Dominic Mills was supported by a Bloomsbury Colleges PhD Studentship (2007-2010). The authors would like to thank both Ozan Gundogdu and Abdi Elmi for their assistance in developing the VDC model.

1. Growth of IEC Monolayers on Special 0.4 &#956;m&#160;Filters
<ol>
	<li>Culture Caco-2 cells in Dulbecco&#39;s modified essential media (DMEM) supplemented with 10% (v/v) fetal calf serum, 100 U/ml penicillin, 100 &#956;g/ml streptomycin and 1% (v/v) nonessential amino acids in a standard tissue culture incubator at 37 &#176;C in 5% CO2 and 95% air. Seed 4 x 105 Caco-2 IECs per 0.4 &#956;m filter and grow to polarization over 21 days, changing the media every 2-3 days.</li>
	<li>Measure the TEER to confirm polarization status of the monolayer using a Volt-Ohm resistance meter. In our studies, the TEER of 21 day Caco-2 cells grown in these 0.4 &#956;m filters is 700&#8211;800 &#937;cm2.</li>
</ol>
2. Preparation of C. jejuni and the Bacterial Medium for the Coculturing Assay
<ol>
	<li>24 hr prior to desired starting point of the VDC coculturing assay, prepare a fresh blood agar plate of C. jejuni and incubate at 37 &#176;C under microaerobic conditions (85% N2, 5% O2, and&#160;10% CO2) in the variable atmosphere incubator.</li>
	<li>At the same time, preincubate 30 ml of brucella broth at 37 &#176;C under microaerobic conditions in a variable atmosphere incubator.</li>
</ol>
3. Preparation and Sterilization of the VDC Half Chambers Prior to the Assay
<ol>
	<li>Completely immerse VDC half chambers as well as the O-rings and the plugs in the sterilization solution.</li>
	<li>Using a sterile 20 ml syringe, flush the sterilization solution through the gas inlets in both half chambers. Failure to do so may result in contamination of the samples during coculturing.</li>
	<li>Leave all components immersed in the sterilization solution for &#62;1 hr.</li>
	<li>Rinse all components with fresh sterile water, using another sterile 20 ml syringe to flush the gas inlets.</li>
</ol>
4. Preparation of the Bacterial Inoculum
<ol>
	<li>Harvest half a plate of C. jejuni growth from the blood agar plate prepared the previous day into 1 ml of the preincubated brucella broth. This should yield ~1010 cfu/ml.</li>
	<li>Measure the optical density of the bacterial suspension at 600 nm to semiquantify bacterial colony forming units (CFUs).</li>
	<li>Adjust the bacterial suspension to the desired inoculum level in 4 ml of the preincubated brucella broth.</li>
	<li>Perform a serial dilution from this final bacterial suspension followed by plating of the appropriate dilutions on blood agar plates in triplicate, then incubate at 37 &#176;C in the variable atmosphere incubator for 48 hr to quantify the number of bacterial CFUs present in the inoculum.</li>
</ol>
5. Setting up the VDC
<ol>
	<li>Place the lower half chamber of a VDC flat onto the bench. Fit an O-ring onto the lower half chamber.</li>
	<li>Detach one filter carrying the IECs from the carrier and wash three times with 400 &#956;l of sterile PBS. Place the filter onto the lower half chamber, making sure the O-ring remains in place.</li>
	<li>Gently lower the upper half chamber into place. Once the two half-chambers are assembled, clamp together using the ring-clamps. Place the VDC horizontally on the bench top, with the two openings facing upwards.</li>
	<li>Add the 4 ml of bacterial inoculum into the apical half chamber.</li>
	<li>Add 4 ml of cell culture medium into the basolateral half chamber.</li>
	<li>Place the end pieces into the openings on both half chambers.</li>
</ol>
6. Attaching the VDC to the Gas Manifold within the Variable Atmosphere Incubator
<ol>
	<li>Place the VDC into the variable atmosphere incubator in close proximity to the gas manifold.</li>
	<li>Open the gas supply regulator connected to the gas manifold. Attach the tube from the manifold into the gas inlet on the basolateral half chamber of the VDC. Attach the gas outlet pipe leading out of the variable atmosphere incubator to one of the outlets in the end-piece on the basolateral half chamber.</li>
	<li>Close off the other outlet in the end-piece on the basolateral half chamber. Open the gas flow on the gas manifold, taking care to open it very slowly to avoid excess gas pressure, as this can lead to expulsion of the basolateral medium.</li>
	<li>The aim is a gas flow of 1 bubble every 2-5 sec. Periodically check on the gas flow during the course of the experiment and adjust if necessary.</li>
</ol>
7. Disassembling the VDC after Coculture
<ol>
	<li>After the appropriate coculture period, close the gas supply regulator connected to the gas manifold. Close off the gas flow into the VDC at the manifold. Disconnect the gas inlet, the gas outlet and the stopper from the VDC.</li>
	<li>Remove the VDC from a variable atmosphere incubator. Remove the apical and basolateral supernatants and store at -80 &#176;C for subsequent analysis.</li>
	<li>Remove the ring clamps and gently take apart the VDC. Remove the filter from the half chamber and transfer to a sterile 6-well cell culture dish. Wash the IECs three times with 400 &#956;l of sterile PBS.</li>
	<li>For enumeration of the total number of interacting bacteria, add 400 &#956;l of sterile PBS containing 0.1% (v/v) Triton X-100 to the IECs and incubate for 20 min at room temperature to lyse the IEC. Perform a serial dilution from this cell lysate followed by plating of the appropriate dilutions on blood agar plates in triplicate, then incubate at 37 &#176;C in the variable atmosphere incubator for 48 hr to quantify the number of interacting bacterial CFUs.</li>
	<li>For enumeration of the total number of invading bacteria, add 400 &#956;l of DMEM cell culture medium containing 150 &#956;g/ml gentamicin to the IECs and incubate for 2 hr in a standard tissue culture incubator at 37 &#176;C in 5% CO2 and 95% air to kill extracellular bacteria, then follow as for step 7.4 above.</li>
</ol>
8. Cleaning the VDC after Coculture
Wash the VDC with sterile water and store for the next round of experiments.

