This project was supported partly by a grant for National Institutes of Health NIAID (for A.J.B. and L.G.A., R01 AI076246). The Salmonella mutant collection was partly supported by National Institutes of Health grants (for M.M., U01 A152237-05, R01 AI07397-01, R01 AI039557-11 and R01 AI075093-01), partly by National Institutes of Health grants (for H.A.P, R21 AI083964-01, 1R0 1AI083646-01, 1R56AI077645, R01 AI075093). We thank Steffen Prowollik for replica plating and confirming the mutants in the collection.

1. Murine Macrophage RAW264.7 Cell Culture
<ol>
	<li>Grow low passage number murine macrophage cells, RAW264.7 (The ATCC&#174; Number, TIB-71) in a T-75 cell culture flask vented filter cap in Dulbecco&#39;s Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 0.5% NaHCO3, and 1% 100x Nonessential amino acids (NEAA) at 37&#176;C, in a 5% CO2 incubator.</li>
	<li>Once cells reach a 60-80% confluence in the flask, use a cell scraper to harvest cells, and count the cells in a hemacytometer and calculate the cell concentration.</li>
	<li>Resuspend the cells and dilute the cell concentration into 2.5 x 105/ml in fresh DMEM cell culture medium. Use multichannel pipettes to plate 200 &#956;l of DMEM cell culture medium containing 5 x 104 cells in each well of 96-well cell culture plates.</li>
	<li>Plate four wells of each Salmonella strain. Set up three separate plates for one set of phagocytic cells invasion assay, and mark them with &#8220;association&#8221;, &#8220;invasion&#8221; and &#8220;replication&#8221;, respectively.</li>
	<li>Place the plates in the 5% CO2 incubator at 37 &#176;C ON to allow the macrophage cells to attach to the bottom of the wells.</li>
</ol>
2. Preparation of Salmonella Wild-type and Mutants
<ol>
	<li>On the same day of preparing the macrophage RAW264.7 cells, pick single colonies of wild-type (WT) Salmonella enterica serotype Typhimurium 14028s, DinvA mutant, DphoP mutant, and the desired test mutant strains, and culture them in Luria-Bertani (LB) broth supplemented with antibiotics as appropriate. Use each set of the phagocytic cells invasion assays to test up to 10 mutant strains (DinvA mutant and DphoP mutant are defective in invasion and intracellular replication, respectively).</li>
	<li>Grow the bacteria for 14 hr at 37 &#176;C with shaking at 220 rpm in 5 ml each of LB broth in loosely capped 14 ml polypropylene in a round bottom tube. LB broth contains appropriate antibiotics, in our case, most of mutant strains are resistant to Kanamycin, 50 &#181;g/ml</li>
	<li>The next day, subculture each of the ON cultures of Salmonella strains in plain 5 ml of LB broths at a ratio of 1:50 for an additional 4 hr with shaking at 220 rpm.</li>
	<li>Read OD600 values of each bacterial culture on a spectrophotometer, and each read should range from 0.6-1.2 to optimize Salmonella pathogenicity island-1 type III secretion system (SPI-1 TTSS) gene expression for invasion.</li>
	<li>Use the formula of 1 OD600 = 7.5 x 108 CFU/ml to estimate the bacterial concentration, then dilute bacteria to a concentration of 5 x 106 CFU/ml in fresh DMEM cell culture medium.</li>
</ol>
3. Invasion Assay in 96-well Culture Plate
<ol>
	<li>Remove three 96-well cell culture plates from the CO2 incubator and wash each well once with 200 &#956;l of 1x PBS buffer.</li>
	<li>After washing and complete removal of PBS, add 200 &#956;l bacteria in DMEM medium (see above) into each well. This results in 1 x&#160;106 Salmonella cells in each well and multiplicity of infection (MOI) of 20:1.</li>
	<li>Centrifuge the plates at 1,000 x&#160;g in a sealed carrier for 10 min, then replace plates (time zero) in a 37 &#176;C, 5% CO2 incubator for 30 min. For each strain, set up at least four duplicate wells.</li>
