Name: automated, high-throughput detection of bacterial adherence to host cells
Uploaded: 2021-09-17T14:00:00
Description: Watch this Scientific Journal Video about Automated, High-Throughput Detection of Bacterial Adherence to Host Cells at JoVE.com

We are thankful to Dr. Kaite Zlotkowski of Biotek Inc. for their technical support. We also thank Dr. Lori Burrows, McMaster University, for the generous gift of the Pseudomonas strains.This work was supported by the Department of Defense under contract number W911NF1920013 to PdF; the Defense Advanced Research Projects Agency (DARPA) and the Department of Interior under Contract No. 140D6319C0029 to PdF. The content of the information does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred.

1. A549 cell culture
<ol>
	<li>Maintain the A549 cell line in F-12K medium supplemented with 10% fetal bovine serum (FBS) and incubate at 37 &#176;C, 5% CO2.</li>
	<li>Change the medium every 3-4 days and passage at 85%-95% confluency.</li>
	<li>Briefly, rinse the cells with 1 x phosphate-buffered saline (PBS, pH 7.4, unless otherwise indicated) and treat with 1 ml of 0.25% Trypsin-0.53 mM ethylenediaminetetraacetic acid (EDTA) solution (submerging the cell layer) for about 2 min at 37 &#176;C.</li>
	<li>Add...

<ol>
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P., Barton, B., Morgenstein, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+Imaging+of+bacterial+cells+for+accurate+cellular+representations+and+precise+protein+localization.">Three-dimensional Imaging of bacterial cells for accurate cellular representations and precise protein localization.</a> Journal of Visualized Experiments. (152), e60350 (2019).</li><li>Hoffmann, S., 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=High-throughput+quantification+of+bacterial-cell+interactions+using+virtual+colony+counts.">High-throughput quantification of bacterial-cell interactions using virtual colony counts.</a> Frontiers in Cellular and Infection Microbiology. 8, 43 (2018).</li><li>Hazan, R., Que, Y. -. A., Maura, D., Rahme, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+high+throughput+determination+of+viable+bacteria+cell+counts+in+96-well+plates.">A method for high throughput determination of viable bacteria cell counts in 96-well plates.</a> BMC Microbiology. 12 (1), 259 (2012).</li><li>Gellatly, S. L., Hancock, R. E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pseudomonas+aeruginosa:+new+insights+into+pathogenesis+and+host+defenses.">Pseudomonas aeruginosa: new insights into pathogenesis and host defenses.</a> Pathogens and Disease. 67, 159-173 (2013).</li><li>Jiang, R. D., Shen, H., Piao, Y. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+morphometrical+analysis+on+the+ultrastructure+of+A549+cells.">The morphometrical analysis on the ultrastructure of A549 cells.</a> Romanian Journal of Morphology and Embryology. 51 (4), 663-667 (2010).</li><li>Farinha, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alteration+of+the+pilin+adhesin+of+Pseudomonas+aeruginosa+PAO+results+in+normal+pilus+biogenesis+but+a+loss+of+adherence+to+human+pneumocyte+cells+and+decreased+virulence+in+mice.">Alteration of the pilin adhesin of Pseudomonas aeruginosa PAO results in normal pilus biogenesis but a loss of adherence to human pneumocyte cells and decreased virulence in mice.</a> Infection and Immunity. 62 (10), 4118-4123 (1994).</li><li>R&#233;glier-Poupet, H., Pellegrini, E., Charbit, A., Berche, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+LpeA,+a+PsaA-Like+membrane+protein+that+promotes+cell+entry+by+Listeria+monocytogenes.">Identification of LpeA, a PsaA-Like membrane protein that promotes cell entry by Listeria monocytogenes.</a> Infection and immunity. 71 (1), 474-482 (2003).</li><li>Ortega, F. E., 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=Adhesion+to+the+host+cell+surface+is+sufficient+to+mediate+Listeria+monocytogenes+entry+into+epithelial+cells.">Adhesion to the host cell surface is sufficient to mediate Listeria monocytogenes entry into epithelial cells.</a> Molecular Biology of the Cell. 28 (22), 2945-2957 (2017).</li></ol>

