Host contributions to construction of three device-associated Candida albicans biofilms

Abstract

Among the most fascinating virulence attributes of Candida is the ability to transition to a biofilm lifestyle. As a biofilm, Candida cells adhere to a surface, such as a vascular catheter, and become encased in an extracellular matrix. During this mode of growth, Candida resists the normal immune response, often causing devastating disease. Based on scanning electron microscopy images, we hypothesized that host cells and proteins become incorporated into clinical biofilms. As a means to gain an understanding of these host-biofilm interactions, we explored biofilm-associated host components by using microscopy and liquid chromatography-mass spectrometry. Here we characterize the host proteins associated with several in vivo rat Candida albicans biofilms, including those from vascular catheter, denture, and urinary catheter models as well as uninfected devices. A conserved group of 14 host proteins were found to be more abundant during infection at each of the niches. The host proteins were leukocyte and erythrocyte associated and included proteins involved in inflammation, such as C-reactive protein, myeloperoxidase, and alarmin S100-A9. A group of 59 proteins were associated with both infected and uninfected devices, and these included matricellular and inflammatory proteins. In addition, site-specific proteins were identified, such as amylase in association with the denture device. Cellular analysis revealed neutrophils as the predominant leukocytes associating with biofilms. These experiments demonstrate that host cells and proteins are key components of in vivo Candida biofilms, likely with one subset associating with the device and another being recruited by the proliferating biofilm.

FIG 1

Host factors promote C. albicans biofilm matrix deposition. Candida biofilms were collected from an in vivo rat vascular biofilm infection model or were grown in vitro or ex vivo (in the presence of blood). Images were obtained by scanning electron microscopy to visualize the matrix. This extracellular material, marked by arrows, encased the in vivo biofilms as well as the ex vivo biofilms but was less abundant on in vitro biofilms. Bar, 10 μm.

FIG 2

Imaging of C. albicans-infected and uninfected devices. Devices were collected from rat biofilm infection models (vascular catheter, urinary catheter, and denture) in the presence or absence of C. albicans biofilm infection. Extracellular material and host cells on devices were visualized by scanning electron microscopy. Bar, 10 μm.

FIG 3

Host proteins associate with C. albicans-infected and uninfected devices. Proteins were collected from the extracellular matrix of C. albicans biofilm-infected devices, analyzed by liquid chromatography-mass spectrometry, and searched against a Rattus norvegicus amino acid sequence database. For uninfected samples, proteins associating with the device surface were similarly analyzed for each niche. Abundances were compared using Scaffold's unweighted spectrum normalization, and data are presented as Voronoi tree maps reflecting relative abundances.

FIG 4

Host proteins are abundant during C. albicans biofilm infection. Proteins were collected from the extracellular matrix of C. albicans biofilm-infected devices, analyzed by liquid chromatography-mass spectrometry, and searched against a Rattus norvegicus amino acid sequence database. For uninfected samples, proteins associating with the device surface were similarly analyzed for each niche. Abundances were compared using Scaffold's unweighted spectrum normalization. Data are presented as a Venn diagram depicting the number of proteins more abundant during infection for each niche.

FIG 5

Host cells associate with C. albicans biofilms in vivo. C. albicans biofilms were collected from a rat vascular catheter model (A), a rat denture model (B), and a urinary catheter model (C and D). Following removal from the device, catheter and denture biofilms were loaded on a Cytospin centrifuge, and slides were processed with Wright stain. Urinary catheter biofilms were examined following thin preparation and Papanicolaou staining. Line arrows in panels A, B, and D mark neutrophils. The block arrow in panel B highlights an epithelial cell. The block arrow in panel C highlights a urothelial cell.