	<li>After 30 min, remove plates from the incubator and wash three times with 200 &#956;l&#160;of 1x PBS to remove unassociated bacteria.</li>
	<li>Following washing, save the plate labeled with &#8220;association&#8221; for further treatment. Add 200 &#956;l of DMEM medium containing 100 &#956;g/ml Gentamicin to each well of the plates marked with &#8220;invasion&#8221; and &#8220;replication&#8221; in order to kill the extracellular Salmonella. Return the plates to 37 &#176;C, 5% CO2 incubator for an additional hr.</li>
	<li>Save one well from each infected strain for recording macrophage cell count, treat the rest of wells on the &#8220;association&#8221; plate with 200 &#956;l of 1x PBS containing 1% Triton X-100 for 10 min. The Triton solution will lyse macrophage cells and release associated Salmonella.</li>
	<li>Harvest Salmonella from each well and place them into 1.5 ml Eppendorf tubes. Perform three 10 fold serial dilutions with 900&#181;l 1x PBS on the harvested samples from each well, vortex is performed between each dilution.</li>
	<li>Plate the third dilution, 10-3, on either LB (WT) or LB Kan (mutants) plates. Label the plates with appropriate Salmonella strain name, dilution number, time point and date.</li>
	<li>After vortexing the third dilution tube, dispense 10 &#181;l sample on the surface of the agar and repeat four times for a total of 5 drops. Be sure to space the five 10 &#956;l drops evenly on the Petri dish plates7.</li>
	<li>After the drops soak into the agar, turn the plates over and incubate overnight at 37 &#176;C, 5% CO2&#160;incubator.</li>
	<li>Treat wells saved for counting of macrophages with 150 &#181;l 1xPBS containing 0.25% Trypsin-EDTA for 10 min.</li>
	<li>After trypsinization, place macrophages into 1.5 ml Eppendorf tubes and treat them with 50 &#181;l of FBS to neutralize Trypsin/EDTA solution, stain the cells with 0.4% Trypan blue and score them through using hemacytometer.</li>
	<li>When the one hr incubation has elapsed, remove the &#8220;invasion&#8221; and &#8220;replication&#8221; plates from the CO2 incubator, and wash each well as &#8220;Step 3.4&#8221;.</li>
	<li>Save the &#8220;invasion&#8221; plate for further treatment as &#8220;Step 3.6-3.12&#8221;.</li>
	<li>Add 200 &#181;l of DMEM medium containing 10 &#956;g/ml Gentamicin to the &#8220;replication&#8221; plate to maintain clearance of extracellular Salmonella in the medium. Return the plate to 37 &#176;C, 5% CO2 incubator for an additional 22.5 hr.</li>
	<li>The next day, remove the &#8220;replication&#8221; plate from 37 &#176;C, 5% CO2 incubator, and wash each well as &#8220;Step 3.4&#8221; and treat them as &#8220;Step 3.6-3.12&#8221;.</li>
	<li>Lastly, remove the agar plates after incubation overnight in 37 &#176;C incubator and score the number of bacterial colonies.</li>
	<li>A good colony distribution should be between 10 and 100 colonies, each spot approximately contains 2 to 20 colonies,&#160;it would be hard to score if there were more than 20 colonies on one spot. If the count is too low or too high, replate the sample with 10-fold higher or lower dilutions as needed.</li>
</ol>
4. Data Analysis
<ol>
	<li>Calculate the CFU (colony formation units per ml) of each plate based on the plating volume and dilution factor.</li>
	<li>Ascertain the number of Salmonella per macrophage through the recorded macrophage cell count from each strain.</li>
	<li>Calculate the geometric means of CFU per macrophage from at least three independent experiments for cell association, invasion or replication, respectively, and normalize further to the WT for the relative value.</li>
	<li>Analyze the data for association, invasion, and replication by Student&#8217;s t-test respectively, by comparing each strain to WT, and determine the statistical significance by the p-value.</li>
</ol>

