The authors would like to acknowledge the University of Lille and the Pasteur Institute of Lille, especially Thierry Chassat and Jean-Pierre Decavel, responsible for animal housing breeding safety and husbandry. This work was supported by the "Soci&#233;t&#233; de Pathologies Infectieuses de Langue Fran&#231;aise" (SPILF).

The regional ethics regional committee for animal experiments has approved this method, in accordance with national and international animal care and use in investigational research guidelines.
1. Sample Collection
<ol>
	<li>Sample storage
	<ol>
		<li>Collect all samples and immediately store at - 20 &#176;C or on ice until freezer storage to avoid deterioration. Place sterile phosphate buffered saline (PBS) on ice to improve broncho-alveolar lavages (BAL) performance.</li>
	</ol>
	</li>
	<li>Surgery
	<ol>
		<li>Sterilize all surgical equipment using an autoclave. 
		NOTE: If possible, it is recommended to use two different sets of instruments for abdominal and thoracic steps to avoid cross-contamination. Required dissection equipment is detailed in Figure 4A</li>
	</ol>
	</li>
</ol>
2. Mice, Bacterial and Yeast Strains
<ol>
	<li>House mice in compliance with local use of animals in research committee guidelines in a ventilated rack without exceeding 5 mice per cage, with food and water ad lib, in a biosafety level 2 housing facility due to the use of biosafety level 2 micro-organisms : P. aeruginosa and C. albicans.</li>
	<li>Keep the bacterial strains at -80 &#176;C in 40% glycerol medium.
	<ol>
		<li>Add bacteria directly from frozen stock into culture tube containing 3 ml of sterile Luria-Bertani broth using a 10 &#181;l inoculation loop. Leave O/N&#160;at 37 &#176;C with orbital shaking (400 rpm) the day before instillation.</li>
		<li>Harvest bacteria by centrifugation at 2,000 x g for 5 min.</li>
		<li>Aspirate the supernatant into an appropriate closed biohazard waste disposal. Observe white adherent pellet at the bottom of culture tube.</li>
		<li>Wash and suspend the pellet using 5 ml of PBS.</li>
		<li>Repeat steps 2.2.2 to 2.2.3 a second time to perform a second wash.</li>
		<li>Resuspend the pelleted bacteria using 1 ml of PBS and brief vortexing.</li>
		<li>Determine the inoculum density using optical densitometer at 600 nm using an Optical Density Meter. A density of 0.9 corresponds to 109 CFU/ml for PAO1, dilute accordingly. 
		NOTE: This result has to be obtained for each used strain by determining density of successive dilutions of a calibrated inoculum.</li>
		<li>Verify the inoculum by serial logarithmic dilutions and plate 100 &#181;l of each dilution on bromocresol purple agar (BCP) plates and O/N culture. Administer each mouse intranasally 50 &#181;l of the solution containing 1 x 108 to 2 x108 CFU per ml (5 x 106 to 1 x107 CFU per mouse).</li>
	</ol>
	</li>
	<li>Use C. albicans SC5314 as a reference strain. Conserve the strain in 40% glycerol medium at -80&#176;C.
	<ol>
		<li>Supplement Yeast-Peptone-Dextrose broth with 0.015% amikacin to avoid bacterial contamination and facilitate further count.</li>
		<li>Add yeast using 10 &#181;l inoculation loop into prepared YPD-broth supplemented with amikacin O/N at 37&#176;C.</li>
		<li>Harvest yeast by centrifugation at 2,000 x g for 5 min.</li>
		<li>Remove supernatant into an appropriate bioharzard waste disposal. White adherent pellet should be observed in the bottom of culture tube.</li>
		<li>Wash and suspend the pelleted bacteria using 5 ml of PBS and brief vortexing.</li>
		<li>Repeat steps 2.2.2 to 2.2.3 a second time to perform a second wash.</li>
		<li>Resuspend the pellet using 1 ml of PBS and brief vortexing.</li>
		<li>Determine the size of the inoculum by counting on a Mallassez hematocytometer using a standard microscope at 40x magnification. 
		NOTE: Concentration (in CFU/ml) is obtained using the following formula: (number of yeast x 105)/(number of counted grid rectangles on the Mallassez hematocytometer).</li>
		<li>Verify by serial logarithmic dilution to 10-5 and 10-6 to confirm that solution contains 2 x 106 CFU/ml.</li>
		<li>Plate on YPD agar plates supplemented with 0.015% amikacin.</li>
	</ol>
	</li>
</ol>
3. Airways Colonization by C. albicans
NOTE: After environmental adaptation, mice are weighed twice a day.
<ol>
	<li>Under a fume hood, deposit 500 &#181;l of Sevoflurane onto a 4 cm x 4 cm gauze (open-drop technique)14.
	<ol>
		<li>Immediately place the gauze on the floor of an approximately 750 ml induction chamber. Immediately place a mesh-raised platform above the gauze to avoid direct contact between the animal and the gauze.</li>
		<li>Close airtight lid and wait 1 to 2 min to allow diffusion of Sevoflurane in the chamber.</li>
		<li>Transfer the mouse from cage to mesh platform and close lid. Light anesthesia with conserved spontaneous breathing should be achieved in 30 to 45 sec.</li>
		<li>Monitor for hypotonia by observing loss of righting reflex at which point the mouse can be removed from the box and instilled.</li>
	</ol>
	</li>
	<li>Intranasal instillation (Can be performed in 10 sec by a trained operator).
	<ol>
		<li>Hold the mouse one-handed nestled on its back held upright (Figure 4B).</li>
		<li>Using index finger, support the head and use the thumb to keep the jaw closed to avoid expectoration (Figure 4C).</li>
		<li>As described at step 2.3.8, ensure that the prepared C. albicans solution contains 2 x106 CFU per ml for an 50 &#181;l instilled volume. 
		NOTE: The second critical point is the instilled volume. A volume lower than 50 &#181;l could result in an insufficient colonization or inhomogeneous instillation of airway, a larger volume may induce drowning/suffocation and death.</li>
		<li>Instil the mouse intra-nasally by approaching the pipette to the nostrils.</li>
		<li>Pipette a 50 &#181;l drop forming a bubble containing the solution on the nostrils, subsequently inhaled by the spontaneously breathing mouse.</li>
		<li>Place mouse in a recovery area (e.g., a large well-aerated bare cage with an overhead heating lamp). Mice must be monitored until complete awakening. Do not leave an animal unattended until it has regained sufficient consciousness to maintain sternal recumbency and righting reflex. At this point, the mouse can be returned to a normal housing cage.</li>
	</ol>
	</li>
</ol>
4. P. aeruginosa-induced Acute Lung Infection
NOTE: Mice are weighed during the four following days. Normally, mice gain weight during C. albicans-mediated airway colonization (Figure 2A).
<ol>
	<li>Prepare the suspension containing P. aeruginosa the day of the instillation after O/N growth (section 2.2).</li>
