We thank Dr. Shahid Mukhtar for critiquing the manuscript and Dr. Xinnian Dong for the sample data analysis file. This work is supported by a NSF-CAREER award (IOS-1350244) to KPM and the UAB Biology Department.

The following text describes a stepwise protocol to perform optimized Psm ES4326 syringe infiltration assay in Arabidopsis. Major procedures of this assay are represented in a simplified flowchart (Figure 1).
1. Plant Growth Conditions
<ol>
	<li>Sow seeds
	<ol>
		<li>Prepare 2 pots (4 in&#160;diameter, 3.75 in&#160;tall) loosely filled with soil and water pots by soaking them from the bottom O/N before draining the excess water.</li>
		<li>Sow 50-100 Arabidopsis seeds, wild-type Col-0 or npr1-1 mutant, on each pot with a folded 70 mm weighing sheet or other paper.</li>
		<li>Cover the pot with a water-sprayed transparent dome to increase the relative humidity to 80-90% (Figure 2A).</li>
	</ol>
	</li>
	<li>Incubate the pot at 4 &#176;C for 72 hr to allow for complete stratification and synchronous germination.</li>
	<li>Transfer the pot to the standard growth conditions (12 hr light/12 hr dark, 21 &#176;C, light intensity 100 &#181;mol/m2/sec, relative humidity 40%) to allow the seed to germinate. Crack the dome to generate a 2-3 in&#160;opening immediately after transfer to the growth room, which will help avoid water condensation.</li>
	<li>When the first true leaf reaches the size of 2-3 mm in length, transplant the seedlings from the pot to a 72-wells flat filled with soil.
	<ol>
		<li>Use a finger or a 1 ml&#160;pipette tip to create a 1-in&#160;deep depression in the middle of the soil surface on the flat.</li>
		<li>Gently separate individual seedlings with as little root damage as possible. Carefully pick up seedlings that have intact roots with forceps.</li>
		<li>Place a single separated seedling together with the adhering soil clump to minimize transplantation shock into the depression and gently pat down the surrounding soil to fill the depression. Discard the extra seedlings and soil into biohazard waste container and dispose in accordance with the local biohazard waste disposal guidelines.</li>
		<li>Water transferred seedlings from the top and completely cover the flat with a water-sprayed transparent dome to maintain 80-90% humidity. Keep the dome on for 3 days, then crack the dome in the morning of day 4 and completely remove it by the end of that day. 
		Note: Sowing seeds can be alternatively performed by stratifying seeds in 1.5 ml&#160;centrifuge tubes containing 1 ml&#160;0.1% agar for 48 hr at 4 &#176;C followed by transferring 2-3 seeds with a glass pipette onto a 72-wells flat filled with soil. Flats need to be covered with a transparent dome that can be removed one week after the germination. Extra seedlings can be removed to leave only one seedling per well.</li>
	</ol>
	</li>
	<li>Water plants every two days by soaking flats in 1-in&#160;water for 20 min, then drain the excess water. 
	Note: The time interval for watering plants depends on the growth room humidity and needs to be determined based on continuous observation of user&#8217;s plant growth facility. Check plants daily to make sure they are well watered. If only few spots are drying, water those plants from the top with a squirt bottle.</li>
	<li>Perform pathogen infection assays (Step 3-5) on plants that are at or near developmental stage # 3.50 (when rosette size is 50% final size), which corresponds to 3-5 weeks old depending on growth conditions (photoperiod, temperature). Do not infect plants after inflorescence emergence (stage # 5) due to onset of age-related resistance38,39.</li>
</ol>
2. Preparation of Culture Media and Plates
<ol>
	<li>Make 1 L of King&#8217;s B (KB) liquid medium. Gently stir 20 g proteose peptone and 2 g potassium phosphate dibasic trihydrate using a magnetic stir bar with 1,000 ml&#160;deionized H2O until there is no visible pellet. Aliquot 100 ml&#160;into 150 ml&#160;glass bottles and autoclave on a 20-min liquid cycle.</li>
	<li>Prepare culture plates with KB solid medium.
	<ol>
		<li>Gently stir 20 g Proteose Peptone, 2 g Potassium Phosphate Dibasic Trihydrate and 15 g Agar with 1,000 ml&#160;deionized H2O. Autoclave.</li>
		<li>Cool down the medium on a magnetic stir plate until it is cool to touch to minimize future condensation and avoid degradation of antibiotics. Add 18 ml&#160;sterile 80% Glycerol and 5 ml&#160;sterile 1 M MgSO4 to the medium. Given that Psm ES4326 carries resistance against streptomycin, add streptomycin into the cooled media to a final concentration of 50 &#181;g ml&#8722;1.</li>
		<li>Pour the plates. Prepare two different sizes of KB media plates: 100 mm x 15 mm and 150 mm x 15 mm Petri dishes. The smaller Petri dish containing medium serves as the primary bacteria culture plate, and the larger Petri dish serves as bacteria counting plate. 
		Note: For the bacteria counting plates, rectangular-shaped plates can be used to reduce the consumables cost since twice as many treatments can be plotted per plate compared to traditional round plates.
		<ol>
			<li>Pour the plates prior to the infection experiment. Store KB medium plates at 4 &#176;C for up to 2-3 months since streptomycin sulfate gradually loses the antibiotic activity40.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
3. Enhanced Disease Susceptibility (EDS)
<ol>
	<li>Day 1 - Streak bacteria on plate
	<ol>
		<li>Two days before the EDS assay, streak Psm ES4326 from -80 &#176;C glycerol stock on a KB-Strep bacterial culture plate and incubate at 28 &#176;C for 24-48 hr.</li>
	</ol>
	</li>
	<li>Day 2 - initiate liquid culture and water plants
	<ol>
		<li>Initiate the liquid culture in a sterile test tube with 4 ml&#160;liquid KB medium containing 50 &#181;g ml&#8722;1 streptomycin and shake at 250 rpm, 28 &#176;C O/N. 
		Note: For EDS infection assay, using 6 plants per genotype is recommended. For STI and MTI assays, 6 plants per genotype per treatment are recommended. For the bacteria inoculum, it is recommended to use a fresh liquid culture with optical density at &#955;600nm between 0.3 and 0.6.</li>
		<li>Mark the petioles of leaves number 5 and 6 with a blunt-end waterproof marker for easy identification of infected tissue at sampling (Figure 1). To enhance the opening of stomata and facilitate the entrance of pathogen solution into the leaf, water the plants well by soaking the flat from the bottom for 20 min, then drain the excess water. 
		Note: Alternatively, cover the flat with a transparent dome and soak it in water for 2-4 hr to increase the stomatal opening.</li>
		<li>Day 3 - Pathogen dilution and syringe infiltration 
		Note: Pathogen infection during morning hours is optimal for pathogen proliferation and development of the most pronounced disease symptoms on susceptible genotypes. Make every effort to keep the infection timing consistent to eliminate the effect of circadian rhythms and diurnal gene regulation41,42, which helps reduce the variation among experimental replications.
		<ol>
			<li>Pellet the bacterial culture in a microcentrifuge 1.5 ml&#160;tube at 9,600 x g for 2 min at RT and discard the supernatant. Resuspend the bacterial pellet with 1 ml&#160;of sterile 10 mM MgCl2. 
			Note: Magnesium cations can enhance the motility and adhesion of P. syringae43. Alternatively, use MgSO4 at the same concentration. Sterile water is an acceptable substitute for the Mg salt solutions.</li>
			<li>Dilute the bacteria suspension with 9 ml&#160;of 10 mM MgCl2 in a 50 ml&#160;centrifuge tube and measure the optical density (OD) of bacteria with a spectrophotometer at &#955;=600 nm. Dilute the bacteria with 10 mM MgCl2 to the final OD600nm=0.0002 for EDS infection assay.</li>
			<li>Infiltrate the leaf with a 1 ml&#160;blunt end needleless syringe (commonly known as the insulin syringe) that contains the diluted bacterial solution.</li>
			<li>Do not fill the syringe up to its full capacity. Fill it up with 0.5-0.6 ml&#160;to allow for a much better control during the infiltration process.</li>
