Conserved Inhibition of Neutrophil Extracellular Trap Release by Clinical Candida albicans Biofilms.

John Kernien,Chad Johnson,Jeniel Nett

doi:10.3390/jof3030049

John Kernien, Chad Johnson

Open Access

https://doi.org/10.3390/jof3030049

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Abstract

Candida albicans biofilms are difficult to eradicate due to their resistance to host defenses and antifungal drugs. Although neutrophils are the primary responder to C. albicans during invasive candidiasis, biofilms resist killing by neutrophils. Prior investigation, with the commonly used laboratory strain SC5314, linked this phenotype to the impaired release of neutrophil extracellular traps (NETs), which are structures of DNA, histones, and antimicrobial proteins involved in extracellular microbial killing. Considering the diversity of C. albicans biofilms, we examined the neutrophil response to a subset of clinical isolates forming biofilms with varying depths and architectures. Using fluorescent staining of DNA and scanning electron microscopy, we found that inhibition of NET release was conserved across the clinical isolates. However, the dampening of the production of reactive oxygen species (ROS) by neutrophils was strain-dependent, suggesting an uncoupling of ROS and NET inhibition. Our findings show that biofilms formed by clinical C. albicans isolates uniformly impair the release of NETs. Further investigation of this pathway may reveal novel approaches to augment immunity to C. albicans biofilm infections.

Highlights

Candida albicans is the most common hospital-acquired fungal pathogen and frequently adopts a biofilm lifestyle, growing in communities which are adherent to medical devices or mucosal surfaces [1,2,3]
Used medical devices, such as vascular catheters, provide a surface for C. albicans to adhere and form resilient biofilms that are resistant to host defenses and conventional antifungal drugs [1,4,5,6,7,8,9,10,34]
Prior investigations utilizing a filamentous isolate of C. albicans linked biofilm immune evasion to the used medical devices, such as vascular catheters, provide a surface for C. albicans to adhere and form resilient biofilms that are resistant to host defenses and conventional antifungal drugs [1,4,5,6,7,8,9,10,34]

Summary

Introduction

Candida albicans is the most common hospital-acquired fungal pathogen and frequently adopts a biofilm lifestyle, growing in communities which are adherent to medical devices or mucosal surfaces [1,2,3]. While the production of NETs may seem to be an ideal method of combatting fungal biofilms given their aggregative form, neutrophils fail to release NETs upon encounter with biofilms formed by C. albicans [19]. Prior investigation examining the neutrophil response to C. albicans biofilms utilized the filamentous laboratory strain SC5314 [19] This isolate produces robust biofilms of protruding hyphal cells which are the first to be encountered by immune cells, and inner yeast cells which appear to be protected. We examine the neutrophil response to clinical isolates of C. albicans selected for their differences in biofilm-forming capacity, architecture, and degree of filamentation. We demonstrate that these phenotypically distinct biofilms uniformly impair the release of NETs

Strains and Inoculum

Microfluidic Device Model and Imaging

Biofilm Formation

Human Neutrophil Collection

Scanning Electron Microscopy

Measurement of ROS

Sytox Green Assays

Fluorescent Imaging

Results

Discussion