	<li>Anesthetize briefly using inhaled Sevoflurane as described above (section 3.1). 
	NOTE: To perform acute lung infection, recommended bacterial burden are suggested in Table 1.</li>
	<li>Instil the mouse as described above (section 3.2) with particular attention to post-instillation recovery.</li>
</ol>
5. Measure of Lung Injury Index
<ol>
	<li>Prepare a solution containing FITC-labeled albumin. Inject this solution 2 hr before animal euthanasia.
	<ol>
		<li>Weigh 0.2 mg of albumin-FITC with the appropriate equipment.</li>
		<li>Add 0.2 mg into 1 ml PBS. Briefly vortex. If not used immediately, place the solution in foil to avoid exposure to ambient light.</li>
		<li>Inject intra-peritoneally 200 &#181;l of FITC-labeled albumin solution to each mouse.</li>
	</ol>
	</li>
	<li>Euthanasia
	<ol>
		<li>Weigh the mice for the last weight data.</li>
		<li>Euthanize a single mouse in accordance with local use of animals in research committee guidelines using one intra-peritoneal injection of a lethal overdose of pentobarbital : 300 &#181;l of 5.47% pentobarbital.</li>
		<li>Remove mouse from the cage and receives lethal injection by operator.</li>
		<li>Following injection, transfer the mouse alone to another cage, hidden from any other animals. Observe the mouse until absence of movement. Confirm death is by absence of movement, particularly respiratory movement, lack of pulse.</li>
		<li>Perform surgical collection of samples on dead animals, therefore without anesthetics nor analgesics.</li>
	</ol>
	</li>
	<li>Surgical sample collection: Thoracic stage. 
	NOTE: To maintain sterile conditions, all surgery is performed using sterile equipment in a biosafety level 2 environment.
	<ol>
		<li>Apply ethanol to the skin. Perform a midline skin incision from sternum to mid abdomen with scissors. From midline incise along the ribcage on either side. Fold back the skin on either side of the thorax to visualize the rib cage.</li>
		<li>Perform a vertical incision of the ribcage on either side going up towards the clavicles in order to be able to recline the entire anterior chest wall with the sternum allowing the perfect visualization of heart and lungs (Figure 5A, 5B).</li>
		<li>Collect blood using a pre-heparined syringe by puncturing the heart next to the interventricular artery. Withdraw a minimum of 500 &#181;l&#160;to obtain at least 100 &#181;l of plasma. Place the blood sample on ice.</li>
		<li>Perform a midline cervical incision to visualize the trachea (Figure 5B and 5C). Carefully dissect the fascia around the trachea. Place a suture behind the trachea (Figure 5C and 5D). Subsequently the suture will be closed around the cannulating needle to ensure proper lavage.</li>
		<li>Catheterize the trachea using the 20-G modified gavage needle (Figure 5D and 4A). Tie a surgical knot around the cannulated trachea with the previously placed suture.</li>
		<li>To perform bronchoalveolar lavages (BAL), gently and progressively inject and draw 500 &#181;l of ice-cold PBS into/from the lung. Place the sample on ice to avoid cellular lysis.</li>
		<li>Repeat step 5.3.6, 3 times to obtain a total of 1,500 &#181;l BAL fluid and pool lavage samples into a 2 ml centrifuge tube (Figure 5E).</li>
		<li>Remove the lungs from the chest. Place a lung segment (size should correspond to the half of one lung or a lobe) into 1.5 ml centrifuge tube and store rapidly at - 80&#176;C.</li>
		<li>Place a lung segment in a pre-weighed hemolysis tube containing PBS to determine bacterial burden and place it on ice.</li>
	</ol>
	</li>
	<li>Surgical sample collection: abdominal stage.
	<ol>
		<li>Perform another incision on the left-side of the abdomen. Observe the spleen through the peritoneum.</li>
		<li>Remove the spleen and place into a second hemolysis tube containing 1 ml PBS and place on ice.</li>
	</ol>
	</li>
	<li>Lung injury index 
	NOTE: Alveolar-capillary membrane permeability is assessed by measuring FITC-labeled-albumin leakage from the vascular compartment to the alveolar-interstitial compartment.
	<ol>
		<li>Centrifuge blood sample and BAL fluid for 10 min at 1,500 x g. Collect the supernatants into new centrifuge tubes. The pellets correspond to recruited plasma or BAL cells and should be placed on ice.</li>
		<li>Add 100 &#181;l of each blood supernatant (plasma, yellow) or BAL supernatant to a 96-well transparent plate (300 &#181;l wells). Place a foil on the plate if not used immediately.</li>
		<li>Measure fluorescence levels in plasma and BAL supernatants using a fluorescence microplate reader (excitation, 487 nm; emission, 520 nm).</li>
		<li>Determine the lung injury index by calculating the fluorescence ratio [(BAL supernatant/blood supernatant) x 100].</li>
	</ol>
	</li>
	<li>Bronchoalveolar lavage (BAL) differential cell count. 
	NOTE: Use the cell pellet obtained from centrifugation of BAL fluid at step 5.5.1.
	<ol>
		<li>If needed, use red-cell lysis buffer. Add 500 &#181;l of red-cell lysis buffer into the centrifuge tube containing the cell pellet. Briefly vortex and leave 10 min on ice. Add 500 &#181;l PBS to stop red-cell lysis.</li>
		<li>Harvest cells by centrifugation for 10 min at 1,500 x g. Remove supernatant and suspend the cell pellet into 1 ml of sterile PBS. Enumerate cells on a Mallassez hematocytometer. Using a Hemacytometer to Count Cells. Concentrate cells on a slide with a cytospin.</li>
		<li>Stain cells using coloration kit allowing cell identification and count (macrophages, lymphocytes, neutrophils).</li>
	</ol>
	</li>
	<li>Lung bacterial burden and bacterial dissemination 
	NOTE: To assess lung bacterial burden and bacterial dissemination, lungs and spleen were respectively collected and stored into pre-weighed hemolysis tubes containing 1 ml of PBS (step 5.3.9).
	<ol>
		<li>Weigh hemolysis tubes containing 1 ml PBS and either lung or spleen. Homogenize the samples with a tissue homogenizer to obtain lung homogenates and spleen homogenates.</li>
		<li>Deposit 100 &#181;l of tissue homogenates into centrifuge tubes containing 900 &#181;l of sterile PBS to obtain serial logarithmic dilutions.</li>
		<li>Plate the two last appropriate diluted samples (10-3 and 10-2) on either BCP-agar for P. aeruginosa or YPD-amikacin-supplemented agar for C. albicans lung and spleen burden determination.</li>
		<li>Incubate the plates O/N at 37 &#176;C. The following day, enumerate the colonies on plates.</li>
		<li>Index the result to lung weight to obtain a CFU per gram of lung. Lung sample sizes are not the same, the results should be expressed in CFU per gram of lung. 
		Formula for the index is: [CFU] x [weight of hemolysis tube and lung] - [weight of hemolysis tube].</li>
	</ol>
	</li>
</ol>