			<li>Expose the lower surface of the leaf on the top of index finger, and then gently adjust the leaf position with the help of thumb. Position the syringe vertically against the leaf surface to ensure that pressure is evenly distributed. Try to avoid the midrib area during the infiltration to reduce leaf damage.</li>
			<li>Slowly push the plunger to infiltrate the bacterial solution; liquid entry into the leaf mesophyll will be visualized as indicated by the darker leaf color. Attempt to infiltrate the entire surface of the leaf. If this is not accomplished in a single attempt, choose another infiltration spot and repeat the actions described above until the entire leaf surface is covered.</li>
			<li>Once completed, gently blot the leaf with absorbent tissue to remove the extra pathogen solution. Visually inspect the infected leaf tissue for damage. 
			Note: The circular syringe impression should not be visible after the infiltration is complete.</li>
			<li>Leave the infiltrated plants to dry for 1-2 hr before returning them into their original growth conditions. Next, spray a clear dome with water and cover the infected plants for 2 hr, then crack the dome to generate a 2-3 in&#160;opening and leave it on throughout the remainder of the infection experiment. 
			Note: Since P. syringae is not an airborne pathogen, there is no risk of spreading the infectious agent to other plants grown in the same facility. However, as an added precaution, avoid physical contact between infected plants and other experimental plants located nearby. Covering the flat with a transparent dome will increase the pathogen virulence and accelerate disease progression. The need for this step and optimal duration of the covering period needs to be determined based on the humidity conditions of the user&#8217;s plant growth facility.</li>
		</ol>
		</li>
		<li>Day 5 - Pre-dry the media plates
		<ol>
			<li>Take the 150 mm x 15 mm KB plates out of the cold storage unit and dry any pre-existing water condensation on the plate. Dry plates by keeping them at RT for roughly 24 hr. To speed up this process, place them in a laminar flow hood with their lids cracked for 30-60 min. 
			Note: This step is critical for the formation of circular droplet on the surface of the plate in the next step.</li>
		</ol>
		</li>
		<li>Day 6 - Quantifying the pathogen growth 
		Note: The following pathogen quantification procedure may be performed at earlier time points after the infection to confirm equal amounts of bacteria are delivered into the leaf, especially when plants have altered leaf morphology.
		<ol>
			<li>Process the infected tissue after the emergence of chlorosis indicated by the yellowing of the infected tissue in the susceptible genotypes, but before the development of necrotic lesions (Figure 2B). 
			Note: Suggested sampling time is three days after the pathogen inoculation. However, since pathogen growth depends on a number of environmental factors, the length of incubation may vary within a range of 2 &#189;-3 &#189; days and needs to be determined by careful observations of the infection progression in user&#8217;s plant growth facility.
			<ol>
				<li>Prepare 6 grinding tubes for each genotype (Figure 1). Place one stainless steel grinding ball and add 500 &#181;l&#160;sterile 10 mM MgCl2 into the each tube.</li>
				<li>Detach the infected leaf from the plant and punch a leaf disc with a 1-hole paper punch (Figure 1). 
				Note: To minimize the sampling error, try to punch each sampled leaf at the same position. Sampling of the leaf disc from the top of the leaf is recommended.</li>
				<li>Randomly place 2 leaf discs (from two different plants) into each grinding tube using forceps.</li>
				<li>Seal the tube and homogenize the tissue with a high-throughput homogenizer at maximum speed (1,600 strokes per minute) for 10 min. Repeat this process if needed until tissue is well homogenized and the solutions turn green due to chlorophyll release from the infected leaves.</li>
			</ol>
			</li>
			<li>While waiting for the homogenization, fill the first 6 rows of a 96-well culture plate with 180 &#181;l&#160;10 mM MgCl2 using a multi-channel pipette and a pipetting reservoir.</li>
			<li>After grinding, transfer 20 &#181;l&#160;of ground tissue suspension into the first row of the 96-well plate and mix by repeated pipetting the liquid up and down. If small fragments of tissue clog the tip, clip it by 2-3 mm to help acquire the correct volume of the solution.
			<ol>
				<li>To provide enough space for the droplet on the top of the plate, space the tissue from different genotypes in alternative rows (Figure 1). To prepare a ten-fold serial dilution, transfer 20 &#181;l&#160;liquid into the second row and repeat this procedure until the sixth dilution.</li>
			</ol>
			</li>
			<li>Transfer 20 &#181;l&#160;of the solution from the 96-well plate onto the 150 mm x 15 mm KB plate using divided pipette tips (Figure 1). Work from the most dilute suspension to the most concentrated. 
			Note: Proceeding from most diluted to most concentrated makes it unnecessary to change pipette tips between the dilutions. If the plate is well pre-dried, the transferred droplet should stay intact on the top of the medium until absorbed (usually 15-30 min). Drying time varies with the RT and humidity.</li>
			<li>Dry the plate at RT with lid cracked. Once no more liquid can be observed on the plate surface, close the lid, invert and incubate the plate at RT or a 28 &#176;C incubator.</li>
			<li>Incubate plates for 40-60 hr until the colonies become visible. Confirm that the growth on the plates reflects the predictable 10-fold drop in colony forming units (cfu) (Figure 2C). Count the bacteria before they overgrow and colonies fuse. Determine the number of bacteria in the lowest dilution that does not have overlapping colonies. Usually, the preferred dilution to be counted will contain between 10-50 colonies. 
			Note: Variation may be present among technical replicates; therefore, the lowest dilution for each replicate should be determined separately.</li>
			<li>To calculate the levels of bacterial proliferation, document the number of the row (R) as well as the number of the bacteria within each technical replicate (T) in writing. Determine the number of colony forming unit &#8211; cfu/leaf disc through the formula: cfu/leaf disc = (T &#215; 10R / 20) &#215; 500 / 2</li>
			<li>Type the data in the following spreadsheet template to produce a graph (Figure 1) (for spreadsheet data analysis template file, see Table 2). Each data point is represented as the mean of six technical replicates on a logarithmic scale. Error bars represent 95% confidence interval of the mean (n = 6). 
			Note: The calculation of 95% confidence intervals needs to be adjusted based on the number of technical replicates.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
4. SA-Triggered Immunity (STI)
<ol>
	<li>Day 1: Follow the same procedure as described in step 3.1.</li>
	<li>Day 2: In addition to watering the plants and initiating the liquid bacterial culture (Step 3.2), induce resistance by external application of SA derivative Sodium Salicylate21. 
	Note: Pure SA has poor water solubility and requires prior pH adjusting, thus it&#8217;s not recommended for this assay.
	<ol>
		<li>To induce SA-mediated defenses against P. syringae and prime the plants for future infection21,24, spray plants with a fine mist of 1 mM Sodium Salicylate or H2O (as mock) 16-24 h before the pathogen infection.</li>
	</ol>
	</li>
	<li>Day 3: Prepare pathogen dilution to OD600nm=0.001 and push the bacteria into the entire leaf surface by syringe infiltration (Step 3.3).</li>
	<li>Day 6: For pathogen quantification and counting process, follow the procedure as described for the EDS assay (Steps 3.4 and 3.5). Plate and count the H2O and Sodium Salicylate &#8211; pretreated samples separately. For wild-type Arabidopsis, a 1-2 log reduction in pathogen growth is expected in the Sodium Salicylate &#8211; pretreated plants.</li>
</ol>
5. MAMP-Triggered Immunity (MTI)

