We thank all members of the Nobile lab for helpful discussions on biofilm assays. This study was supported by National Institutes of Health (NIH) grant R21 AI125801 (to C.J.N.). D.L.R. was supported by a doctoral fellowship from The University of California Institute for Mexico and the United States (UC-MEXUS) and Consejo Nacional de Ciencia y Technologia (CONACYT).

<ol>
	<li>Nobile, C. J., Johnson, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Candida+albicans+Biofilms+and+Human+Disease.">Candida albicans Biofilms and Human Disease.</a> Annu Rev Microbiol. 69, 71-92 (2015).</li><li>Kojic, E. M., Darouiche, R. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Candida+infections+of+medical+devices.">Candida infections of medical devices.</a> Clin Microbiol Rev. 17 (2), 255-267 (2004).</li><li>Fox, E. P., Nobile, C. J., Dietrich, L. A., Friedmann, T. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Candida albicans: Symptoms, Causes and Treatment Options. , 1-24 (2013).</li><li>Gulati, M., Nobile, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Candida+albicans+biofilms:+development,+regulation,+and+molecular+mechanisms.">Candida albicans biofilms: development, regulation, and molecular mechanisms.</a> Microbes Infect. 18 (5), 310-321 (2016).</li><li>Uppuluri, P., 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=Dispersion+as+an+important+step+in+the+Candida+albicans+biofilm+developmental+cycle.">Dispersion as an important step in the Candida albicans biofilm developmental cycle.</a> PLoS Pathog. 6 (3), e1000828 (2010).</li><li>Andes, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+characterization+of+an+in+vivo+central+venous+catheter+Candida+albicans+biofilm+model.">Development and characterization of an in vivo central venous catheter Candida albicans biofilm model.</a> Infect Immun. 72 (10), 6023-6031 (2004).</li><li>Nett, J. E., Marchillo, K., Spiegel, C. A., Andes, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+validation+of+an+in+vivo+Candida+albicans+biofilm+denture+model.">Development and validation of an in vivo Candida albicans biofilm denture model.</a> Infect Immun. 78 (9), 3650-3659 (2010).</li><li>Nett, J. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rat+indwelling+urinary+catheter+model+of+Candida+albicans+biofilm+infection.">Rat indwelling urinary catheter model of Candida albicans biofilm infection.</a> Infect Immun. 82 (12), 4931-4940 (2014).</li><li>Krom, B. P., Willems, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Vitro+Models+for+Candida+Biofilm+Development.">In Vitro Models for Candida Biofilm Development.</a> Methods Mol Biol. 1356, 95-105 (2016).</li><li>Hawser, S. P., Douglas, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biofilm+formation+by+Candida+species+on+the+surface+of+catheter+materials+in+vitro.">Biofilm formation by Candida species on the surface of catheter materials in vitro.</a> Infect Immun. 62 (3), 915-921 (1994).</li><li>Ramage, G., Vande Walle, K., Wickes, B. L., Lopez-Ribot, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Standardized+method+for+in+vitro+antifungal+susceptibility+testing+of+Candida+albicans+biofilms.">Standardized method for in vitro antifungal susceptibility testing of Candida albicans biofilms.</a> Antimicrob Agents Chemother. 45 (9), 2475-2479 (2001).</li><li>Nett, J. E., Cain, M. T., Crawford, K., Andes, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimizing+a+Candida+biofilm+microtiter+plate+model+for+measurement+of+antifungal+susceptibility+by+tetrazolium+salt+assay.">Optimizing a Candida biofilm microtiter plate model for measurement of antifungal susceptibility by tetrazolium salt assay.</a> J Clin Microbiol. 49 (4), 1426-1433 (2011).</li><li>Krom, B. P., Cohen, J. B., McElhaney Feser, G. E., Cihlar, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimized+candidal+biofilm+microtiter+assay.">Optimized candidal biofilm microtiter assay.</a> J Microbiol Methods. 68 (2), 421-423 (2007).</li><li>Lohse, M. B., 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=Assessment+and+Optimizations+of+Candida+albicans+In+Vitro+Biofilm+Assays.">Assessment and Optimizations of Candida albicans In Vitro Biofilm Assays.</a> Antimicrob Agents Chemother. 61 (5), (2017).</li><li>Winter, M. B., 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=Global+Identification+of+Biofilm-Specific+Proteolysis+in+Candida+albicans.">Global Identification of Biofilm-Specific Proteolysis in Candida albicans.</a> mBio. 7 (5), (2016).</li><li>Nobile, C. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+recently+evolved+transcriptional+network+controls+biofilm+development+in+Candida+albicans.">A recently evolved transcriptional network controls biofilm development in Candida albicans.</a> Cell. 148 (1-2), 126-138 (2012).</li><li>Fox, E. P., 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=An+expanded+regulatory+network+temporally+controls+Candida+albicans+biofilm+formation.">An expanded regulatory network temporally controls Candida albicans biofilm formation.</a> Mol Microbiol. 96 (6), 1226-1239 (2015).</li><li>Nobile, C. J., Mitchell, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+cell-surface+genes+and+biofilm+formation+by+the+C.+albicans+transcription+factor+Bcr1p.">Regulation of cell-surface genes and biofilm formation by the C. albicans transcription factor Bcr1p.</a> Curr Biol. 15 (12), 1150-1155 (2005).</li><li>Baker, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> At the bench: A laboratory navigator. 27, (2005).</li></ol>