<ol>
	<li>Mills, D. C., 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=Increase+in+Campylobacter+jejuni+invasion+of+intestinal+epithelial+cells+under+low-oxygen+coculture+conditions+that+reflect+the+in+vivo+environment.">Increase in Campylobacter jejuni invasion of intestinal epithelial cells under low-oxygen coculture conditions that reflect the in vivo environment.</a> Infect. Immun. 80, 1690-1698 (2012).</li><li>Marteyn, B., 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=Modulation+of+Shigella+virulence+in+response+to+available+oxygen+in+vivo.">Modulation of Shigella virulence in response to available oxygen in vivo.</a> Nature. 465, 355-358 (2010).</li><li>Dorrell, N., Wren, B. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+second+century+of+Campylobacter+research:+recent+advances,+new+opportunities+and+old+problems.">The second century of Campylobacter research: recent advances, new opportunities and old problems.</a> Curr. Opin. Infect. Dis. 20, 514-518 (2007).</li><li>Young, K. T., Davis, L. M., Dirita, V. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Campylobacter+jejuni:+molecular+biology+and+pathogenesis.">Campylobacter jejuni: molecular biology and pathogenesis.</a> Nat. Rev. Microbiol. 5, 665-679 (2007).</li><li>Hu, L., Kopecko, D. J., Nachamkin, I., Szymanski, C. M., Blaser, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+17.">Chapter 17.</a> Campylobacter. , 297-313 (2008).</li><li>Everest, P. H., 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=Differentiated+Caco-2+cells+as+a+model+for+enteric+invasion+by+Campylobacter+jejuni+and+C.+coli.">Differentiated Caco-2 cells as a model for enteric invasion by Campylobacter jejuni and C. coli.</a> J. Med. Microbiol. 37, 319-325 (1992).</li><li>Konkel, M. E., Hayes, S. F., Joens, L. A., Cieplak, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characteristics+of+the+internalization+and+intracellular+survival+of+Campylobacter+jejuni+in+human+epithelial+cell+cultures.">Characteristics of the internalization and intracellular survival of Campylobacter jejuni in human epithelial cell cultures.</a> Microb. Pathog. 13, 357-370 (1992).</li><li>Monteville, M. R., Konkel, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fibronectin-facilitated+invasion+of+T84+eukaryotic+cells+by+Campylobacter+jejuni+occurs+preferentially+at+the+basolateral+cell+surface.">Fibronectin-facilitated invasion of T84 eukaryotic cells by Campylobacter jejuni occurs preferentially at the basolateral cell surface.</a> Infect. Immun. 70, 6665-6671 (2002).</li><li>Friis, L. M., Pin, C., Pearson, B. M., Wells, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+cell+culture+methods+for+investigating+Campylobacter+invasion+mechanisms.">In vitro cell culture methods for investigating Campylobacter invasion mechanisms.</a> J. Microbiol. Methods. 61, 145-160 (2005).</li><li>Schuller, S., Phillips, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microaerobic+conditions+enhance+type+III+secretion+and+adherence+of+enterohaemorrhagic+Escherichia+coli+to+polarized+human+intestinal+epithelial+cells.">Microaerobic conditions enhance type III secretion and adherence of enterohaemorrhagic Escherichia coli to polarized human intestinal epithelial cells.</a> Environ. Microbiol. 12, 2426-2435 (2010).</li><li>Cottet, S., Corthesy-Theulaz, I., Spertini, F., Corthesy, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microaerophilic+conditions+permit+to+mimic+in+vitro+events+occurring+during+in+vivo+Helicobacter+pylori+infection+and+to+identify+Rho/Ras-associated+proteins+in+cellular+signaling.">Microaerophilic conditions permit to mimic in vitro events occurring during in vivo Helicobacter pylori infection and to identify Rho/Ras-associated proteins in cellular signaling.</a> J. Biol. Chem. 277, 33978-33986 (2002).</li></ol>

We have nothing to disclose.

The use of in vitro cell culture methods to study the interactions of bacterial pathogens with host cells is a technique widely employed in many research laboratories. However as such cell culture assays are performed under aerobic conditions, these in vitro models may not accurately represent the in vivo environment in which the host-pathogen interactions take place. The widely used in vitro infection models are especially inappropriate for studying microaerophilic C. jejuni ...