Note: In this assay, we use Arabidopsis wild-type Col-0 and mutant fls2 and efr plants. FLS2 and EFR are plasma membrane-localized Pattern Recognition Receptors (PRRs) that can recognize flg22 and elf18, respectively9,10. Loss of each PRR results in the insensitivity to the specific type of MAMP, which is indicated by the unaltered pathogen growth in the mutant following external MAMP pre-treatment and syringe infiltration with Psm ES4326.
<ol>
	<li>Day 1 and 2: Follow the same procedure as described in Step 3.1 and 3.2.</li>
	<li>Day 3: MAMP pre-treatment and Pathogen infection
	<ol>
		<li>To establish the MAMP-Triggered Immunity, prepare 1 &#181;M solution of flagellin epitope flg22 or EF-Tu epitope elf18 and syringe-infiltrate it into the entire leaf surface 4 h before the pathogen infection (Steps 3.3.3-3.3.6). This will allow for induction of MAMP-mediated defenses against P. syringae and prime the plants for future infection6,37. 
		Note: Publicly available microarray data revealed the maximum transcriptional reprogramming of MAMP-responsive genes happens 4 h after flg22 or elf18 treatment37,44. Thus, 4 hr is the recommended duration of the MAMP pre-treatment that results in achieving a clear difference in the pathogen growth between MAMP-treated Col-0 and fls2 and efr mutants.</li>
		<li>Remove the extra MAMP solution with absorbent tissue and leave the plants uncovered to speed the liquid absorption process within the leaf. To account for the wounding effect from syringe pressure infiltration, infiltrate H2O into the leaves of control plants.</li>
		<li>Prepare pathogen dilution to OD600nm=0.001 and push the bacteria into the entire leaf surface of MAMP/H2O pre-treated leaf by syringe infiltration (Step 3.3).</li>
	</ol>
	</li>
	<li>Day 6: For pathogen quantification and counting process, follow the procedure as described in Step 3.4 and 3.5. Plate and count the H2O and MAMP&#8211;pretreated samples separately. In wild-type Arabidopsis, a 1-2 log reduction in pathogen growth is expected in the MAMP&#8211;pretreated plants, with somewhat stronger reduction mediated by flg22 compared to elf18.</li>
</ol>

The authors have nothing to disclose.

With decreasing available farmland and increasing population, researchers around the world are challenged with pressing needs for crop improvement. The yield can be greatly influenced by various biotic and abiotic stresses. Among them, pathogen infection is one of the leading causes of crop yield reduction, responsible for approximately 12% losses in the U.S. alone45. To resolve this issue, massive research has been conducted in the model Arabidopsis - P. syringae pathosystem to comprehensively charac...

Due to their sessile nature, plants are constantly threatened by a plethora of pathogens exhibiting various lifestyles and nutritional strategies1. To a first approximation, biotrophic pathogens maintain their host alive to retrieve nutrients, while necrotrophic pathogens actively secret toxins and enzymes to kill host tissue and feed on the dead cells1. Another group of pathogens, termed hemibiotrophs, begins their infection course with the biotrophic stage and shifts to the necrotrophic stage upon reaching a certain threshold of pathogen accumulation2. In order to effectively defend themselves against these microorganisms, plants have evolved a complicated innate immune system equipped with multiple surveillance mechanisms to detect the pathogen attack and trigger localized programmed cell death3 as well as Systemic Acquired Resistance (SAR)4. Current research is focused on characterizing the essential signaling components and cross-talks within the plant immune system5.

As proposed in the &#8220;Zig-Zag&#8221; model5, the first layer of the plant innate immune response requires the presence of plasma membrane-localized Pattern Recognition Receptors (PRRs) to detect the invasion of a microbe. PRRs are able to recognize Microbe-Associated Molecular Patterns (MAMPs) and establish MAMP-Triggered Immunity (MTI)6. Besides inducing a transcriptional upregulation of genes encoding antimicrobial PR proteins7, MTI leads to a variety of events that arrest pathogen growth, including the production of Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS), deposition of callose to the cell wall as well as the activation of multiple kinase signaling pathways8.
Until now, several MAMPs have been identified to trigger MTI in Arabidopsis, including bacterial flg229 (a 22 amino acid fragment derived from flagellin), elf1810 (18 amino acids from the bacterial translation elongation factor Tu) and a structural cell wall component peptidoglycans11. To establish a successful infection, some specialized pathogens have evolved the ability to secret virulence effector proteins into the intracellular or intercellular spaces, and consequently repress MTI and trigger Effector-Triggered Susceptibility (ETS)12,13. For instance, virulence effectors can inactivate Mitogen-Activated Protein Kinase (MAPK) phosphorylation cascades of MTI to induce the disease development within the infected tissue14-16. During the dynamic co-evolution between hosts and pathogens, plants also developed the counterattack strategy to recognize the effector proteins and attenuate the pathogen virulence molecules17. This direct or indirect effector recognition is mediated by disease resistance (R) proteins18. Most of them are members of NB-LRR (Nucleotide Binding and Leucine-Rich Repeats) family19. The perception of an avirulent effector by an R protein elicits a stronger and broader immune response characterized as Effector-Triggered Immunity (ETI)20. Besides inducing the expression of defense genes21 and the production of defense metabolites22, ETI often leads to a rapid localized programmed cell death known as Hypersensitive Response (HR) to restrict the pathogen from spreading into the adjacent tissue3.
In addition to the localized programmed cell death23, plants are capable of initiating a long-term and system-wide immune response termed Systemic Acquired Resistance (SAR)4. Upon challenge with a biotrophic pathogen, plant cells trigger the biosynthesis and accumulation of an endogenous phytohormone salicylic acid (SA) and PR proteins in both local and systemic tissues24. Through this process, a heightened state of preparedness is achieved in the uninfected leaves that allows for mounting faster defense responses during a subsequent infection by a broad spectrum of pathogens24. SA and its synthetic analogs such as benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) and 2,6-dichloroisonicotinic acid (INA) are capable of chemically inducing Salicylic Acid (SA)-Triggered Immunity (STI) upon external application24. Nonexpressor of Pathogenesis-Related genes 1 (NPR1) is proposed to be one of the SA receptors and functions as a major transcriptional regulator during SA-mediated defense response in both local and systemic tissues21,25,26. It has been conclusively demonstrated that NPR1 is required for SAR establishment and the loss of NPR1 leads to dramatic susceptibility towards Pseudomonas syringae25.
To extensively characterize the molecular contribution of plant components in the plant-pathogen interactions, multiple bioassays have been developed to measure specific defense events, including ROS burst27, callose deposition28, defense genes expression and accumulation of their protein products21. While these individual assays can provide insights into a specific form of the plant immune response, none of them, however, are able to represent the complete defense response on the whole plant level. Conversely, quantification of pathogen growth after infection provides an overall estimation of immune response at the organismal level. Therefore, the development and optimization of a precise and highly standardized pathogen inoculation assay is critical to fuel up the research and discoveries on the Arabidopsis immune responses.
Pseudomonas syringae, a Gram-negative bacterium, was identified as a phytopathogen capable of causing disease in a range of plant hosts including Arabidopsis29. As the model plant-pathogen system, the Arabidopsis - P. syringae interaction has been widely applied to understand the molecular mechanisms underlying plant defense responses29. Until now, over 50 P. syringae pathovars have been identified based on their ability to infect different plant species30 . P. syringae pv. tomato DC3000(Pst DC3000)31and P. syringae pv. maculicola ES4326 (Psm ES4326)32 are the two most widely used and extensively characterized virulent strains. Aside from being recognized by the plant and triggering the MTI response, Pst DC3000 and Psm ES4326 are capable of secreting virulent effector proteins to suppress MTI and trigger ETS to favor the pathogen growth31,33.
To functionally dissect the interaction between Arabidopsis and P. syringae, multiple&#160;pathogen infection methods have been developed based on the pathogen delivery approach. For soil-grown plants, pathogen can be delivered by syringe infiltration, vacuum infiltration, dip inoculation and spray inoculation29,34. Recently, seedling flood-inoculation assay was developed to perform large-scale screens on tissue culture plates-grown young Arabidopsis plants35. Syringe infiltration, as one of the most commonly used approach, manually delivers the pathogen into the apoplast through the natural leaf openings termed stomata29. Through this approach, equal amounts of P. syringae can be infiltrated into the infected leaf and the strength of plant immune response is inversely correlated to the pathogen growth levels. Therefore, quantification of pathogen growth serves as an optimal approach to evaluate the immune function at the whole plant level. In addition, syringe infiltration can distinguish the local and systemic tissue, which can be applicable in characterizing the molecular mechanisms underlying SAR36.
In the following protocol, we describe an optimized syringe infiltration assay with Psm ES4326 to screen Arabidopsis mutants for enhanced disease susceptibility (EDS). This protocol will employ two Arabidopsis genotypes: a wild-type ecotype Columbia-0 (Col-0) plants (control) and npr1-1 loss-of-function&#160;mutants (hypersusceptible) that will be infected with virulent bacterial strain Psm ES432637. The npr1-1 mutant carries a point mutation within the ankyrin-repeat consensus sequence of the NPR1 molecule, which alters the highly conserved histidine to tyrosine and renders the protein non-functional25. In addition, a number of modifications of the syringe infiltration assay are described that allow quantification of defects in the specific layers of immune response, including MTI and STI.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>MetroMix 360&#160;</td>
			<td>Grosouth</td>
			<td>SNGMM360</td>
			<td></td>
		</tr>
		<tr>
			<td>Large pots</td>
			<td>Grosouth</td>
			<td>TEKUVCC10TC</td>
			<td></td>
		</tr>
		<tr>
			<td>12x6 Inserts</td>
			<td>Grosouth</td>
			<td>LM1206</td>
			<td></td>
		</tr>
		<tr>
			<td>11x21 Flats with no holes</td>
			<td>Grosouth</td>
			<td>LM1020</td>
			<td></td>
		</tr>
		<tr>
			<td>11x21 Flats with holes</td>
			<td>Grosouth</td>
			<td>LM1020H</td>
			<td></td>
		</tr>
		<tr>
			<td>Vinyl propagation domes</td>
			<td>Grosouth</td>
			<td>CW-221</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteose Peptone</td>
			<td>Fisher Scientific</td>
			<td>DF0122-17-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Phosphate Dibasic Trihydrate&#160;</td>
			<td>MP Biomedicals</td>
			<td>151946</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar&#160;</td>
			<td>Fisher Scientific</td>
			<td>A360-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptomycin sulfate</td>
			<td>Bio Basic Inc</td>
			<td>SB0494</td>
			<td></td>
		</tr>
		<tr>
			<td>100x15mm Petri dishes</td>
			<td>Fisher Scientific</td>
			<td>FB0875713</td>
			<td></td>
		</tr>
		<tr>
			<td>150x15mm Petri dishes</td>
			<td>Fisher Scientific</td>
			<td>R80150</td>
			<td></td>
		</tr>
		<tr>
			<td>Rectangular plate</td>
			<td>Fisher Scientific</td>
			<td>12-565-450&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2 Hexahydrate</td>
			<td>Bio Basic Inc</td>
			<td>MB0328</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Bio Basic Inc</td>
			<td>GB0232</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4&#160;</td>
			<td>Bio Basic Inc</td>
			<td>MN1988</td>
			<td></td>
		</tr>
		<tr>
			<td>1 mL syringe</td>
			<td>Fisher Scientific</td>
			<td>NC9992493&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Kimwipe</td>
			<td>Fisher Scientific</td>
			<td>06-666-A</td>
			<td></td>
		</tr>
		<tr>
			<td>Grinding tubes&#160;</td>
			<td>Denville Scientific</td>
			<td>B1257</td>
			<td></td>
		</tr>
		<tr>
			<td>Caps for grinding tubes</td>
			<td>Denville Scientific</td>
			<td>B1254</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel grinding ball</td>
			<td>Fisher Scientific</td>
			<td>2150</td>
			<td></td>
		</tr>
		<tr>
			<td>96-well plate&#160;</td>
			<td>Fisher Scientific</td>
			<td>12-556-008</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Salicylate</td>
			<td>Sigma Aldrich</td>
			<td>s3007-1kg</td>
			<td></td>
		</tr>
		<tr>
			<td>flg22 (QRLSTGSRINSAKDDAAGLQIA)</td>
			<td>Genescript</td>
			<td>Made to order</td>
			<td></td>
		</tr>
		<tr>
			<td>elf18 (Ac-SKEKFERTKPHVNVGTIG)</td>
			<td>Genescript</td>
			<td>Made to order</td>
			<td></td>
		</tr>
		<tr>
			<td>Hole puncher</td>
			<td>Staples</td>
			<td>146308</td>
			<td></td>
		</tr>
		<tr>
			<td>Biophotometer plus</td>
			<td>Eppendorf</td>
			<td>952000006</td>
			<td></td>
		</tr>
		<tr>
			<td>PowerGen High-Throughput Homogenizer</td>
			<td>Fisher Scientific</td>
			<td>02-215-503</td>
			<td></td>
		</tr>
		<tr>
			<td>Accu spin micro centrifuge</td>
			<td>Fisher Scientific</td>
			<td>13-100-675</td>
			<td></td>
		</tr>
		<tr>
			<td>Multichannel pipette (10-100 &#181;l)</td>
			<td>Eppendorf</td>
			<td>3122 000.043</td>
			<td></td>
		</tr>
		<tr>
			<td>Multichannel pipette (30-300&#181;l)</td>
			<td>Eppendorf</td>
			<td>3122 000.060</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette (20&#181;l)</td>
			<td>Eppendorf</td>
			<td>3120 000.038</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette tips</td>
			<td>Fisher Scientific</td>
			<td>3552-HR</td>
			<td></td>
		</tr>
		<tr>
			<td>Sharpie permanent marker</td>
			<td>Staples</td>
			<td>507130</td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL tube</td>
			<td>Eppendorf</td>
			<td>22363204</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fisher Scientific</td>
			<td>08-890</td>
			<td></td>
		</tr>
	</tbody>
</table>

bacterial leaf infiltration assay for fine characterization of plant defense responses using the arabidopsis thaliana-pseudomonas syringae pathosystem

In the absence of specialized mobile immune cells, plants utilize their localized programmed cell death and Systemic Acquired Resistance to defend themselves against pathogen attack. The contribution of a specific Arabidopsis gene to the overall plant immune response can be specifically and quantitatively assessed by assaying the pathogen growth within the infected tissue. For over three decades, the hemibiotrophic bacterium Pseudomonas syringae pv. maculicola ES4326 (Psm ES4326) has been widely applied as the model pathogen to investigate the molecular mechanisms underlying the Arabidopsis immune response. To deliver pathogens into the leaf tissue, multiple inoculation methods have been established, e.g., syringe infiltration, dip inoculation, spray, vacuum infiltration, and flood inoculation. The following protocol describes an optimized syringe infiltration method to deliver virulent Psm ES4326 into leaves of adult soil-grown Arabidopsis plants and accurately screen for enhanced disease susceptibility (EDS) towards this pathogen. In addition, this protocol can be supplemented with multiple pre-treatments to further dissect specific immune defects within different layers of plant defense, including Salicylic Acid (SA)-Triggered Immunity (STI) and MAMP-Triggered Immunity (MTI).

The protocol we describe here represents an optimized P. syringae syringe infiltration assay to quantitatively evaluate the immune response in Arabidopsis plants. As illustrated in Figure 1, the syringe infiltration of Psm ES4326 is followed by pathogen extraction and quantification via serial dilutions and colonies enumeration.
As described in Step 3 within the protocol text, Enhanced Disease Susceptibility (EDS) against Psm ES4326 can be a...

Watch this Scientific Journal Video about Bacterial Leaf Infiltration Assay for Fine Characterization of Plant Defense Responses using the Arabidopsis thaliana-Pseudomonas syringae Pathosystem at JoVE

Bacterial Leaf Infiltration Assay for Fine Characterization of Plant Defense Responses using the Arabidopsis thaliana-Pseudomonas syringae Pathosystem

Quantification of pathogen growth is a powerful tool to characterize various Arabidopsis thaliana (hereafter: Arabidopsis) immune responses. The method described here presents an optimized syringe infiltration assay to quantify the Pseudomonas syringae pv. maculicola ES4326 growth in adult Arabidopsis leaves.

Bacterial Leaf Infiltration Assay for Fine Characterization of Plant Defense Responses using the Arabidopsis thaliana-Pseudomonas syringae Pathosystem

In the absence of specialized mobile immune cells, plants utilize their localized programmed cell death and Systemic Acquired Resistance to defend ...

bacterial-leaf-infiltration-assay-for-fine-characterization-plant

Research

Education

JoVE Journal

JoVE Core

Biology

Immunology and Infection

Plant Biology

Plant Responses to the Environment

SCIENTISTS IN ACTION

21.5K Views.  University of Alabama at Birmingham. Quantification of pathogen growth is a powerful tool to characterize various Arabidopsis thaliana (hereafter: Arabidopsis) immune responses. The method described here presents an optimized syringe infiltration assay to quantify the Pseudomonas syringae pv. maculicola ES4326 growth in adult Arabidopsis leaves.

Video: Bacterial Leaf Infiltration Assay for Fine Characterization of Plant Defense Responses using the Arabidopsis thaliana-Pseudomonas syringae Pathosystem

Assay for Pathogen-Associated Molecular Pattern (PAMP)-Triggered Immunity (PTI) in Plants

To perceive potential pathogens in their environment, plants use pattern recognition receptors (PRRs) present on their plasma membranes. PRRs recognize conserved microbial features called pathogen-associated molecular patterns (PAMPs) and this detection leads to PAMP-triggered immunity (PTI), which effectively prevents colonization of plant tissues by non-pathogens1,2. The most well studied system in PTI is the FLS2-dependent pathway3. FLS2 recognizes the PAMP flg22 that is a component of bacterial flagellin. 
Successful pathogens possess virulence factors or effectors that can suppress PTI and allow the pathogen to cause disease1. Some plants in turn possess resistance genes that detect effectors or their activity, which leads to effector-triggered immunity (ETI)2.
We describe a cell death-based assay for PTI modified from Oh and Collmer4. The assay was standardized in N. benthamiana, which is being used increasingly as a model system for the study of plant-pathogen interactions5. PTI is induced by infiltration of a non-pathogenic bacterial strain into leaves. Seven hours later, a bacterial strain that either causes disease or which activates ETI is infiltrated into an area overlapping the original infiltration zone. PTI induced by the first infiltration is able to delay or prevent the appearance of cell death due to the second challenge infiltration. Conversely, the appearance of cell death in the overlapping area of inoculation indicates a breakdown of PTI. 
Four different combinations of inducers of PTI and challenge inoculations were standardized (Table 1). The assay was tested on non-silenced N. benthamiana plants that served as the control and plants silenced for FLS2 that were predicted to be compromised in their ability to develop PTI.

Assay for Pathogen-Associated Molecular Pattern PAMP-Triggered Immunity PTI in Plants

A cell death-based assay for PTI in Nicotiana benthamiana plants is described.

To perceive potential pathogens in their environment, plants use pattern recognition receptors (PRRs) present on their plasma membranes. PRRs recognize ...

Assessing Stomatal Response to Live Bacterial Cells using Whole Leaf Imaging

Stomata are natural openings in the plant epidermis responsible for gas exchange between plant interior and environment. They are formed by a pair of guard cells, which are able to close the stomatal pore in response to a number of external factors including light intensity, carbon dioxide concentration, and relative humidity (RH). The stomatal pore is also the main route for pathogen entry into leaves, a crucial step for disease development. Recent studies have unveiled that closure of the pore is effective in minimizing bacterial disease development in Arabidopsis plants; an integral part of plant innate immunity. Previously, we have used epidermal peels to assess stomatal response to live bacteria (Melotto et al. 2006); however maintaining favorable environmental conditions for both plant epidermal peels and bacterial cells has been challenging. Leaf epidermis can be kept alive and healthy with MES buffer (10 mM KCl, 25 mM MES-KOH, pH 6.15) for electrophysiological experiments of guard cells. However, this buffer is not appropriate for obtaining bacterial suspension. On the other hand, bacterial cells can be kept alive in water which is not proper to maintain epidermal peels for long period of times. When an epidermal peel floats on water, the cells in the peel that are exposed to air dry within 4 hours limiting the timing to conduct the experiment. An ideal method for assessing the effect of a particular stimulus on guard cells should present minimal interference to stomatal physiology and to the natural environment of the plant as much as possible. We, therefore, developed a new method to assess stomatal response to live bacteria in which leaf wounding and manipulation is greatly minimized aiming to provide an easily reproducible and reliable stomatal assay. The protocol is based on staining of intact leaf with propidium iodide (PI), incubation of staining leaf with bacterial suspension, and observation of leaves under laser scanning confocal microscope. Finally, this method allows for the observation of the same live leaf sample over extended periods of time using conditions that closely mimic the natural conditions under which plants are attacked by pathogens.

We have developed a simple and reproducible protocol to access stomatal response to live bacteria. This method minimizes wounding and manipulation of the leaf as compared to the use of epidermal peels reported previously.

Stomata are natural openings in the plant epidermis responsible for gas exchange between plant interior and environment. They are formed by a pair of ...

Microwave Assisted Rapid Diagnosis of Plant Virus Diseases by Transmission Electron Microscopy

Investigations of ultrastructural changes induced by viruses are often necessary to clearly identify viral diseases in plants. With conventional sample preparation for transmission electron microscopy (TEM) such investigations can take several days1,2 and are therefore not suited for a rapid diagnosis of plant virus diseases. Microwave fixation can be used to drastically reduce sample preparation time for TEM investigations with similar ultrastructural results as observed after conventionally sample preparation3-5. Many different custom made microwave devices are currently available which can be used for the successful fixation and embedding of biological samples for TEM investigations5-8. In this study we demonstrate on Tobacco Mosaic Virus (TMV) infected Nicotiana tabacum plants that it is possible to diagnose ultrastructural alterations in leaves in about half a day by using microwave assisted sample preparation for TEM. We have chosen to perform this study with a commercially available microwave device as it performs sample preparation almost fully automatically5 in contrast to the other available devices where many steps still have to be performed manually6-8 and are therefore more time and labor consuming. As sample preparation is performed fully automatically negative staining of viral particles in the sap of the remaining TMV-infected leaves and the following examination of ultrastructure and size can be performed during fixation and embedding.

This study describes a method that allows the rapid and clear diagnosis of plant virus diseases in about half a day by using a combination of microwave assisted plant sample preparation for transmission electron microscopy and negative staining methods.

Investigations of ultrastructural changes induced by viruses are often necessary to clearly identify viral diseases in plants. With conventional sample ...

Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes

Listeria monocytogenes (Listeria) is a Gram-positive facultative intracellular pathogen1. Mouse studies typically employ intravenous injection of Listeria, which results in systemic infection2. After injection, Listeria quickly disseminates to the spleen and liver due to uptake by CD8&alpha;+ dendritic cells and Kupffer cells3,4. Once phagocytosed, various bacterial proteins enable Listeria to escape the phagosome, survive within the cytosol, and infect neighboring cells5. During the first three days of infection, different innate immune cells (e.g. monocytes, neutrophils, NK cells, dendritic cells) mediate bactericidal mechanisms that minimize Listeria proliferation. CD8+ T cells are subsequently recruited and responsible for the eventual clearance of Listeria from the host, typically within 10 days of infection6.
Successful clearance of Listeria from infected mice depends on the appropriate onset of host immune responses6	. There is a broad range of sensitivities amongst inbred mouse strains7,8. Generally, mice with increased susceptibility to Listeria infection are less able to control bacterial proliferation, demonstrating increased bacterial load and/or delayed clearance compared to resistant mice. Genetic studies, including linkage analyses and knockout mouse strains, have identified various genes for which sequence variation affects host responses to Listeria infection6,8-14. Determination and comparison of infection kinetics between different mouse strains is therefore an important method for identifying host genetic factors that contribute to immune responses against Listeria. Comparison of host responses to different Listeria strains is also an effective way to identify bacterial virulence factors that may serve as potential targets for antibiotic therapy or vaccine design.
We describe here a straightforward method for measuring bacterial load (colony forming units [CFU] per tissue) and preparing single-cell suspensions of the liver and spleen for FACS analysis of immune responses in Listeria-infected mice. This method is particularly useful for initial characterization of Listeria infection in novel mouse strains, as well as comparison of immune responses between different mouse strains infected with Listeria. We use the Listeria monocytogenes EGD strain15 that, when cultured on blood agar, exhibits a characteristic halo zone around each colony due to &beta;-hemolysis1 (Figure 1). Bacterial load and immune responses can be determined at any time-point after infection by culturing tissue homogenate on blood agar plates and preparing tissue cell suspensions for FACS analysis using the protocols described below. We would note that individuals who are immunocompromised or pregnant should not handle Listeria, and the relevant institutional biosafety committee and animal facility management should be consulted before work commences.

Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes

Listeria monocytogenes is a model organism for studying immune responses and genetic susceptibility to intracellular bacteria in mice. This method enables one to measure bacterial load and generate single-cell suspensions of the liver and spleen from mice for FACS analysis to determine changes in immune cells due to Listeria infection.

Listeria monocytogenes (Listeria) is a Gram-positive facultative intracellular pathogen1. Mouse studies typically employ intravenous injection of ...

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 ...

Systemic Bacterial Infection and Immune Defense Phenotypes in Drosophila Melanogaster

The fruit fly Drosophila melanogaster is one of the premier model organisms for studying the function and evolution of immune defense. Many aspects of innate immunity are conserved between insects and mammals, and since Drosophila can readily be genetically and experimentally manipulated, they are powerful for studying immune system function and the physiological consequences of disease. The procedure demonstrated here allows infection of flies by introduction of bacteria directly into the body cavity, bypassing epithelial barriers and more passive forms of defense and allowing focus on systemic infection. The procedure includes protocols for the measuring rates of host mortality, systemic pathogen load, and degree of induction of the host immune system. This infection procedure is inexpensive, robust and quantitatively repeatable, and can be used in studies of functional genetics, evolutionary life history, and physiology.

Systemic Bacterial Infection and Immune Defense Phenotypes in Drosophila Melanogaster

Drosophila melanogaster is an outstanding model organism for studying innate immune systems and the physiological consequences of infection and disease. This protocol describes how to deliver robust and quantitatively repeatable bacterial infections to D. melanogaster, and how to subsequently measure infection severity and quantify the host immune response.

The fruit fly Drosophila melanogaster is one of the premier model organisms for studying the function and evolution of immune defense. Many aspects of ...

Application of Long-term cultured Interferon-&#947; Enzyme-linked Immunospot Assay for Assessing Effector and Memory T Cell Responses in Cattle

Effector and memory T cells are generated through developmental programing of na&#239;ve cells following antigen recognition. If the infection is controlled up to 95 % of the T cells generated during the expansion phase are eliminated (i.e., contraction phase) and memory T cells remain, sometimes for a lifetime. In humans, two functionally distinct subsets of memory T cells have been described based on the expression of lymph node homing receptors. Central memory T cells express C-C chemokine receptor 7 and CD45RO and are mainly located in T-cell areas of secondary lymphoid organs. Effector memory T cells express CD45RO, lack CCR7 and display receptors associated with lymphocyte homing to peripheral or inflamed tissues. Effector T cells do not express either CCR7 or CD45RO but upon encounter with antigen produce effector cytokines, such as interferon-&#947;. Interferon-&#947; release assays are used for the diagnosis of bovine and human tuberculosis and detect primarily effector and effector memory T cell responses. Central memory T cell responses by CD4+ T cells to vaccination, on the other hand, may be used to predict vaccine efficacy, as demonstrated with simian immunodeficiency virus infection of non-human primates, tuberculosis in mice, and malaria in humans. Several studies with mice and humans as well as unpublished data on cattle, have demonstrated that interferon-&#947; ELISPOT assays measure central memory T cell responses. With this assay, peripheral blood mononuclear cells are cultured in decreasing concentration of antigen for 10 to 14 days (long-term culture), allowing effector responses to peak and wane; facilitating central memory T cells to differentiate and expand within the culture.

Application of Long-term cultured Interferon-&amp;#947; Enzyme-linked Immunospot Assay for Assessing Effector and Memory T Cell Responses in Cattle

Long-term cultured interferon-&#947; enzyme-linked immunospot assay is used as a measure of central memory responses and correlates with protective anti-mycobacterial vaccine responses. With this assay, peripheral blood mononuclear cells are stimulated with mycobacterial antigens and interleukin-2 for 14 days, enabling differentiation and expansion of central memory T cells.

Effector and memory T cells are generated through developmental programing of na&#239;ve cells following antigen recognition. If the infection is ...

Characterization of Thymus-dependent and Thymus-independent Immunoglobulin Isotype Responses in Mice Using Enzyme-linked Immunosorbent Assay

Antibodies, also termed as immunoglobulins (Ig), secreted by differentiated B lymphocytes, plasmablasts/plasma cells, in humoral immunity provide a formidable defense against invading pathogens via diverse mechanisms. One major goal of vaccination is to induce protective antigen-specific antibodies to prevent life-threatening infections. Both thymus-dependent (TD) and thymus-independent (TI) antigens can elicit robust antigen-specific IgM responses and can also induce the production of isotype-switched antibodies (IgG, IgA and IgE) as well as the generation of memory B cells with the help provided by antigen presenting cells (APCs). Here, we describe a protocol to characterize TD and TI Ig isotype responses in mice using enzyme-linked immunosorbent assay (ELISA). In this protocol, TD and TI Ig responses are elicited in mice by intraperitoneal (i.p.) immunization with hapten-conjugated model antigens TNP-KLH (in alum) and TNP-polysaccharide (in PBS), respectively. To induce TD memory response, a booster immunization of TNP-KLH in alum is given at 3 weeks after the first immunization with the same antigen/adjuvant. Mouse sera are harvested at different time points before and after immunization. Total serum Ig levels and TNP-specific antibodies are subsequently quantified using Ig isotype-specific Sandwich and indirect ELISA, respectively. In order to correctly quantify the serum concentration of each Ig isotype, the samples need to be appropriately diluted to fit within the linear range of the standard curves. Using this protocol, we have consistently obtained reliable results with high specificity and sensitivity. When used in combination with other complementary methods such as flow cytometry, in vitro culture of splenic B cells and immunohistochemical staining (IHC), this protocol will allow researchers to gain a comprehensive understanding of antibody responses in a given experimental setting.

In this paper, we describe a protocol to characterize T-dependent and T-independent immunoglobulin (Ig) isotype responses in mice using ELISA. This method used alone or in combination with flow cytometry will allow researchers to identify differences in B cell-mediated Ig isotype responses in mice following T-dependent and T-independent antigen immunization.

Antibodies, also termed as immunoglobulins (Ig), secreted by differentiated B lymphocytes, plasmablasts/plasma cells, in humoral immunity provide a ...

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' ...

Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens

A key aspect of the immune response to bacterial colonization of the host is phagocytosis. An opsonophagocytic killing assay (OPKA) is an experimental procedure in which phagocytic cells are co-cultured with bacterial units. The immune cells will phagocytose and kill the bacterial cultures in a complement-dependent manner. The efficiency of the immune-mediated cell killing is dependent on a number of factors and can be used to determine how different bacterial cultures compare with regard to resistance to cell death. In this way, the efficacy of potential immune-based therapeutics can be assessed against specific bacterial strains and/or serotypes. In this protocol, we describe a simplified OPKA that utilizes basic culture conditions and cell counting to determine bacterial cell viability after co-culture with treatment conditions and HL-60 immune cells. This method has been successfully utilized with a number of different pneumococcal serotypes, capsular and acapsular strains, and other bacterial species. The advantages of this OPKA protocol are its simplicity, versatility (as this assay is not limited to antibody treatments as opsonins), and minimization of time and reagents to assess basic experimental groups.

This opsonophagocytic killing assay is used to compare the ability of phagocytic immune cells to respond to and kill bacteria based on different treatments and/or conditions. Classically, this assay serves as the gold&#160;standard for assessing effector functions of antibodies raised against a bacterium as opsonin.

A key aspect of the immune response to bacterial colonization of the host is phagocytosis. An opsonophagocytic killing assay (OPKA) is an experimental ...