Summary

Adhesion of Candida parapsilosis to Bovine Serum Albumin under Fluid Shear

Published: May 13, 2021
doi:

Summary

Adhesion is an important first step in colonization and pathogenesis for Candida. Here, an in vitro assay is described to measure adhesion of C. parapsilosis isolates to immobilized proteins under fluid shear. A multichannel microfluidics device is used to compare multiple samples in parallel, followed by quantification using fluorescence imaging.

Abstract

C. parapsilosis (Cp) is an emerging cause of bloodstream infections in certain populations. The Candida clade, including Cp, is increasingly developing resistance to the first and the second line of antifungals. Cp is frequently isolated from hands and skin surfaces, as well as the GI tract. Colonization by Candida predisposes individuals to invasive bloodstream infections. To successfully colonize or invade the host, yeast must be able to rapidly adhere to the body surfaces to prevent elimination by host defense mechanisms. Here we describe a method to measure adhesion of Cp to immobilized proteins under physiologic fluid shear, using an end-point adhesion assay in a commercially available multichannel microfluidic device. This method is optimized to improve reproducibility, minimize subjectivity, and allow for the fluorescent quantification of individual isolates. We also demonstrate that some clinical isolates of Cp show increased adhesion when grown in conditions mimicking a mammalian host, whereas a frequently used lab strain, CDC317, is non-adhesive under fluid shear.

Introduction

Candida spp. are common commensal organisms on human skin and mucosae that can lead to invasive diseases among the immunocompromised with substantial associated morbidity, mortality, and cost1,2,3. Although C. albicans remains an important cause of these infections, non-albicans species such as C. parapsilosis, C. glabrata, C. krusei, C. tropicalis, and C. auris are being increasingly recognized, especially in vulnerable populations and with frequent resistance to available antifungal drugs4. Non-albicans species present distinct elements of biology and pathogenesis that are under active investigation.

Adhesion is an important first step in colonization and pathogenesis. Interference with this step may therefore offer an opportunity to stop disease progression at an early stage. Studies of Candida adhesion and invasion have been predominantly focused on static conditions5,6. These studies have helped define the structure and functions of fungal adhesins in disease7,8,9. However, adhesion in the bloodstream, gastro-intestinal (GI) tracts, and urinary tracts, and in catheters must occur under conditions of fluid shear flow which places unique constraints upon adhesion. Adhesion under shear requires rapid catch bond formation and the ability to withstand strong pulling forces produced due to the movement of liquids10,11. The C. albicans adhesin, Als5 has been shown to facilitate shear dependent adhesion12,13. CpAls7 (CpALS4800) has been previously shown to mediate adhesion of Cp to epithelial cells, and a knockout showed decreased virulence in a urinary tract infection model14. We demonstrated that CpALS4800 promotes adhesion under physiologically relevant fluid shear conditions15.

Candida colonization and pathogenesis have been extensively studied in the animal models16,17,18. The most frequently used models are murine mucosal and bloodstream infections but invertebrate models, such as Galleria larvae, are increasingly being used because of the low cost, rapid throughput, and simplicity. Animal models recapitulate many steps of the human disease process in both the pathogen and host, including the host adaptive and innate immune responses, interactions of yeast with tissues and the microbiota, and yeast responses to the host environment. In contrast, in vitro adhesion assays permit the focus specifically on the adhesion step, and on the experimental manipulation of variables such as shear force, growth conditions of yeast, and adhesion to specific substrates.

Because Cp is capable of growth in both humans and environmental sources, it is likely to be capable of sensing and responding to different environments. In support of this notion, multiple clinical isolates of Cp show low adhesion under fluid shear when grown in the standard yeast growth medium, yeast-peptone-dextrose (YPD), but switch to strong adhesion when grown for a few hours at 37 °C in the tissue-culture medium 199 (M199)15,19. A detailed protocol is provided here for a medium throughput assay that permits the measurement of adhesion of multiple yeast samples that run in parallel, under defined conditions of growth, fluid shear, temperature, and substrate. The assay has been designed to maximize reproducibility, and to allow for the use of clinical isolates of Cp, as well as strains that have been experimentally manipulated in the lab. The assay as described here, for Cp adhesion to a bovine serum albumin (BSA) substrate, demonstrates that clinical isolates exhibit a range of adhesion, whereas two commonly used lab strains, CDC317 and CLIB214 show poor adhesion.

Protocol

Candida spp. are classified as Biosafety Level 2 organisms and should be handled using appropriate precautions. 1. Growth and induction of clinical strains Streak Cp strains on 1% (m/v) yeast extract, 2% (m/v) peptone, 2% (m/v) dextrose (YPD) 2% (m/v) agar plates, and grow at 22 °C. NOTE: Plates may be stored on the lab bench and re-used over the following week. The day prior to the adhesion assay, transfer approximately 6 colonies of each strain to a…

Representative Results

Using the methods described in the Protocol section, adhesion of 6 strains of Cp was compared (Table 1) Strain Description Reference/Source JMB81 Invasive clinical isolate from infant blood culture 30 JMB77 Invasive clinical isolate from infant blood culture 30</td…

Discussion

The data resulting from the above protocol can be analyzed using a standard spreadsheet software. Data are expressed as "adhesion index", which is calculated as follows: The BinaryArea value for each set of 10 images (representing the yeast coverage for a single channel) is summed across the images, and the mean and standard deviation are calculated for the summed area of each channel pair. The channel area measured in step 4.2 represents the maximum possible area in a single field of view that might ever be cove…

Declarações

The authors have nothing to disclose.

Acknowledgements

This work was supported by a grant from the William and Mary Oh-William and Elsa Zopfi Professorship in Pediatrics for Perinatal Research, the Kilguss Research Core, and an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P30GM114750.

Materials

Bioflux 200 Fluxion Bioflux 200
Bioflux Microfluidics plates, 48 well, low shear Fluxion 910-0004
Bovine Serum Albumin (BSA) Fraction V Fisher Scientific BP1605
Calcofluor Fluorescent Brightener Sigma-Aldrich F3543
DAPI filter set 440/40 Nikon
Dulbecco’s Phosphate-Buffered Saline (DPBS+) Corning Cellgro 21-030-CM With calcium and magnesium
Hank’s Balanced Salt Solution, 1X (HBSS+) Corning Cellgro 21-023-CM With calcium and magnesium, without phenol red
Inverted microscope with Perfect Focus Nikon Ti-E
M199 medium Lonza 12-117Q With Earle's salts and HEPES
Motorized Stage Nikon Ti-S-E
Nikon 20x lambda Plan-Apo objective Nikon
NIS-Elements software 5.02 Nikon
Spectra fluorescent LED light source Lumencor SPECTRA-X3
Zyla 4.2 sCMOS camera Andor Zyla 4.2

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Shaw, S. K., Longley, S. J., Laforce-Nesbitt, S. S., Bliss, J. M. Adhesion of Candida parapsilosis to Bovine Serum Albumin under Fluid Shear. J. Vis. Exp. (171), e62648, doi:10.3791/62648 (2021).

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