This work was supported by awards from the National Science Foundation (Award# 0920274) and the South Carolina Experiment Station Project SC-1700340. This paper isTechnical Contribution No. 6283 of the Clemson University Experiment Station. The authors thank Dr. Lukasz Kozubowski for his helpful advice in development of this final protocol and Dr. Cheryl Ingram-Smith, Katie Glenn, and Grace Kisirkoi for their critical reading of the manuscript.

NOTE: The overall scheme of this protocol is outlined in Figure 1.
1. C. neoformans Preparation
<ol>
	<li>For each transformation reaction, grow a 2-3 ml&#160;O/N culture of C. neoformans in YPD medium at 30 &#176;C shaking at 250 rpm.</li>
	<li>Centrifuge the O/N culture for 5 min at 900 x g at 10 &#176;C and discard the supernatant.</li>
	<li>Resuspend each cell pellet in 300 &#956;l of Yeast Peptone Dextrose (YPD) medium.</li>
	<li>Using glass beads, gently spread 300 &#956;l of the washed cell suspension onto YPD agar containing 1 M sorbitol.</li>
	<li>Allow plates to dry at ambient temperature for 3-4 hr.</li>
</ol>
2. Gold Microcarrier Preparation
<ol>
	<li>Resuspend 0.25 g of 0.6 &#956;m gold beads in 1 ml of ddH2O, centrifuge for 1 min at 900 x g to pellet the beads, and remove the supernatant.</li>
	<li>Resuspend the gold beads in 1 ml of 100% ethanol.</li>
	<li>Distribute the beads into 4 tubes, 250 &#956;l each, and add 750 &#956;l of 100% ethanol.</li>
	<li>Store gold bead aliquots at 4 &#176;C.</li>
</ol>
3. DNA Preparation
<ol>
	<li>Prepare orange macrocarrier biolistic discs by submerging them in 100% ethanol using forceps. Place discs into a large petri dish containing drierite to dry (make sure the drierite does not touch the discs).</li>
	<li>Once dry, press the macrocarrier discs into the silver disc holders (previously wiped down with 100% ethanol).</li>
	<li>Vortex gold beads (prepared as in step 2) and aliquot 12 &#181;l into a 1.5 ml microcentrifuge tube, one tube per transformation.</li>
	<li>Add to each tube in order: 2 &#181;g of DNA (preferably 2 &#181;l of 1 &#181;g/&#181;l of DNA), 10 &#956;l 2.5 M CaCl2, and 2 &#956;l 1 M spermidine free base.</li>
	<li>Set up a negative control as in step 3.4 but with no DNA.</li>
	<li>Vortex each tube and incubate at ambient temperature for 5 min. Gently flick each tube occasionally to resuspend the settled beads during this incubation.</li>
	<li>Spin tubes at 225 x g for 30 sec to pellet the DNA-coated gold beads. Carefully remove the supernatant (by pipetting or aspiration) and discard.</li>
	<li>Resuspend beads completely in 600 &#181;l of 100% ethanol by slowly pipetting up and down.</li>
	<li>Spin tubes at 225 x g for 30 sec to pellet the beads without packing. Carefully remove and discard the supernatant.</li>
	<li>Resuspend the DNA-coated gold beads in 8 &#181;l of 100% ethanol by slowly pipetting up and down.</li>
	<li>Pipette the DNA-coated gold beads onto the center of the biolistic disc in a 1 cm diameter and allow to dry. 
	NOTE: A dried gold circle visible on the center of the biolistic disc indicates that a sufficient concentration of gold beads is present. 
	NOTE: The macrocarrier discs loaded with DNA-coated gold beads are now ready for use with the gene gun.</li>
</ol>
4. Operating the Gene Gun
<ol>
	<li>Turn on the vacuum pump.</li>
	<li>Turn on the helium gas by turning the knob counterclockwise until a pressure of approximately 2,200 psi is reached on the pressure gauge.</li>
	<li>Turn on the gene gun by flipping the red switch on the left.</li>
	<li>Be sure that the flow rates for the vacuum and the vent are adjusted so the vacuum will reach 28 inches Hg within 15 sec.</li>
	<li>Be sure the distance between the rupture disc and macrocarrier is approximately 3/8 inch.</li>
	<li>Clean the entire chamber by wiping down with ethanol.</li>
	<li>Submerge the rupture discs in 100% ethanol. Allow to dry on a sterile surface (e.g., Petri dish).</li>
	<li>Use a torque wrench to loosen the rupture disc holder. Insert a clean rupture disc into the holder. Screw the rupture disc holder back into place and tighten with torque wrench by turning it once to the right. 
	NOTE: Rupture discs will be replaced following each shoot.</li>
	<li>Submerge the mesh screens in 100% ethanol. Allow to dry on a sterile surface (e.g., Petri dish).</li>
	<li>Once dry, place a washed mesh screen on the white plastic mounting plate. Place the macrocarrier disc holder DNA side down into the disc chamber. Screw on the silver cap, and place the mounting plate in the highest slot. 
	NOTE: The mesh screen will be replaced after each shoot.</li>
	<li>Place a YPD agar plate containing 1 M sorbitol on the bottom plate.</li>
	<li>Shut chamber door and lock into place.</li>
	<li>Push and hold the middle red switch up to engage vacuum and allow the vacuum to reach 28 inches Hg. Once proper vacuum level is reached, move this switch to the down position. When ready, hold down the red switch on the right to fire. When the rupture disc pops, immediately release the fire button and push the middle red switch to the middle position to vent the chamber to 0 psi.</li>
	<li>Clean out rupture disc debris and turn off the gene gun. Then turn off the helium gas by turning the knob clockwise, and finally, turn off the vacuum pump.</li>
</ol>
5. Plating Transformed Cells
<ol>
	<li>Allow the transformation plates to sit at RT for 4 hr to allow the cells to recover.</li>
	<li>Pipette 700 &#181;l of YPD onto the plate. Use a cell scraper to gently scrape the cells off of the agar and pipette liquid into a sterile 1.5 ml microfuge tube. Repeat this step to ensure all cells have been recovered from the plate.</li>
	<li>Pellet cells at 225 x g for 30 sec. Remove and discard the supernatant.</li>
	<li>Resuspend the pellet in 500 &#181;l of YPD.</li>
	<li>Pipette 100 &#181;l of the cell suspension onto the center of the YPD + antibiotic plates and spread using glass beads.</li>
	<li>Leave inverted plates at RT for 3-4 days. As colonies appear, patch onto new YPD + antibiotic plates.</li>
</ol>
6. Genomic DNA Isolation for PCR
NOTE: This is a modified version using reagents from a DNA purification kit (See Table of Materials).
<ol>
	<li>Grow a 5 ml culture of each of the C. neoformans transformants in YPD liquid at 30 &#176;C shaking at 250 rpm O/N.</li>
	<li>Pellet 3 ml of cells at 900 x g, and resuspend in 600 &#181;l of nuclei lysis solution.</li>
	<li>Add the suspension to a new 1.5 ml microcentrifuge tube with 200 &#181;l of 0.5 mm acid washed glass beads.</li>
	<li>Homogenize for 45 sec in a mini beadbeater at ambient temperature, cool tube on ice, and repeat.</li>
	<li>Allow sample to settle on ice for 2 min and transfer supernatant to a new 1.5 ml tube. Add 200 &#181;l of protein precipitation solution to each tube, (100 &#181;l for every 600 &#181;l of supernatant recovered) and vortex vigorously for 20 sec.</li>
	<li>Allow samples to settle on ice for 5 min, and centrifuge at 11,000 x g for 3 min.</li>
	<li>Transfer the supernatant to a clean 1.5 ml tube containing 300 &#181;l of RT isopropanol. Gently mix by inversion.</li>
	<li>Centrifuge samples at 11,000 x g for 2 min, carefully remove the supernatant, and drain the tubes onto paper towels.</li>
	<li>Add 300 &#181;l of RT 70% ethanol to each tube, and gently invert to wash the pellet.</li>
	<li>Centrifuge samples at 11,000 x g for 2 min, and carefully remove all of the ethanol.</li>
	<li>Drain the tube onto clean paper towels, and allow the pellet to air dry for 10-15 min.</li>
	<li>Add 50 &#181;l of DNA rehydration solution and 1.5 &#181;l of RNase solution to each pellet and vortex.</li>
	<li>Centrifuge samples for 5 sec to remove all of the liquid from the cap.</li>
	<li>Incubate samples at 37 &#176;C for 15 min.</li>
	<li>Rehydrate the DNA by incubating the samples at 65 &#176;C for 1 hr.</li>
	<li>Quantify DNA spectrophotometrically by measuring the absorbance at 260 nm (an A260 reading of 1.0 is equivalent to ~50 &#181;g/ml double-stranded DNA), and use up to 200 ng in each PCR reaction.</li>
</ol>
7. RNA Isolation for Reverse Transcriptase-PCR.
<ol>
	<li>Using a RNA purification kit (See Table of Materials), follow the manufacturer&#8217;s instructions to isolate RNA from yeast cells using a minibeadbeater.</li>
	<li>Quantify the concentration of the RNA by measuring the absorbance at 260 nm (an A260 reading of 1.0 is equivalent to ~40 &#181;g/ml single-stranded RNA).</li>
	<li>Using an RT-PCR kit (See Table of Materials), follow the manufacturer&#8217;s instructions to set up RT-PCR reactions with approximately 1 &#181;g of RNA. For the results obtained in this study, use the primers listed in Table 1.</li>
</ol>

<ol>
	<li>Price, M. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryptococcusneoformans+requires+a+functional+glycolytic+pathway+for+disease+but+not+persistence+in+the+host.">Cryptococcusneoformans requires a functional glycolytic pathway for disease but not persistence in the host.</a> MBio. 2, e00103-e00111 (2011).</li><li>Bubb, W. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heteronuclear+NMR+studies+of+metabolites+produced+by+Cryptococcusneoformans+in+culture+media:+identification+of+possible+virulence+factors.">Heteronuclear NMR studies of metabolites produced by Cryptococcusneoformans in culture media: identification of possible virulence factors.</a> Magn Reson Med. 42, 442-453 (1999).</li><li>Himmelreich, U., 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=Identification+of+metabolites+of+importance+in+the+pathogenesis+of+pulmonary+cryptococcoma+using+nuclear+magnetic+resonance+spectroscopy.">Identification of metabolites of importance in the pathogenesis of pulmonary cryptococcoma using nuclear magnetic resonance spectroscopy.</a> Microbes Infect. 5, 285-290 (2003).</li><li>Wright, L., 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=Metabolites+released+by+Cryptococcusneoformans+var.+neoformans+and+var.+gattii+differentially+affect+human+neutrophil+function.">Metabolites released by Cryptococcusneoformans var. neoformans and var. gattii differentially affect human neutrophil function.</a> Microbes Infect. 4, 1427-1438 (2002).</li><li>Hu, G., Cheng, P. Y., Sham, A., Perfect, J. R., Kronstad, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+adaptation+in+Cryptococcusneoformans+during+early+murine+pulmonary+infection.">Metabolic adaptation in Cryptococcusneoformans during early murine pulmonary infection.</a> Mol Microbiol. 69, 1456-1475 (2008).</li><li>Ingram-Smith, C., Martin, S. R., Smith, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acetate+kinase:+not+just+a+bacterial+enzyme.">Acetate kinase: not just a bacterial enzyme.</a> Trends Microbiol. 14, 249-253 (2006).</li><li>Davidson, R. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+disruption+by+biolistic+transformation+in+serotype+D+strains+of+Cryptococcus+neoformans.">Gene disruption by biolistic transformation in serotype D strains of Cryptococcus neoformans.</a> Fungal Genet Biol: FG &amp; B. 29, 38-48 (2000).</li><li>Toffaletti, D. L., Rude, T. H., Johnston, S. A., Durack, D. T., Perfect, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+transfer+in+Cryptococcusneoformans+by+use+of+biolistic+delivery+of+DNA.">Gene transfer in Cryptococcusneoformans by use of biolistic delivery of DNA.</a> J. Bacteriol. 175, 1405-1411 (1993).</li><li>Edman, J. C., Kwon-Chung, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+the+URA5+gene+from+Cryptococcusneoformans+var.+neoformans+and+its+use+as+a+selective+marker+for+transformation.">Isolation of the URA5 gene from Cryptococcusneoformans var. neoformans and its use as a selective marker for transformation.</a> Mol Cell Biol. 10, 4538-4544 (1990).</li><li>Chang, Y. C., Kwon-Chung, K. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complementation+of+a+capsule-deficient+mutation+of+Cryptococcus+neoformans+restores+its+virulence.">Complementation of a capsule-deficient mutation of Cryptococcus neoformans restores its virulence.</a> Mol Cell Biol. 14, 4912-4919 (1994).</li><li>Del Poeta, 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=Topoisomerase+I+is+essential+in+Cryptococcusneoformans:+role+In+pathobiology+and+as+an+antifungal+target.">Topoisomerase I is essential in Cryptococcusneoformans: role In pathobiology and as an antifungal target.</a> Genetics. 152, 167-178 (1999).</li><li>McClelland, C. M., Chang, Y. C., Kwon-Chung, K. 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We have nothing to disclose.

Utilizing this protocol, biolistic transformation can be accomplished in which linear DNA is integrated into a desired locus in the Cryptococcus neoformans genome by homologous recombination. Certain steps in the protocol can have a dramatic effect on the effectiveness/efficiency of the transformation. For a successful transformation, it is imperative that the DNA utilized in the shoot has a concentration of at least 1 &#181;g. However, the volume of DNA added to the gold beads can be increased in the chance the...

Cryptococcus neoformans, an invasive opportunistic pathogen of the central nervous system, is the most frequent cause of fungal meningitis resulting in more than 625,000 deaths per year worldwide 1. Acetate has been shown to be a major fermentation product during cryptococcal infection 2,3,4, and genes encoding enzymes from three putative acetate-producing pathways have been shown to be upregulated during infection 5. This suggests that acetate production and transport may be a necessary and required part of the pathogenic process; however, the significance of this is not yet understood. One possible pathway for acetate production is the xylulose 5-phosphate/fructose 6-phosphate phosphoketolase (Xfp) - acetate kinase (Ack), a pathway previously thought to be present only in bacteria but recently identified in both euascomycete as well as basidiomycete fungi, including&#160;C. neoformans&#160;6.
To determine the localization of these enzymes of this pathway in the cell, a construct carrying a neomycin resistance gene downstream of an ACK gene fusion to the fluorescent tag mCherry (ACK:mCherry:Neo) will be introduced into C. neoformans using the well-established method of biolistic transformation 7,8. Although electroporation is an efficient method for transformation of plasmids that will be maintained as episomes into Cryptococcus 9, it is not useful in creating stable homologous transformants 8. Only&#160;biolistic&#160;delivery using a gene gun&#160;provides&#160;an effective means to transform&#160;linear&#160;DNAs&#160;that will be integrated into the genome by homologous recombination. For example, Edman et al. showed that of the transformants resulting from electroporation of a plasmid-borne URA5 selectable marker into C. neoformansura5 mutants, just 0.001 to 0.1% of transformants were stable 9. Chang et al. achieved just a 0.25% stable transformation efficiency using electroporation to reconstitute capsule production in an acapsular mutant 10. Unlike electroporation, biolistic transformation has been shown to result in stable transformation efficiency of 2-50% depending on the gene that is being altered 7,8,11. 
This visual experiment will provide a step-by-step demonstration of biolistic transformation of the linear ACK:mCherry:Neo DNA construct into C. neoformans, and will describe how to confirm its proper integration via homologous recombination into the&#160;ack&#160;locus. The protocol demonstrated here is a modification of the method developed in the Perfect laboratory 8.

<table border="0" cellpadding="0" cellspacing="0" width="798">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:273px;">Product</td>
			<td style="width:171px;">Company</td>
			<td style="width:99px;">Catalog #</td>
			<td style="width:255px;">Website</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.6 &#956;m gold beads</td>
			<td>Bio-Rad</td>
			<td>165-2262</td>
			<td>http://www.bio-rad.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Spermadine-free base</td>
			<td>Sigma- Aldrich</td>
			<td>S0266</td>
			<td>https://www.sigmaaldrich.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">G418 - Sulfate (Neomycin)</td>
			<td>Gold Biotechnology</td>
			<td>G-418-10</td>
			<td>www.goldbio.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hygromycin</td>
			<td>Gold Biotechnology</td>
			<td>H-270-1</td>
			<td>www.goldbio.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1350 psi Rupture Discs</td>
			<td>Bio-Rad</td>
			<td>165-2330</td>
			<td>http://www.bio-rad.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Stopping Screens</td>
			<td>Bio-Rad</td>
			<td>165-2336</td>
			<td>http://www.bio-rad.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Macrocarriers discs</td>
			<td>Bio-Rad</td>
			<td>165-2335</td>
			<td>http://www.bio-rad.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">YPD Broth</td>
			<td>Becton Dickinson &#38; Co.</td>
			<td>242820</td>
			<td>www.bd.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agar</td>
			<td>Becton Dickinson &#38; Co.</td>
			<td>214530</td>
			<td>www.bd.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sorbitol</td>
			<td>Fisher Scientific</td>
			<td>BP439</td>
			<td>http://www.fishersci.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PDS-1000/He System</td>
			<td>Bio-Rad</td>
			<td>165-2257</td>
			<td>http://www.bio-rad.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microscope</td>
			<td>Zeiss</td>
			<td>Axio</td>
			<td>http://www.zeiss.com/microscopy</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">KOD One Step PCR Kit</td>
			<td>EMD Millipore</td>
			<td>71086-4</td>
			<td>http://www.emdmillipore.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">One Step RT-PCR Kit</td>
			<td>Qiagen</td>
			<td>210212</td>
			<td>www.qiagen.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Wizard Genomic DNA Purification Kit</td>
			<td>Promega</td>
			<td>A1120</td>
			<td>www.promega.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RNeasy Mini Kit</td>
			<td>Qiagen</td>
			<td>74104</td>
			<td>www.qiagen.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mini Beadbeater - 1</td>
			<td>BioSpecs</td>
			<td>3110BX</td>
			<td>http://www.biospec.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microfuge 18 Centrifuge</td>
			<td>Beckman Coulter</td>
			<td>F241.5P</td>
			<td>www.beckmancoulter.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microplate Spectrophotometer</td>
			<td>BioTek</td>
			<td>EPOCH</td>
			<td>www.biotek.com</td>
		</tr>
	</tbody>
</table>

biolistic transformation of a fluorescent tagged gene into the opportunistic fungal pathogen cryptococcus neoformans

The basidiomycete Cryptococcus neoformans, an invasive opportunistic pathogen of the central nervous system, is the most frequent cause of fungal meningitis worldwide resulting in more than 625,000 deaths per year worldwide.&#160;Although electroporation has been developed for the transformation of plasmids in Cryptococcus, only&#160;biolistic&#160;delivery provides&#160;an effective means to transform&#160;linear&#160;DNA&#160;that can be integrated into the genome by homologous recombination.&#160;
Acetate has been shown to be a major fermentation product during cryptococcal infection, but the significance of this is not yet known.&#160;A bacterial pathway composed of the enzymes xylulose-5-phosphate/fructose-6-phosphate phosphoketolase (Xfp) and acetate kinase (Ack) is one of three potential pathways for acetate production in C. neoformans. Here, we demonstrate the biolistic transformation of a construct, which has the gene encoding Ack fused to the fluorescent tag mCherry, into&#160;C. neoformans. We then confirm integration of the ACK-mCherry fusion into the&#160;ACK&#160;locus.

A successful biolistic transformation of C. neoformans can be obtained by following this protocol scheme (Figure 1). With biolistic transformation, a successful shoot of the coated gold beads is indicated by a gold ring visible on the plate after the DNA is shot (Figure 2A). Colonies should appear within 4 to 5 days when left at room temperature after plating the recovered cells from the YPD + 1M sorbitol plates onto selective media. Transforming 2 &#181;g of DNA should result i...

Watch this Scientific Journal Video about Biolistic Transformation of a Fluorescent Tagged Gene into the Opportunistic Fungal Pathogen Cryptococcus neoformans at JoVE.com

Biolistic Transformation of a Fluorescent Tagged Gene into the Opportunistic Fungal Pathogen Cryptococcus neoformans

Biolistic transformation is a method used to generate stable integration of DNA into the genome of the opportunistic pathogen Cryptococcus neoformans through homologous recombination. We will demonstrate biolistic transformation of a construct, which has the gene encoding acetate kinase fused to the fluorescent tag mCherry into&#160;C. neoformans.

Biolistic Transformation of a Fluorescent Tagged Gene into the Opportunistic Fungal Pathogen Cryptococcus neoformans

The basidiomycete Cryptococcus neoformans, an invasive opportunistic pathogen of the central nervous system, is the most frequent cause of fungal ...

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Immunology and Infection

9.8K Views.  Clemson University. Biolistic transformation is a method used to generate stable integration of DNA into the genome of the opportunistic pathogen Cryptococcus neoformans through homologous recombination. We will demonstrate biolistic transformation of a construct, which has the gene encoding acetate kinase fused to the fluorescent tag mCherry into C. neoformans.

Video: Biolistic Transformation of a Fluorescent Tagged Gene into the Opportunistic Fungal Pathogen Cryptococcus neoformans

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 ...

Use of the EpiAirway Model for Characterizing Long-term Host-pathogen Interactions

Nontypeable Haemophilus influenzae (NTHi) are human-adapted Gram-negative bacteria that can cause recurrent and chronic infections of the respiratory mucosa 1; 2. To study the mechanisms by which these organisms survive on and inside respiratory tissues, a model in which successful long-term co-culture of bacteria and human cells can be performed is required. We use primary human respiratory epithelial tissues raised to the air-liquid interface, the EpiAirway model (MatTek, Ashland, MA). These are non-immortalized, well-differentiated, 3-dimensional tissues that contain tight junctions, ciliated and nonciliated cells, goblet cells that produce mucin, and retain the ability to produce cytokines in response to infection. 
This biologically relevant in vitro model of the human upper airway can be used in a number of ways; the overall goal of this method is to perform long-term co-culture of EpiAirway tissues with NTHi and quantitate cell-associated and internalized bacteria over time. As well, mucin production and the cytokine profile of the infected co-cultures can be determined. This approach improves upon existing methods in that many current protocols use submerged monolayer or Transwell cultures of human cells, which are not capable of supporting bacterial infections over extended periods3. For example, if an organism can replicate in the overlying media, this can result in unacceptable levels of cytotoxicity and loss of host cells, arresting the experiment. The EpiAirway model allows characterization of long-term host-pathogen interactions. Further, since the source for the EpiAirway is normal human tracheo-bronchial cells rather than an immortalized line, each is an excellent representation of actual human upper respiratory tract tissue, both in structure and in function4.
For this method, the EpiAirway tissues are weaned off of anti-microbial and anti-fungal compounds for 2 days prior to delivery, and all procedures are performed under antibiotic-free conditions. This necessitates special considerations, since both bacteria and primary human tissues are used in the same biosafety cabinet, and are co-cultured for extended periods.

This method allows characterization of extended bacterial co-culture with EpiAirways, primary human respiratory epithelial tissue grown at the air-liquid interface, a biologically relevant in vitro model. The approach can be used with any microbe that is amenable to long-term co-culture.

Nontypeable Haemophilus influenzae  (NTHi) are human-adapted Gram-negative bacteria that can cause recurrent and chronic infections of the respiratory ...

A Functional Whole Blood Assay to Measure Viability of Mycobacteria, using Reporter-Gene Tagged BCG or M.Tb (BCG lux/M.Tb lux)

Functional assays have long played a key role in measuring of immunogenicity of a given vaccine. This is conventionally expressed as serum bactericidal titers. Studies of serum bactericidal titers in response to childhood vaccines have enabled us to develop and validate cut-off levels for protective immune responses and such cut-offs are in routine use. No such assays have been taken forward into the routine assessment of vaccines that induce primarily cell-mediated immunity in the form of effector T cell responses, such as TB vaccines. In the animal model, the performance of a given vaccine candidate is routinely evaluated in standardized bactericidal assays, and all current novel TB-vaccine candidates have been subjected to this step in their evaluation prior to phase 1 human trials. The assessment of immunogenicity and therefore likelihood of protective efficacy of novel anti-TB vaccines should ideally undergo a similar step-wise evaluation in the human models now, including measurements in bactericidal assays.
Bactericidal assays in the context of tuberculosis vaccine research are already well established in the animal models, where they are applied to screen potentially promising vaccine candidates. Reduction of bacterial load in various organs functions as the main read-out of immunogenicity. However, no such assays have been incorporated into clinical trials for novel anti-TB vaccines to date.
Although there is still uncertainty about the exact mechanisms that lead to killing of mycobacteria inside human macrophages, the interaction of macrophages and T cells with mycobacteria is clearly required. The assay described in this paper represents a novel generation of bactericidal assays that enables studies of such key cellular components with all other cellular and humoral factors present in whole blood without making assumptions about their relative individual contribution. The assay described by our group uses small volumes of whole blood and has already been employed in studies of adults and children in TB-endemic settings. We have shown immunogenicity of the BCG vaccine, increased growth of mycobacteria in HIV-positive patients, as well as the effect of anti-retroviral therapy and Vitamin D on mycobacterial survival in vitro. Here we summarise the methodology, and present our reproducibility data using this relatively simple, low-cost and field-friendly model.
Note: Definitions/Abbreviations
BCG lux = M. bovis BCG, Montreal strain, transformed with shuttle plasmid pSMT1 carrying the luxAB genes from Vibrio harveyi, under the control of the mycobacterial GroEL (hsp60) promoter. 
CFU = Colony Forming Unit (a measure of mycobacterial viability).

A Functional Whole Blood Assay to Measure Viability of Mycobacteria, using Reporter-Gene Tagged BCG or M.Tb BCG lux/M.Tb lux

We describe an alternative approach to the enumeration of mycobacteria in vitro, which uses reporter-gene tagged mycobacteria instead of colony-forming units (CFU). &#x201C;Survival&#x201D; of organisms as well as host response-markers are measured simultaneously, providing a low-cost, versatile and functional system for studies of host/pathogen interactions in the context of tuberculosis.

Functional assays have long played a key role in measuring of immunogenicity of a given vaccine. This is conventionally expressed as serum bactericidal ...

Live-cell Video Microscopy of Fungal Pathogen Phagocytosis

Phagocytic clearance of fungal pathogens, and microorganisms more generally, may be considered to consist of four distinct stages: (i) migration of phagocytes to the site where pathogens are located; (ii) recognition of pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs); (iii) engulfment of microorganisms bound to the phagocyte cell membrane, and (iv) processing of engulfed cells within maturing phagosomes and digestion of the ingested particle. Studies that assess phagocytosis in its entirety are informative1, 2, 3, 4, 5 but are limited in that they do not normally break the process down into migration, engulfment and phagosome maturation, which may be affected differentially. Furthermore, such studies assess uptake as a single event, rather than as a continuous dynamic process. We have recently developed advanced live-cell imaging technologies, and have combined these with genetic functional analysis of both pathogen and host cells to create a cross-disciplinary platform for the analysis of innate immune cell function and fungal pathogenesis. These studies have revealed novel aspects of phagocytosis that could only be observed using systematic temporal analysis of the molecular and cellular interactions between human phagocytes and fungal pathogens and infectious microorganisms more generally. For example, we have begun to define the following: (a) the components of the cell surface required for each stage of the process of recognition, engulfment and killing of fungal cells1, 6, 7, 8; (b) how surface geometry influences the efficiency of macrophage uptake and killing of yeast and hyphal cells7; and (c) how engulfment leads to alteration of the cell cycle and behavior of macrophages 9, 10.
In contrast to single time point snapshots, live-cell video microscopy enables a wide variety of host cells and pathogens to be studied as continuous sequences over lengthy time periods, providing spatial and temporal information on a broad range of dynamic processes, including cell migration, replication and vesicular trafficking. Here we describe in detail how to prepare host and fungal cells, and to conduct the video microscopy experiments. These methods can provide a user-guide for future studies with other phagocytes and microorganisms.

We describe methods for live-cell video microscopy of Candida albicans phagocytosis by macrophages. These methods enable stage-specific analysis of macrophage migration, recognition, engulfment and phagosome maturation and reveal novel aspects of phagocytosis.

Phagocytic clearance of fungal pathogens, and microorganisms more generally, may be considered to consist of four distinct stages: (i) migration of ...

The Citrobacter rodentium Mouse Model: Studying Pathogen and Host Contributions to Infectious Colitis

This protocol outlines the steps required to produce a robust model of infectious disease and colitis, as well as the methods used to characterize Citrobacter rodentium infection in mice. C. rodentium is a gram negative, murine specific bacterial pathogen that is closely related to the clinically important human pathogens enteropathogenic E. coli and enterohemorrhagic E. coli. Upon infection with C. rodentium, immunocompetent mice suffer from modest and transient weight loss and diarrhea. Histologically, intestinal crypt elongation, immune cell infiltration, and goblet cell depletion are observed. Clearance of infection is achieved after 3 to 4 weeks. Measurement of intestinal epithelial barrier integrity, bacterial load, and histological damage at different time points after infection, allow the characterization of mouse strains susceptible to infection.
The virulence mechanisms by which bacterial pathogens colonize the intestinal tract of their hosts, as well as specific host responses that defend against such infections are poorly understood. Therefore the C. rodentium model of enteric bacterial infection serves as a valuable tool to aid in our understanding of these processes. Enteric bacteria have also been linked to Inflammatory Bowel Diseases (IBDs). It has been hypothesized that the maladaptive chronic inflammatory responses seen in IBD patients develop in genetically susceptible individuals following abnormal exposure of the intestinal mucosal immune system to enteric bacteria. Therefore, the study of models of infectious colitis offers significant potential for defining potentially pathogenic host responses to enteric bacteria. C. rodentium induced colitis is one such rare model that allows for the analysis of host responses to enteric bacteria, furthering our understanding of potential mechanisms of IBD pathogenesis; essential in the development of novel preventative and therapeutic treatments.

The Citrobacter rodentium Mouse Model: Studying Pathogen and Host Contributions to Infectious Colitis

Citrobacter rodentium infection provides a valuable model to study enteric bacterial infections as well as host immune responses and colitis in mice. This protocol outlines the measurement of barrier integrity, pathogen load and histological damage allowing for the thorough characterization of pathogen and host contributions to murine infectious colitis.

This protocol  outlines the steps required to produce a robust model of infectious disease and  colitis, as well as the methods used to characterize ...

A Comparative Approach to Characterize the Landscape of Host-Pathogen Protein-Protein Interactions

Significant efforts were gathered to generate large-scale comprehensive protein-protein interaction network maps. This is instrumental to understand the pathogen-host relationships and was essentially performed by genetic screenings in yeast two-hybrid systems. The recent improvement of protein-protein interaction detection by a Gaussia luciferase-based fragment complementation assay now offers the opportunity to develop integrative comparative interactomic approaches necessary to rigorously compare interaction profiles of proteins from different pathogen strain variants against a common set of cellular factors.
This paper specifically focuses on the utility of combining two orthogonal methods to generate protein-protein interaction datasets: yeast two-hybrid (Y2H) and a new assay, high-throughput Gaussia princeps protein complementation assay (HT-GPCA) performed in mammalian cells.
A large-scale identification of cellular partners of a pathogen protein is performed by mating-based yeast two-hybrid screenings of cDNA libraries using multiple pathogen strain variants. A subset of interacting partners selected on a high-confidence statistical scoring is further validated in mammalian cells for pair-wise interactions with the whole set of pathogen variants proteins using HT-GPCA. This combination of two complementary methods improves the robustness of the interaction dataset, and allows the performance of a stringent comparative interaction analysis. Such comparative interactomics constitute a reliable and powerful strategy to decipher any pathogen-host interplays.

This article focuses on the identification of high-confident interaction datasets between host and pathogen proteins using a combination of two orthogonal methods: yeast two-hybrid followed by a high-throughput interaction assay in mammalian cells called HT-GPCA.

Significant efforts were gathered to generate  large-scale comprehensive protein-protein interaction network maps. This is  instrumental to understand the ...

Visualizing Non-lytic Exocytosis of Cryptococcus neoformans from Macrophages Using Digital Light Microscopy

Many aspects of the infection of macrophages by Cryptococcus neoformans have been extensively studied and well defined. However, one particular interaction that is not clearly understood is non-lytic exocytosis. In this process, yeast cells are released into the extracellular space by a poorly understood mechanism that leaves both the macrophage and Cn viable. Here, we describe how to follow a large number of individually infected macrophages for a 24 hr infection period by time-lapsed microscopy. Infected macrophages are housed in a heating chamber with a CO2 atmosphere attached to a microscope that provides the same conditions as a cell-culture incubator. Live digital microscopy can provide information about the dynamic interactions between a host and pathogen that is not available from static images. Being able to visualize each infected cell can provide clues as to how macrophages handle fungal infections, and vice versa. This technique is a powerful tool in studying the dynamics that are behind a complex phenomenon.

Visualizing Non-lytic Exocytosis of Cryptococcus neoformans from Macrophages Using Digital Light Microscopy

We describe how to visualize macrophage-C. neoformans (Cn) interactions in real time, with specific emphasis on the process of non-lytic exocytosis using digital light microscopy. Using this technique individually infected macrophages can be studied to ascertain various aspects of this phenomenon.

Many aspects of the infection of macrophages by Cryptococcus neoformans have been extensively studied and well defined. However, one particular ...

Macrophage Cholesterol Depletion and Its Effect on the Phagocytosis of Cryptococcus neoformans

Cryptococcosis is a life-threatening infection caused by pathogenic fungi of the genus Cryptococcus. Infection occurs upon inhalation of spores, which are able to replicate in the deep lung. Phagocytosis of Cryptococcus by macrophages is one of the ways that the disease is able to spread into the central nervous system to cause lethal meningoencephalitis. Therefore, study of the association between Cryptococcus and macrophages is important to understanding the progression of the infection. The present study describes a step-by-step protocol to study macrophage infectivity by C. neoformansin vitro. Using this protocol, the role of host sterols on host-pathogen interactions is studied. Different concentrations of methyl--cyclodextrin (MCD) were used to deplete cholesterol from murine reticulum sarcoma macrophage-like cell line J774A.1. Cholesterol depletion was confirmed and quantified using both a commercially available cholesterol quantification kit and thin layer chromatography. Cholesterol depleted cells were activated using Lipopolysacharide (LPS) and Interferon gamma (IFN&#947;) and infected with antibody-opsonized Cryptococcus neoformans wild-type H99 cells at an effector-to-target ratio of 1:1. Infected cells were monitored after 2 hr of incubation with C. neoformans and their phagocytic index was calculated. Cholesterol depletion resulted in a significant reduction in the phagocytic index. The presented protocols offer a convenient method to mimic the initiation of the infection process in a laboratory environment and study the role of host lipid composition on infectivity.

Macrophage Cholesterol Depletion and Its Effect on the Phagocytosis of Cryptococcus neoformans

In this article, a protocol for infection of macrophages with Cryptococcus neoformans is described. Also, a method for sterol depletion from the macrophages is explained. These protocols provide a guide to study fungal infections in vitro and examine the role of sterols in such infections.

Cryptococcosis is a life-threatening infection caused by pathogenic fungi of the genus Cryptococcus. Infection occurs upon inhalation of spores, which are ...

Loop-mediated Isothermal Amplification (LAMP) Assays for the Species-specific Detection of Eimeria that Infect Chickens

Eimeria species parasites, protozoa which cause the enteric disease coccidiosis, pose a serious threat to the production and welfare of chickens. In the absence of effective control clinical coccidiosis can be devastating. Resistance to the chemoprophylactics frequently used to control Eimeria is common and sub-clinical infection is widespread, influencing feed conversion ratios and susceptibility to other pathogens such as Clostridium perfringens. Despite the availability of polymerase chain reaction (PCR)-based tools, diagnosis of Eimeria infection still relies almost entirely on traditional approaches such as lesion scoring and oocyst morphology, but neither is straightforward. Limitations of the existing molecular tools include the requirement for specialist equipment and difficulties accessing DNA as template. In response a simple field DNA preparation protocol and a panel of species-specific loop-mediated isothermal amplification (LAMP) assays have been developed for the seven Eimeria recognised to infect the chicken. We now provide a detailed protocol describing the preparation of genomic DNA from intestinal tissue collected post-mortem, followed by setup and readout of the LAMP assays. Eimeria species-specific LAMP can be used to monitor parasite occurrence, assessing the efficacy of a farm&#8217;s anticoccidial strategy, and to diagnose sub-clinical infection or clinical disease with particular value when expert surveillance is unavailable.

Loop-mediated Isothermal Amplification LAMP Assays for the Species-specific Detection of Eimeria that Infect Chickens

Diagnosis of Eimeria infection in chickens remains demanding. Parasite morphology- and host pathology-led approaches are commonly inconclusive, while molecular approaches based on PCR have proven demanding in cost and expertise. The aim of this protocol is to establish loop-mediated isothermal amplification (LAMP) as a straightforward molecular diagnostic for eimerian infection.

Eimeria species parasites, protozoa which cause the enteric disease coccidiosis, pose a serious threat to the production and welfare of chickens. In the ...

Foodborne Pathogen Screening Using Magneto-fluorescent Nanosensor: Rapid Detection of E. Coli O157:H7

Enterohemorrhagic Escherichia coli O157:H7 has been linked to both waterborne and foodborne illnesses, and remains a threat despite the food- and water-screening methods used currently. While conventional bacterial detection methods, such as polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISA) can specifically detect pathogenic contaminants, they require extensive sample preparation and lengthy waiting periods. In addition, these practices demand sophisticated laboratory instruments and settings, and must be executed by trained professionals. Herein, a protocol is proposed for a simpler diagnostic technique that features the unique combination of magnetic and fluorescent parameters in a nanoparticle-based platform. The proposed multiparametric magneto-fluorescent nanosensors (MFnS) can detect E. coli O157:H7 contamination with as little as 1 colony-forming unit present in solution within less than 1 h. Furthermore, the ability of MFnS to remain highly functional in complex media such as milk and lake water has been verified. Additional specificity assays were also used to demonstrate the ability of MFnS to only detect the specific target bacteria, even in the presence of similar bacterial species. The pairing of magnetic and fluorescent modalities allows for the detection and quantification of pathogen contamination in a wide range of concentrations, exhibiting its high performance in both early- and late-stage contamination detection. The effectiveness, affordability, and portability of the MFnS make them an ideal candidate for point-of-care screening for bacterial contaminants in a wide range of settings, from aquatic reservoirs to commercially packaged foods.

Foodborne Pathogen Screening Using Magneto-fluorescent Nanosensor: Rapid Detection of E. Coli O157:H7

The overall goal of this protocol is to synthesize functional nanosensors for the portable, cost-effective, and rapid detection of specifically targeted pathogenic bacteria through a combination of magnetic relaxation and fluorescence emission modalities.