The interactions of bacterial pathogens with host cells have been investigated extensively using in vitro cell culture methods. Using such cell culture assays, bacterial adhesion to host cells, identification of host cell receptors, host cell signaling pathways and bacterial invasion of host cells have all been studied in detail, resulting in many important observations. However such cell culture assays are performed under aerobic conditions that may not be representative of the in vivo environment. A major limitation of in vitro models used to study gastrointestinal infections is that culture conditions including high oxygen levels generally favor eukaryotic cell survival. However conditions in the intestinal lumen will be almost anaerobic. Enteric pathogens in a very low oxygen environment express virulence genes whose expression changes under aerobic conditions2. As such, data obtained using standard cell culture models may give an inaccurate indication of bacterial interactions with host cells.
Campylobacter jejuni is the leading causative agent of bacterial acute gastroenteritis worldwide, with symptoms that range from mild diarrhea to severe inflammatory enteritis. The majority of C. jejuni infections result in uncomplicated gastroenteritis, however C. jejuni is also the most commonly identified infectious agent in peripheral neuropathies including Guillain-Barr&#233; syndrome (GBS). In the UK, it is estimated that there are over 500,000 cases of enteritis caused by C. jejuni infection each year with a predicted cost to the UK economy of &#163;580 million. In the developing world, C. jejuni is a leading cause of mortality among children. Despite the undoubted importance of Campylobacter infection and decades of research, including thorough genomics-based analysis, C. jejuni pathogenesis is still poorly understood, in contrast to other enteric pathogens such as Salmonella, Escherichia coli, Shigella, and Vibrio cholerae. The lack of a convenient small animal model is one major reason for this3. Also the widely used in vitro infection models are more inappropriate for studying microaerophilic C. jejuni than for other enteric pathogens that are facultative anaerobes. Whilst C. jejuni is recognized as an invasive pathogen, the mechanisms of C. jejuni invasion of intestinal epithelial cells (IECs) are still unclear4,5. C. jejuni invasion has been shown to be dependent on either microfilaments, microtubules, a combination of both or neither5. The confusion in this area is most probably due to the use of inappropriate in vitro assay conditions.
A number of different cell culture assays have been used to investigate the interactions of C. jejuni with host cells. Caco-26, INT 4077, and T848 cell lines have all been used to study the adhesion and invasion capabilities of different C. jejuni strains. However, the levels of bacterial adhesion and invasion for C. jejuni with IECs are dramatically lower than for other enteric pathogens9. The coculturing of C. jejuni with IECs is normally performed in a CO2 incubator under conditions close to atmospheric oxygen levels, required for the survival of IECs. C. jejuni gene expression will be very different in the low oxygen environment of the intestinal lumen compared to atmospheric oxygen conditions.
The use of a Vertical Diffusion Chamber (VDC) system has been developed which permits the coculture of bacteria and host cells under different medium and gas conditions1,10,11. This system mimics the conditions in the human intestine where bacteria will be under conditions of very low oxygen whilst tissue will be supplied with oxygen from the blood stream. Polarized IEC monolayers grown in special 0.4 &#956;m filters were placed into a VDC creating an apical and basolateral compartment, which were individually filled with bacterial broth and cell culture medium respectively (Figure 1). The VDC was placed into the variable atmosphere incubator containing 85% N2, 5% O2, and&#160;10% CO2 at 37 &#176;C, representing optimum conditions for C. jejuni. The apical compartment was left open and exposed to the microaerobic atmosphere within the variable atmosphere incubator, whilst the sealed basolateral compartment was supplied with oxygen by constant administration of 5% CO2/95% O2 gas mixture with an outlet tube preventing accumulation of pressure. Caco-2 cell survival and monolayer integrity under these conditions were confirmed by monitoring the transepithelial electrical resistance (TEER) across the monolayer over 24 hr to demonstrate survival of the Caco-2 cell monolayer and physical separation of the apical and basolateral compartments under low oxygen conditions in the apical compartment. The TEER of monolayers in VDCs maintained in the variable atmosphere incubator (microaerobic conditions) and in a standard cell culture CO2 incubator (aerobic conditions) showed no significant differences, indicating integrity of the cell monolayer under different atmospheric conditions1. Under microaerobic conditions, tight junctions remained present and evenly distributed between the cell borders with an occludin staining pattern similar to cells maintained under aerobic conditions1.
The interactions of C. jejuni with Caco-2 and T84 cells in the VDC were investigated by assessing bacterial interaction (adhesion and invasion) and invasion. Two different C. jejuni wild-type strains were used1. C. jejuni 11168H is a hypermotile derivative of the original sequence strain NCTC11168. The 11168H strain shows much higher colonization levels in a chick colonization model and is thus considered a suitable strain to use for host-pathogen interaction studies. 81-176 is a human isolate and is one of the most invasive widely studied laboratory strains. C. jejuni strains were added to the apical compartment of a VDC under either microaerobic or aerobic conditions. We observed higher rates for both interaction and invasion were recorded for C. jejuni under microaerobic conditions1. The increased C. jejuni interactions were not due to an increase in bacterial numbers under microaerobic conditions1. This data supports our hypothesis that the low oxygen environment in the apical compartment of the VDC enhances bacteria-host interactions and indicates that the invasive properties of C. jejuni are increased under these conditions. This was the first report of the use of the VDC model to study an invasive bacterial pathogen and highlights the significance of performing in vitro infection assays under conditions that more closely mimic the in vivo situation. The VDC model could be used to study the host-pathogen interactions for many different bacterial species.