Clarissa J. Nobile is a founder of BioSynesis, Inc., a company developing inhibitors and diagnostics of C. albicans biofilms.

The customizable microfluidic biofilm assay described here allows for the visualization of biofilm formation in real-time at a single cell level when exposed to a fixed rate laminar flow and constant temperature. It provides a powerful means to study the development of biofilms in wild-type and mutant strains, and the effects of antimicrobial agent treatments on biofilms under conditions that mimic physiological conditions observed in clinical settings. Unlike most in vitro biofilm assays, this method allows for the examination of a developing biofilm in real-time as it forms.
This method can be used in a high-throughput manner, where up to 24 samples can be run simultaneously to assess biofilm formation. The method can also be used to conduct genetic screens of mutant libraries to identify genes required for normal biofilm development and can be used to assess the effectivity against biofilms of antimicrobial compounds of interest in compound library screens. We anticipate that future applications of this microfluidic device will include such screens. We note, however, that certain drug treatment testing will be limited by the thickness of the biofilm formed using this microfluidic device as biofilms grown for &#62;16 h tend to clog the viewing channel. Thus, drug testing experiments will need to be performed for &#60;16 h.
Overall, this device is highly customizable and versatile, and can be adjusted to assess different microbial species across kingdoms, flow rates, temperatures, incubation times, and media. The method described provides information about a number of different aspects of biofilm formation, including initial cell adherence, biofilm maturation, and cell dispersal. Although we only report results for single-species biofilm formation here, this protocol could also be adapted to study dual- and mixed-species biofilm formation.
Two steps are critical to successfully perform this protocol. First, air bubbles in the system must be avoided by preheating the media at the experimental temperature. One common misstep is the dilution of cells in media that was not preheated. Cells should be diluted in the same media that is being used for the inlet wells. Second, the flow of cells from outlet to inlet wells must be carefully monitored; if the cells flow too far, the inlet media will become contaminated and the experiment will not yield interpretable results. On the other hand, if the cells are not allowed to move all the way into the viewing channel, then no cells will be visible in the channel during the experiment, leading to blank images. Additional key points to keep in mind are that the volume and movement between wells in the microfluidic plate are linked together for each column, and it is important to maintain as much media consistency as possible (with similar viscosity, cell density, and composition) and similarly sized cells (if possible), as different media and different cell sizes will have different flow rates in the column. During the experiment, the backflow of the cells is monitored using a microscope; however, only two channels can be viewed at one time (using a 10X objective). Thus, it is highly recommended to perform a mock experiment to measure the time required to flow from outlet to inlet wells using the cells and media planned to be used in the actual experiment.
In general, we highly recommend use of this microfluidic biofilm assay as an in vitro assay to be utilized before in vivo animal testing. The assay, however, is still an in vitro assay, and results will need to be validated in relevant animal models. In our experiences, the results of this microfluidic biofilm assay have had the best predictive value for in vivo biofilm assays compared with other in vitro assays we have assessed14.