<ol>
	<li>Haraga, A., Ohlson, M. B., Miller, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Salmonellae+interplay+with+host+cells.">Salmonellae interplay with host cells.</a> Nat Rev Microbiol. 6, 53-66 (2008).</li><li>Mandell, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interaction+of+intraleukocytic+bacteria+and+antibiotics.">Interaction of intraleukocytic bacteria and antibiotics.</a> The Journal of clinical investigation. 52, 1673-1679 (1973).</li><li>Elsinghorst, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+invasion+by+gentamicin+resistance.">Measurement of invasion by gentamicin resistance.</a> Methods Enzymol. 236, 405-420 (1994).</li><li>Elsinghorst, E. A., Weitz, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epithelial+cell+invasion+and+adherence+directed+by+the+enterotoxigenic+Escherichia+coli+tib+locus+is+associated+with+a+104-kilodalton+outer+membrane+protein.">Epithelial cell invasion and adherence directed by the enterotoxigenic Escherichia coli tib locus is associated with a 104-kilodalton outer membrane protein.</a> Infect Immun. 62, 3463-3471 (1994).</li><li>Behlau, I., Miller, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+PhoP-repressed+gene+promotes+Salmonella+typhimurium+invasion+of+epithelial+cells.">A PhoP-repressed gene promotes Salmonella typhimurium invasion of epithelial cells.</a> J Bacteriol. 175, 4475-4484 (1993).</li><li>Hueck, C. J., 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=Salmonella+typhimurium+secreted+invasion+determinants+are+homologous+to+Shigella+Ipa+proteins.">Salmonella typhimurium secreted invasion determinants are homologous to Shigella Ipa proteins.</a> Mol Microbiol. 18, 479-490 (1995).</li><li>Steele-Mortimer, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Infection+of+epithelial+cells+with+Salmonella+enterica.">Infection of epithelial cells with Salmonella enterica.</a> Methods Mol Biol. 431, 201-211 (2008).</li><li>Foster, J. W., Spector, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+Salmonella+survive+against+the+odds.">How Salmonella survive against the odds.</a> Annu Rev Microbiol. 49, 145-174 (1995).</li><li>Edwards, A. M., Massey, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Invasion+of+human+cells+by+a+bacterial+pathogen.">Invasion of human cells by a bacterial pathogen.</a> Journal of visualized experiments JoVE. 10, (2011).</li><li>Molinari, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+played+by+the+group+A+streptococcal+negative+regulator+Nra+on+bacterial+interactions+with+epithelial+cells.">The role played by the group A streptococcal negative regulator Nra on bacterial interactions with epithelial cells.</a> Mol Microbiol. 40, 99-114 (2001).</li><li>Van der Velden, A. W., Lindgren, S. W., Worley, M. J., Heffron, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Salmonella+pathogenicity+island+1-independent+induction+of+apoptosis+in+infected+macrophages+by+Salmonella+enterica+serotype+typhimurium.">Salmonella pathogenicity island 1-independent induction of apoptosis in infected macrophages by Salmonella enterica serotype typhimurium.</a> Infect Immun. 68, 5702-5709 (2000).</li><li>Santos, R. L., Zhang, S., Tsolis, R. M., Baumler, A. J., Adams, 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=Morphologic+and+molecular+characterization+of+Salmonella+typhimurium+infection+in+neonatal+calves.">Morphologic and molecular characterization of Salmonella typhimurium infection in neonatal calves.</a> Vet Pathol. 39, 200-215 (2002).</li><li>Lawhon, S. D., 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=Role+of+SPI-1+secreted+effectors+in+acute+bovine+response+to+Salmonella+enterica+Serovar+Typhimurium+a+systems+biology+analysis+approach.">Role of SPI-1 secreted effectors in acute bovine response to Salmonella enterica Serovar Typhimurium a systems biology analysis approach.</a> PLoS One. 6, e26869 (2011).</li><li>Drecktrah, D., Knodler, L. A., Galbraith, K., Steele-Mortimer, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Salmonella+SPI1+effector+SopB+stimulates+nitric+oxide+production+long+after+invasion.">The Salmonella SPI1 effector SopB stimulates nitric oxide production long after invasion.</a> Cell Microbiol. 7, 105-113 (2005).</li></ol>

We have nothing to disclose.

The Gentamicin protection assay is widely used to study the invasion and replication of intracellular bacterial pathogens inside host cell, and it is especially an important biological tool for studying pathogens, like Salmonella, whose invasion is the prerequisite step for establishing infection1. The standard Gentamicin protection assay in Salmonella research community is implemented in 24-well culture dish5. Though the use of 48 or even 96-well plates were discussed before for h...

Nontyphoidal Salmonella are important causes of enteric diseases in all vertebrates. Salmonellosis in humans is among the top bacterial food-borne diseases1. Characterization of the molecular mechanisms that underpin the interactions of Salmonella with their animal hosts is mainly achieved through the study of Salmonella enterica serotype Typhimurium (STM) in tissue culture and animal models of infection. Gaining insights in STM-host interactions will help us understand how Salmonella survive and grow inside host cells. The first challenge in studying these interactions is to identify as many participating factors as possible from both host and pathogen, but these endeavors are largely obstructed by the significant difficulties of dealing with two independent complex biological systems simultaneously, i.e., host and Salmonella, under physiological conditions. Additionally, the large repertoire of Salmonella and host genes potentially encoding factors involved in host interactions require high-throughput biological platform to tackle this challenge.
A modified, standardized assay to phenotype Salmonella association, invasion&#160;and replication in macrophages with high-throughput capacity was developed to examine a large set of genes likely engaging in Salmonella-host interactions. The Gentamicin protection assay was developed in 19732, but was first thoroughly described by Elsinghorst in 19943,4. It has now become a standard tool for studying many intracellular bacterial pathogens ex vivo, including Salmonella5,6. Internalized bacteria avoid being killed by some antibiotics, like Gentamicin, that cannot penetrate eukaryotic cells3. By taking advantage of this phenomenon, the Gentamicin protection assay measures the survival and growth of intracellular bacterial pathogens. Three events during the infection, i.e., association with eukaryotic cells, invasion and replication, can be evaluated for intracellular bacterial pathogens based on the time interval between infection, Gentamicin treatment, and further incubation (Figure&#160;1). Eukaryotic cell lines provide a physiological environment that is less complex than relevant animal models for host-pathogen interaction studies.
The Gentamicin protection assay is an appropriate platform to study STM-host interactions, but the standard assay in a 24-well culture dish has low-throughput capacity. Computational analysis of in vivo datasets identified 149 Salmonella gene products that are predicted to interact with approximately 300 host gene products (unpublished data). The standard Gentamicin protection assay does not have the capacity to phenotype this number of mutants efficiently.
In addition, the Gentamicin protection assay can theoretically detect the invasion of even a single bacterium. Because of this inherent sensitivity, the raw data are susceptible to technical variances when repeated at different times. The internal controls and relative data presentation after normalization are essential for meaningful interpretation of the results. Given these considerations, a modified, standardized Gentamicin protection assay was developed to enhance testing capacity and increase precision.
The following protocol is detailed and illustrated to perform the modified Gentamicin protection assay using 96-well culture dishes and the murine macrophage RAW264.7 cell line. Compared to the standard protocol in 24-well culture dishes, the modified protocol has the following advantages: 1) Using 96-well culture dishes allows up to 10 different mutant strains to be phenotyped including internal positive and negative controls with sufficient statistical power; 2) The variance of results is significantly reduced, because the mutant strains are tested in the same culture dish and at the same time; 3) The use of multichannel pipettes increases throughput while reducing operator fatigue. Lastly, comparing to 24-well culture dishes, concerns of less host cells per well in 96-well culture dish were addressed through protocol optimization and standardization.
In summary, the modified, standardized assay to in vitro phenotype Salmonella or other bacterial association, invasion and replication in phagocytic cells increases precision and achieves high-throughput capacity while reducing operator fatigue.

<table><tbody><tr><td>Dulbecco&#039;s Modified Eagle Medium (DMEM)</td><td>Life Technologies</td><td>11965</td><td></td></tr><tr><td>Fetal bovine serum</td><td>HyClone</td><td>SH30910.03</td><td></td></tr><tr><td>T-75 Cell culture flask vented filter cap</td><td>Nest Biotechnology</td><td>708003</td><td></td></tr><tr><td>100x Non-Essential Amino Acids</td><td>Life Technologies</td><td>11140</td><td></td></tr><tr><td>Cell scraper</td><td>BD Falcon</td><td>353086</td><td></td></tr><tr><td>96-well Cell culture plate</td><td>Corning Incorporated</td><td>3595</td><td></td></tr><tr><td>Luria-Bertani (LB) broth</td><td>MP Biomedicals</td><td>3002-075</td><td></td></tr><tr><td>14 ml Polypropylene Round-Bottom Tube</td><td>BD Falcon</td><td>352059</td><td></td></tr><tr><td>PBS pH 7.4 (1x)</td><td>Life Technologies</td><td>10010</td><td></td></tr><tr><td>Triton X-100</td><td>Sigma</td><td>T-8787</td><td></td></tr><tr><td>Kanamycin solution</td><td>Sigma</td><td>K0254</td><td></td></tr><tr><td>Gentamicin solution</td><td>Sigma</td><td>G1272</td><td></td></tr><tr><td>0.25% Trypsin-EDTA</td><td>Life Technologies</td><td>25200</td><td></td></tr><tr><td>Trypan blue</td><td>Sigma</td><td>T8154</td><td></td></tr></tbody></table>

high-throughput assay to phenotype salmonella enterica typhimurium association, invasion, and replication in macrophages

Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying Salmonella-host interactions are&#160;important to elucidate the molecular pathogenesis of Salmonella infection. The Gentamicin protection assay to phenotype Salmonella association, invasion and replication in phagocytic cells was adapted to allow high-throughput screening to define the roles of deletion mutants of Salmonella enterica serotype Typhimurium in host interactions using RAW 264.7 murine macrophages. Under this protocol, the variance in measurements is significantly reduced compared to the standard protocol, because wild-type and multiple mutant strains can be tested in the same culture dish and at the same time. The use of multichannel pipettes increases the throughput and enhances precision. Furthermore, concerns related to using less host cells per well in 96-well culture dish were addressed. Here, the protocol of the modified in vitro Salmonella invasion assay using phagocytic cells was successfully employed to phenotype 38 individual Salmonella deletion mutants for association, invasion and intracellular replication. The in vitro phenotypes are presented, some of which were subsequently confirmed to have in vivo phenotypes in an animal model. Thus, the modified, standardized assay to phenotype Salmonella association, invasion and replication in macrophages with high-throughput capacity could be utilized more broadly to study bacterial-host interactions.

See representative results (Figure 2) after the data are plotted based on the modified phagocytic cell invasion assay. The data include five different strains, WT, &#916;invA, &#916;phoP, mutant A, and mutant B. &#916;invA,&#160;known to be defective for invasion, and &#916;phoP known to be defective for replication8, are used as positive controls to assess the experimental validity. Indeed, in the modified invasion assay, a &#916;invA mutant is int...

Watch this Scientific Journal Video about High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages at JoVE.com

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

A high-throughput assay to in vitro phenotype Salmonella or other bacterial association, invasion, and replication in phagocytic cells with high-throughput capacity was developed. The method was employed to evaluate Salmonella gene knockout mutant strains for their involvements in host-pathogen interactions.

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

Salmonella species are zoonotic pathogens and leading causes of food borne illnesses in humans and livestock1. Understanding the mechanisms underlying ...

high-throughput-assay-to-phenotype-salmonella-enterica-typhimurium

Research

JoVE Journal

Immunology and Infection

12.6K Views.  Texas A&M University.  Een high-throughput assay in vitro fenotype Salmonella of andere bacteriële vereniging, invasie en replicatie in fagocytische cellen met hoge doorvoer capaciteit ontwikkeld. De methode werd gebruikt om Salmonella-gen knock-out mutantstammen evalueren op hun betrokkenheid in gastheer-pathogeen interacties. 

Video: High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

Analyzing Cellular Internalization of Nanoparticles and Bacteria by Multi-spectral Imaging Flow Cytometry

Nanoparticulate systems have emerged as valuable tools in vaccine delivery through their ability to efficiently deliver cargo, including proteins, to antigen presenting cells1-5. Internalization of nanoparticles (NP) by antigen presenting cells is a critical step in generating an effective immune response to the encapsulated antigen. To determine how changes in nanoparticle formulation impact function, we sought to develop a high throughput, quantitative experimental protocol that was compatible with detecting internalized nanoparticles as well as bacteria. To date, two independent techniques, microscopy and flow cytometry, have been the methods used to study the phagocytosis of nanoparticles. The high throughput nature of flow cytometry generates robust statistical data. However, due to low resolution, it fails to accurately quantify internalized versus cell bound nanoparticles. Microscopy generates images with high spatial resolution; however, it is time consuming and involves small sample sizes6-8. Multi-spectral imaging flow cytometry (MIFC) is a new technology that incorporates aspects of both microscopy and flow cytometry that performs multi-color spectral fluorescence and bright field imaging simultaneously through a laminar core. This capability provides an accurate analysis of fluorescent signal intensities and spatial relationships between different structures and cellular features at high speed.
	Herein, we describe a method utilizing MIFC to characterize the cell populations that have internalized polyanhydride nanoparticles or Salmonella enterica serovar Typhimurium. We also describe the preparation of nanoparticle suspensions, cell labeling, acquisition on an ImageStreamX system and analysis of the data using the IDEAS application. We also demonstrate the application of a technique that can be used to differentiate the internalization pathways for nanoparticles and bacteria by using cytochalasin-D as an inhibitor of actin-mediated phagocytosis.

In this article, we describe a method utilizing multi-spectral imaging flow cytometry to quantify the internalization of polyanhydride nanoparticles or bacteria by RAW 264.7 cells.

Nanoparticulate  systems have emerged as valuable tools in vaccine delivery through their  ability to efficiently deliver cargo, including proteins, to ...

Bioengineering

A Microscopic Phenotypic Assay for the Quantification of Intracellular Mycobacteria Adapted for High-throughput/High-content Screening

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since several decades, the sudden burst of multi- and extensively-drug resistant strains is a serious threat for the control of tuberculosis. Therefore, it is essential to identify new targets and pathways critical for the causative agent of the tuberculosis, Mycobacterium tuberculosis (Mtb) and to search for novel chemicals that could become TB drugs. One approach is to set&#160;up methods suitable for the genetic and chemical screens of large scale libraries enabling the search of a needle in a haystack. To this end, we developed a phenotypic assay relying on the detection of fluorescently labeled Mtb within fluorescently labeled host&#160;cells using automated confocal microscopy. This in vitro assay allows an image based quantification of the colonization process of Mtb&#160;into the host and was optimized for the 384-well microplate format, which is proper for screens of siRNA-, chemical compound- or Mtb mutant-libraries. The images are then processed for multiparametric analysis, which provides read&#160;out inferring on the pathogenesis of Mtb&#160;within host cells.

Here, we describe a phenotypic assay applicable to the High-throughput/High-content screens of small-interfering synthetic RNA (siRNA), chemical compound, and Mycobacterium tuberculosis mutant libraries. This method relies on the detection of fluorescently labeled Mycobacterium tuberculosis within fluorescently labeled host&#160;cell using automated confocal microscopy.

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since ...

Forward Genetics Screens Using Macrophages to Identify Toxoplasma gondii Genes Important for Resistance to IFN-&#947;-Dependent Cell Autonomous Immunity

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan pathogen. The parasite invades and replicates within virtually any warm blooded vertebrate cell type. During parasite invasion of a host cell, the parasite creates a parasitophorous vacuole (PV) that originates from the host cell membrane independent of phagocytosis within which the parasite replicates. While IFN-dependent-innate and cell mediated immunity is important for eventual control of infection, innate immune cells, including neutrophils, monocytes and dendritic cells, can also serve as vehicles for systemic dissemination of the parasite early in infection. An approach is described that utilizes the host innate immune response, in this case macrophages, in a forward genetic screen to identify parasite mutants with a fitness defect in infected macrophages following activation but normal invasion and replication in na&#239;ve macrophages. Thus, the screen isolates parasite mutants that have a specific defect in their ability to resist the effects of macrophage activation. The paper describes two broad phenotypes of mutant parasites following activation of infected macrophages: parasite stasis versus parasite degradation, often in amorphous vacuoles. The parasite mutants are then analyzed to identify the responsible parasite genes specifically important for resistance to induced mediators of cell autonomous immunity. The paper presents a general approach for the forward genetics screen that, in theory, can be modified to target parasite genes important for resistance to specific antimicrobial mediators. It also describes an approach to evaluate the specific macrophage antimicrobial mediators to which the parasite mutant is susceptible. Activation of infected macrophages can also promote parasite differentiation from the tachyzoite to bradyzoite stage that maintains chronic infection. Therefore, methodology is presented to evaluate the importance of the identified parasite gene to establishment of chronic infection.

Forward Genetics Screens Using Macrophages to Identify Toxoplasma gondii Genes Important for Resistance to IFN-&#947;-Dependent Cell Autonomous Immunity

Forward genetics is a powerful approach to identify genes in intracellular pathogens important for resistance to cell autonomous immunity. The current approach uses innate immune cells, specifically macrophages, to identify novel Toxoplasma gondii genes important for immune evasion.

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan pathogen. The parasite invades and replicates within ...

Quantification of Cytosolic vs. Vacuolar Salmonella in Primary Macrophages by Differential Permeabilization

Intracellular bacterial pathogens can replicate in the cytosol or in specialized pathogen-containing vacuoles (PCVs). To reach the cytosol, bacteria like Shigella flexneri and Francisella novicida need to induce the rupture of the phagosome. In contrast, Salmonella typhimurium replicates in a vacuolar compartment, known as Salmonella-containing vacuole (SCV). However certain mutants of Salmonella fail to maintain SCV integrity and are thus released into the cytosol. The percentage of cytosolic vs. vacuolar bacteria on the level of single bacteria can be measured by differential permeabilization, also known as phagosome-protection assay. The approach makes use of the property of detergent digitonin to selectively bind cholesterol. Since the plasma membrane contains more cholesterol than other cellular membranes, digitonin can be used to selectively permeabilize the plasma membrane while leaving intracellular membranes intact. In brief, following infection with the pathogen expressing a fluorescent marker protein (e.g. mCherry among others), the plasma membrane of host cells is permeabilized with a short incubation in digitonin containing buffer. Cells are then washed and incubated with a primary antibody (coupled to a fluorophore of choice) directed against the bacterium of choice (e.g. anti-Salmonella-FITC) and washed again. If unmarked bacteria are used, an additional step can be done, in which all membranes are permeabilized and all bacteria stained with a corresponding antibody. Following the staining, the percentage of vacuolar and cytosolic bacteria can be quantified by FACS or microscopy by counting single or double-positive events. Here we provide experimental details for use of this technique with the bacterium Salmonella typhimurium. The advantage of this assay is that, in contrast to other assay, it provides a quantification on the level of single bacteria, and if analyzed by microscopy provides the exact number of cytosolic and vacuolar bacteria in a given cell.

Quantification of Cytosolic vs. Vacuolar Salmonella in Primary Macrophages by Differential Permeabilization

We describe the quantification of cytosolic and vacuolar Salmonella typhimurium in bone-marrow derived macrophages using differential digitonin permeabilization.

Intracellular bacterial pathogens can replicate in the cytosol or in specialized pathogen-containing vacuoles (PCVs). To reach the cytosol, bacteria like ...

Isolation of Salmonella typhimurium-containing Phagosomes from Macrophages

Salmonella typhimurium is a facultative intracellular bacterium that causes gastroenteritis in humans. After invasion of the lamina propria, S. typhimurium bacteria are quickly detected and phagocytized by macrophages, and contained in vesicles known as phagosomes in order to be degraded. Isolation of S. typhimurium-containing phagosomes have been widely used to study how S. typhimurium infection alters the process of phagosome maturation to prevent bacterial degradation. Classically, the isolation of bacteria-containing phagosomes has been performed by sucrose gradient centrifugation. However, this process is time-consuming, and requires specialized equipment and a certain degree of dexterity. Described here is a simple and quick method for the isolation of S. typhimurium-containing phagosomes from macrophages by coating the bacteria with biotin-streptavidin-conjugated magnetic beads. Phagosomes obtained by this method can be suspended in any buffer of choice, allowing the utilization of isolated phagosomes for a broad range of assays, such as protein, metabolite, and lipid analysis. In summary, this method for the isolation of S. typhimurium-containing phagosomes is specific, efficient, rapid, requires minimum equipment, and is more versatile than the classical method of isolation by sucrose gradient-ultracentrifugation.

Isolation of Salmonella typhimurium-containing Phagosomes from Macrophages

We describe here a simple and quick method for the isolation of Salmonella typhimurium-containing phagosomes from macrophages by coating the bacteria with biotin and streptavidin.

Salmonella typhimurium is a facultative intracellular bacterium that causes gastroenteritis in humans. After invasion of the lamina propria, S. ...

NF-&#954;B-dependent Luciferase Activation and Quantification of Gene Expression in Salmonella Infected Tissue Culture Cells

The dimeric transcription factor NF-&#954;B regulates many cellular response pathways, including inflammatory pathways by inducing the expression of various cytokines and chemokines. NF-&#954;B is constitutively expressed and is sequestered in the cytosol by the inhibitory protein nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha (I&#954;B&#945;). Activation of NF-&#954;B requires the degradation of I&#954;B&#945;, which then exposes a nuclear localization signal on NF-&#954;B and promotes its trafficking to the nucleus. Once in the nucleus, NF-&#954;B binds to the promotor region of NF-&#954;B target genes such as interleukin 6 (IL-6) and IL-23, to promote their expression.
The activation of NF-&#954;B occurs independently of transcription or translation. Therefore, the activation state of NF-&#954;B must be measured either by quantifying NF-&#954;B specifically in the nucleus, or by quantifying expression of NF-&#954;B target genes. In this protocol, cells stably transfected with an NF-&#954;B::luciferase reporter construct are assayed for NF-&#954;B activation using in vitro tissue culture techniques. These cells are infected with Salmonella Typhimurium to activate NF-&#954;B, which traffics to the nucleus and binds to &#954;B sites in the promoter region of luciferase, inducing its expression. Cells are lysed and analyzed with the luciferase assay system. The amount of luciferase produced by the cells correlates with the intensity of the luminescence signal, which is detected by a plate reader. The luminescence signal generated by this procedure provides a quick and highly sensitive method by which to assess NF-&#954;B activation under a range of conditions. This protocol also utilizes quantitative reverse transcription PCR (RT-qPCR) to detect relative mRNA levels that are indicative of gene expression.

Here, we present a protocol to quickly and easily measure nuclear factor kappa-light-chain-enhancer of activated B cells (NF-&#954;B) activation in cell lines expressing NF-&#954;B::luciferase reporter constructs, via measurements of luminescence in the cell lysate. Additionally, gene expression is determined via RT-qPCR isolated from cells infected with Salmonella Typhimurium.

The dimeric transcription factor NF-&#954;B regulates many cellular response pathways, including inflammatory pathways by inducing the expression of ...

Characterizing Salmonella Typhimurium-induced Septic Peritonitis in Mice

Sepsis is a dysregulated host immune response to microbial invasion or tissue damage, leading to organ injury at a site distant from that of the infection or damage. Currently, the widely used mice models of sepsis include lipopolysaccharide (LPS)-induced endotoxemia, cecal ligation and puncture (CLP), and monobacterial infection model systems. This protocol describes a method to study the host responses during Salmonella Typhimurium infection-induced septic peritonitis in mice. S. Typhimurium, a Gram-negative intracellular pathogen, causes typhoid-like disease in mice.
This protocol elaborates the culture preparation, induction of septic peritonitis in mice through intraperitoneal injection, and methods to study systemic host responses. Furthermore, the assessment of bacterial burden in different organs and the flow cytometric analysis of increased neutrophil numbers in the peritoneal lavage is presented. Salmonella Typhimurium-induced sepsis in mice leads to an increase in proinflammatory cytokines and rapid infiltration of neutrophils in the peritoneal cavity, leading to lower survival.
Every step in this protocol has been optimized, resulting in high reproducibility of the pathogenesis of septic peritonitis. This model is useful for studying immunological responses during bacterial sepsis, the roles of different genes in disease progression, and the effects of drugs to attenuate sepsis.

Characterizing Salmonella Typhimurium-induced Septic Peritonitis in Mice

This protocol describes the induction of Gram-negative monobacterial sepsis in a mouse model system. The model is useful in investigating the inflammatory and lethal host responses during sepsis.

Sepsis is a dysregulated host immune response to microbial invasion or tissue damage, leading to organ injury at a site distant from that of the infection ...

Automated Analysis of Intracellular Phenotypes of Salmonella Using ImageJ

Salmonella is an enteric pathogen able to invade the intestinal epithelium and replicate in enterocytes, both inside Salmonella-specific vacuoles and free in the cytosol (cytosolic hyper-replication). These different phenotypes of intracellular replication drive to different pathways of pathogenesis, i.e., cytosolic hyper-replication induces inflammatory cell death and extrusion into the gut lumen, while vacuolar replication leads to trans-epithelium penetration and systemic spread. Significant effort was made to create microscopy tools to study the behavior of Salmonella inside invaded cells, such as the pCHAR-Duo fluorescence reporter plasmid that allows discrimination between vacuolar and cytosolic bacteria by differential expression of mCherry and GFP. However, intracellular phenotypes are often manually scored, a time-consuming procedure that limits analysis to a small number of samples and cells. To overcome these limitations, two complementary and automated image analyses were developed using ImageJ, a freely available image analysis software. In the high-throughput protocol, epithelial cells were infected with Salmonella carrying pCHAR-Duo using 96-well plates. Imaging was performed using an automated fluorescence microscope. Then, two image analysis methods were applied to measure the intracellular behavior of Salmonella at different detail levels. The first method measures the overall intracellular bacterial load and the extent of cytosolic hyper-replication. It is fast and allows the scoring of a high number of cells and samples, making it suitable for high-throughput assays such as screening experiments. The second method performs single-cell analysis to determine the percentage of infected cells, the mean vacuolar load of Salmonella, and the cytosolic hyper-replication rate giving greater details about Salmonella behavior inside epithelial cells. The protocols can be performed by specifically designed ImageJ scripts to automatically run batch analyses of the major steps of Salmonella-enterocyte interaction.

Automated Analysis of Intracellular Phenotypes of Salmonella Using ImageJ

Salmonella invades and replicates inside intestinal epithelial cells both in Salmonella-specific vacuoles and free in the cytosol (hyper-replication). A high-throughput fluorescence microscopy-based protocol is described here to quantify the intracellular phenotypes of Salmonella by two complementary image analyses through ImageJ, reaching single-cell resolution and scoring.

Salmonella is an enteric pathogen able to invade the intestinal epithelium and replicate in enterocytes, both inside Salmonella-specific vacuoles and free ...

An In Vitro Assay to Quantify the Intracellular Growth of Parasite in Macrophages

Source: Sarkar, A., et al. <a href="https://app.jove.com/v/57486">Quantification of Intracellular Growth Inside Macrophages is a Fast and Reliable Method for Assessing the Virulence of Leishmania Parasites.</a> J. Vis. Exp. (2018).
This video demonstrates an assay to quantify the intracellular growth of parasites in bone marrow-derived macrophages (BMMs). The macrophage cells are infected with the motile and non-motile invasive stages of Leishmania, metacyclic promastigotes and amastigotes, respectively. The parasites invade the macrophages, getting internalized into a parasitophorous vacuole and multiplying inside. The intracellular parasite growth is quantified using a microscope upon fluorescently staining the macrophage and parasite nuclei.

1. Plating BMMs on Coverslips for Infection 

	Prepare 6-well tissue culture plates by placing four (4) sterile 12 mm glass coverslips (autoclaved and ...

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Immunology

Immunodiagnostics

Specialized Assays

An Assay to Quantify Cytosolic and Vacuolar Salmonella in Infected Primary Macrophages

Source: Meunier, E., et al. <a href="https://app.jove.com/v/52960">Quantification of Cytosolic vs. Vacuolar Salmonella in Primary Macrophages by Differential Permeabilization.</a> J. Vis. Exp. (2015).
This video demonstrates an assay to quantify cytosolic and vacuolar Salmonella typhimurium inside bone marrow-derived macrophages using differential permeabilization. The macrophages are infected with a fluorescent protein-expressing Salmonella, which is internalized inside a specialized vacuolar structure called Salmonella-containing vacuole or SCV. A subset of bacteria escape the SCV and enter the cytosol. The cholesterol-rich plasma membrane of macrophages is permeabilized using digitonin, leaving the SCV intact. Upon labeling the cytosolic bacteria with a fluorescently tagged antibody, the percentage of vacuolar and cytosolic bacteria is quantified using fluorescence-activated cell sorting (FACS).

High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages

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