<table border="1">
	<tbody>
		<tr>
			<td>Material Name</td>
			<td>Company</td>
			<td>Catalogue Number</td>
			<td>Comments (optional)</td>
		</tr>
		<tr>
			<td>Speciality vertical diffusion system for use with Snapwell inserts</td>
			<td>Harvard Apparatus</td>
			<td>66-0001</td>
			<td>Manifold &#38; six Snapwell chambers</td>
		</tr>
		<tr>
			<td>Caps</td>
			<td>Harvard Apparatus</td>
			<td>66-0020</td>
			<td></td>
		</tr>
		<tr>
			<td>O-rings</td>
			<td>Harvard Apparatus</td>
			<td>66-0007</td>
			<td></td>
		</tr>
		<tr>
			<td>Clamps</td>
			<td>Harvard Apparatus</td>
			<td>66-0012</td>
			<td></td>
		</tr>
		<tr>
			<td>Snapwell filters (pore size 0.4 &#956;m)</td>
			<td>Corning Costar</td>
			<td>3407</td>
			<td></td>
		</tr>
		<tr>
			<td>Millicell ERS-2 Volt-Ohm resistance meter</td>
			<td>Millipore</td>
			<td>MERS00002</td>
			<td></td>
		</tr>
		<tr>
			<td>WPA Lightwave II spectrophotometer</td>
			<td>Biochrom</td>
			<td>80-3003-72</td>
			<td></td>
		</tr>
	</tbody>
</table>

enteric bacterial invasion of intestinal epithelial cells in vitro is dramatically enhanced using a vertical diffusion chamber model

The interactions of bacterial pathogens with host cells have been investigated extensively using in vitro cell culture methods. However as such cell culture assays are performed under aerobic conditions, these in vitro models may not accurately represent the in vivo environment in which the host-pathogen interactions take place. We have developed an in vitro model of infection that permits the coculture of bacteria and host cells under different medium and gas conditions. The Vertical Diffusion Chamber (VDC) model mimics the conditions in the human intestine where bacteria will be under conditions of very low oxygen whilst tissue will be supplied with oxygen from the blood stream. Placing polarized intestinal epithelial cell (IEC) monolayers grown in Snapwell inserts into a VDC creates separate apical and basolateral compartments. The basolateral compartment is filled with cell culture medium, sealed and perfused with oxygen whilst the apical compartment is filled with broth, kept open and incubated under microaerobic conditions. Both Caco-2 and T84 IECs can be maintained in the VDC under these conditions without any apparent detrimental effects on cell survival or monolayer integrity. Coculturing experiments performed with different C. jejuni wild-type strains and different IEC lines in the VDC model with microaerobic conditions in the apical compartment reproducibly result in an increase in the number of interacting (almost 10-fold) and intracellular (almost 100-fold) bacteria compared to aerobic culture conditions1. The environment created in the VDC model more closely mimics the environment encountered by C. jejuni in the human intestine and highlights the importance of performing in vitro infection assays under conditions that more closely mimic the in vivo reality. We propose that use of the VDC model will allow new interpretations of the interactions between bacterial pathogens and host cells.

Coculturing experiments performed with a C. jejuni wild-type strain and IECs in the VDC model with microaerobic conditions in the apical compartment have demonstrated an increase in the number of interacting (almost 10-fold) and intracellular (almost 100-fold) bacteria compared to aerobic culture conditions in a time-dependent manner1. This observation was reproducible using two different C. jejuni wild-type strains (11168H and 81-176) and two different IEC lines (Caco-2 and T84), highlightin...

Watch this Scientific Journal Video about Enteric Bacterial Invasion Of Intestinal Epithelial Cells In Vitro Is Dramatically Enhanced Using a Vertical Diffusion Chamber Model at JoVE.com

Enteric Bacterial Invasion Of Intestinal Epithelial Cells In Vitro Is Dramatically Enhanced Using a Vertical Diffusion Chamber Model

Performing cell culture assays for investigating bacterial adhesion and invasion under aerobic conditions is usually unrepresentative of the in vivo environment. A Vertical Diffusion Chamber model allows study of interactions of the human pathogen Campylobacter jejuni with intestinal epithelial cells under more in vivo-like conditions, resulting in enhanced bacterial invasion.

Enteric Bacterial Invasion Of Intestinal Epithelial Cells In Vitro Is Dramatically Enhanced Using a Vertical Diffusion Chamber Model

The interactions of bacterial pathogens with host cells have been investigated extensively using in vitro cell culture methods. However as such cell ...

enteric-bacterial-invasion-intestinal-epithelial-cells-vitro-is

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Immunology and Infection

13.7K Views.  London School of Hygiene & Tropical Medicine. Performing cell culture assays for investigating bacterial adhesion and invasion under aerobic conditions is usually unrepresentative of the in vivo environment. A Vertical Diffusion Chamber model allows study of interactions of the human pathogen Campylobacter jejuni with intestinal epithelial cells under more in vivo-like conditions, resulting in enhanced bacterial invasion.