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<li>Nseir, S., Ader, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Pseudomonas+aeruginosa+and+Candida+albicans%3A+do+they+really+need+to+stick+together%5BTitle%5D)+AND+%22Crit.+Care+Med%22%5BJournal%5D)">Pseudomonas aeruginosa and Candida albicans: do they really need to stick together.</a> Crit. Care Med. 37 (3), 1164-1166 (2009).</li>
<li>Hibbing, M. E., Fuqua, C., Parsek, M. R., Peterson, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Bacterial+competition%3A+surviving+and+thriving+in+the+microbial+jungle%5BTitle%5D)+AND+%22Nat.+Rev.+Micro%22%5BJournal%5D)">Bacterial competition: surviving and thriving in the microbial jungle.</a> Nat. Rev. Micro. 8 (1), 15-25 (2010).</li>
<li>Gibbons, D. L., Spencer, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mouse+and+human+intestinal+immunity%3A+same+ballpark%2C+different+players%3B+different+rules%2C+same+score%5BTitle%5D)+AND+%22Mucosal+Immunol%22%5BJournal%5D)">Mouse and human intestinal immunity: same ballpark, different players; different rules, same score.</a> Mucosal Immunol. 4 (2), 148-157 (2011).</li>
<li>Ariffin, J. K., Sweet, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Differences+in+the+repertoire%2C+regulation+and+function+of+Toll-like+Receptors+and+inflammasome-forming+Nod-like+Receptors+between+human+and+mouse%5BTitle%5D)+AND+%22Curr.+Opi.+Micro.%22%5BJournal%5D)">Differences in the repertoire, regulation and function of Toll-like Receptors and inflammasome-forming Nod-like Receptors between human and mouse.</a> Curr. Opi. Micro.. , (2013).</li>
<li>Slutsky, A. S., Ranieri, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ventilator-Induced+Lung+Injury%5BTitle%5D)+AND+%22NEJM%22%5BJournal%5D)">Ventilator-Induced Lung Injury.</a> NEJM. 369 (22), 2126-2136 (2013).</li>
<li>Peleg, A. Y., Hogan, D. A., Mylonakis, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Medically+important+bacterial-fungal+interactions%5BTitle%5D)+AND+%22Nat.+Rev.+Micro%22%5BJournal%5D)">Medically important bacterial-fungal interactions.</a> Nat. Rev. Micro. 8 (5), 340-349 (2010).</li>
<li>Roux, D., Gaudry, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Candida+albicans+impairs+macrophage+function+and+facilitates+Pseudomonas+aeruginosa+pneumonia+in+rat%5BTitle%5D)+AND+%22Crit.+Care+Med%22%5BJournal%5D)">Candida albicans impairs macrophage function and facilitates Pseudomonas aeruginosa pneumonia in rat.</a> Crit. Care Med. 37 (3), 1062-1067 (2009).</li>
<li>Mear, J. B., Gosset, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Candida+albicans+Airway+Exposure+Primes+the+Lung+Innate+Immune+Response+against+Pseudomonas+aeruginosa+Infection+through+Innate+Lymphoid+Cell+Recruitment+and+Interleukin-22-Associated+Mucosal+Response%5BTitle%5D)+AND+%22Infect.+Immun%22%5BJournal%5D)">Candida albicans Airway Exposure Primes the Lung Innate Immune Response against Pseudomonas aeruginosa Infection through Innate Lymphoid Cell Recruitment and Interleukin-22-Associated Mucosal Response.</a> Infect. Immun. 82 (1), 306-315 (2013).</li>
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<li>Stover, C. K., Pham, X. Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Complete+genome+sequence+of+Pseudomonas+aeruginosa+PAO1%2C+an+opportunistic+pathogen%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">Complete genome sequence of Pseudomonas aeruginosa PAO1, an opportunistic pathogen.</a> Nature. 406 (6799), 959-964 (2000).</li>
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The authors have nothing to disclose.