The protocol describes an automated approach for enumerating bacterial attachment to host cells. The described approach has several attractive advantages over conventional methods. First, this approach enables the precise quantification of the number of microbial pathogen cells that are attached to individual host cells. Importantly, this quantification can be performed without the need for laborious bacterial harvesting, serial dilutions, plating on solid media, and determination of CFUs10,<...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/62764">Automated, High-Throughput Detection of Bacterial Adherence to Host Cells</a>. The Authors section was updated.
The Authors section was updated from:
Jing Yang1, Qing-Ming Qin1, Paul de Figueiredo1,2 
1Department of Microbial Pathogenesis and Immunology, Texas A&#38;M Health Science Center 
2Department of Veterinary Pathobiology, Texas A&#38;M College of Veterinary Medicine
to:
Jing Yang1, Qing-Ming Qin1, Erin Van Schaik1, James E. Samuel1, Paul de Figueiredo1,2 
1Department of Microbial Pathogenesis and Immunology, Texas A&#38;M Health Science Center 
2Department of Veterinary Pathobiology, Texas A&#38;M College of Veterinary Medicine

An erratum was issued for:&#160;<a href="https://www.jove.com/t/62764">Automated, High-Throughput Detection of Bacterial Adherence to Host Cells</a>. The Authors section was updated.

Erratum: Automated, High-Throughput Detection of Bacterial Adherence to Host Cells