Video: Enteric Bacterial Invasion Of Intestinal Epithelial Cells In Vitro Is Dramatically Enhanced Using a Vertical Diffusion Chamber Model

In vitro Biofilm Formation in an 8-well Chamber Slide

The chronic nature of many diseases is attributed to the formation of bacterial biofilms which are recalcitrant to traditional antibiotic therapy. Biofilms are community-associated bacteria attached to a surface and encased in a matrix. The role of the extracellular matrix is multifaceted, including facilitating nutrient acquisition, and offers significant protection against environmental stresses (e.g. host immune responses). In an effort to acquire a better understanding as to how the bacteria within a biofilm respond to environmental stresses we have used a protocol wherein we visualize bacterial biofilms which have formed in an 8-well chamber slide. The biofilms were stained with the BacLight Live/Dead stain and examined using a confocal microscope to characterize the relative biofilm size, and structure under varying incubation conditions. Z-stack images were collected via confocal microscopy and analyzed by COMSTAT. This protocol can be used to help elucidate the mechanism and kinetics by which biofilms form, as well as identify components that are important to biofilm structure and stability.

In vitro Biofilm Formation in an 8-well Chamber Slide

This article describes the procedure for the formation and visualization of a bacterial biofilm grown within an 8-well chamber slide

The chronic nature of many diseases is attributed to the formation of bacterial biofilms which are recalcitrant to traditional antibiotic therapy. ...

Using Luciferase to Image Bacterial Infections in Mice

Imaging is a valuable technique that can be used to monitor biological processes. In particular, the presence of cancer cells, stem cells, specific immune cell types, viral pathogens, parasites and bacteria can be followed in real-time within living animals 1-2. Application of bioluminescence imaging to the study of pathogens has advantages as compared to conventional strategies for analysis of infections in animal models3-4. Infections can be visualized within individual animals over time, without requiring euthanasia to determine the location and quantity of the pathogen. Optical imaging allows comprehensive examination of all tissues and organs, rather than sampling of sites previously known to be infected. In addition, the accuracy of inoculation into specific tissues can be directly determined prior to carrying forward animals that were unsuccessfully inoculated throughout the entire experiment. Variability between animals can be controlled for, since imaging allows each animal to be followed individually. Imaging has the potential to greatly reduce animal numbers needed because of the ability to obtain data from numerous time points without having to sample tissues to determine pathogen load3-4.
This protocol describes methods to visualize infections in live animals using bioluminescence imaging for recombinant strains of bacteria expressing luciferase. The click beetle (CBRLuc) and firefly luciferases (FFluc) utilize luciferin as a substrate5-6. The light produced by both CBRluc and FFluc has a broad wavelength from 500 nm to 700 nm, making these luciferases excellent reporters for the optical imaging in living animal models7-9. This is primarily because wavelengths of light greater than 600 nm are required to avoid absorption by hemoglobin and, thus, travel through mammalian tissue efficiently. Luciferase is genetically introduced into the bacteria to produce light signal10. Mice are pulmonary inoculated with bioluminescent bacteria intratracheally to allow monitoring of infections in real time. After luciferin injection, images are acquired using the IVIS Imaging System. During imaging, mice are anesthetized with isoflurane using an XGI-8 Gas Anethesia System. Images can be analyzed to localize and quantify the signal source, which represents the bacterial infection site(s) and number, respectively. After imaging, CFU determination is carried out on homogenized tissue to confirm the presence of bacteria. Several doses of bacteria are used to correlate bacterial numbers with luminescence. Imaging can be applied to study of pathogenesis and evaluation of the efficacy of antibacterial compounds and vaccines.

Methods for bioluminescence imaging of bacterial infections in living animals are decribed. Pathogens are modified to express luciferase allowing optical whole body imaging of infections in live animals. Animal models can be infected with luciferase expressing pathogens and the resulting course of disease visualized in real-time by bioluminescence imaging.

Imaging is a valuable technique that can be used to monitor biological processes.  In particular, the presence of cancer cells, stem cells, specific ...