Animal models, particularly mammals, are useful to elucidate complex mechanisms of host-pathogen interaction in the fields of immunity. Of course, the need for information obtainable only from animal models must be essential; otherwise, use of animals must be replaced by in vitro models. This animal model illustrates the insight that can only be provided by an animal model since the interaction between pathogens is mediated by a multi-component host response. Mice currently used to study this host-pathogen inter...

Animal models, especially mice, have been extensively used to explore immune responses against pathogens. Although innate and acquired immunity differ between rodents and humans7, the ease in breeding and the development of knockouts for numerous genes, make mice an excellent model to study immune responses8. The immune response is complex and results from the interaction of a pathogen, the resident microbial flora and several immune (lymphocytes, neutrophils, macrophages) and non-immune (epithelial cells, endothelial cells) cellular types2. In vitro studies do not allow observing these complex interactions and mainly focus on unique cell-pathogen interactions. While animal models must be used with caution and limited to very specific and relevant questions, mouse models provide a good insight into the mammal immune response in vivo and may address parts of important clinical questions7.
In the airways, the microbial community is complex associating a large number of different microorganisms6. While what constitutes a &#34;normal&#34; airway microbiome remains to be determined, resident communities are frequently polymicrobial, and originate from diverse ecological sources. Patients with suppurative chronic lung disease (cystic fibrosis, bronchectasis) or mechanically ventilated patients exhibit a particular flora due to colonization of the airways by environmentally-acquired microorganisms9. Pseudomonas aeruginosa and Candida albicans are both problem pathogens5, frequently isolated together from tracheobronchial samples, and responsible of severe opportunistic infection in these patients, especially in the intensive care unit (ICU)4.
Isolation of these microorganisms during acute pneumonia in ICU results in anti-microbial treatment against P. aeruginosa but yeast are usually not considered pathogenic at this site5. In vitro interactions between P. aeruginosa and C. albicans have been widely reported and showed that these microorganisms can affect the growth and the survival of each other but studies could not conclude if the presence of C. albicans is detrimental or beneficial for the host10. Mouse models were developed to address this relevance of P. aeruginosa&#160;and C. albicans&#160;in vivo, but the interaction between microorganisms was not the key point. Indeed, the model was established to evaluate the involvement of C. albicans in host immune response, and outcome.
A previous model established by Roux et al already used an initial colonization with C. albicans followed by an acute lung infection induced by P. aeruginosa. Using their model, the authors found a deleterious role of prior C. albicans colonization11. However Roux et al used a high load of C. albicans in their model with 2 x 106 CFU/mouse during 3 consecutive days. We established a 4-day model of C. albicans airway colonization, or at least persistence without lung injury, In this model C. albicans was retrieved up to 4 days after a single instillation of 105 CFU per mouse (Figure 2B) 12,13. After 4 days, no evidence of inflammatory cell recruitment, inflammatory cytokine production nor epithelial damage was observed. At 24 - 48 hr, at the peak presence of C. albicans, even though a cellular and cytokine innate immune response was observed, there was no evidence of lung injury. Surprisingly, mice thus colonized with C. albicans 48 hr prior to intranasal instillation of P. aeruginosa had attenuated infection compared to mice with P. aeruginosa infection alone. Indeed, mice exhibited lesser lung injury and decreased bacterial burden12,13.
Several hypotheses could explain this beneficial effect of prior colonization with C. albicans on P. aeruginosa-mediated acute lung infection. First, an interspecies cross-talk involving each microorganisms quorum-sensing systems, the homoserinelactone-based P. aeruginosa system and the farnesol-based C. albicans system, were evaluated. Second, C. albicans acting as a &#34;decoy&#34; target for P. aeruginosa diverting the pathogen from lung epithelial cells was studied. Both hypotheses were invalidated (unpublished data). The third hypothesis was that of a &#34;priming&#34; of the innate immune system by C. albicans responsible for an enhanced subsequent innate response against P. aeruginosa. This last hypothesis was confirmed. Indeed C. albicans colonization led to a priming of innate immunity through IL-22, mainly secreted by innate lymphoid cells, resulting in increased bacterial clearance and reduced lung injury12.
In conclusion, the host is a central actor in the interaction between microorganisms modulating the innate immune response and involving different inflammatory cell types. While these complex immune interactions can be dissected in vitro the initial hypotheses can only be provided by appropriate in&#160;vivo models. The following protocol provides an example of in vivo study of host-mediated pathogen interaction that may be adapted to others microorganisms.