Bacterial adhesion is a process whereby bacteria attach to other cells or surfaces. Successful establishment of infection by bacterial pathogens requires adhesion to host cells, colonization of tissues, and in some cases, invasion of host cells1,2,3. Emerging infectious diseases constitute major public health threats, as evidenced by the recent COVID-19 pandemic4,5,6. Importantly, new or emerging pathogens may not be readily discerned using genomic-based approaches, especially in cases where the pathogen has been engineered to evade detection or does not contain genomic signatures that identify it as pathogenic. Therefore, the identification of potential pathogens using methods that directly assess hallmarks of pathogenicity, like bacterial adherence to host cells, can play a critical role in pathogen identification.
Bacterial adherence to host cells has been used to evaluate mechanisms of bacterial pathogenesis for decades1,7. Microscopic imaging8,9 and the enumeration of bacterial colony-forming unit (CFU)10,11,12,13 by post-infection plating are two well-developed laboratory methods for testing microbial adherence and/or infection of host cells14. Considering the micrometer scale size of bacterial cells, the enumeration of the adherent bacterial cells generally requires the use of advanced high-magnification microscopy techniques, as well as high-resolution imaging approaches, including electron microscopy, expansion microscopy (ExM)15,16, and three-dimensional imaging17. Alternatively, the enumeration of bacteria bound to or internalized within host cells can be performed by plating the dilution series of harvested bacteria on solid agar and counting the resultant CFUs10,12,13. This method is laborious and includes many manual steps, which introduces difficulties in establishing a standardized or automated procedure required for high-throughput analyses18,19. Therefore, the development of new methods for evaluating host cell attachment would address current limitations in the field.
One such method is described here that uses automated high throughput microscopy, combined with high throughput image processing and statistical analysis. To demonstrate the approach, experiments with several bacterial pathogens were performed, including Pseudomonas aeruginosa, an opportunistic Gram-negative bacterial pathogen of humans, animals, and plants14,20, which is frequently found to colonize the respiratory tract of patients with impaired host defense functions. This approach optimized the microscopic imaging process described in previous studies14,20. The imaging detection was simplified by fluorescence-labeled host cells and bacteria to rapidly track the proximity of them, which dramatically reduced the microscopy workload to get high-resolution images for distinguishing bacteria. In addition, the automated statistical analysis of images in counting host cells and bacteria replaced the hand-on experiment of bacterial CFU plating to estimate the ratio of adherent bacterial counts per host cell. To confirm the compatibility of this method, multiple bacterial strains and host cell types have also been tested, like Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, and Klebsiella pneumoniae, as well as human umbilical vein endothelial cells (HUVECs), and the results support the diversity and effectiveness of the method.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr >
			<td >10x PBS</td>
			<td >VWR</td>
			<td >45001-130</td>
			<td ></td>
		</tr>
		<tr >
			<td >4&#8242;,6-diamidino-2-phenylindole (DAPI)</td>
			<td >Thermo Fisher</td>
			<td>62248</td>
			<td>Host cell staining dye</td>
		</tr>
		<tr >
			<td >96 well plate</td>
			<td >Corning</td>
			<td >3882</td>
			<td>Half area well, flat clear bottom</td>
		</tr>
		<tr >
			<td >A549 cells</td>
			<td >ATCC&#160;</td>
			<td >CCL 185</td>
			<td>Mammalian cell line</td>
		</tr>
		<tr >
			<td >BactoView Live Red</td>
			<td >Biotium</td>
			<td >40101</td>
			<td>Bacteria staning dye</td>
		</tr>
		<tr >
			<td >Centrifuge</td>
			<td >Eppendorf</td>
			<td >5810R</td>
			<td></td>
		</tr>
		<tr >
			<td >CFSE cell division tracker</td>
			<td >BioLegend</td>
			<td >423801</td>
			<td></td>
		</tr>
		<tr >
			<td >Cytation 5&#160;</td>
			<td >BioTek</td>
			<td >Cytation 5&#160;</td>
			<td>Cell imaging multi-mode reader</td>
		</tr>
		<tr >
			<td >E. coli</td>
			<td ></td>
			<td ></td>
			<td>Laboratory stock&#160;</td>
		</tr>
		<tr >
			<td >EGM bulletKit</td>
			<td >Lonza</td>
			<td >CC-3124</td>
			<td>HUVEC cell culture medium</td>
		</tr>
		<tr >
			<td >EHEC</td>
			<td ></td>
			<td ></td>
			<td >NIST collections</td>
		</tr>
		<tr >
			<td >F-12k medium</td>
			<td >ATCC&#160;</td>
			<td >302004</td>
			<td>A549 cell culture medium</td>
		</tr>
		<tr >
			<td >Fetal bovine serum</td>
			<td >Corning</td>
			<td >35-016-CV</td>
			<td></td>
		</tr>
		<tr >
			<td >HUVEC</td>
			<td ></td>
			<td ></td>
			<td>Laboratory stock&#160;</td>
		</tr>
		<tr >
			<td >L. monocytogenes</td>
			<td ></td>
			<td ></td>
			<td >NIST collections</td>
		</tr>
		<tr >
			<td >OD600 DiluPhotometer</td>
			<td >IMPLEN</td>
			<td ></td>
			<td></td>
		</tr>
		<tr >
			<td >P. aeruginosa</td>
			<td ></td>
			<td ></td>
			<td>Dr. Lori Burrows laboratory stock</td>
		</tr>
		<tr >
			<td >P. aeruginosa &#916;pilA</td>
			<td ></td>
			<td ></td>
			<td>Dr. Lori Burrows laboratory stock</td>
		</tr>
		<tr >
			<td >S. agalactiae</td>
			<td ></td>
			<td ></td>
			<td >NIST collections</td>
		</tr>
		<tr >
			<td >S. aureus</td>
			<td >BEI</td>
			<td >NR-46543</td>
			<td></td>
		</tr>
		<tr >
			<td >S. aureus &#916;saeR</td>
			<td >BEI</td>
			<td >NR-48164</td>
			<td></td>
		</tr>
		<tr >
			<td >S. rubidaea</td>
			<td ></td>
			<td ></td>
			<td >NIST collections</td>
		</tr>
		<tr >
			<td >Typical soy broth</td>
			<td >Growcells</td>
			<td >MBPE-4040</td>
			<td></td>
		</tr>
	</tbody>
</table>

