We are grateful for the financial support from the Natural Science Foundation of Shaanxi Province (grant number 2021SF-118) and the National Natural Science Foundation of China (grant numbers 81973409, 82204631).

The animals were purchased from Xi&#39;an Jiaotong University. All animal experiment procedures were approved by the Institutional Animal Ethical Committee of Xi&#39;an Jiaotong University (approval number: SCXK [Shaanxi] 2021-103). The mice were kept for one week with 5 mice per cage. They were allowed free access to food and water. The animals were maintained at room temperature (RT; 24 &#176;C &#177; 1 &#176;C) and light/dark cycle (12 h/12 h) before the study was performed.
1. Buffer and equipment preparation
<ol>
	<li>C. albicans cell culture
	<ol>
		<li>Inoculate a monoclonal colony of C. albicans (SC5314) from a yeast extract peptone dextrose (YPD) plate medium with an inoculating loop into 5 mL of YPD liquid medium (YPD + 50 &#181;g/mL carbenicillin).</li>
		<li>Shake C. albicans cells subsequently at a speed of 220 rpm at 30 &#176;C overnight.</li>
		<li>Centrifuge the suspension at 400 x g for 5 min at RT. Resuspend the C. albicans cells in normal saline and dilute the concentration of cells&#160;to 1 x 106 cells/mL via visually adjusting the turbidity to be the same as a 0.5 McFarland.</li>
	</ol>
	</li>
	<li>Preparation of normal saline
	<ol>
		<li>Weigh 0.9 g of sodium chloride and dissolve in 100 mL of deionized water to prepare 0.9% normal saline.</li>
	</ol>
	</li>
	<li>Surgical instruments preparation
	<ol>
		<li>Autoclave (121 &#176;C, 30 min) the surgical instruments (scissors, forceps, hemostatic forceps, needle holders, suture needles) and titanium-nickel alloy wire (about 0.5 mm in diameter) before use.</li>
	</ol>
	</li>
</ol>
2. Mouse PJI model establishment
<ol>
	<li>Randomly divide 30 C57BL/6 mice (male, 15-20 g) into 3 groups (10 mice/group), namely, control group, blank implant group (titanium-nickel wire implantation without C. albicans infection), and PJI group (titanium-nickel wire implantation with C. albicans infection).</li>
	<li>Anesthetize the mice with 1-4% isoflurane inhalation before removing the hair on the left hindlimb and disinfecting it with iodine. The loss of the righting reflex and no response to the toe stimulation confirms the depth of anesthesia. While&#160;anesthetizing, apply ophthalmic ointment on both eyes to prevent corneal dryness and to replenish heat during surgery and recovery.</li>
	<li>For the mice in the control group, do not provide any treatment. Provide them free access to water and food.</li>
	<li>For the mice in the blank implant group and PJI group, make a 5 mm longitudinal incision on the knee of each left hindlimb with a #10 blade or a sterile razor to expose joints.</li>
	<li>Make a hole of 5 mm in length in the femoral intramedullary canal by inserting a sterile syringe (26 G) needle.</li>
	<li>Insert a smooth nickel-titanium alloy wire (0.5 mm in diameter, 5 mm in length) into the hole before being cut with scissors (Figure 1).</li>
	<li>For the mice in the blank implant group, add 2 &#181;L of YPD medium along the nickel-titanium alloy wire drop by drop before closing the wound layer by layer using a nylon suture (0.15 mm diameter).</li>
	<li>For the mice in the PJI group, inoculate 2 &#181;L of C. albicans cells&#160;(1 &#215; 106 cells/mL) into the joint space of mice along the nickel-titanium alloy wire drop by drop before closing the wound layer by layer using a nylon suture.</li>
	<li>House the mice with free access to water and food for 14 days. Administer meloxicam by subcutaneous injection (4 mg/kg) every 24 h for up to 3 days.</li>
	<li>After 14 days, anesthetize the mice with 3% isoflurane before euthanizing the mice by cervical dislocation.</li>
</ol>
3. PJI model evaluation
<ol>
	<li>Evaluation of infections in major organs
	<ol>
		<li>Collect the kidneys, liver, and spleen from the mice after euthanizing.</li>
		<li>Add 500 &#181;L of sterile normal saline in each organ and grind the tissues on a homogenizer at&#160;4 &#176;C.</li>
		<li>Add 100 &#181;L of the homogenate prepared in step 3.1.2 to a YPD plate before spreading it evenly with a bent rod.</li>
		<li>Place the YPD plates inverted into a 37 &#176;C incubator for 48 h.</li>
		<li>Observe and count the number of colonies visually.</li>
	</ol>
	</li>
	<li>Observation of C. albicans and biofilms on the implants
	<ol>
		<li>Carefully cut the skin over the joint of the mice with scissors before collecting the implant with tweezers.</li>
		<li>Keep the implants immersed in a 2.5% glutaraldehyde solution for fixation at 4 &#176;C for 48 h.</li>
		<li>Rinse the implants with sterile PBS three times before immersing them in 1% osmium acid solution for 3 h.</li>
		<li>Rinse the implants with sterile PBS three times before immersing them in 50%, 70%, 80%, 90%, and 100% ethanol solutions for 15 min for dehydration.</li>
		<li>Keep the implants immersed in tert-butanol for 30 min three times before freeze-drying the implants.</li>
		<li>Fix the implant samples to the sample stage, sputter coat the implant with gold (10 nm coating), and observe it under a scanning electronic microscope (SEM) under a high vacuum and 1.5 kV.</li>
	</ol>
	</li>
	<li>Pathological analysis of the femur tissues
	<ol>
		<li>Collect the femoral tissues with scissors after euthanizing the mice.</li>
		<li>Immerse the femur tissues in 4% paraformaldehyde solution for fixation at 4 &#176;C for 48 h.</li>
		<li>Place the femur tissues in 10% formalin for 1 week.</li>
		<li>Dehydrate the femur tissues by immersing them in 50%, 70%, 80%, 90%, and 100% ethanol solutions for 15 min, respectively.</li>
		<li>Embed the dehydrated femur tissues in paraffin before sectioning the tissues into 4 &#181;m samples using a microtome.</li>
		<li>Stain the femur sections with hematoxylin and eosin by following a standard protocol before pathological analysis21.</li>
	</ol>
	</li>
</ol>