<table><tbody><tr><td>Sevorane, Sevoflurane</td><td>Abott</td><td>05458-02</td><td>250 ml plastic bottle</td></tr><tr><td>Fluorescence Reader Mithras&amp;nbsp; LB940</td><td>Berthold Technologies</td><td>reference in first column</td><td>no comment</td></tr><tr><td>Bromo-cresol purple agar</td><td>Biomerieux</td><td>43021</td><td>20x per unit</td></tr><tr><td>Pentobarbital sodique 5.47%</td><td>CEVA</td><td>6742145</td><td>100 ml plastic bottle</td></tr><tr><td>2-headed valve&amp;nbsp;</td><td>Distrimed</td><td>92831</td><td>no comment</td></tr><tr><td>Sterile inoculation loop 10 &amp;micro;l</td><td>Dutscher</td><td>10175</td><td>x1,000 conditioning</td></tr><tr><td>Insuline syringes 1 ml</td><td>Dutscher</td><td>30003</td><td>per 100 conditioning</td></tr><tr><td>2 positions Culture tube 8 ml</td><td>Dutscher</td><td>64300</td><td>no comment</td></tr><tr><td>Ultrospec 10&amp;nbsp;</td><td>General Electric life sciences</td><td>80-2116-30</td><td>no comment</td></tr><tr><td>Hemolysis tubes 13 x 75 mm&amp;nbsp;</td><td>Gosselin</td><td>W1773X</td><td>per 100</td></tr><tr><td>PBS - Phosphate-Buffered Saline</td><td>Life technologies</td><td>10010023</td><td>packaged in 500 ml</td></tr><tr><td>amikacin 1 g</td><td>Mylan</td><td>62516778</td><td>per 10&amp;nbsp;</td></tr><tr><td>Heparin 10,000 UI in 2 ml</td><td>Pan pharma</td><td>9128701</td><td>10x per unit</td></tr><tr><td>RAL 555 coloration kit</td><td>RAL Diagnostics</td><td>361550</td><td>3 flacons of 100 mL</td></tr><tr><td>1.5 ml microcentrifuge tube</td><td>Sarstedt</td><td>55.526.006</td><td>x 1000</td></tr><tr><td>Transparent 300 &amp;micro;l 96-well plate</td><td>Sarstedt</td><td>82 1581500</td><td>no comment</td></tr><tr><td>Yest-peptone-Dextrose Broth</td><td>Sigma</td><td>95763</td><td>in powder</td></tr><tr><td>FITC-albumin</td><td>Sigma</td><td>A9771</td><td>in powder</td></tr><tr><td>Luria Bertani Broth</td><td>Sigma</td><td>L3022</td><td>in powder</td></tr><tr><td>25-gauge needle</td><td>Terumo or unisharp</td><td>A231</td><td>x 100 conditioning</td></tr><tr><td>Cytocentrifuge</td><td>Thermo Scientific</td><td>A78300003</td><td>no comment</td></tr></tbody></table>

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.

As seen previously during the protocol description, the experiment needs 5 day to complete (Figure 1: experiment timeline). One operator is solicited during the entire run of the experiment and can handle the processes up to a maximum of 10 mice. If more animals are required, two persons are needed particularly for surgical sample collection. Indeed all samples must be collected in under 2 hr to avoid an increased passive alveolar-capillary leakage of FITC-labeled albumin in the last mice.
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Watch this Scientific Journal Video about Studying Microbial Communities In Vivo: A Model of Host-mediated Interaction Between Candida Albicans and Pseudomonas Aeruginosa in the Airways at JoVE.com

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 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 ...

studying-microbial-communities-vivo-model-host-mediated-interaction

Research

JoVE Journal

Immunology and Infection

8.8K Views.  Université Lille. 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.

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

Co-culture Models of Pseudomonas aeruginosa Biofilms Grown on Live Human Airway Cells

Bacterial biofilms have been associated with a number of different human diseases, but biofilm development has generally been studied on non-living surfaces. In this paper, we describe protocols for forming Pseudomonas aeruginosa biofilms on human airway epithelial cells (CFBE cells) grown in culture. In the first method (termed the Static Co-culture Biofilm Model), P. aeruginosa is incubated with CFBE cells grown as confluent monolayers on standard tissue culture plates. Although the bacterium is quite toxic to epithelial cells, the addition of arginine delays the destruction of the monolayer long enough for biofilms to form on the CFBE cells. The second method (termed the Flow Cell Co-culture Biofilm Model), involves adaptation of a biofilm flow cell apparatus, which is often used in biofilm research, to accommodate a glass coverslip supporting a confluent monolayer of CFBE cells. This monolayer is inoculated with P. aeruginosa and a peristaltic pump then flows fresh medium across the cells. In both systems, bacterial biofilms form within 6-8 hours after inoculation. Visualization of the biofilm is enhanced by the use of P. aeruginosa strains constitutively expressing green fluorescent protein (GFP). The Static and Flow Cell Co-culture Biofilm assays are model systems for early P. aeruginosa infection of the Cystic Fibrosis (CF) lung, and these techniques allow different aspects of P. aeruginosa biofilm formation and virulence to be studied, including biofilm cytotoxicity, measurement of biofilm CFU, and staining and visualizing the biofilm.

Co-culture Models of Pseudomonas aeruginosa Biofilms Grown on Live Human Airway Cells

This paper describes different methods of growing Pseudomonas aeruginosa biofilms on cultured human airway epithelial cells. These protocols can be adapted to study different aspects of biofilm formation, including visualization of the biofilm, staining of the biofilm, measuring the colony forming units (CFU) of the biofilm, and studying biofilm cytotoxicity.

Bacterial biofilms have been associated with a number of different human diseases, but biofilm development has generally been studied on non-living ...