automated, high-throughput detection of bacterial adherence to host cells

Identification of emerging bacterial pathogens is critical for human health and security. Bacterial adherence to host cells is an essential step in bacterial infections and constitutes a hallmark of potential threat. Therefore, examining the adherence of bacteria to host cells can be used as a component of bacterial threat assessment. A standard method for enumerating bacterial adherence to host cells is to co-incubate bacteria with host cells, harvest the adherent bacteria, plate the harvested cells on solid media, and then count the resultant colony forming units (CFU). Alternatively, bacterial adherence to host cells can be evaluated using immunofluorescence microscopy-based approaches. However, conventional strategies for implementing these approaches are time-consuming and inefficient. Here, a recently developed automated fluorescence microscopy-based imaging method is described. When combined with high-throughput image processing and statistical analysis, the method enables rapid quantification of bacteria that adhere to host cells. Two bacterial species, Gram-negative Pseudomonas aeruginosa and Gram-positive Listeria monocytogenes and corresponding negative controls, were tested to demonstrate the protocol. The results show that this approach rapidly and accurately enumerates adherent bacteria and significantly reduces experimental workloads and timelines.

To develop the fluorescence imaging-based bacterial adherence assay, P. aeruginosa strain PAO1 and its negative-adherence counterpart E. coli were used to test the protocol effectiveness, as the adherence of these bacteria to A549 cells had been reported14,20,22. First, GFP- labeled P. aeruginosa (PAO1) and GFP-labeled E. coli were co-incubated with a human immortalized epithelial cell line A5...

Watch this Scientific Journal Video about Automated, High-Throughput Detection of Bacterial Adherence to Host Cells at JoVE.com

Automated, High-Throughput Detection of Bacterial Adherence to Host Cells

Detection of host-bacterial pathogen interactions based on phenotypic adherence using high-throughput fluorescence labeling imaging along with automated statistical analysis methods enables rapid evaluation of potential bacterial interactions with host cells.

Identification of emerging bacterial pathogens is critical for human health and security. Bacterial adherence to host cells is an essential step in ...

This method provides a rapid, high-throughput detection of bacteria adherence to host cells. Compared to the conventional plating methods, it reduce hands-on time required for the quantification of the adherent bacteria. This technique is automated, time-saving and very reproducible.It also a widely applied both to most of the host cells. This method, there is very straightforward. For the first trial, the conditions like the multiplicity of infection, and also the host bacteria co-incubation time must be optimized.First harvest the bacterial cultures at an exponential phase by centrifugation at 13, 000 times G for two minutes at room temperature. After washing the cells pallet with one milliliter PBS, resuspend the bacterial palette in one milliliter PBS. Determine the concentrations of bacterial suspension by measuring optical density at 600 nanometers.Then, for staining the bacterial suspension, add two microliters of the 500 fold concentrated stock green or red staining dye into one milliliter of bacterial suspension to dilute the dye one fold. Incubate the cells at room temperature for 30 minutes with gentle rotation in the dark. After 30 minutes, centrifuge the stained bacteria at 13, 000 times G for two minutes and resuspend the pellet in one milliliter of PBS.Collect the stained bacterial cells by centrifugation at 13, 000 times G for two minutes. Resuspend the pellet in one milliliter of fresh F12 K medium and measure the optical density of each culture at 600 nanometers. Subsequentially dilute the cultures to the desired concentrations based on the multiplicity of infection and host cell concentration.For Bacterial Adherence Assay, wash the previously cultured A549 cell mono layers three times by adding 100 microliters of warm PBS to each well and gently pipette up and down. Then discard PBS. Alternatively, after adding PBS, wait for 10 seconds and then remove PBS using vacuum.To determine the kinetics of bacterial association, overlay the cells with 100 microliters of desired concentrations of bacterial suspension with different multiplicity of infection. Spin down the bacteria and incubate the infected A549 cells at 37 degrees Celsius and 5%carbon dioxide for an additional one hour. Remove the unbound bacteria by washing the mono layers five times with warm PBS as demonstrated.Next, fix the cells by adding 100 microliters of 4%formaldehyde in all the wells of a 96 well plate on the ice. After 15 minutes, wash the plate three times with PBS to remove the fixation solution. Stain in the nuclei with 50 nanograms per milliliter DAPI stain for 10 minutes at room temperature.After washing the cells with PBS, cover the infected A549 cells with 100 microliters of PBS to avoid drying and then store the plate at four degrees Celsius for up to two days in the dark or proceed for imaging. To maintain the data integrity, randomly and manually pick five locations of each well to capture the images at 20 times magnification. Capture the fluorescent images of bacteria under GFP channels, A549 cells under DAPI, and for the bacteria stained by the red fluorescent dye use PE Si five channel.Set the parameters of the rolling ball for smoothing and auto measure the point spread function of image deconvolution based on the objective for achieving better resolution. Measure the fluorescence intensity of the host cells and bacteria. Set the weakest fluorescence intensity of host cells and bacteria as the thresholds for cell count and count all the bacteria proximate to a host cell within 15 micrometers distance as the adherence bacteria.Once the cells have been counted from all the automated images, analyze critical readouts, such as host cell counts, cell sizes and shapes, total bacterial counts, and the average bacterial account per host cell, which is the most important indicator to determine bacterial adherence. After one hour of co incubation, pseudomonas aeruginosa strain PAO1 adhered to A549 cells in a dose dependent fashion. Similar results were also observed when gram-positive bacteria listeria monocytogenes and its negative control bacillus subtilis.A representative image of host adherent P aeruginosa segmentation demonstrates the ease of counting bacterial cells using this protocol. The results of the automated analyses include bacterial and host cell counts, the average bacterial counts per host cell and host cell sizes and areas representing the status of host cell health, bacterial adherence level and bacterial cyto toxicity. Apart from A549 cells, HUVECs were also tested for adherence assay.Serratia rubidaea and streptococcus agalactiae were adherent to HUVEC, but not to A549 cells, and which demonstrates the effective detection and suitability of multiple hosts to study the host bacteria interactions using this method. Host cells should reach around 90 to 100%confluence to minimize the undesirable bacteria adherence to the bottom of the wells. This technique will allowed researchers to explore the new mechanisms, the host-pest interactions.