Establishing a Mouse Model for Candida albicans Biofilm-Related PJI

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L., Wilson, D., Hube, B. <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+pathogenicity+mechanisms.">Candida albicans pathogenicity mechanisms.</a> Virulence. 4 (2), 119-128 (2013).</li><li>Fan, F., 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=Candida+albicans+biofilms:+antifungal+resistance,+immune+evasion,+and+emerging+therapeutic+strategies.">Candida albicans biofilms: antifungal resistance, immune evasion, and emerging therapeutic strategies.</a> International Journal of Antimicrobial Agents. 60 (5-6), 106673 (2022).</li><li>Tong, Y., Tang, 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+infection+and+intestinal+immunity.">Candida albicans infection and intestinal immunity.</a> Microbiological Research. 198, 27-35 (2017).</li><li>Kanaguchi, N., 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=Effects+of+salivary+protein+flow+and+indigenous+microorganisms+on+initial+colonization+of+Candida+albicans+in+an+in+vivo+model.">Effects of salivary protein flow and indigenous microorganisms on initial colonization of Candida albicans in an in vivo model.</a> Bmc Oral Health. 12, 36 (2012).</li><li>Gulati, M., Nobile, C. 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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> Annual Review of Microbiology. 69, 71-92 (2015).</li><li>Mack, 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=Biofilm+formation+in+medical+device-related+infection.">Biofilm formation in medical device-related infection.</a> The International Journal of Artificial Organs. 29 (4), 343-359 (2006).</li><li>Miller, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Periprosthetic+joint+infection:+A+review+of+antibiotic+treatment.">Periprosthetic joint infection: A review of antibiotic treatment.</a> JBJS Reviews. 8 (7), e1900224 (2020).</li><li>Brown, T. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Periprosthetic+joint+infection+with+fungal+pathogens.">Periprosthetic joint infection with fungal pathogens.</a> The Journal of Arthroplasty. 33 (8), 2605-2612 (2018).</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> Clinical Microbiology Reviews. 17 (2), 255-267 (2004).</li><li>Schoof, 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=Fungal+periprosthetic+joint+infection+of+the+hip:+a+systematic+review.">Fungal periprosthetic joint infection of the hip: a systematic review.</a> Orthopedic Reviews (Pavia). 7 (1), 5748 (2015).</li><li>Izakovicova, P., Borens, O., Trampuz, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Periprosthetic+joint+infection:+current+concepts+and+outlook.">Periprosthetic joint infection: current concepts and outlook.</a> EFORT Open Reviews. 4 (7), 482-494 (2019).</li><li>Tande, A. J., Patel, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prosthetic+joint+infection.">Prosthetic joint infection.</a> Clinical Microbiology Reviews. 27 (2), 302-345 (2014).</li><li>Stocks, G., Janssen, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Infection+in+patients+after+implantation+of+an+orthopedic+device.">Infection in patients after implantation of an orthopedic device.</a> ASAIO Journal. 46 (6), S41-S46 (2000).</li><li>Shahi, A., Tan, T. L., Chen, A. F., Maltenfort, M. 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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The infection caused by the contamination of surgical instruments or the surgical environment during surgery is the major reason for most implant infections24,25,26,27. Therefore, a mouse C. albicans biofilm-related PJI model was constructed in this study. Compared to the traditional PJI model in which sterile stainless-steel particles suspended in saline were used as the implant, a ni...