Long Term Chronic Pseudomonas aeruginosa Airway Infection in Mice

A mouse model of chronic airway infection is a key asset in cystic fibrosis (CF) research, although there are a number of concerns regarding the model itself. Early phases of inflammation and infection have been widely studied by using the Pseudomonas aeruginosa agar-beads mouse model, while only few reports have focused on the long-term chronic infection in vivo. The main challenge for long term chronic infection remains the low bacterial burden by P. aeruginosa and the low percentage of infected mice weeks after challenge, indicating that bacterial cells are progressively cleared by the host.
This paper presents a method for obtaining efficient long-term chronic infection in mice. This method is based on the embedding of the P. aeruginosa clinical strains in the agar-beads in vitro, followed by intratracheal instillation in C57Bl/6NCrl mice. Bilateral lung infection is associated with several measurable read-outs including weight loss, mortality, chronic infection, and inflammatory response. The P. aeruginosa RP73 clinical strain was preferred over the PAO1 reference laboratory strain since it resulted in a comparatively lower mortality, more severe lesions, and higher chronic infection. P. aeruginosa colonization may persist in the lung for over three months. Murine lung pathology resembles that of CF patients with advanced chronic pulmonary disease.
This murine model most closely mimics the course of the human disease and can be used both for studies on the pathogenesis and for the evaluation of novel therapies.

Long Term Chronic Pseudomonas aeruginosa Airway Infection in Mice

We describe the agar-beads method to establish persistent long-term chronic Pseudomonas aeruginosa airway infection in the mouse model.

A mouse model of chronic airway infection is a key asset in cystic fibrosis (CF) research, although there are a number of concerns regarding the model ...

Candida albicans Biofilm Development on Medically-relevant Foreign Bodies in a Mouse Subcutaneous Model Followed by Bioluminescence Imaging

Candida albicans biofilm development on biotic and/or abiotic surfaces represents a specific threat for hospitalized patients. So far, C. albicans biofilms have been studied predominantly in vitro but there is a crucial need for better understanding of this dynamic process under in vivo conditions. We developed an in vivo subcutaneous rat model to study C. albicans biofilm formation. In our model, multiple (up to 9) Candida-infected devices are implanted to the back part of the animal. This gives us a major advantage over the central venous catheter model system as it allows us to study several independent biofilms in one animal. Recently, we adapted this model to study C. albicans biofilm development in BALB/c mice. In this model, mature C. albicans biofilms develop within 48 hr and demonstrate the typical three-dimensional biofilm architecture. The quantification of fungal biofilm is traditionally analyzed post mortem and requires host sacrifice. Because this requires the use of many animals to perform kinetic studies, we applied non-invasive bioluminescence imaging (BLI) to longitudinally follow up in vivo mature C. albicans biofilms developing in our subcutaneous model. C. albicans cells were engineered to express the Gaussia princeps luciferase gene (gLuc) attached to the cell wall. The bioluminescence signal is produced by the luciferase that converts the added substrate coelenterazine into light that can be measured. The BLI signal resembled cell counts obtained from explanted catheters. Non-invasive imaging for quantifying in vivo biofilm formation provides immediate applications for the screening and validation of antifungal drugs under in vivo conditions, as well as for studies based on host-pathogen interactions, hereby contributing to a better understanding of the pathogenesis of catheter-associated infections.

Candida albicans Biofilm Development on Medically-relevant Foreign Bodies in a Mouse Subcutaneous Model Followed by Bioluminescence Imaging

We present an experimental procedure of Candida albicans biofilm development in a mouse subcutaneous model. Fungal biofilms were quantified by determining the number of colony forming units and by a non-invasive bioluminescence imaging, where the amount of light that is produced corresponds with the number of viable cells.

Candida albicans biofilm development on biotic and/or abiotic surfaces represents a specific threat for hospitalized patients. So far, C. albicans ...

Medicine

P. aeruginosa Infected 3D Co-Culture of Bronchial Epithelial Cells and Macrophages at Air-Liquid Interface for Preclinical Evaluation of Anti-Infectives

fDrug research for the treatment of lung infections is progressing towards predictive in vitro models of high complexity. The multifaceted presence of bacteria in lung models can re-adapt epithelial arrangement, while immune cells coordinate an inflammatory response against the bacteria in the microenvironment. While in vivo models have been the choice for testing new anti-infectives in the context of cystic fibrosis, they still do not accurately mimic the in vivo conditions of such diseases in humans and the treatment outcomes. Complex in vitro models of the infected airways based on human cells (bronchial epithelial and macrophages) and relevant pathogens could bridge this gap and facilitate the translation of new anti-infectives into the clinic. For such purposes, a co-culture model of the human cystic fibrosis bronchial epithelial cell line CFBE41o- and THP-1 monocyte-derived macrophages has been established, mimicking an infection of the human bronchial mucosa by P. aeruginosa at air-liquid interface (ALI) conditions. This model is set up in seven days, and the following parameters are simultaneously assessed: epithelial barrier integrity, macrophage transmigration, bacterial survival, and inflammation. The present protocol describes a robust and reproducible system for evaluating drug efficacy and host responses that could be relevant for discovering new anti-infectives and optimizing their aerosol delivery to the lungs.

P. aeruginosa Infected 3D Co-Culture of Bronchial Epithelial Cells and Macrophages at Air-Liquid Interface for Preclinical Evaluation of Anti-Infectives

We describe a protocol for a three-dimensional co-culture model of infected airways, using CFBE41o- cells, THP-1 macrophages, and Pseudomonas aeruginosa, established at the air-liquid interface. This model provides a new platform to simultaneously test antibiotic efficacy, epithelial barrier function, and inflammatory markers.

fDrug research for the treatment of lung infections is progressing towards predictive in vitro models of high complexity. The multifaceted presence of ...