Invasion of Human Cells by a Bacterial Pathogen

Here we will describe how we study the invasion of human endothelial cells by bacterial pathogen Staphylococcus aureus . The general protocol can be applied to the study of cell invasion by virtually any culturable bacterium. The stages at which specific aspects of invasion can be studied, such as the role of actin rearrangement or caveolae, will be highlighted. Host cells are grown in flasks and when ready for use are seeded into 24-well plates containing Thermanox coverslips. Using coverslips allows subsequent removal of the cells from the wells to reduce interference from serum proteins deposited onto the sides of the wells (to which S. aureus would attach). Bacteria are grown to the required density and washed to remove any secreted proteins (e.g. toxins). Coverslips with confluent layers of endothelial cells are transferred to new 24-well plates containing fresh culture medium before the addition of bacteria. Bacteria and cells are then incubated together for the required amount of time in 5% CO2 at 37&deg;C. For S. aureus this is typically between 15-90 minutes. Thermanox coverslips are removed from each well and dip-washed in PBS to remove unattached bacteria. If total associated bacteria (adherent and internalised) are to be quantified, coverslips are then placed in a fresh well containing 0.5% Triton X-100 in PBS. Gentle pipetting leads to complete cell lysis and bacteria are enumerated by serial dilution and plating onto agar. If the number of bacteria that have invaded the cells is needed, coverslips are added to wells containing 500 &mu;l tissue culture medium supplemented with gentamicin and incubation continued for 1 h, which will kill all external bacteria. Coverslips can then be washed, cells lysed and bacteria enumerated by plating onto agar as described above. If the experiment requires direct visualisation, coverslips can be fixed and stained for light, fluorescence or confocal microscopy or prepared for electron microscopy.

A general protocol for the study of invasion of host cells by a bacterial pathogen, focusing on Staphylococcus aureus and human endothelial cells.

Here we will describe how we study the invasion of human endothelial cells by bacterial pathogen Staphylococcus aureus . The general protocol can be ...

In Vitro Assay of Bacterial Adhesion onto Mammalian Epithelial Cells

To cause infections, bacteria must colonize their host. Bacterial pathogens express various molecules or structures able to promote attachment to host cells1. These adhesins rely on interactions with host cell surface receptors or soluble proteins acting as a bridge between bacteria and host. Adhesion is a critical first step prior to invasion and/or secretion of toxins, thus it is a key event to be studied in bacterial pathogenesis. Furthermore, adhered bacteria often induce exquisitely fine-tuned cellular responses, the studies of which have given birth to the field of 'cellular microbiology'2. Robust assays for bacterial adhesion on host cells and their invasion therefore play key roles in bacterial pathogenesis studies and have long been used in many pioneer laboratories3,4. These assays are now practiced by most laboratories working on bacterial pathogenesis.
Here, we describe a standard adherence assay illustrating the contribution of a specific adhesin. We use the Escherichia coli strain 27875, a human pathogenic strain expressing the autotransporter Adhesin Involved in Diffuse Adherence (AIDA). As a control, we use a mutant strain lacking the aidA gene, 2787&Delta;aidA (F. Berthiaume and M. Mourez, unpublished), and a commercial laboratory strain of E. coli, C600 (New England Biolabs). The bacteria are left to adhere to the cells from the commonly used HEp-2 human epithelial cell line. This assay has been less extensively described before6.

In Vitro Assay of Bacterial Adhesion onto Mammalian Epithelial Cells

This protocol is a simple bacterial adhesion assay consisting in counting the numbers of bacterial colony forming units that are adhered onto cultured cells. The assay is robust, independent of the adhesin studied, and numerous variations are used in most laboratories working on bacterial pathogenesis.

To cause infections, bacteria must colonize their host. Bacterial pathogens express various molecules or structures able to promote attachment to host ...

Application of a Mouse Ligated Peyer&#x2019;s Patch Intestinal Loop Assay to Evaluate Bacterial Uptake by M cells

The inside of our gut is inhabited with enormous number of commensal bacteria. The mucosal surface of the gastrointestinal tract is continuously exposed to them and occasionally to pathogens. The gut-associated lymphoid tissue (GALT) play a key role for induction of the mucosal immune response to these microbes1, 2. To initiate the mucosal immune response, the mucosal antigens must be transported from the gut lumen across the epithelial barrier into organized lymphoid follicles such as Peyer's patches. This antigen transcytosis is mediated by specialized epithelial M cells3, 4. M cells are atypical epithelial cells that actively phagocytose macromolecules and microbes. Unlike dendritic cells (DCs) and macrophages, which target antigens to lysosomes for degradation, M cells mainly transcytose the internalized antigens. This vigorous macromolecular transcytosis through M cells delivers antigen to the underlying organized lymphoid follicles and is believed to be essential for initiating antigen-specific mucosal immune responses. However, the molecular mechanisms promoting this antigen uptake by M cells are largely unknown. We have previously reported that glycoprotein 2 (Gp2), specifically expressed on the apical plasma membrane of M cells among enterocytes, serves as a transcytotic receptor for a subset of commensal and pathogenic enterobacteria, including Escherichia coli and Salmonella enterica serovar Typhimurium (S. Typhimurium), by recognizing FimH, a component of type I pili on the bacterial outer membrane 5. Here, we present a method for the application of a mouse Peyer's patch intestinal loop assay to evaluate bacterial uptake by M cells. This method is an improved version of the mouse intestinal loop assay previously described 6, 7. The improved points are as follows: 1. Isoflurane was used as an anesthetic agent. 2. Approximately 1 cm ligated intestinal loop including Peyer's patch was set up. 3. Bacteria taken up by M cells were fluorescently labeled by fluorescence labeling reagent or by overexpressing fluorescent protein such as green fluorescent protein (GFP). 4. M cells in the follicle-associated epithelium covering Peyer's patch were detected by whole-mount immunostainig with anti Gp2 antibody. 5. Fluorescent bacterial transcytosis by M cells were observed by confocal microscopic analysis. The mouse Peyer's patch intestinal loop assay could supply the answer what kind of commensal or pathogenic bacteria transcytosed by M cells, and may lead us to understand the molecular mechanism of how to stimulate mucosal immune system through M cells.

