by growing Staphylococcus aureus and Candida albicans together in SCFM2, then inoculating with P. aeruginosa for an additional 24 h and treating with meropenem. The lack of a direct connection between compound efficacy measures in pre-clinical testing and clinical trial results has cast doubt on the applicability of current laboratory screening tools. This model allows us to understand the impact of relevant factors on P. aeruginosa gene expression, including genes contributing to resistance and virulence, thereby bridging this gap.

This study outlines a framework for developing an aggregate polymicrobial biofilm model and optimizing an RNA extraction protocol to assess Pseudomonas aeruginosa gene expression reflective of the cystic fibrosis lung environment. Applications include evaluating antimicrobial effects and studying antibiotic alternatives under conditions relevant to cystic fibrosis.

Standard pre-clinical testing methods for novel antimicrobial therapeutics used to treat chronic lung infections in people with cystic fibrosis do not ...

Visualization of Internalized Anaerobic Bacteria within Host Endothelial Cells

Source: Wunsch, C. M. et. al., <a href="https://app.jove.com/v/53408">Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells.</a> J. Vis. Exp. (2015)
In this video, we demonstrate a procedure to visualize internalized Porphyromonas gingivalis, an anaerobic pathogenic bacterium, within human endothelial cells using confocal microscopy. The bacteria are stained with a fluorescent dye while the host endothelial cell actin cytoskeleton is labeled with a different fluorescent dye. The internalized Porphyromonas gingivalis inside endothelial cells are visualized using confocal microscopy.

1. Internalization of Bacteria into Host Cells (Fluorescent Microscopy)
Note: P. gingivalis is labeled with ...

JoVE Encyclopedia of Experiments

Immunology

Immunodiagnostics

Imaging and Visualization Techniques

A Bacterial Infection Assay for Studying Anaerobic Bacteria-Host Cell Interactions

Source: Wunsch, C. M., et al. <a href="https://app.jove.com/v/53408">Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells.</a> J. Vis. Exp. (2015)
This video demonstrates a technique for assessing the ability of Porphyromonas gingivalis, an anaerobic pathogenic bacterium, to adhere to and invade human umbilical vein endothelial cells (HUVECs). After infecting the host cells with the bacteria, the host cells are lysed to release both adhered and internalized bacteria. When the lysate is plated in an appropriate medium, the presence of colonies indicates successful bacteria-host cell interactions.

The following protocols will describe methods for culturing and studying the invasion by the anaerobic species, P. gingivalis; however, these protocols ...

Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells

Summary

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Chapters in this video

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

A Mouse Model for Pathogen-induced Chronic Inflammation at Local and Systemic Sites

Robust Ligature-Induced Model of Murine Periodontitis for the Evaluation of Oral Neutrophils

Models of Murine Vaginal Colonization by Anaerobically Grown Bacteria

Organotypic Tissue Model Systems for Investigating Host-Pathogen Interactions In Vitro

Establishing Stable Binary Cultures of Symbiotic Saccharibacteria from the Oral Cavity

Measuring the Migration and Biofilm Formation of Various Bacteria

Cystic Fibrosis Aggregate Biofilm Model to Study Infection-relevant Gene Expression

Visualization of Internalized Anaerobic Bacteria within Host Endothelial Cells

A Bacterial Infection Assay for Studying Anaerobic Bacteria-Host Cell Interactions