Hyphal content determines the compression strength of Candida albicans biofilms

Abstract

Candida albicans is the most frequently isolated human fungal pathogen among species causing biofilm-related clinical infections. Mechanical properties of Candida biofilms have hitherto been given no attention, despite the fact that mechanical properties are important for selection of treatment or dispersal of biofilm organisms due to a bodily fluid flow. The aim of this study was to identify the factors that determine the compression strength of Candida biofilms. Biofilms of C. albicans wild-type parental strain Caf2-1, mutant strain Chk24 lacking Chk1p [known to be involved in regulation of morphogenesis (yeast-to-hyphae transition)] and gene-reconstructed strain Chk23 were evaluated for their resistance to compression, along with biofilms of Candida tropicalis GB 9/9 and Candida parapsilosis GB 2/8, derived from used voice prosthetic biofilms. Additionally, cell morphologies within the biofilm, cell-surface hydrophobicities and extracellular polymeric substance composition were determined. Our results suggest that the hyphae-to-yeast ratio influences the compression strength of C. albicans biofilms. Biofilms with a hyphal content .50 % possessed significantly higher compressive strength and were more difficult to destroy by vortexing and sonication than biofilms with a lower hyphal content. However, when the amount of extracellular DNA (eDNA) in biofilms of C. albicans Caf2-1 and Chk24 increased, biofilm strength declined, suggesting that eDNA may influence biofilm integrity adversely. INTRODUCTIONBiofilms are populations of micro-organisms embedded in an extracellular polymeric substance (EPS) (Costerton et al., 1987). The biofilm mode of growth is beneficial for micro-organisms, as it provides a higher degree of stability than a planktonic existence, and organisms within a biofilm are more resistant to environmental challenges (Hall-Stoodley et al., 2004), such as low nutrient availability, high fluid shear and antibiotic and antimicrobial agents (Baker & Banfield, 2003;Battin et al., 2001;Donlan & Costerton, 2002;Elasri & Miller, 1999;Stewart & Costerton, 2001). The damage caused by the formation of biofilms is a widespread problem, ranging from pipeline corrosion and biofouling of ship hulls and food-processing equipment to clinical infections, such as endocarditis and cystic fibrosis pneumonia (Beech & Gaylarde, 1999;Callow & Callow, 2002;Costerton et al., 1999;Kumar & Anand, 1998). Many clinical infections due to biofilms are implant-related and occur when micro-organisms adhere to the surfaces of biomaterials used in, for example, prosthetic heart valves, voice prostheses, joint replacements, vascular grafts and urinary catheters (Costerton et al., 1999;Donlan, 2001).Biofilms can consist of bacterial or fungal species or a mixture of both. For instance, in the case of vascular catheter-related infections or voice prosthetic biofilms, the most commonly isolated microbial species are Grampositive Staphylococcus epidermidis and Staphylococcus aureus, and the fungus Candida albicans (Hampton & Sherertz, 19...

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

“…Additionally, a screen for biofilm-defective mutants revealed that all of the mutants were also defective in hyphal development, emphasizing the link between morphogenesis and biofilm formation (486). More recently, it was found that the hypha-to-yeast ratio of a biofilm influences its compression strength, and biofilms with a hyphal content of over 50% have a higher compressive strength and are significantly more difficult to disrupt (445). Proteins produced in response to filamentous growth cues, including cell wall proteins such as adhesins, have unique and specific functions in biofilm formation.…”

Extracellular DNA Release Acts as an Antifungal Resistance Mechanism in Mature Aspergillus fumigatus Biofilms

“…Recent studies have shown that eDNA is also an important component of Candida biofilms, including those of C. albicans, Candida tropicalis, and Candida parapsilosis (17,29,30). In C. albicans, eDNA has been shown to contribute to maintenance and stability of mature biofilms, but not to their establishment (17,29), and as a regulator of biofilm cell antifungal resistance (31).…”

Role of Phosphatidylinositol Phosphate Signaling in the Regulation of the Filamentous-Growth Mitogen-Activated Protein Kinase Pathway

“…In pathogenic fungi, like Candida albicans, an orthologous differentiation MAPK pathway (called the Cek1p pathway) regulates filamentous/hyphal growth and biofilm formation (23)(24)(25). These behaviors are critical for virulence (24,(26)(27)(28)(29)(30). Studies of filamentous growth in a genetically tractable fungal system like S. cerevisiae provides information about the genetic basis of fungal behaviors that can be applied to other species, including pathogens.…”