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JoVE Journal

Immunology and Infection

High-throughput Detection Method for Influenza Virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

Quantitative High-throughput Single-cell Cytotoxicity Assay For T Cells

Cancer immunotherapy can harness the specificity of immune response to target and eliminate tumors. Adoptive cell therapy (ACT) based on the adoptive transfer of T cells genetically modified to express a chimeric antigen receptor (CAR) has shown considerable promise in clinical trials1-4. There are several advantages to using CAR+ T cells for the treatment of cancers including the ability to target non-MHC restricted antigens and to functionalize the T cells for optimal survival, homing and persistence within the host; and finally to induce apoptosis of CAR+ T cells in the event of host toxicity5.
Delineating the optimal functions of CAR+ T cells associated with clinical benefit is essential for designing the next generation of clinical trials. Recent advances in live animal imaging like multiphoton microscopy have revolutionized the study of immune cell function in vivo6,7. While these studies have advanced our understanding of T-cell functions in vivo, T-cell based ACT in clinical trials requires the need to link molecular and functional features of T-cell preparations pre-infusion with clinical efficacy post-infusion, by utilizing in vitro assays monitoring T-cell functions like, cytotoxicity and cytokine secretion. Standard flow-cytometry based assays have been developed that determine the overall functioning of populations of T cells at the single-cell level but these are not suitable for monitoring conjugate formation and lifetimes or the ability of the same cell to kill multiple targets8.
Microfabricated arrays designed in biocompatible polymers like polydimethylsiloxane (PDMS) are a particularly attractive method to spatially confine effectors and targets in small volumes9. In combination with automated time-lapse fluorescence microscopy, thousands of effector-target interactions can be monitored simultaneously by imaging individual wells of a nanowell array. We present here a high-throughput methodology for monitoring T-cell mediated cytotoxicity at the single-cell level that can be broadly applied to studying the cytolytic functionality of T cells.

We describe a single-cell high-throughput assay to measure cytotoxicity of T cells when incubated with tumor target cells. This method employs a dense, elastomeric array of sub-nanoliter wells (~100,000 wells/array) to spatially confine the T cells and target cells at defined ratios and is coupled to fluorescence microscopy to monitor effector-target conjugation and subsequent apoptosis.