Application of a Mouse Ligated Peyer&amp;#8217;s Patch Intestinal Loop Assay to Evaluate Bacterial Uptake by M cells

M cells in a specialized follicle-associated epithelium covering Peyer&#x2019;s patches play an important role for the mucosal immunosurveillance in gut-associated lymphoid tissue. Here we described the evaluation method for bacterial transcytosis by M cells in vivo. This method provides a method to understand M-cell function in the immune system.

The inside of our gut is inhabited with enormous number of commensal bacteria. The mucosal surface of the gastrointestinal tract is continuously exposed ...

Determination of Tolerable Fatty Acids and Cholera Toxin Concentrations Using Human Intestinal Epithelial Cells and BALB/c Mouse Macrophages

The positive role of fatty acids in the prevention and alleviation of non-human and human diseases have been and continue to be extensively documented. These roles include influences on infectious and non-infectious diseases including prevention of inflammation as well as mucosal immunity to infectious diseases. Cholera is an acute intestinal illness caused by the bacterium Vibrio cholerae. It occurs in developing nations and if left untreated, can result in death. While vaccines for cholera exist, they are not always effective and other preventative methods are needed. We set out to determine tolerable concentrations of three fatty acids (oleic, linoleic and linolenic acids) and cholera toxin using mouse BALB/C macrophages and human intestinal epithelial cells, respectively. We solubilized the above fatty acids and used cell proliferation assays to determine the concentration ranges and specific concentrations of the fatty acids that are not detrimental to human intestinal epithelial cell viability. We solubilized cholera toxin and used it in an assay to determine the concentration ranges and specific concentrations of cholera toxin that do not statistically decrease cell viability in BALB/C macrophages. 
We found the optimum fatty acid concentrations to be between 1-5 ng/&mu;l, and that for cholera toxin to be &lt; 30 ng per treatment. This data may aid future studies that aim to find a protective mucosal role for fatty acids in prevention or alleviation of cholera infections.

We set out to determine tolerable concentrations of three fatty acids (oleic, linoleic and linolenic acids) and cholera toxin that did not significantly and adversely affect cell survival by solubilizing the fatty acids and the toxin and using them in cell survival assays.

The positive role of fatty acids in the prevention and alleviation of non-human and  human diseases have been and continue to be extensively documented. ...

In vitro Coculture Assay to Assess Pathogen Induced Neutrophil Trans-epithelial Migration

Mucosal surfaces serve as protective barriers against pathogenic organisms.&#160;Innate immune responses are activated upon sensing pathogen leading to the infiltration of tissues with migrating inflammatory cells, primarily neutrophils.&#160;This process has the potential to be destructive to tissues if excessive or held in an unresolved state.&#160; Cocultured in vitro models can be utilized to study the unique molecular mechanisms involved in pathogen induced neutrophil trans-epithelial migration.&#160;This type of model provides versatility in experimental design with opportunity for controlled manipulation of the pathogen, epithelial barrier, or neutrophil.&#160;Pathogenic infection of the apical surface of polarized epithelial monolayers grown on permeable transwell filters instigates physiologically relevant basolateral to apical trans-epithelial migration of neutrophils applied to the basolateral surface.&#160;The in vitro model described herein demonstrates the multiple steps necessary for demonstrating neutrophil migration across a polarized lung epithelial monolayer that has been infected with pathogenic P. aeruginosa (PAO1).&#160;Seeding and culturing of permeable transwells with human derived lung epithelial cells is described, along with isolation of neutrophils from whole human blood and culturing of PAO1 and nonpathogenic K12 E. coli (MC1000).&#160; The emigrational process and quantitative analysis of successfully migrated neutrophils that have been mobilized in response to pathogenic infection is shown with representative data, including positive and negative controls.&#160;This in vitro model system can be manipulated and applied to other mucosal surfaces.&#160;Inflammatory responses that involve excessive neutrophil infiltration can be destructive to host tissues and can occur in the absence of pathogenic infections.&#160;A better understanding of the molecular mechanisms that promote neutrophil trans-epithelial migration through experimental manipulation of the in vitro coculture assay system described herein has significant potential to identify novel therapeutic targets for a range of mucosal infectious as well as inflammatory diseases.

In vitro Coculture Assay to Assess Pathogen Induced Neutrophil Trans-epithelial Migration

Neutrophil trans-epithelial migration in response to mucosal bacterial infection contributes to epithelial injury and clinical disease.&#160;An in vitro model has been developed that combines pathogen, human neutrophils, and polarized human epithelial cell layers grown on transwell filters to facilitate investigations towards unraveling the molecular mechanisms orchestrating this phenomenon.

Mucosal surfaces serve as protective barriers against pathogenic organisms.&#160;Innate immune responses are activated upon sensing pathogen leading to ...