Candida albicans is a commensal member of the human microbiota, however it is also an opportunistic pathogen, capable of causing superficial and severe fungal infections1,2. A major virulence trait of C. albicans is its ability to form resilient and drug resistant biofilms, communities of cells adhered to a surface and enclosed in an extracellular matrix material1,3. C. albicans biofilms are highly structured, containing several layers of multiple cell types (round budding yeast-form cells, oval pseudohyphal cells, and tubular hyphal cells)4. C. albicans biofilm development begins with the adherence of round yeast-form cells to a surface (seeding the biofilm), followed by the proliferation of these cells on the surface, and then the maturation of the immature biofilm structure into a fully-formed biofilm that is surrounded by extracellular matrix material4. The mature biofilm is predominantly composed of elongated hyphal cells that form dense and interconnecting networks, providing the architectural stability to the biofilm4. Throughout the biofilm life cycle, round budding yeast cells disperse from the mature biofilm, and may travel to other regions of the body to cause disseminated infections or seed new biofilms at other sites4,5. C. albicans can form biofilms on biotic surfaces, such as mucosal surfaces and throughout host tissue, and on abiotic surfaces, such as catheters, pacemakers, dentures, and prosthetic joints. Due to the recalcitrant properties of biofilms, they are extremely difficult to eradicate, and in many cases the only effective treatment strategy is removal of the infected device4. It is thus crucial to investigate biofilm formation under conditions similar to those observed in clinical settings.
There are several critical in vivo animal models used to study C. albicans biofilm formation6,7,8; however, these studies can be costly, time consuming, and are limited by the number of strains and antimicrobial agents that can be tested at a given time. In vitro biofilm assays, on the other hand, allow for the rapid, high-throughput assessment of antifungal compounds and mutant strains, and are much more cost-effective and ethical than biofilm assays carried out in animal models9,10,11,12,13,14. Here we describe an in vitro assay that we developed and optimized to observe biofilm formation temporally under laminar flow using a customizable microfluidic device14,15. The assay allows for the visualization of each stage of biofilm formation, including the initial adherence step, cell proliferation, biofilm maturation, and cell dispersion. The assay is also useful to visualize cell morphology changes throughout the development of a biofilm.
Microtiter plates, which are typically utilized for in vitro biofilm assays, while high throughput, do not allow for controlled flow conditions. Traditional laminar flow cell systems allow for the continuous assessment of biofilm formation in controlled flow conditions, but these are often time consuming to set up and tend to have limited dynamic range control and throughput. The microfluidic device utilized here overcomes these limitations by combining high throughput plates (containing 48 wells) with a built-in laminar flow chamber and is highly reproducible, versatile, and customizable.
Here, we describe a protocol for the use of a commercially available automated microfluidic device to assess biofilm formation of a wild-type C. albicans strain, the effects of a known antifungal agent on the development of a biofilm, and biofilm formation in two mutant strains (bcr1&#916;/&#916; and efg1 &#916;/&#916;) that were previously reported to have biofilm defects in vitro and in vivo16,17,18. The described protocol can be used to test the efficacy of antimicrobial agents in inhibiting biofilm formation throughout the development of a biofilm, and to identify genes required for normal biofilm development by screening mutant libraries.

<table>
	<tbody>
		<tr>
			<td>BioFlux 1000z</td>
			<td>Fluxion</td>
			<td></td>
			<td>Automated microfluidic device for live cell analysis</td>
		</tr>
		<tr>
			<td>48-well plate 0-20 dyne</td>
			<td>Fluxion</td>
			<td>910-0047</td>
			<td>Microfluidic plate</td>
		</tr>
		<tr>
			<td>Montage Software</td>
			<td>Fluxion</td>
			<td>Version 7.8.4.0</td>
			<td>Visualization analysis software</td>
		</tr>
		<tr>
			<td>ImageJ Software</td>
			<td>NIH</td>
			<td>https://imagej.nih.gov/ij/</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast Extract</td>
			<td>Criterion</td>
			<td>C7341</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Peptone</td>
			<td>BD Biosciences</td>
			<td>211677</td>
			<td></td>
		</tr>
		<tr>
			<td>Dextrose (D-Glucose)</td>
			<td>Fisher Scientific</td>
			<td>D163</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Phosphate Monobasic</td>
			<td>Fisher Scientific</td>
			<td>P285-500</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI-1640</td>
			<td>Sigma-Aldrich</td>
			<td>R6504</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Sigma-Aldrich</td>
			<td>M3183</td>
			<td></td>
		</tr>
		<tr>
			<td>Nutrient Broth</td>
			<td>Criterion</td>
			<td>C6471</td>
			<td></td>
		</tr>
		<tr>
			<td>Difco D-Mannitol</td>
			<td>BD Biosciences</td>
			<td>217020</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Criterion</td>
			<td>C5001</td>
			<td></td>
		</tr>
		<tr>
			<td>Amphotericin B</td>
			<td>Corning</td>
			<td>30-003-CF</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterile Inoculating Loops</td>
			<td>VWR</td>
			<td>30002-094</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri Dishes with Clear Lid</td>
			<td>Fisher Scientific</td>
			<td>FB0875712</td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable Cuvettes</td>
			<td>Fisher Scientific</td>
			<td>14-955-127</td>
			<td></td>
		</tr>
		<tr>
			<td>Lens Paper</td>
			<td>VWR</td>
			<td>52846-001</td>
			<td></td>
		</tr>
		<tr>
			<td>Microplate and Cuvette Spectrophotometer</td>
			<td>BioTek</td>
			<td>EPOCH2TC</td>
			<td></td>
		</tr>
		<tr>
			<td>Shaking Incubator</td>
			<td>Eppendorf</td>
			<td>M12820004</td>
			<td></td>
		</tr>
	</tbody>
</table>

visualization of biofilm formation in candida albicans using an automated microfluidic device

Candida albicans is the most common fungal pathogen of humans, causing about 15% of hospital-acquired sepsis cases. A major virulence attribute of C. albicans is its ability to form biofilms, structured communities of cells attached to biotic and abiotic surfaces. C. albicans biofilms can form on host tissues, such as mucosal layers, and on medical devices, such as catheters, pacemakers, dentures, and joint prostheses. Biofilms pose significant clinical challenges because they are highly resistant to physical and chemical perturbations, and can act as reservoirs to seed disseminated infections. Various in vitro assays have been utilized to study C. albicans biofilm formation, such as microtiter plate assays, dry weight measurements, cell viability assays, and confocal scanning laser microscopy. All of these assays are single end-point assays, where biofilm formation is assessed at a specific time point. Here, we describe a protocol to study biofilm formation in real-time using an automated microfluidic device under laminar flow conditions. This method allows for the observation of biofilm formation as the biofilm develops over time, using customizable conditions that mimic those of the host, such as those encountered in vascular catheters. This protocol can be used to assess the biofilm defects of genetic mutants as well as the inhibitory effects of antimicrobial agents on biofilm development in real-time.

We performed the microfluidic biofilm assay described here using a wild-type C. albicans strain under two media conditions (RPMI-1640 and Spider media), the wild-type strain in the presence of the known antifungal drug amphotericin B (16 &#181;g/mL) in RPMI, and two mutant strains previously reported to have defects in biofilm formation (bcr1&#916;/&#916; and efg1 &#916;/&#916;) in Spider media.
Video 1 shows the development of a wild-type biofilm in RPMI-1640 medium and the effects of the antifungal drug, amphotericin B, on biofilm formation. Under wild-type conditions, several cells strongly adhere to the channel, the cells form hyphae as time progresses, and a thick biofilm can be observed with intercalating hyphae and yeast cells. Towards the end of the microfluidic experiment, the wild-type biofilm completely fills the viewing channel. The presence of amphotericin B, however, has a pronounced effect on reducing the biofilm. Specifically, the adherence of cells is diminished, and, unlike untreated conditions, in the presence of amphotericin B, several cells can be seen flowing away with the shear flow of the media. As time progresses, the cells fail to form hyphae and a biofilm is not formed. These differences are also shown in Figure 3, which depicts 4 time-points from the assay at 0 h, 2 h, 6 h, and 12 h.
Video 2 shows the development of a wild-type biofilm and two previously reported biofilm-defective mutants (bcr1 &#916;/&#916; and efg1 &#916;/&#916;) in Spider media. Both bcr1 &#916;/&#916; and efg1 &#916;/&#916; strains show severely reduced biofilm formation compared to the isogenic wild-type strain. For the efg1 &#916;/&#916; strain, we observed that the adhered cells do not form hyphae and the resulting biofilm is severely defective. For the bcr1 &#916;/&#916; strain, we observed that not only is the bcr1 &#916;/&#916; strain defective in biofilm formation, but it also displays a clear adherence defect, where cells can be seen drifting in the direction of the shear flow as they fail to adhere to the viewing channel. These differences are also shown in Figure 4, which depicts 4 time points from the assay at 0 h, 2 h, 6 h, and 12 h.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56743/56743fig1.jpg" /> 
Figure 1: Microfluidic instrument used in this experiment. Panel A shows the microfluidic instrument used, panel B shows the interface plate, panel C shows a schematic outline of a single viewing channel (stage) and three sub-stages captured by the camera during the experiment, and panel D shows a schematic outline of the 48-well microfluidic plate used with a schematic of the outlet and inlet wells and viewing window. <a href="https://cloudflare.jove.com/files/ftp_upload/56743/56743fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56743/56743fig2.jpg" /> 
Figure 2: Select screenshots of imaging modulesoftware and microfluidic plate control system. Panel A shows the Control Module, that contains the controls for the microfluidic plate, and panel B shows the imaging module window, the &#39;Move Stage to Absolute Position&#39; (MAP) module, the &#39;Multi-dimensional Acquisition&#39; (MDA) module, and the &#39;Sample Reload Adjustment&#39; (SRA) module. <a href="https://cloudflare.jove.com/files/ftp_upload/56743/56743fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56743/56743fig3.jpg" /> 
Figure 3: Exposure to amphotericin B results in biofilm formation defects. Time dependent visualization of biofilm formation in RPMI-1640 media (Column 1), and RPMI-1640 media supplemented with 16 &#181;g/mL amphotericin B (Column 2) under dynamic flow (0.5 dyne/cm2) at 37 &#176;C for 12 h post-adherence in the microfluidic system. Representative 0 h (post-adherence and initial wash), 2 h, 6 h, and 12 h images (top to bottom) are shown for the isogenic wild-type strain SN250 (Columns 1 and 2). Scale bars are 20 &#181;m in each panel. Corresponding time lapse videos of biofilm formation are provided in Video 1. <a href="https://cloudflare.jove.com/files/ftp_upload/56743/56743fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56743/56743fig4.jpg" /> 
Figure 4: Deletion of BCR1 or EFG1 results in biofilm formation defects. Time dependent visualization of biofilm formation in Spider media (Columns 1-3) under dynamic flow (0.5 dyne/cm2) at 37 &#176;C for 12 h post-adherence in the microfluidic system. Representative 0 h (post-adherence and initial wash), 2 h, 6 h, and 12 h images (top to bottom) are shown for the isogenic wild-type strain SN250 (Column 1), bcr1&#916;/&#916; strain (Column 2), and efg1 &#916;/&#916; strain (Column 3). Scale bars are 20 &#181;m in each panel. Corresponding time lapse videos of biofilm formation are provided in Video 2. <a href="https://cloudflare.jove.com/files/ftp_upload/56743/56743fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Video 1: <a href="http://cloudflare.jove.com/files/ftp_upload/56743/Video-1-WT_and_WT_plus_AmpB.mp4">Please click here to download this file.</a>
Video 2: <a href="http://cloudflare.jove.com/files/ftp_upload/56743/Video-2-WT_bcr1_efg1_Mutants.mp4">Please click here to download this file.</a>

Watch this Scientific Journal Video about Visualization of Biofilm Formation in Candida albicans Using an Automated Microfluidic Device at JoVE.com

Visualization of Biofilm Formation in Candida albicans Using an Automated Microfluidic Device

This protocol describes the use of a customizable automated microfluidic device to visualize biofilm formation in Candida albicans under host physiological conditions.

Visualization of Biofilm Formation in Candida albicans Using an Automated Microfluidic Device

Candida albicans is the most common fungal pathogen of humans, causing about 15% of hospital-acquired sepsis cases. A major virulence attribute of C. ...

visualization-biofilm-formation-candida-albicans-using-an-automated

Nanyang Technological University

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JoVE Journal

Immunology and Infection

10.5K Views.  University of California, Merced. This protocol describes the use of a customizable automated microfluidic device to visualize biofilm formation in Candida albicans under host physiological conditions.

Video: Visualization of Biofilm Formation in Candida albicans Using an Automated Microfluidic Device

A 96 Well Microtiter Plate-based Method for Monitoring Formation and Antifungal Susceptibility Testing of Candida albicans Biofilms

Candida albicans remains the most frequent cause of fungal infections in an expanding population of compromised patients and candidiasis is now the third most common infection in US hospitals. Different manifestations of candidiasis are associated with biofilm formation, both on host tissues and/or medical devices (i.e. catheters). Biofilm formation carries negative clinical implications, as cells within the biofilms are protected from host immune responses and from the action of antifungals. We have developed a simple, fast and robust in vitro model for the formation of C. albicans biofilms using 96 well microtiter-plates, which can also be used for biofilm antifungal susceptibility testing. The readout of this assay is colorimetric, based on the reduction of XTT (a tetrazolium salt) by metabolically active fungal biofilm cells. A typical experiment takes approximately 24 h for biofilm formation, with an additional 24 h for antifungal susceptibility testing. Because of its simplicity and the use of commonly available laboratory materials and equipment, this technique democratizes biofilm research and represents an important step towards the standardization of antifungal susceptibility testing of fungal biofilms.

A 96 Well Microtiter Plate-based Method for Monitoring Formation and Antifungal Susceptibility Testing of Candida albicans Biofilms

We describe a simple, rapid and robust method for the formation of Candida albicans biofilms using 96 well microtiter plates and its utility in antifungal susceptibility testing of cells within biofilms.

Candida albicans remains the most frequent cause of fungal infections in an expanding population of compromised patients and candidiasis is now the third ...

Microtiter Dish Biofilm Formation Assay

Biofilms are communities of microbes attached to surfaces, which can be found in medical, industrial and natural settings. In fact, life in a biofilm probably represents the predominate mode of growth for microbes in most environments. Mature biofilms have a few distinct characteristics. Biofilm microbes are typically surrounded by an extracellular matrix that provides structure and protection to the community. Microbes growing in a biofilm also have a characteristic architecture generally comprised of macrocolonies (containing thousands of cells) surrounded by fluid-filled channels. Biofilm-grown microbes are also notorious for their resistance to a range of antimicrobial agents including clinically relevant antibiotics.
The microtiter dish assay is an important tool for the study of the early stages in biofilm formation, and has been applied primarily for the study of bacterial biofilms, although this assay has also been used to study fungal biofilm formation. Because this assay uses static, batch-growth conditions, it does not allow for the formation of the mature biofilms typically associated with flow cell systems. However, the assay has been effective at identifying many factors required for initiation of biofilm formation (i.e, flagella, pili, adhesins, enzymes involved in cyclic-di-GMP binding and metabolism) and well as genes involved in extracellular polysaccharide production. Furthermore, published work indicates that biofilms grown in microtiter dishes do develop some properties of mature biofilms, such a antibiotic tolerance and resistance to immune system effectors.
This simple microtiter dish assay allows for the formation of a biofilm on the wall and/or bottom of a microtiter dish. The high throughput nature of the assay makes it useful for genetic screens, as well as testing biofilm formation by multiple strains under various growth conditions. Variants of this assay have been used to assess early biofilm formation for a wide variety of microbes, including but not limited to, pseudomonads, Vibrio cholerae, Escherichia coli, staphylocci, enterococci, mycobacteria and fungi.
In the protocol described here, we will focus on the use of this assay to study biofilm formation by the model organism Pseudomonas aeruginosa. In this assay, the extent of biofilm formation is measured using the dye crystal violet (CV). However, a number of other colorimetric and metabolic stains have been reported for the quantification of biofilm formation using the microtiter plate assay. The ease, low cost and flexibility of the microtiter plate assay has made it a critical tool for the study of biofilms.

The assay describes a rapid means to measure early biofilm formation in bacteria and fungi. This method uses a microtiter plate as the substratum for microbial biofilm formation, and the biofilm is visualized using crystal violet strain. The assay provides either a qualitative or quantitative assay for early biofilm formation.

Biofilms are communities of microbes attached to surfaces, which can be found in medical, industrial and natural settings.  In fact, life in a biofilm ...

In vitro Biofilm Formation in an 8-well Chamber Slide

The chronic nature of many diseases is attributed to the formation of bacterial biofilms which are recalcitrant to traditional antibiotic therapy. Biofilms are community-associated bacteria attached to a surface and encased in a matrix. The role of the extracellular matrix is multifaceted, including facilitating nutrient acquisition, and offers significant protection against environmental stresses (e.g. host immune responses). In an effort to acquire a better understanding as to how the bacteria within a biofilm respond to environmental stresses we have used a protocol wherein we visualize bacterial biofilms which have formed in an 8-well chamber slide. The biofilms were stained with the BacLight Live/Dead stain and examined using a confocal microscope to characterize the relative biofilm size, and structure under varying incubation conditions. Z-stack images were collected via confocal microscopy and analyzed by COMSTAT. This protocol can be used to help elucidate the mechanism and kinetics by which biofilms form, as well as identify components that are important to biofilm structure and stability.

In vitro Biofilm Formation in an 8-well Chamber Slide

This article describes the procedure for the formation and visualization of a bacterial biofilm grown within an 8-well chamber slide

The chronic nature of many diseases is attributed to the formation of bacterial biofilms which are recalcitrant to traditional antibiotic therapy. ...

Studying Microbial Communities In Vivo: A Model of Host-mediated Interaction Between Candida Albicans and Pseudomonas Aeruginosa in the Airways

Studying host-pathogen interaction enables us to understand the underlying mechanisms of the pathogenicity during microbial infection. The prognosis of the host depends on the involvement of an adapted immune response against the pathogen1. Immune response is complex and results from interaction of the pathogens and several immune or non-immune cellular types2. In vitro studies cannot characterise these interactions and focus on cell-pathogen interactions. Moreover, in the airway3, particularly in patients with suppurative chronic lung disease or in mechanically ventilated patients, polymicrobial communities are present and complicate host-pathogen interaction. Pseudomonas aeruginosa and Candida albicans are both problem pathogens4, frequently isolated from tracheobronchial samples, and associated to severe infections, especially in intensive care unit5. Microbial interactions have been reported between these pathogens in vitro but the clinical impact of these interactions remains unclear6. To study the interactions between C. albicans and P. aeruginosa, a murine model of C. albicans airways colonization, followed by a P. aeruginosa-mediated acute lung infection was performed.

Studying Microbial Communities In Vivo: A Model of Host-mediated Interaction Between Candida Albicans and Pseudomonas Aeruginosa in the Airways

While in vitro study of host-pathogen interactions allow the characterization of specific immune responses, in vivo models are required to observe the effects of complex responses. Using Candida albicans exposure followed by Pseudomonas aeruginosa-mediated lung infection, we established a murine model of microbial interactions involved in ventilator-associated pneumonia pathogenicity.

Studying host-pathogen interaction enables us to understand the underlying mechanisms of the pathogenicity during microbial infection. The prognosis of ...

Visualizing the Effects of Sputum on Biofilm Development Using a Chambered Coverglass Model

Biofilms consist of groups of bacteria encased in a self-secreted matrix. They play an important role in industrial contamination as well as in the development and persistence of many health related infections. One of the most well described and studied biofilms in human disease occurs in chronic pulmonary infection of cystic fibrosis patients. When studying biofilms in the context of the host, many factors can impact biofilm formation and development. In order to identify how host factors may affect biofilm formation and development, we used a static chambered coverglass method to grow biofilms in the presence of host-derived factors in the form of sputum supernatants. Bacteria are seeded into chambers and exposed to sputum filtrates. Following 48 hr of growth, biofilms are stained with a commercial biofilm viability kit prior to confocal microscopy and analysis. Following image acquisition, biofilm properties can be assessed using different software platforms. This method allows us to visualize key properties of biofilm growth in presence of different substances including antibiotics.

This protocol describes the visualization of biofilm development following exposure to host-factors using a slide chamber model. This model allows for direct visualization of biofilm development as well as analysis of biofilm parameters using computer software programs.

Biofilms consist of groups of bacteria encased in a self-secreted matrix. They play an important role in industrial contamination as well as in the ...

Bile Salt-induced Biofilm Formation in Enteric Pathogens: Techniques for Identification and Quantification

Biofilm formation is a dynamic, multistage process that occurs in bacteria under harsh environmental conditions or times of stress. For enteric pathogens, a significant stress response is induced during gastrointestinal transit and upon bile exposure, a normal component of human digestion. To overcome the bactericidal effects of bile, many enteric pathogens form a biofilm hypothesized to permit survival when transiting through the small intestine. Here we present methodologies to define biofilm formation through solid-phase adherence assays as well as extracellular polymeric substance (EPS) matrix detection and visualization. Furthermore, biofilm dispersion assessment is presented to mimic the analysis of events triggering release of bacteria during the infection process. Crystal violet staining is used to detect adherent bacteria in a high-throughput 96-well plate adherence assay. EPS production assessment is determined by two assays, namely microscopy staining of the EPS matrix and semi-quantitative analysis with a fluorescently-conjugated polysaccharide binding lectin. Finally, biofilm dispersion is measured through colony counts and plating. Positive data from multiple assays support the characterization of biofilms and can be utilized to identify bile salt-induced biofilm formation in other bacterial strains.

This protocol enables the reader to analyze bile salt-induced biofilm formation in enteric pathogens using a multifaceted approach to capture the dynamic nature of bacterial biofilms by assessing adherence, extracellular polymeric substance matrix formation, and dispersion.

Biofilm formation is a dynamic, multistage process that occurs in bacteria under harsh environmental conditions or times of stress. For enteric pathogens, ...

Deep Dermal Injection As a Model of Candida albicans Skin Infection for Histological Analyses

The skin is an extremely extended organ of the body and, due to this large surface, it is continuously exposed to microorganisms. Skin damage can easily lead to infections in the dermis which can, in turn, result in the dissemination of pathogens into the bloodstream. Understanding how the immune system fights infections at the very early stage and how the host can eliminate the pathogens is an important step to set the base for future therapeutic interventions. Here we describe a model of Candida albicans infection that can visualize the processes that occur early during an infection, including when the pathogen has passed the epithelial barrier, as well as the immune response elicited by the C. albicans invasion. We used this infection model to perform histological analyses that show the immune cells that infiltrate the skin as well as the presence and localization of the pathogen. Samples collected after the infection can be processed for RNA extraction.

Deep Dermal Injection As a Model of Candida albicans Skin Infection for Histological Analyses

Here we describe a protocol that allows histological and molecular analysis of skin samples after Candida albicans intradermal injection. This protocol maintains the structural integrity of the skin and allows for the localization of tissue-resident or newly recruited immune cells as well as the pathogen distribution.

The skin is an extremely extended organ of the body and, due to this large surface, it is continuously exposed to microorganisms. Skin damage can easily ...

Daily Phototherapy with Red Light to Regulate Candida albicans Biofilm Growth

Here, we present a protocol to assess the outcomes of per diem red light treatment on the growth of Candida albicans biofilm. To increase the planktonic growth of C. albicans SN425, the inoculums grew on Yeast Nitrogen Base media. For biofilm formation, RPMI 1640 media, which have high concentrations of amino acids, were applied to help biofilm growth. Biofilms of 48 h were treated twice a day for a period of 1 min with a non-coherent light device (red light; wavelength = 635 nm; energy density = 87.6 J&#183;cm-2). As a positive control (PC), 0.12% chlorhexidine (CHX) was applied, and as a negative control (NC), 0.89% NaCl was applied to the biofilms. Colony forming units (CFU), dry-weight, soluble and insoluble exopolysaccharides were quantified after treatments. Briefly, the protocol presented here is simple, reproducible and provides answers regarding viability, dry-weight and extracellular polysaccharide amounts after red light treatment.

Daily Phototherapy with Red Light to Regulate Candida albicans Biofilm Growth

Here, we present a protocol to assess the outcome of red light application on the growth of Candida albicans biofilm. A non-coherent red light device with the wavelength of 635 nm and energy density of 87.6 J&#183;cm-2 was applied throughout the growth of Candida albicans biofilms for 48 h.

Here, we present a protocol to assess the outcomes of per diem red light treatment on the growth of Candida albicans biofilm. To increase the planktonic ...

Visualization of Candida albicans in the Murine Gastrointestinal Tract Using Fluorescent In Situ Hybridization

Candida albicans is a fungal component of the gut microbiota in humans and many other mammals. Although C. albicans does not cause symptoms in most colonized hosts, the commensal reservoir does serve as a repository for infectious disease, and the presence of high fungal titers in the gut is associated with inflammatory bowel disease. Here, we describe a method to visualize C. albicans cell morphology and localization in a mouse model of stable gastrointestinal colonization. Colonization is established using a single dose of C. albicans in animals that have been treated with oral antibiotics. Segments of gut tissue are fixed in a manner that preserves the architecture of luminal contents (microorganisms and mucus) as well as the host mucosa. Finally, fluorescent in situ hybridization is performed using probes against fungal rRNA to stain for C. albicans and hyphae. A key advantage of this protocol is that it allows for simultaneous observation of C. albicans cell morphology and its spatial association with host structures during gastrointestinal colonization.

Visualization of Candida albicans in the Murine Gastrointestinal Tract Using Fluorescent In Situ Hybridization

The purpose of this protocol is to visualize Candida albicans cell shape and localization in the mammalian gastrointestinal tract.

Candida albicans is a fungal component of the gut microbiota in humans and many other mammals. Although C. albicans does not cause symptoms in most ...

Clarifying and Imaging Candida albicans Biofilms

The microbial fungus Candida albicans can undergo a change from commensal colonization to virulence that is strongly correlated with its ability to switch from yeast-form growth to hyphal growth. Cells initiating this process become adherent to surfaces as well as to each other, with the resulting development of a biofilm colony. This commonly occurs not only on mucosal tissue surfaces in yeast infections, but also on medical implants such as catheters. It is well known that biofilm cells are resistant to antifungal drugs, and that cells that shed from the biofilm can lead to dangerous systemic infections. Biofilms range from heavily translucent to opaque due to refractive heterogeneity. Therefore, fungal biofilms are difficult to study by optical microscopy. To visualize internal structural, cellular, and subcellular features, we clarify fixed intact biofilms by stepwise solvent exchange to a point of optimal refractive index matching. For C. albicans biofilms, sufficient clarification is attained with methyl salicylate (n = 1.537) to enable confocal microscopy from apex to base in 600 &#181;m biofilms with little attenuation. In this visualization protocol we outline phase contrast refractometry, the growth of laboratory biofilms, fixation, staining, solvent exchange, the setup for confocal fluorescence microscopy, and representative results.

Clarifying and Imaging Candida albicans Biofilms

To view and quantify the internal features of Candida albicans biofilms, we prepare fixed intact specimens that are clarified by refractive index matching. Then, optical sectioning microscopy can be used to obtain three-dimensional image data though the full thickness of the biofilm.

The microbial fungus Candida albicans can undergo a change from commensal colonization to virulence that is strongly correlated with its ability to switch ...