Establishing a Mouse Model for Candida albicans Biofilm-Related PJI

A Periprosthetic Joint Candida albicans Infection Model in Mouse

Periprosthetic joint infection (PJI) is one of the common infections caused by Candida albicans (C. albicans), which increasingly concerns surgeons and scientists. Generally, biofilms that can shield C. albicans from antibiotics and immune clearance are formed at the infection site. Surgery involving the removal of the infected implant, debridement, antimicrobial treatment, and reimplantation is the gold standard for the treatment of PJI. Thus, establishing animal PJI models is of great significance for the research and development of new drugs or therapeutics for PJI. In this study, a smooth nickel-titanium alloy wire, a widely used implant in orthopedic clinics, was inserted into the femoral joint of a C57BL/6 mouse before the C. albicans were inoculated into the articular cavity along the wire. After 14 days, mature and thick biofilms were observed on the surface of implants under a scanning electronic microscope (SEM). A significantly reduced bone trabecula was found in the H&amp;E staining of the infected joint specimens. To sum up, a mouse PJI model with the advantages of easy operation, high successful rate, high repeatability, and high clinical correlation was established. This is expected to be an important model for clinical studies of C. albicans biofilm-related PJI prevention.

Author Spotlight: Advancing Research on Candida albicans Biofilm-Associated Prosthetic Joint Infections 

Periprosthetic joint infection (PJI) caused by dangerous pathogens is common in clinical orthopedics. Existing animal models cannot accurately simulate the actual situation of PJI. Here, we established a Candida albicans biofilm-associated PJI mouse model to research and develop new therapeutics for PJI.

Periprosthetic joint infection (PJI) is one of the common infections caused by Candida albicans (C. albicans), which increasingly concerns surgeons and ...

Establishing a Mouse Model for Candida albicans-Associated Catheter-Related Infection

A Catheter-Related Candida albicans Infection Model in Mouse

Catheter-related infection (CRI) is a common nosocomial infection caused by candida albicans during catheter implantation. Typically, biofilms are formed on the outer surface of the catheter and lead to disseminated infections, which are fatal to patients. There are no effective prevention and treatment management in clinics. Therefore, it is urgent to establish an animal model of CRI for the preclinical screening of new strategies for its prevention and treatment. In this study, a polyethylene catheter, a widely used medical catheter, was inserted into the back of the BALB/c mice after hair removal. Candida albicans ATCC MYA-2876 (SC5314) expressing enhanced green fluorescent protein was subsequently inoculated on the skin's surface along the catheter. Intense fluorescence was observed on the surface of the catheter under a fluorescent microscope 3 days later. Mature and thick biofilms were found on the surface of the catheter via scanning electron microscopy. These results indicated the adhesion, colonization, and biofilm formation of candida albicans on the surface of the catheter. The hyperplasia of the epidermis and the infiltration of inflammatory cells in the skin specimens indicated the histopathological changes of the CRI-associated skin. To sum up, a mouse CRI model was successfully established. This model is expected to be helpful in the research and development of therapeutic management for candida albicans associated CRI.

Author Spotlight: Enhancing Candida albicans Detection in Catheter Infections Using Fluorescent Protein Tagging 

We establish a mouse model of C.albicans-associated catheter-related infection (CRI), in which biofilm forms on the catheter, and the interaction between C.albicans and host correlates well with the clinical CRI. This model helps screen therapies for C.albicans biofilm-associated CRI, laying a foundation for clinical transformation.

Catheter-related infection (CRI) is a common nosocomial infection caused by candida albicans during catheter implantation. Typically, biofilms are formed ...

Establishing a Lung-on-Chip Model for Respiratory Infection Studies

Immunocompetent Alveolus-on-Chip Model for Studying Alveolar Mucosal Immune Responses

We introduce an advanced immunocompetent lung-on-chip model designed to replicate the human alveolar structure and function. This innovative model employs a microfluidic-perfused biochip that supports an air-liquid interface mimicking the environment in the human alveoli. Tissue engineering is used to integrate key cellular components, including endothelial cells, macrophages, and epithelial cells, to create a representative tissue model of the alveolus. The model facilitates in-depth examinations of the mucosal immune responses to various pathogens, including viruses, bacteria, and fungi, thereby advancing our understanding of lung immunity. The primary goal of this protocol is to provide details for establishing this alveolus-on-chip model as a robust in vitro platform for infection studies, enabling researchers to closely observe and analyze the complex interactions between pathogens and the host's immune system within the pulmonary environment. This is achieved through the application of microfluidic-based techniques to simulate key physiological conditions of the human alveoli, including blood flow and biomechanical stimulation of endothelial cells, alongside maintaining an air-liquid interface crucial for the realistic exposure of epithelial cells to air. The model system is compatible with a range of standardized assays, such as immunofluorescence staining, cytokine profiling, and colony-forming unit (CFU)/plaque analysis, allowing for comprehensive insights into immune dynamics during infection. The Alveolus-on-chip is composed of essential cell types, including human distal lung epithelial cells (H441) and human umbilical vein endothelial cells (HUVECs) separated by porous polyethylene terephthalate (PET) membranes, with primary monocyte-derived macrophages strategically positioned between the epithelial and endothelial layers. The tissue model enhances the ability to dissect and analyze the nuanced factors involved in pulmonary immune responses in vitro. As a valuable tool, it should contribute to the advancement of lung research, providing a more accurate and dynamic in vitro model for studying the pathogenesis of respiratory infections and testing potential therapeutic interventions.

Author Spotlight: Developing a Microfluidic Lung-on-Chip Model for In-Depth Study of Human Immune Response and Infection Mechanisms

Lung-on-chip models surpass traditional 2D cultures by mimicking the air-liquid interface and endothelial cell perfusion, simulating blood flow and nutrient exchange crucial for lung physiology studies. This enhances lung research relevance, offering a dynamic, physiologically accurate environment to advance the understanding and treatment of respiratory infections.