Cancer immunotherapy can harness the specificity of  immune response to target and eliminate tumors. Adoptive cell therapy (ACT)  based on the adoptive ...

Automated Separation of C. elegans Variably Colonized by a Bacterial Pathogen

The wormsorter is an instrument analogous to a FACS machine that is used in studies of Caenorhabditis elegans, typically to sort worms based on expression of a fluorescent reporter. Here, we highlight an alternative usage of this instrument, for sorting worms according to their degree of colonization by a GFP-expressing pathogen. This new usage allowed us to address the relationship between colonization of the worm intestine and induction of immune responses. While C. elegans immune responses to different pathogens have been documented, it is still unknown what initiates them. The two main possibilities (which are not mutually exclusive) are recognition of pathogen-associated molecular patterns, and detection of damage caused by infection. To differentiate between the two possibilities, exposure to the pathogen must be dissociated from the damage it causes. The wormsorter enabled separation of worms that were extensively-colonized by the Gram-negative pathogen Pseudomonas aeruginosa, with the damage likely caused by pathogen load, from worms that were similarly exposed, but not, or marginally, colonized. These distinct populations were used to assess the relationship between pathogen load and the induction of transcriptional immune responses. The results suggest that the two are dissociated, supporting the possibility of pathogen recognition.

Automated Separation of C. elegans Variably Colonized by a Bacterial Pathogen

The wormsorter facilitates genetic screens in Caenorhabditis elegans by sorting worms according to expression of fluorescent reporters. Here, we describe a new usage:&#160;sorting according to colonization by a GFP-expressing pathogen, and we employ it to examine the poorly understood role of pathogen recognition in initiating immune responses.

The wormsorter is an instrument analogous to a FACS machine that is used in studies of Caenorhabditis elegans, typically to sort worms based on expression ...

Microscopy-based Assays for High-throughput Screening of Host Factors Involved in Brucella Infection of Hela Cells

Brucella species are facultative intracellular pathogens that infect animals as their natural hosts. Transmission to humans is most commonly caused by direct contact with infected animals or by ingestion of contaminated food and can lead to severe chronic infections.
Brucella can invade professional and non-professional phagocytic cells and replicates within endoplasmic reticulum (ER)-derived vacuoles. The host factors required for Brucella entry into host cells, avoidance of lysosomal degradation, and replication in the ER-like compartment remain largely unknown. Here we describe two assays to identify host factors involved in Brucella entry and replication in HeLa cells. The protocols describe the use of RNA interference, while alternative screening methods could be applied. The assays are based on the detection of fluorescently labeled bacteria in fluorescently labeled host cells using automated wide-field microscopy. The fluorescent images are analyzed using a standardized image analysis pipeline in CellProfiler which allows single cell-based infection scoring.
In the endpoint assay, intracellular replication is measured two days after infection. This allows bacteria to traffic to their replicative niche where proliferation is initiated around 12 hr after bacterial entry. Brucella which have successfully established an intracellular niche will thus have strongly proliferated inside host cells. Since intracellular bacteria will greatly outnumber individual extracellular or intracellular non-replicative bacteria, a strain constitutively expressing GFP can be used. The strong GFP signal is then used to identify infected cells.
In contrast, for the entry assay it is essential to differentiate between intracellular and extracellular bacteria. Here, a strain encoding for a tetracycline-inducible GFP is used. Induction of GFP with simultaneous inactivation of extracellular bacteria by gentamicin enables the differentiation between intracellular and extracellular bacteria based on the GFP signal, with only intracellular bacteria being able to express GFP. This allows the robust detection of single intracellular bacteria before intracellular proliferation is initiated.

Microscopy-based Assays for High-throughput Screening of Host Factors Involved in Brucella Infection of Hela Cells

Two assays for microscopy-based high-throughput screening of host factors involved in Brucella infection are described. The entry assay detects host factors required for Brucella entry and the endpoint assay those required for intracellular replication. While applicable for alternative approaches, siRNA screening in HeLa cells is used to illustrate the protocols.