Assessing Bacterial Invasion of Cardiac Cells in Culture and Heart Colonization in Infected Mice Using Listeria monocytogenes

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that is capable of causing serious invasive infections in immunocompromised patients, the elderly, and pregnant women. The most common manifestations of listeriosis in humans include meningitis, encephalitis, and fetal abortion. A significant but much less documented sequelae of invasive L. monocytogenes infection involves the heart. The death rate from cardiac illness can be up to 35% despite treatment, however very little is known regarding L. monocytogenes colonization of cardiac tissue and its resultant pathologies. In addition, it has recently become apparent that subpopulations of L. monocytogenes have an enhanced capacity to invade and grow within cardiac tissue. This protocol describes in detail in vitro and in vivo methods that can be used for assessing cardiotropism of L. monocytogenes isolates. Methods are presented for the infection of H9c2 rat cardiac myoblasts in tissue culture as well as for the determination of bacterial colonization of the hearts of infected mice. These methods are useful not only for identifying strains with the potential to colonize cardiac tissue in infected animals, but may also facilitate the identification of bacterial gene products that serve to enhance cardiac cell invasion and/or drive changes in heart pathology. These methods also provide for the direct comparison of cardiotropism between multiple L. monocytogenes strains.

Assessing Bacterial Invasion of Cardiac Cells in Culture and Heart Colonization in Infected Mice Using Listeria monocytogenes

Listeria monocytogenes causes fetal infections in pregnant women and meningitis in susceptible populations. Subpopulations of bacteria can colonize cardiac tissue, causing myocarditis in patients and laboratory animals. Here we present a protocol that describes how to assess L. monocytogenes cardiac cell invasion in vitro and cardiac colonization in infected animals.

Listeria monocytogenes is a Gram-positive facultative intracellular pathogen that is capable of causing serious invasive infections in immunocompromised ...

Immunofluorescence Analysis of Stress Granule Formation After Bacterial Challenge of Mammalian Cells

Fluorescent imaging of cellular components is an effective tool to investigate host-pathogen interactions. Pathogens can affect many different features of infected cells, including organelle ultrastructure, cytoskeletal network organization, as well as cellular processes such as Stress Granule (SG) formation. The characterization of how pathogens subvert host processes is an important and integral part of the field of pathogenesis. While variable phenotypes may be readily visible, the precise analysis of the qualitative and quantitative differences in the cellular structures induced by pathogen challenge is essential for defining statistically significant differences between experimental and control samples. SG formation is an evolutionarily conserved stress response that leads to antiviral responses and has long been investigated using viral infections1. SG formation also affects signaling cascades and may have other still unknown consequences2. The characterization of this stress response to pathogens other than viruses, such as bacterial pathogens, is currently an emerging area of research3. For now, quantitative and qualitative analysis of SG formation is not yet routinely used, even in the viral systems. Here we describe a simple method for inducing and characterizing SG formation in uninfected cells and in cells infected with a cytosolic bacterial pathogen, which affects the formation of SGs in response to various exogenous stresses. Analysis of SG formation and composition is achieved by using a number of different SG markers and the spot detector plug-in of ICY, an open source image analysis tool.

We describe a method for the qualitative and quantitative analysis of stress granule formation in mammalian cells after the cells are challenged with bacteria and a number of different stresses. This protocol can be applied to investigate the cellular stress granule response in a wide range of host-bacterial interactions.

Fluorescent imaging of cellular components is an effective tool to investigate host-pathogen interactions. Pathogens can affect many different features of ...

A High-throughput Shigella-specific Bactericidal Assay

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing activity by assessing the ability of antibodies in serum to bind to bacteria and activate complement. This complement activation results in the lysis and killing of the target bacteria. These assays are valuable because they go beyond quantifying antibody production to elucidate the biological functions that these antibodies have, allowing researchers to study the role that antibodies may play in preventing infection. SBAs have been used to study immune responses for many human pathogens, but there is no widely accepted methodology for Shigella at present. Historically, SBAs have been very labor-intensive, requiring many time-consuming steps to accurately quantify surviving bacteria. This protocol describes a simple, robust, and high-throughput assay that measures functional antibodies specific for Shigella in serum in vitro. The method described here offers many advantages over traditional SBAs, including the use of frozen bacterial stocks, 96 well assay plates, a micro-culture system, and automated colony-counting. All of these modifications make this assay less labor-intensive and more high-throughput. This protocol is simpler and faster to perform than traditional SBAs while still using simple technologies and readily available reagents. The protocol has been successfully applied in multiple independent laboratories and the assay is robust and reproducible. The assay can be used to assess immune responses in pre-clinical as well as clinical studies. Quantifying shigellacidal antibody titers both before and after antigen exposure (either by immunization or infection) allows for a broader understanding of how functional antibody responses are generated and their contribution to protective immunity. The development of this standardized, well-characterized assay may greatly facilitate Shigella vaccine design.

A High-throughput Shigella-specific Bactericidal Assay

Here we present a protocol to measure Shigellacidal activity of antibodies in serum. Serum is mixed with bacteria and exogenous complement, incubated, and the reaction mixture is plated on agar plates. Viable bacteria form colonies which are counted, using an automated colony enumerator, and used to determine the bactericidal titer.

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing ...