The authors thank the Ellison Medical Foundation for their support. We wish also to thank members of the Abby Dernburg laboratory for assistance with using the wormsorter.

1. Obtaining a Synchronized Culture of Young Adult Animals
<ol>
	<li>Grow worms on several NGM plates seeded with OP50-1 E. coli&#160;bacteria (10x&#160;concentrated from a saturated culture) until many worms have reached the gravid stage.</li>
	<li>Treat gravid animals with egg-prep solution to obtain a synchronized culture (eggs).</li>
	<li>Plate eggs on several 60-mm NGM plates seeded with 10x&#160;concentrated OP50-1 at a density of roughly 150-200 eggs/plate.</li>
	<li>Incubate plates at 25&#160;&#176;C for 2 days (until worms have reached the L4 - Young Adult stage).</li>
</ol>
2. Preparing Pseudomonas aeruginosa&#160;Plates and Infecting Worms
<ol>
	<li>On the day of the egg-prep (step 1.1) inoculate a PA14::GFP culture into 2 ml of King&#8217;s B media containing rifampicin at a final concentration of 100 &#956;g/ml. Incubate the culture at 37&#160;&#176;C with agitation O/N.</li>
	<li>Plate the PA14::GFP culture onto as many Slow Killing Plates (SKP) as needed for the assay. On each 150&#160;mm SKP Petri dish pipette 75-100 &#956;l of saturated culture and spread evenly using a sterile glass spreader. Incubate the plates at 37&#160;&#176;C for 20-24 hr.</li>
	<li>Remove plates from incubator and allow them to cool to RT (~20 min). Using M9 buffer, wash worms from step 1.4 onto PA14::GFP plates in a minimal volume of liquid. When using 150&#160;mm plates, several hundred worms can be placed on a single plate.</li>
	<li>Incubate plates at 25&#160;&#176;C for 18-21 hr. For P. aeruginosa-exposed young adult worms, this is the time window displaying the optimal distribution of colonized vs noncolonized animals.</li>
</ol>
3. Setting up the Wormsorter
Before performing the sample sort, ensure that the machine is functioning properly. Details can be obtained at http://www.unionbio.com/support/documents.aspx?id=43, and the essential steps are outlined below.
<ol>
	<li>Set the sheath valve pressure to approximately 5 psi&#160;(4.5-5.5 range).</li>
	<li>To verify that sheath fluid flow rate is appropriate, place a 15&#160;ml conical tube beneath the dispenser, turn on the sheath valve, and turn off the sorter valve. Hold the tube beneath the dispenser for 60 sec. The volume in the tube should be 9-10 ml. If it is outside this range, adjust the sheath valve pressure accordingly.</li>
	<li>To ensure that sheath fluid flow rate (set as in step 3.2) will allow accurate sorting, test the sort rate using 40 &#956;m control particles:</li>
	<li>Turn off the sheath valve. Add about 25 ml of control particle solution to the reservoir.</li>
	<li>Turn on the sheath valve, and the sample valve.</li>
	<li>On the computer software, navigate to the &#34;control particle mode&#34; and click acquire.</li>
	<li>Make sure the particle flow rate is ~5-8 particles/sec, with a TOF (Time Of Flight) approximating the width of the particle, 40 &#956;m. Such a TOF indicates that only a single 40 &#956;m object is passing through at a time. If values are outside of this range, adjust the settings (following directions above) accordingly.</li>
</ol>
4. Sorting Colonized vs. Noncolonized Worms
<ol>
	<li>Using M9, wash worms into 15-ml conical tubes. Allow adult worms to sink to the bottom of the tube by gravity and remove the supernatant. Fill the tube with fresh M9. Repeat this process 3-4x. This removes a large proportion of larvae as well as excess bacteria and takes about 10 min.</li>
	<li>Add worms to the wormsorter reservoir with a gently-mixing small stir bar.</li>
	<li>Adjust initial signal gain by setting the Green PMT to 600 and the Red and Yellow PMT to 200.</li>
	<li>Begin acquiring data to adjust settings.</li>
	<li>Aim for a sort rate of 25-30 events (worms) per sec. If the number rate is too high, dilute the worms in the reservoir with M9 accordingly. If the rate is too low, add more worms in a small volume of M9.</li>
	<li>If the experiment requires a very stringent separation of colonized vs noncolonized worms, set the &#34;coincidence check&#34; to &#34;pure&#34;. This ensures that in the event two objects occur too close to each other or in the same drop, the machine rejects the drop rather than collecting it.</li>
	<li>To sort the population of interest, draw gates around the axes indicating size (to obtain adult worms) and fluorescence intensity (i.e. high for colonized, low for noncolonized). The values for fluorescence gating must be determined empirically.</li>
	<li>Place a multi-well plate or a Petri dish underneath the dispenser to collect worms&#160;then open the sort valve to begin sorting worms.</li>
	<li>Collect a small population of animals to verify under the microscope that the sorted population is the population of interest. If not, adjust the gating parameters accordingly and continue with sample collection.</li>
</ol>

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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=Distinct+pathogenesis+and+host+responses+during+infection+of+C.+elegans+by+P.+aeruginosa+and+S.+aureus.">Distinct pathogenesis and host responses during infection of C. elegans by P. aeruginosa and S. aureus.</a> PLoS Pathog. 6, (2010).</li><li>Pukkila-Worley, R., Ausubel, F. M., Mylonakis, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Candida+albicans+infection+of+Caenorhabditis+elegans+induces+antifungal+immune+defenses.">Candida albicans infection of Caenorhabditis elegans induces antifungal immune defenses.</a> PLoS Pathog. , (2011).</li><li>Shapira, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+conserved+role+for+a+GATA+transcription+factor+in+regulating+epithelial+innate+immune+responses.">A conserved role for a GATA transcription factor in regulating epithelial innate immune responses.</a> Proc. Natl. Acad. Sci. U.S.A. 103, 14086-14091 (2006).</li><li>Troemel, E. R., 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=p38+MAPK+regulates+expression+of+immune+response+genes+and+contributes+to+longevity+in+C.+elegans.">p38 MAPK regulates expression of immune response genes and contributes to longevity in C. elegans.</a> PLoS Genet. , 183 (2006).</li><li>Twumasi-Boateng, K., Shapira, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissociation+of+immune+responses+from+pathogen+colonization+supports+pattern+recognition+in+C.+elegans.">Dissociation of immune responses from pathogen colonization supports pattern recognition in C. elegans.</a> PLoS One. , 7 (2012).</li><li>Jakobsen, 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=The+alkaloid+compound+harmane+increases+the+lifespan+of+Caenorhabditis+elegans+during+bacterial+infection,+by+modulating+the+nematode's+innate+immune+response.">The alkaloid compound harmane increases the lifespan of Caenorhabditis elegans during bacterial infection, by modulating the nematode's innate immune response.</a> PLoS One. 8, (2013).</li><li>Portal-Celhay, C., Bradley, E. R., 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=Control+of+intestinal+bacterial+proliferation+in+regulation+of+lifespan+in+Caenorhabditis+elegans.">Control of intestinal bacterial proliferation in regulation of lifespan in Caenorhabditis elegans.</a> BMC Microbiol. 12, 49 (2012).</li><li>Troemel, E. R., Felix, M. A., Whiteman, N. K., Barriere, A., Ausubel, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microsporidia+are+natural+intracellular+parasites+of+the+nematode+Caenorhabditis+elegans.">Microsporidia are natural intracellular parasites of the nematode Caenorhabditis elegans.</a> PLoS Biol. 6, 2736-2752 (2008).</li><li>Montalvo-Katz, S., Huang, H., Appel, M. 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The authors have nothing to disclose.

The method we describe takes advantage of fluorescent labeling of entities outside of the worm, to follow interactions between the worm and its environment. In the case we present, separation was based on labeling of a pathogen and was employed to separate worms with heavy pathogen load from those with no (or light) load. Subsequent gene expression analysis found no difference in immune responses between the two groups suggesting that they were independent of pathogen load. The signal that initiates the response was show...

Automatic worm sorting is much like FACS, operating by measuring a fluorescent signal&#160;in a worm (typically provided by transgenic expression of reporter proteins) as it passes straightened in a tube, allowing redirection either to a collection tube/well or to a waste container&#160;according to gating parameters set by the researcher1. The wormsorter can facilitate research in many ways; an example of employing it as an analytical tool is a study that followed spatiotemporal patterns of promoter activity for almost 1,000 genes2. 
However, the major use of the wormsorter is in genetic screens, following target gene expression levels or localization of fluorescent protein along the axis of the worm3-5.
Here, we describe a new application for the wormsorter, in following colonization of the worm by a fluorescently tagged pathogen. With this as a tool we focused on the relationship between pathogen colonization/load and the immune response, to gain new insights into the mechanisms responsible for initiation of immune responses in the worm.
In virtually all organisms studied to date, initiation of innate immune responses to microbial pathogens depends on recognition of pathogen-associated molecular patterns (PAMPs), and/or danger/damage-associated molecular patterns (DAMPs)6,7. The first are conserved microbial structures that include components of the microbial cell wall, its flagellum, or its lipid bilayer6; the second, include both released molecules (e.g. ATP8), altered proteins or other markers of altered cellular processes9,10. Both types of signals are recognized by proteins designated as pattern recognition receptors (PRRs), which upon specific binding of a pattern molecule activate a chain of events leading to a protective response. C. elegans has been extremely useful as a tractable model to dissect various aspects of host-pathogen interactions, but one thing that is not well understood is how immune responses are initiated in the worm. None of the putative receptors that are orthologous to pattern recognition receptors (PRRs) in other organisms have been shown to bind PAMPs, and many of the orthologs of PRRs that are pivotal for immune responses in other organisms show a surprisingly limited contribution to worm pathogen responses and resistance. For example, the Drosophila&#160;Toll receptor, which is essential for resisting Gram positive pathogens, is represented in C. elegans by a sole homolog, tol-1, which contributes to protection from the Gram negative pathogen Salmonella Typhimurium11, but not from other tested Gram-negative, or -positive pathogens11,12 . These observations, combined with data indicating that immune responses could be induced by disrupting cellular protein translation has led some to suggest that C. elegans primarily detects DAMPs9,13,14. Nevertheless, reports describing ability of dead pathogens to induce immune responses suggest that PAMP binding may be have an important role in pathogen recognition in C. elegans15,16. Previous work focusing on immune responses in age-synchronized genetically identical C. elegans populations, demonstrated large individual variability in intestinal colonization by the bacterial Gram-negative pathogen Pseudomonas aeruginosa.
However, transcriptional profiling studies treated these variably-colonized populations as one entity17,18. Taking advantage of this variability, we developed a protocol focusing an automated wormsorter to separate differentially colonized populations of Caenorhabditis elegans exposed to GFP-expressing P. aeruginosa. Examining gene expression in differently-colonized populations facilitated assessment of the relationship between pathogen load (and the associated damage) and immune responses and provided new insights about pathogen recognition in C. elegans19. Below we describe the protocol, which could be applied to sort worms infected with any fluorescently labeled pathogen.
To potential users it should be noted that the number of worms required to be sorted out depends on the nature of the subsequent analyses and protocols in use. For example, in the case of microarray gene expression analysis, &#62;1,000 worms will be required to obtain enough RNA, if standard protocols are used, but ~100 worms would suffice if amplification is employed, allowing fast collection of material and thus minimizing stress to the worms.

<table border="0" cellpadding="0" cellspacing="0" width="927">
	<colgroup>
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:261px;">M9 Buffer</td>
			<td style="width:139px;">Prepared in house</td>
			<td style="width:527px;">Recipe at wormbook.org</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Rifampicin&#160;</td>
			<td>Sigma</td>
			<td>R3501</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Egg prep solution&#160;</td>
			<td>Prepared in house</td>
			<td>50ml water ; 40ml bleach ; 10ml of 10N Sodium Hydroxide&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NGM plates&#160;</td>
			<td>Prepared in house</td>
			<td>Recipe at wormbook.org</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">SKP plates</td>
			<td>Prepared in house</td>
			<td>Recipe same as NGM only 0.35% peptone instead of 0.25%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Control test particles&#160;</td>
			<td>Union Biometrica&#160;</td>
			<td>310-5071-001</td>
		</tr>
	</tbody>
</table>

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.

When age-matched, genetically identical C. elegans are exposed to P. aeruginosa, a wide distribution is observed in levels of colonization (Figure 1A). With the help of the protocol described here efficient separation of noncolonized from colonized worms can be achieved (Figure&#160;1B). Unlike noncolonized worms, colonized worms show signs of damage, such as sluggishness and reduced defecation19. The latter may be a reason why worms colonized by P. aerug...

Watch this Scientific Journal Video about Automated Separation of C. elegans Variably Colonized by a Bacterial Pathogen at JoVE.com

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.

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 ...

automated-separation-c-elegans-variably-colonized-bacterial

Research

JoVE Journal

Immunology and Infection

8.3K Views.  University of California, Berkeley. The wormsorter facilitates genetic screens in Caenorhabditis elegans by sorting worms according to expression of fluorescent reporters. Here, we describe a new usage: 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.

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

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 ...

One-day Workflow Scheme for Bacterial Pathogen Detection and Antimicrobial Resistance Testing from Blood Cultures

Bloodstream infections are associated with high mortality rates because of the probable manifestation of sepsis, severe sepsis and septic shock1. Therefore, rapid administration of adequate antibiotic therapy is of foremost importance in the treatment of bloodstream infections. The critical element in this process is timing, heavily dependent on the results of bacterial identification and antibiotic susceptibility testing. Both of these parameters are routinely obtained by culture-based testing, which is time-consuming and takes on average 24-48 hours2, 4. The aim of the study was to develop DNA-based assays for rapid identification of bloodstream infections, as well as rapid antimicrobial susceptibility testing. The first assay is a eubacterial 16S rDNA-based real-time PCR assay complemented with species- or genus-specific probes5. Using these probes, Gram-negative bacteria including Pseudomonas spp., Pseudomonas aeruginosa and Escherichia coli as well as Gram-positive bacteria including Staphylococcus spp., Staphylococcus aureus, Enterococcus spp., Streptococcus spp., and Streptococcus pneumoniae could be distinguished. Using this multiprobe assay, a first identification of the causative micro-organism was given after 2 h.
Secondly, we developed a semi-molecular assay for antibiotic susceptibility testing of S. aureus, Enterococcus spp. and (facultative) aerobe Gram-negative rods6. This assay was based on a study in which PCR was used to measure the growth of bacteria7. Bacteria harvested directly from blood cultures are incubated for 6 h with a selection of antibiotics, and following a Sybr Green-based real-time PCR assay determines inhibition of growth. The combination of these two methods could direct the choice of a suitable antibiotic therapy on the same day (Figure 1). In conclusion, molecular analysis of both identification and antibiotic susceptibility offers a faster alternative for pathogen detection and could improve the diagnosis of bloodstream infections.

The design of a straightforward one-day workflow scheme for bacterial pathogen diagnostics enables the rapid recognition of bloodstream infections. The inclusion of eight clinically relevant bacterial targets and their antibiotic resistance profiles offers the clinician an initial insight on the same day, which can lead to more adequate therapy.

Bloodstream infections are associated with high mortality rates because of the probable manifestation of sepsis, severe sepsis and septic shock1. ...

Saliva, Salivary Gland, and Hemolymph Collection from Ixodes scapularis Ticks

Ticks are found worldwide and afflict humans with many tick-borne illnesses. Ticks are vectors for pathogens that cause Lyme disease and tick-borne relapsing fever (Borrelia spp.), Rocky Mountain Spotted fever (Rickettsia rickettsii), ehrlichiosis (Ehrlichia chaffeensis and E. equi), anaplasmosis (Anaplasma phagocytophilum), encephalitis (tick-borne encephalitis virus), babesiosis (Babesia spp.), Colorado tick fever (Coltivirus), and tularemia (Francisella tularensis) 1-8. To be properly transmitted into the host these infectious agents differentially regulate gene expression, interact with tick proteins, and migrate through the tick 3,9-13. For example, the Lyme disease agent, Borrelia burgdorferi, adapts through differential gene expression to the feast and famine stages of the tick's enzootic cycle 14,15. Furthermore, as an Ixodes tick consumes a bloodmeal Borrelia replicate and migrate from the midgut into the hemocoel, where they travel to the salivary glands and are transmitted into the host with the expelled saliva 9,16-19.
As a tick feeds the host typically responds with a strong hemostatic and innate immune response 11,13,20-22. Despite these host responses, I. scapularis can feed for several days because tick saliva contains proteins that are immunomodulatory, lytic agents, anticoagulants, and fibrinolysins to aid the tick feeding 3,11,20,21,23. The immunomodulatory activities possessed by tick saliva or salivary gland extract (SGE) facilitate transmission, proliferation, and dissemination of numerous tick-borne pathogens 3,20,24-27. To further understand how tick-borne infectious agents cause disease it is essential to dissect actively feeding ticks and collect tick saliva. This video protocol demonstrates dissection techniques for the collection of hemolymph and the removal of salivary glands from actively feeding I. scapularis nymphs after 48 and 72 hours post mouse placement. We also demonstrate saliva collection from an adult female I. scapularis tick.

Saliva, Salivary Gland, and Hemolymph Collection from Ixodes scapularis Ticks

The collection of infected tick hemolymph, salivary glands, and saliva is important to study how tick-borne pathogens cause disease. In this protocol we demonstrate how to collect hemolymph and salivary glands from feeding Ixodes scapularis nymphs. We also demonstrate saliva collection from female I. scapularis adults.

Ticks are found worldwide and afflict humans with many tick-borne illnesses. Ticks are vectors for pathogens that cause Lyme disease and tick-borne ...

Visualization of Bacterial Toxin Induced Responses Using Live Cell Fluorescence Microscopy

Bacterial toxins bind to cholesterol in membranes, forming pores that allow for leakage of cellular contents and influx of materials from the external environment. The cell can either recover from this insult, which requires active membrane repair processes, or else die depending on the amount of toxin exposure and cell type1. In addition, these toxins induce strong inflammatory responses in infected hosts through activation of immune cells, including macrophages, which produce an array of pro-inflammatory cytokines2. Many Gram positive bacteria produce cholesterol binding toxins which have been shown to contribute to their virulence through largely uncharacterized mechanisms.
Morphologic changes in the plasma membrane of cells exposed to these toxins include their sequestration into cholesterol-enriched surface protrusions, which can be shed into the extracellular space, suggesting an intrinsic cellular defense mechanism3,4. This process occurs on all cells in the absence of metabolic activity, and can be visualized using EM after chemical fixation4. In immune cells such as macrophages that mediate inflammation in response to toxin exposure, induced membrane vesicles are suggested to contain cytokines of the IL-1 family and may be responsible both for shedding toxin and disseminating these pro-inflammatory cytokines5,6,7. A link between IL-1&beta; release and a specific type of cell death, termed pyroptosis has been suggested, as both are caspase-1 dependent processes8. To sort out the complexities of this macrophage response, which includes toxin binding, shedding of membrane vesicles, cytokine release, and potentially cell death, we have developed labeling techniques and fluorescence microscopy methods that allow for real time visualization of toxin-cell interactions, including measurements of dysfunction and death (Figure 1). Use of live cell imaging is necessary due to limitations in other techniques. Biochemical approaches cannot resolve effects occurring in individual cells, while flow cytometry does not offer high resolution, real-time visualization of individual cells. The methods described here can be applied to kinetic analysis of responses induced by other stimuli involving complex phenotypic changes in cells.

Methods for purifying the cholesterol binding toxin streptolysin O from recombinant E. coli and visualization of toxin binding to live eukaryotic cells are described. Localized delivery of toxin induces rapid and complex changes in targeted cells revealing novel aspects of toxin biology.

Bacterial toxins bind to cholesterol in membranes, forming pores that allow for leakage of cellular contents and influx of materials from the external ...

Imaging InlC Secretion to Investigate Cellular Infection by the Bacterial Pathogen Listeria monocytogenes

Bacterial intracellular pathogens can be conceived as molecular tools to dissect cellular signaling cascades due to their capacity to exquisitely manipulate and subvert cell functions which are required for the infection of host target tissues. Among these bacterial pathogens, Listeria monocytogenes is a Gram positive microorganism that has been used as a paradigm for intracellular parasitism in the characterization of cellular immune responses, and which has played instrumental roles in the discovery of molecular pathways controlling cytoskeletal and membrane trafficking dynamics. In this article, we describe a robust microscopical assay for the detection of late cellular infection stages of L. monocytogenes based on the fluorescent labeling of InlC, a secreted bacterial protein which accumulates in the cytoplasm of infected cells; this assay can be coupled to automated high-throughput small interfering RNA screens in order to characterize cellular signaling pathways involved in the up- or down-regulation of infection.

Imaging InlC Secretion to Investigate Cellular Infection by the Bacterial Pathogen Listeria monocytogenes

Listeria monocytogenes is a Gram positive bacterial pathogen frequently used as a major model for the study of intracellular parasitism. Imaging late L. monocytogenes infection stages within the context of small-interfering RNA screens allows for the global study of cellular pathways required for bacterial infection of target host cells.

Bacterial intracellular  pathogens can be conceived as molecular tools to dissect cellular signaling  cascades due to their capacity to exquisitely ...

Generation and Multi-phenotypic High-content Screening of Coxiella burnetii Transposon Mutants

Invasion and colonization of host cells by bacterial pathogens depend on the activity of a large number of prokaryotic proteins, defined as virulence factors, which can subvert and manipulate key host functions. The study of host/pathogen interactions is therefore extremely important to understand bacterial infections and develop alternative strategies to counter infectious diseases. This approach however, requires the development of new high-throughput assays for the unbiased, automated identification and characterization of bacterial virulence determinants. Here, we describe a method for the generation of a GFP-tagged mutant library by transposon mutagenesis and the development of high-content screening approaches for the simultaneous identification of multiple transposon-associated phenotypes. Our working model is the intracellular bacterial pathogen Coxiellaburnetii, the etiological agent of the zoonosis Q fever, which is associated with severe outbreaks with a consequent health and economic burden. The obligate intracellular nature of this pathogen has, until recently, severely hampered the identification of bacterial factors involved in host pathogen interactions, making of Coxiella the ideal model for the implementation of high-throughput/high-content approaches.

Generation and Multi-phenotypic High-content Screening of Coxiella burnetii Transposon Mutants

Coxiella burnetii is an obligate intracellular Gram-negative bacterium responsible for the zoonotic disease Q fever. Here we describe methods for the generation of Coxiella fluorescent transposon mutants as well as the automated identification and analysis of the resulting internalization, replication and cytotoxic phenotypes.

Invasion and colonization of host cells by bacterial pathogens depend on the activity of a large number of prokaryotic proteins, defined as virulence ...

Unravelling the Function of a Bacterial Effector from a Non-cultivable Plant Pathogen Using a Yeast Two-hybrid Screen

Unravelling the molecular mechanisms of disease manifestations is important to understand pathologies and symptom development in plant science. Bacteria have evolved different strategies to manipulate their host metabolism for their own benefit. This bacterial manipulation is often coupled with severe symptom development or the death of the affected plants. Determining the specific bacterial molecules responsible for the host manipulation has become an important field in microbiological research. After the identification of these bacterial molecules, called &#34;effectors,&#34; it is important to elucidate their function. A straightforward approach to determine the function of an effector is to identify its proteinaceous binding partner in its natural host via a yeast two-hybrid (Y2H) screen. Normally the host harbors numerous potential binding partners that cannot be predicted sufficiently by any in silico algorithm. It is thus the best choice to perform a screen with the hypothetical effector against a whole library of expressed host proteins. It is especially challenging if the causative agent is uncultivable like phytoplasma. This protocol provides step-by-step instructions for DNA purification from a phytoplasma-infected woody host plant, the amplification of the potential effector, and the subsequent identification of the plant&#39;s molecular interaction partner with a Y2H screen. Even though Y2H screens are commonly used, there is a trend to outsource this technique to biotech companies that offer the Y2H service at a cost. This protocol provides instructions on how to perform a Y2H in any decently equipped molecular biology laboratory using standard lab techniques.

Bacterial effector proteins are important for establishing successful infections. This protocol describes the experimental identification of proteinaceous binding partners of a bacterial effector protein in its natural plant host. Identifying these effector interactions via yeast two-hybrid screens has become an important tool in unravelling molecular pathogenicity strategies.

Unravelling the molecular mechanisms of disease manifestations is important to understand pathologies and symptom development in plant science. Bacteria ...

Enrichment of Bacterial Lipoproteins and Preparation of N-terminal Lipopeptides for Structural Determination by Mass Spectrometry

Lipoproteins are important constituents of the bacterial cell envelope and potent activators of the mammalian innate immune response. Despite their significance to both cell physiology and immunology, much remains to be discovered about novel lipoprotein forms, how they are synthesized, and the effect of the various forms on host immunity. To enable thorough studies on lipoproteins, this protocol describes a method for bacterial lipoprotein enrichment and preparation of N-terminal tryptic lipopeptides for structural determination by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Expanding on an established Triton X-114 phase partitioning method for lipoprotein extraction and enrichment from the bacterial cell membrane, the protocol includes additional steps to remove non-lipoprotein contaminants, increasing lipoprotein yield and purity. Since lipoproteins are commonly used in Toll-like receptor (TLR) assays, it is critical to first characterize the N-terminal structure by MALDI-TOF MS. Herein, a method is presented to isolate concentrated hydrophobic peptides enriched in N-terminal lipopeptides suitable for direct analysis by MALDI-TOF MS/MS. Lipoproteins that have been separated by Sodium Dodecyl Sulfate Poly-Acrylamide Gel Electrophoresis (SDS-PAGE) are transferred to a nitrocellulose membrane, digested in situ with trypsin, sequentially washed to remove polar tryptic peptides, and finally eluted with chloroform-methanol. When coupled with MS of the more polar trypsinized peptides from wash solutions, this method provides the ability to both identify the lipoprotein and characterize its N-terminus in a single experiment. Intentional sodium adduct formation can also be employed as a tool to promote more structurally informative fragmentation spectra. Ultimately, enrichment of lipoproteins and determination of their N-terminal structures will permit more extensive studies on this ubiquitous class of bacterial proteins.

The enrichment of bacterial lipoproteins using a non-ionic surfactant phase partitioning method is described for direct use in TLR assays or other applications. Further steps are detailed to prepare N-terminal tryptic lipopeptides for structural characterization by mass spectrometry.

Lipoproteins are important constituents of the bacterial cell envelope and potent activators of the mammalian innate immune response. Despite their ...

A High-throughput, High-content, Liquid-based C. elegans Pathosystem

The number of new drugs identified by traditional, in vitro screens has waned, reducing the success of this approach in the search for new weapons to combat multiple drug resistance. This has led to the conclusion that researchers do not only need to find new drugs, but also need to develop new ways of finding them. Amongst the most promising candidate methods are whole-organism, in vivo assays that use high-throughput, phenotypic readouts and hosts that range from Caenorhabditis elegans to Danio rerio. These hosts have several powerful advantages, including dramatic reductions in false positive hits, as compounds that are toxic to the host and/or biounavailable are typically dropped in the initial screen, prior to costly follow up.
Here we show how our assay has been used to interrogate host variation in the well-documented C. elegans&#8212;Pseudomonas aeruginosa liquid killing pathosystem. We also demonstrate several extensions of this well-worked out technique. For example, we are able to carry out high-throughput genetic screens using RNAi in 24- or 96-well plate formats to query host factors in this host-pathogen interaction. Using this assay, whole genome screens can be completed in only a few months, which can dramatically simplify the task of identifying drug targets, potentially without the need for laborious biochemical purification approaches.
We also report here a variation of our method that substitutes the gram-positive bacterium Enterococcus faecalis for the gram-negative pathogen P. aeruginosa. Much as is the case for P. aeruginosa, killing by E. faecalis is time-dependent. Unlike previous C. elegans&#8212;E. faecalis assays, our assay for E. faecalis does not require preinfection, improving its safety profile and reducing the chances of contaminating liquid-handling equipment. The assay is highly robust, showing ~95% death rates 96 h post infection.

A High-throughput, High-content, Liquid-based C. elegans Pathosystem

Here we describe a protocol that is an adaptable, whole host, high-content screening tool that can be utilized to study host-pathogen interactions and be used for drug discovery.

The number of new drugs identified by traditional, in vitro screens has waned, reducing the success of this approach in the search for new weapons to ...

Automated Behavioral Analysis of Large C. elegans Populations Using a Wide Field-of-view Tracking Platform

Caenorhabditis elegans is a well-established animal model in biomedical research, widely employed in functional genomics and ageing studies. To assess the health and fitness of the animals under study, one typically relies on motility readouts, such as the measurement of the number of body bends or the speed of movement. These measurements usually involve manual counting, making it challenging to obtain good statistical significance, as time and labor constraints often limit the number of animals in each experiment to 25 or less. Since high statistical power is necessary to obtain reproducible results and limit false positive and negative results when weak phenotypic effects are investigated, efforts have recently been made to develop automated protocols focused on increasing the sensitivity of motility detection and multi-parametric behavioral profiling. In order to extend the limit of detection to the level needed to capture the small phenotypic changes that are often crucial in genetic studies and drug discovery, we describe here a technological development that enables the study of up to 5,000 individual animals simultaneously, increasing the statistical power of the measurements by about 1,000-fold compared to manual assays and about 100-fold compared to other available automated methods.

Automated Behavioral Analysis of Large C. elegans Populations Using a Wide Field-of-view Tracking Platform

We describe protocols for using the wide field-of-view nematode tracking platform (WF-NTP), which enables high-throughput phenotypic characterization of large populations of Caenorhabditis elegans. These protocols can be used to characterize subtle behavioral changes in mutant strains or in response to pharmacological treatment in a highly scalable fashion.

Caenorhabditis elegans is a well-established animal model in biomedical research, widely employed in functional genomics and ageing studies. To assess the ...