Biofilm Formation by Cryptococcus neoformans
- Authors: Luis R. Martinez1, Arturo Casadevall2
- Editors: Mahmoud Ghannoum3, Matthew Parsek4, Marvin Whiteley5, Pranab Mukherjee6
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VIEW AFFILIATIONS HIDE AFFILIATIONSAffiliations: 1: New York Institute of Technology, College of Osteopathic Medicine, Department of Biomedical Sciences, Old Westbury, NY 11568; 2: Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205; 3: Case Western Reserve University, Cleveland, OH; 4: University of Washington, Seattle, WA; 5: University of Texas at Austin, Austin, TX; 6: Case Western Reserve University, Cleveland, OH
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Received 06 August 2014 Accepted 04 September 2014 Published 05 June 2015
- Correspondence: Arturo Casadevall, [email protected]

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Abstract:
The fungus Cryptococcus neoformans possesses a polysaccharide capsule and can form biofilms on medical devices. The increasing use of ventriculoperitoneal shunts to manage intracranial hypertension associated with cryptococcal meningoencephalitis highlights the importance of investigating the biofilm-forming properties of this organism. Like other microbe-forming biofilms, C. neoformans biofilms are resistant to antimicrobial agents and host defense mechanisms, causing significant morbidity and mortality. This chapter discusses the recent advances in the understanding of cryptococcal biofilms, including the role of its polysaccharide capsule in adherence, gene expression, and quorum sensing in biofilm formation. We describe novel strategies for the prevention or eradication of cryptococcal colonization of medical prosthetic devices. Finally, we provide fresh thoughts on the diverse but interesting directions of research in this field that may result in new insights into C. neoformans biology.
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Citation: Martinez L, Casadevall A. 2015. Biofilm Formation by Cryptococcus neoformans. Microbiol Spectrum 3(3):MB-0006-2014. doi:10.1128/microbiolspec.MB-0006-2014.




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Abstract:
The fungus Cryptococcus neoformans possesses a polysaccharide capsule and can form biofilms on medical devices. The increasing use of ventriculoperitoneal shunts to manage intracranial hypertension associated with cryptococcal meningoencephalitis highlights the importance of investigating the biofilm-forming properties of this organism. Like other microbe-forming biofilms, C. neoformans biofilms are resistant to antimicrobial agents and host defense mechanisms, causing significant morbidity and mortality. This chapter discusses the recent advances in the understanding of cryptococcal biofilms, including the role of its polysaccharide capsule in adherence, gene expression, and quorum sensing in biofilm formation. We describe novel strategies for the prevention or eradication of cryptococcal colonization of medical prosthetic devices. Finally, we provide fresh thoughts on the diverse but interesting directions of research in this field that may result in new insights into C. neoformans biology.

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Figures

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FIGURE 1
Images of a mature C. neoformans biofilm grown on polystyrene plates reveal a highly organized architecture. (A) Scanning electron microscopy image of a C. neoformans biofilm shows fungal cells (white arrow) surrounded by large amounts of EPM. Scale bar: 10 μm. This scanning electron microscopy image was originally published elsewhere ( 17 ). (B) Confocal microscopy image of a cryptococcal biofilm demonstrates a complex structure with internal regions of metabolically active cells interwoven with extracellular polysaccharide material. The thickness of a mature biofilm is approximately 55 μm. This confocal microscopy image was originally published elsewhere ( 14 ).

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FIGURE 2
Model of antibody-mediated inhibition of C. neoformans biofilm formation. In the absence of mAb, C. neoformans cells release capsular polysaccharide which is involved in attachment to the plastic surface. In the presence of a mAb specific to C. neoformans polysaccharide capsule, the immunoglobulin prevents capsular polysaccharide release, which blocks the adhesion of the yeast cells to the surface. Light microscopic images of spots formed by C. neoformans during ELISA spot assay. Images were obtained after 2 h of incubation of fungal cells in the absence and presence of GXM-binding mAb in a polystyrene microtiter plates. Scale bar: 50 μm. The model and light microscopy images in this figure were originally published elsewhere ( 14 ).

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FIGURE 3
Light microscopy images of the EPM of a mature C. neoformans biofilm stained with GXM-specific mAb. Images of a mature biofilm show that capsular-binding mAb binds and darkly stains shed capsular polysaccharide. (A) Picture was taken using a 10× power field. Scale bar: 50 μm. (B) Picture was taken using a 40× power field. Scale bar: 10 μm. Black and white arrows denote yeast cells and EPM, respectively. These light microscopy images were originally published elsewhere ( 16 ).

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FIGURE 4
Schematic of radioimmunotherapy of a biofilm with an antibody labeled with alpha-emitting radionuclide. The “direct hit” effect is the killing of a cell by radiation emanating from a radiolabeled antibody molecule bound to this cell. “Cross-fire” is the killing of a cell by radiation emanating from a radiolabeled antibody bound to an adjacent or a distant cell. “Bystander” denotes the death of an unirradiated cell through the signaling from irradiated cells.
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