Brucella species are facultative intracellular pathogens that infect animals as their natural hosts. Transmission to humans is most commonly caused by ...

Implementation of a Permeable Membrane Insert-based Infection System to Study the Effects of Secreted Bacterial Toxins on Mammalian Host Cells

Many bacterial pathogens secrete potent toxins to aid in the destruction of host tissue, to initiate signaling changes in host cells or to manipulate immune system responses during the course of infection. Though methods have been developed to successfully purify and produce many of these important virulence factors, there are still many bacterial toxins whose unique structure or extensive post-translational modifications make them difficult to purify and study in in vitro systems. Furthermore, even when pure toxin can be obtained, there are many challenges associated with studying the specific effects of a toxin under relevant physiological conditions. Most in vitro cell culture models designed to assess the effects of secreted bacterial toxins on host cells involve incubating host cells with a one-time dose of toxin. Such methods poorly approximate what host cells actually experience during an infection, where toxin is continually produced by bacterial cells and allowed to accumulate gradually during the course of infection. This protocol describes the design of a permeable membrane insert-based bacterial infection system to study the effects of Streptolysin S, a potent toxin produced by Group A Streptococcus, on human epithelial keratinocytes. This system more closely mimics the natural physiological environment during an infection than methods where pure toxin or bacterial supernatants are directly applied to host cells. Importantly, this method also eliminates the bias of host responses that are due to direct contact between the bacteria and host cells. This system has been utilized to effectively assess the effects of Streptolysin S (SLS) on host membrane integrity, cellular viability, and cellular signaling responses. This technique can be readily applied to the study of other secreted virulence factors on a variety of mammalian host cell types to investigate the specific role of a secreted bacterial factor during the course of infection.

Here, a method using a permeable membrane insert-based infection system to study the effects of Streptolysin S, a secreted toxin produced by Group A Streptococcus, on keratinocytes is described. This system can be readily applied to the study of other secreted bacterial proteins on various host cell types during infection.

Many bacterial pathogens secrete potent toxins to aid in the destruction of host tissue, to initiate signaling changes in host cells or to manipulate ...

High-throughput Detection of Respiratory Pathogens in Animal Specimens by Nanoscale PCR

Nanoliter scale real-time PCR uses spatial multiplexing to allow multiple assays to be run in parallel on a single plate without the typical drawbacks of combining reactions together. We designed and evaluated a panel based on this principle to rapidly identify the presence of common disease agents in dogs and horses with acute respiratory illness. This manuscript describes a nanoscale diagnostic PCR workflow for sample preparation, amplification, and analysis of target pathogen sequences, focusing on procedures that are different from microliter scale reactions. In the respiratory panel presented, 18 assays were each set up in triplicate, accommodating up to 48 samples per plate. A universal extraction and pre-amplification workflow was optimized for high-throughput sample preparation to accommodate multiple matrices and DNA and RNA based pathogens. Representative data are presented for one RNA target (influenza A matrix) and one DNA target (equine herpesvirus 1). The ability to quickly and accurately test for a comprehensive, syndrome-based group of pathogens is a valuable tool for improving efficiency and ergonomics of diagnostic testing and for acute respiratory disease diagnosis and management.

High-throughput testing of DNA and RNA based pathogens by nanoscale PCR is described using a syndromic canine and equine respiratory PCR panel.

Nanoliter scale real-time PCR uses spatial multiplexing to allow multiple assays to be run in parallel on a single plate without the typical drawbacks of ...

A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.

Fecal-oral transmission of acute gastroenteritis occurs from time to time, especially when people who handled food and water are infected by Salmonella spp./Shigella spp. The gold standard method for the detection of Salmonella spp./Shigella spp. is direct culture but this is labor-intensive and time-consuming. Here, we describe a high-throughput platform for Salmonella spp./Shigella spp. screening, using real-time polymerase chain reaction (PCR) combined with guided culture. There are two major stages: real-time PCR and the guided culture. For the first stage (real-time PCR), we explain each step of the method: sample collection, pre-enrichment, DNA extraction and real-time PCR. If the real-time PCR result is positive, then the second stage (guided culture) is performed: selective culture, biochemical identification and serological characterization. We also illustrate representative results generated from it. The protocol described here would be a valuable platform for the rapid, specific, sensitive and high-throughput screening of Salmonella spp./Shigella spp.