Candida albicans (C. albicans) commensally reside in many parts of the human body1, which is also the most common opportunistic pathogen that causes life-threatening invasive fungal infections, especially in immunocompromised patients2,3. C. albicans can transform between yeast and mycelium states as a polymorphic fungus. The mycelium state exhibits higher virulence, stronger adhesion, and invasion of cells and tissues4,5. Besides, C. albicans can form biofilms on the surfaces of biomedical materials such as dentures, catheters, and stents1,6,7. The dense three-dimensional structure of biofilms restricts the infiltration of antifungal drugs, expresses drug-resistant genes, and down-regulates the metabolism of fungal cells to resist immune system clearance6,7. Therefore, biofilms-related infections&#160;are quite challenging in clinics8.
Staphylococcus aureus, coagulase-negative staphylococcus, and enterobacter are the main pathogens causing PJI9. Although the incidence of fungal PJI is relatively low (about 1%)10, the treatment cost of fungal PJI is higher11, the treatment cycle is longer11, and the treatment success rate is lower10 than bacterial PJI. In recent years, the incidence of fungal PJI has been increasing year-by-year10. Candida PJI accounts for 77%-84% of fungal PJI10,12, and C. albicans is the most common in Candida (54%). Therefore, fungal PJI needs to be studied.
Currently, PJI is treated via revision surgery by (1) removing the infected implant, (2) debridement, (3) antimicrobial treatment, and (4) reimplantation. After thorough debridement, an antibiotic containing bone cement is placed, and the patient is treated with antibiotics systemically for more than 6 weeks to effectively control the infection before a new implant is placed13. However, this method cannot fully eliminate pathogens in tissues, and recurrent infections treated with long-term antimicrobial therapy are highly likely to develop in drug-resistant strains14,15,16.
Establishing animal models of PJI is important for the research and development of new drugs or therapeutics for PJI. In the development of PJI, large dead spaces are formed around the prosthesis, leading to the formation of hematomas, which further block the blood supply of the surrounding tissues and impair the effect of antibiotics11,15. Due to the difficulty in mimicking the surrounding environment of the prosthesis, traditional animal models cannot accurately simulate the actual situation of PJI17,18.
In this paper, a C. albicans biofilm-associated PJI model in mice was constructed by using a clinically widely used titanium-nickel wire to simulate joint implants19,20. This PJI model exhibits the advantages of easy operation, high successful rate, high repeatability, and high clinical correlation. It is expected to be an important model for studying the prevention and treatment of C. albicans biofilm-related PJI.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.5 Mactutrius turbidibris</td>
			<td>Shanghai Lujing Technology Co., Ltd</td>
			<td>5106063</td>
			<td></td>
		</tr>
		<tr>
			<td>4 &#176;C refrigerator</td>
			<td>Electrolux (China) Electric Co., Ltd</td>
			<td>ESE6539TA</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Beijing Aoboxing Bio-tech Co., Ltd</td>
			<td>01-023</td>
			<td></td>
		</tr>
		<tr>
			<td>Analytical balances</td>
			<td>Shimadzu</td>
			<td>ATX124</td>
			<td></td>
		</tr>
		<tr>
			<td>Autoclaves Sterilizer</td>
			<td>SANYO</td>
			<td>MLS-3750</td>
			<td></td>
		</tr>
		<tr>
			<td>Carbenicillin</td>
			<td>Amresco</td>
			<td>C0885</td>
			<td></td>
		</tr>
		<tr>
			<td>Eclipse Ci Nikon upright optical microscope&#160;</td>
			<td>Nikon</td>
			<td>Eclipse Ts2-FL</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Macklin&#160;</td>
			<td>D823520</td>
			<td></td>
		</tr>
		<tr>
			<td>Inoculation ring</td>
			<td>Thermo Scientific</td>
			<td>251586</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>RWD</td>
			<td>20210103</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Xi&#39;an Jingxi Shuanghe Pharmaceutical Co., Ltd</td>
			<td>20180108</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Beyotime Biotechnology</td>
			<td>P0099</td>
			<td></td>
		</tr>
		<tr>
			<td>Peptone</td>
			<td>Beijing Aoboxing Bio-tech Co., Ltd</td>
			<td>01-001</td>
			<td></td>
		</tr>
		<tr>
			<td>RWD R550 multi-channel small animal anesthesia machine&#160;</td>
			<td>RWD</td>
			<td>R550</td>
			<td></td>
		</tr>
		<tr>
			<td>SEM</td>
			<td>Hitachi</td>
			<td>TM-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Temperature incubator</td>
			<td>Shanghai Zhichu Instrument Co., Ltd</td>
			<td>ZQTY-50N</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrapure water water generator</td>
			<td>Heal Force</td>
			<td>NW20VF</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasound machine</td>
			<td>Do-Chrom</td>
			<td>DS10260D</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>Thermo Scientific&#160;Oxoid</td>
			<td>LP0021B</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Transferring the samples onto a plate medium and counting colonies after overnight incubation is commonly used to assess the local pathogen load near the lesion22,23. In our study, the microbial culture of liver, kidney, and spleen samples was negative, indicating that the model in this study only led to local infection instead of systemic infection in the mice23.
The SEM images of the implants are shown in <str...