We introduce an advanced immunocompetent lung-on-chip model designed to replicate the human alveolar structure and function. This innovative model employs ...

Adaptable CF Model for Antimicrobial Testing and Microbial Dynamics Analysis

Development of a Polymicrobial Colony Biofilm Model to Test Antimicrobials in Cystic Fibrosis

A range of bacteria biofilm models exist for the testing of antibiotics. However, many of these are limited to a single experimental output, such as colony-forming units or metabolic activity. Furthermore, many biofilm models do not reflect the biological and physiochemical properties of the human host environment. This is an important issue in many conditions, but most noticeably in cystic fibrosis (CF). A large proportion of people with CF suffer from both chronic and intermittent infections, and in vitro, antibiotic susceptibility testing poorly correlates with patient treatment outcomes. Some biofilm models incorporate CF lung-relevant media, including synthetic sputum mimics, but do not consider the polymicrobial nature of the environment, which alters biofilm architecture, physiology, and the way microbes respond to treatment. The solid-air interface colony biofilm model described here is highly adaptable and incorporates both CF-relevant media and a polymicrobial context. This model can also be used for mid-throughput screening of antimicrobials and to study their effect on polymicrobial dynamics. Output measurements from the model can be colony-forming units, metabolic activity, and confocal microscopy analysis. The model can easily be adapted to different microorganisms, media, temperatures, and variable oxygen conditions and can be used to test a wide range of chemical, biological, and physical treatments.

This methodology allows for the establishment of a polymicrobial biofilm model in cystic fibrosis for antimicrobial sensitivity testing in research and clinical laboratories. This model provides accurate and reliable results over a range of outputs.

A range of bacteria biofilm models exist for the testing of antibiotics. However, many of these are limited to a single experimental output, such as ...

In Vitro Polymicrobial Interactions in Cystic Fibrosis Lung Infections

Growing a Cystic Fibrosis-Relevant Polymicrobial Biofilm to Probe Community Phenotypes

Most in vitro models lack the capacity to fully probe bacterial phenotypes emerging from the complex interactions observed in real-life environments. This is particularly true in the context of hard-to-treat, chronic, and polymicrobial biofilm-based infections detected in the airways of individuals living with cystic fibrosis (CF), a multiorgan genetic disease. While multiple microbiome studies have defined the microbial compositions detected in the airway of people with CF (pwCF), no in vitro models thus far have fully integrated critical CF-relevant lung features. Therefore, a significant knowledge gap exists in the capacity to investigate the mechanisms driving the pathogenesis of mixed species CF lung infections. Here, we describe a recently developed four-species microbial community model, including Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus sanguinis, and Prevotella melaninogenica grown in CF-like conditions. Through the utilization of this system, clinically relevant phenotypes such as antimicrobial&#160;recalcitrance of several pathogens were observed and explored at the molecular level. The usefulness of this in vitro model resides in its standardized workflow that can facilitate the study of interspecies interactions in the context of chronic CF lung infections.

This protocol describes a cystic fibrosis (CF) lung-relevant four-species polymicrobial biofilm model that can be used to explore the impact of bacterial interspecies interactions.

Most in vitro models lack the capacity to fully probe bacterial phenotypes emerging from the complex interactions observed in real-life environments. This ...

Biology

Anti-Infective Efficacy in Cystic Fibrosis with Aggregate Biofilm Models

Cystic Fibrosis Aggregate Biofilm Model to Study Infection-relevant Gene Expression

Standard pre-clinical testing methods for novel antimicrobial therapeutics used to treat chronic lung infections in people with cystic fibrosis do not reflect the environmental conditions of the hostile lung niche. Current reductionist testing conditions can lead to the progression of compounds along a preclinical pipeline without evidence of their activity under cystic fibrosis lung niche-appropriate conditions. Several approaches used to study traditional antimicrobials may not be suitable for antibiotic alternatives, including anti-virulence therapeutics like anti-quorum sensing agents and siderophore inhibitors. This protocol documents an aggregate biofilm model of Pseudomonas aeruginosa to compare resistance and infection-relevant gene expression in single-species and multi-species cultures (Staphylococcus aureus and Candida albicans), examining colony-forming unit (CFU) reductions and changes in gene expression, using algD as an exemplar. The model was optimized for small, static volumes of bacterial cultures to allow the study of novel compounds in the discovery phase of the drug development pipeline, where compound quantities may be limited. Single-species P. aeruginosa biofilms were formed in Synthetic Cystic Fibrosis Medium 2 (SCFM2) for 24 h before treatment with meropenem at different concentrations (1, 16, and 256 &#181;g/mL) for a further 24 h. Polymicrobial biofilms were established by growing Staphylococcus aureus and Candida albicans together in SCFM2, then inoculating with P. aeruginosa for an additional 24 h and treating with meropenem. The lack of a direct connection between compound efficacy measures in pre-clinical testing and clinical trial results has cast doubt on the applicability of current laboratory screening tools. This model allows us to understand the impact of relevant factors on P. aeruginosa gene expression, including genes contributing to resistance and virulence, thereby bridging this gap.

This study outlines a framework for developing an aggregate polymicrobial biofilm model and optimizing an RNA extraction protocol to assess Pseudomonas aeruginosa gene expression reflective of the cystic fibrosis lung environment. Applications include evaluating antimicrobial effects and studying antibiotic alternatives under conditions relevant to cystic fibrosis.

Standard pre-clinical testing methods for novel antimicrobial therapeutics used to treat chronic lung infections in people with cystic fibrosis do not ...

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

Summary

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