A High-throughput Platform for the Screening of Salmonella spp./Shigella spp.

Salmonella spp./Shigella spp. are common pathogens attributed to diarrhea. Here, we describe a high-throughput platform for the screening of Salmonella spp./Shigella spp. using real-time PCR combined with guided culture.

Fecal-oral transmission of acute gastroenteritis occurs from time to time, especially when people who handled food and water are infected by Salmonella ...

High-throughput Measurement of Plasma Membrane Resealing Efficiency in Mammalian Cells

In their physiological environment, mammalian cells are often subjected to mechanical and biochemical stresses that result in plasma membrane damage. In response to these damages, complex molecular machineries rapidly reseal the plasma membrane to restore its barrier function and maintain cell survival. Despite 60 years of research in this field, we still lack a thorough understanding of the cell resealing machinery. With the goal of identifying cellular components that control plasma membrane resealing or drugs that can improve resealing, we have developed a fluorescence-based high-throughput assay that measures the plasma membrane resealing efficiency in mammalian cells cultured in microplates. As a model system for plasma membrane damage, cells are exposed to the bacterial pore-forming toxin listeriolysin O (LLO), which forms large 30-50 nm diameter proteinaceous pores in cholesterol-containing membranes. The use of a temperature-controlled multi-mode microplate reader allows for rapid and sensitive spectrofluorometric measurements in combination with brightfield and fluorescence microscopy imaging of living cells. Kinetic analysis of the fluorescence intensity emitted by a membrane impermeant nucleic acid-binding fluorochrome reflects the extent of membrane wounding and resealing at the cell population level, allowing for the calculation of the cell resealing efficiency. Fluorescence microscopy imaging allows for the enumeration of cells, which constitutively express a fluorescent chimera of the nuclear protein histone 2B, in each well of the microplate to account for potential variations in their number and allows for eventual identification of distinct cell populations. This high-throughput assay is a powerful tool expected to expand our understanding of membrane repair mechanisms via screening for host genes or exogenously added compounds that control plasma membrane resealing.

Here we describe a high-throughput fluorescence-based assay that measures the plasma membrane resealing efficiency through fluorometric and imaging analyses in living cells. This assay can be used for screening drugs or target genes that regulate plasma membrane resealing in mammalian cells.

In their physiological environment, mammalian cells are often subjected to mechanical and biochemical stresses that result in plasma membrane damage. In ...

Using a Bacterial Pathogen to Probe for Cellular and Organismic-level Host Responses

There are a variety of strategies bacterial pathogens employ to survive and proliferate once inside the eukaryotic cell. The so-called 'cytosolic' pathogens (Listeria monocytogenes, Shigella flexneri, Burkholderia pseudomallei, Francisella tularensis, and Rickettsia spp.) gain access to the infected cell cytosol by physically and enzymatically degrading the primary vacuolar membrane. Once in the cytosol, these pathogens both proliferate as well as generate sufficient mechanical forces to penetrate the plasma membrane of the host cell in order to infect new cells. Here, we show how this terminal step of the cellular infection cycle of L. monocytogenes (Lm) can be quantified by both colony-forming unit assays and flow cytometry and give examples of how both pathogen- and host-encoded factors impact this process. We also show a close correspondence of Lm infection dynamics of cultured cells infected in vitro and those of hepatic cells derived from mice infected in vivo. These function-based assays are relatively simple and can be readily scaled up for discovery-based high-throughput screens for modulators of eukaryotic cell function.

We describe both in vitro and in vivo infection assays that can be used to analyze the activities of host-encoding factors.

There are a variety of strategies bacterial pathogens employ to survive and proliferate once inside the eukaryotic cell. The so-called 'cytosolic' ...

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 ...