Watch this Scientific Journal Video about Advancing Research on Candida albicans Biofilm-Associated Prosthetic Joint Infections at JoVE.com

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.

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 ...

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Immunology and Infection

665 Views.  Xi’an Jiaotong University. 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.

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

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 ...

Protocols for Vaginal Inoculation and Sample Collection in the Experimental Mouse Model of Candida vaginitis

Vulvovaginal candidiasis (VVC), caused by Candida species, is a fungal infection of the lower female genital tract that affects approximately 75% of otherwise healthy women during their reproductive years18,32-34. Predisposing factors include antibiotic usage, uncontrolled diabetes and disturbance in reproductive hormone levels due to pregnancy, oral contraceptives or hormone replacement therapies33,34. Recurrent VVC (RVVC), defined as three or more episodes per year, affects a separate 5 to 8% of women with no predisposing factors33.
An experimental mouse model of VVC has been established and used to study the pathogenesis and mucosal host response to Candida3,4,11,16,17,19,21,25,37. This model has also been employed to test potential antifungal therapies in vivo13,24. The model requires that the animals be maintained in a state of pseudoestrus for optimal Candida colonization/infection6,14,23. Under such conditions, inoculated animals will have detectable vaginal fungal burden for weeks to months. Past studies show an extremely high parallel between the animal model and human infection relative to immunological and physiological properties3,16,21. Differences, however, include a lack of Candida as normal vaginal flora and a neutral vaginal pH in the mice.
Here, we demonstrate a series of key methods in the mouse vaginitis model that include vaginal inoculation, rapid collection of vaginal specimens, assessment of vaginal fungal burden, and tissue preparations for cellular extraction/isolation. This is followed by representative results for constituents of vaginal lavage fluid, fungal burden, and draining lymph node leukocyte yields. With the use of anesthetics, lavage samples can be collected at multiple time points on the same mice for longitudinal evaluation of infection/colonization. Furthermore, this model requires no immunosuppressive agents to initiate infection, allowing immunological studies under defined host conditions. Finally, the model and each technique introduced here could potentially give rise to use of the methodologies to examine other infectious diseases of the lower female genital tract (bacterial, parasitic, viral) and respective local or systemic host defenses.

Protocols for Vaginal Inoculation and Sample Collection in the Experimental Mouse Model of Candida vaginitis

Key techniques to be used in the evaluation of Candida vaginitis in an experimental animal model are described. The methods will allow rapid collection of vaginal specimens and lymphocytes from draining lumbar lymph nodes. These techniques could give rise to mouse models of other diseases in the female lower genital tract.

Vulvovaginal candidiasis (VVC), caused by Candida species, is a fungal infection of the lower female genital tract that affects approximately 75% of ...

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 ...

Influenza A Virus Studies in a Mouse Model of Infection

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone considering direct medical and hospitalization expenses and work absenteeism2. Animal models are crucial in Influenza A virus (IAV) studies to evaluate viral pathogenesis, host-pathogen interactions, immune responses, and the efficacy of current and/or novel vaccine approaches as well as antivirals. Mice are an advantageous small animal model because their immune system is evolutionarily similar to that found in humans, they are available from commercial vendors as genetically identical subjects, there are multiple strains that can be exploited to evaluate the genetic basis of infections, and they are relatively inexpensive and easy to manipulate. To recapitulate IAV infection in humans via the airways, mice are first anesthetized prior to intranasal inoculation with infectious IAVs under proper biosafety containment. After infection, the pathogenesis of IAVs is determined by monitoring daily the morbidity (body weight loss) and mortality (survival) rate. In addition, viral pathogenesis can also be evaluated by assessing virus replication in the upper (nasal mucosa) or lower (lungs) respiratory tract of infected mice. Humoral responses upon IAV infection can be rapidly evaluated by non-invasive bleeding and secondary antibody detection assays aimed at detecting the presence of total or neutralizing antibodies. Here, we describe the common methods used to infect mice intranasally (i.n) with IAV and evaluate pathogenesis, humoral immune responses and protection efficacy.

Influenza A viruses (IAVs) are important human respiratory pathogens. To understand the pathogenicity of IAVs and to perform preclinical testing of novel vaccine approaches, animal models mimicking human physiology are required. Here, we describe techniques to evaluate IAV pathogenesis, humoral responses and vaccine efficacy using a mouse model of infection.

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone ...

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.

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.

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

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 ...

Intracranial Subarachnoidal Route of Infection for Investigating Roles of Streptococcus suis Biofilms in Meningitis in a Mouse Infection Model

Streptococcus suis is not only a major bacterial pathogen of pigs worldwide but also an emerging zoonotic agent. In humans and pigs, meningitis is a major manifestation of S. suis infections. A suitable infection model is an essential tool to understand the mechanisms of diseases caused by pathogens. Several routes of infection in mice have been developed to study the pathogenesis of S. suis infection. However, the intraperitoneal, intranasal, and intravenous routes of infection are not suitable for studying the roles of S. suis surface components in meningitis directly in the brain, such as the extracellular matrix from biofilms. Although intracisternal inoculation has been used for S. suis infection, the precise injection site has not been described. Here, the intracranial subarachnoidal route of infection was described in a mouse model to investigate the roles of biofilms in S. suis meningitis. S. suis planktonic cells or biofilm state cells were directly injected into the subarachnoid space of mice through the injection site located 3.5 mm rostral from the bregma. Histopathological analysis and increased mRNA expression of TLR2 and cytokines of the brain tissue from mice injected with biofilm state cells clearly indicated that S. suis biofilm plays definitive roles in S. suis meningitis. This route of infection has obvious advantages over other routes of infection, allowing the study of the host-bacterium interaction. Furthermore, it permits the effect of bacterial components on host immune responses directly in the brain to be assessed, and mimics bacterial entrance into the central nervous system. This route of infection can be extended for investigating the mechanisms of meningitis caused by other bacteria. In addition, it can also be used to test the efficacy of drugs against bacterial meningitis.

Intracranial Subarachnoidal Route of Infection for Investigating Roles of Streptococcus suis Biofilms in Meningitis in a Mouse Infection Model

Here, we describe the intracranial subarachnoidal route of infection in mice to study roles of biofilms in Streptococcus suis meningitis. This infection model is also suitable for studying the pathogenesis of other bacterial meningitis and the efficacy of new drugs against bacterial meningitis.

Streptococcus suis is not only a major bacterial pathogen of pigs worldwide but also an emerging zoonotic agent. In humans and pigs, meningitis is a major ...

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 ...