Large-scale production and isolation of Candida biofilm extracellular matrix

Secretion of the fungal toxin candidalysin is dependent on conserved precursor peptide sequences

The opportunistic fungal pathogen Candida albicans damages host cells via its peptide toxin, candidalysin. Before secretion, candidalysin is embedded in a precursor protein, Ece1, which consists of a signal peptide, the precursor of candidalysin and seven non-candidalysin Ece1 peptides (NCEPs), and is found to be conserved in clinical isolates. Here we show that the Ece1 polyprotein does not resemble the usual precursor structure of peptide toxins. C. albicans cells are not susceptible to their own toxin, and single NCEPs adjacent to candidalysin are sufficient to prevent host cell toxicity. Using a series of Ece1 mutants, mass spectrometry and anti-candidalysin nanobodies, we show that NCEPs play a role in intracellular Ece1 folding and candidalysin secretion. Removal of single NCEPs or modifications of peptide sequences cause an unfolded protein response (UPR), which in turn inhibits hypha formation and pathogenicity in vitro. Our data indicate that the Ece1 precursor is not required to block premature pore-forming toxicity, but rather to prevent intracellular auto-aggregation of candidalysin sequences.

Candida albicans extracellular vesicles trigger type I IFN signalling via cGAS and STING

The host type I interferon (IFN) pathway is a major signature of inflammation induced by the human fungal pathogen, Candida albicans. However, the molecular mechanism for activating this pathway in the host defence against C. albicans remains unknown. Here we reveal that mice lacking cyclic GMP-AMP synthase (cGAS)-stimulator of IFN genes (STING) pathway components had improved survival following an intravenous challenge by C. albicans. Biofilm-associated C. albicans DNA packaged in extracellular vesicles triggers the cGAS-STING pathway as determined by induction of interferon-stimulated genes, IFNβ production, and phosphorylation of IFN regulatory factor 3 and TANK-binding kinase 1. Extracellular vesicle-induced activation of type I IFNs was independent of the Dectin-1/Card9 pathway and did not require toll-like receptor 9. Single nucleotide polymorphisms in cGAS and STING potently altered inflammatory cytokine production in human monocytes challenged by C. albicans. These studies provide insights into the early innate immune response induced by a clinically significant fungal pathogen.

Role of the extracellular matrix in Candida biofilm antifungal resistance

Clinical infection due to Candida species frequently involve growth in biofilm communities. Recalcitrance despite antifungal therapy leads to disease persistence associated with high morbidity and mortality. Candida possesses several tools allowing evasion of antifungal effects. Among these, protection of biofilm cells via encasement by the extracellular matrix is responsible for a majority drug resistance phenotype. The Candida matrix composition is complex and includes a mannan-glucan complex linked to antifungal drug sequestration. This mechanism of resistance is conserved across the Candida genus and impacts each of the available antifungal drug classes. The exosome pathway is responsible for delivery and assembly of much of the Candida extracellular matrix as functional vesicle protein and polysaccharide cargo. Investigations demonstrate the vesicle matrix delivery pathway is a useful fungal biofilm drug target. Further elucidation of the vesicle pathway, as well as understanding the roles of biofilm driven cargo may provide additional targets to aid the diagnosis, prevention, and treatment of Candida biofilms.

A common vesicle proteome drives fungal biofilm development

Candida species are commensal organisms commonly interacting in the same host niche. In the pathogenic state, they frequently grow as a biofilm, often in mixed infections. The present studies observe a reliance upon common extracellular vesicle cargo for biofilm structure and function supporting interactions among species. The results reveal a vesicle cargo-driven coordination among Candida species during biofilm formation.

Extracellular vesicles mediate community interactions among cells ranging from unicellular microbes to complex vertebrates. Extracellular vesicles of the fungal pathogen Candida albicans are vital for biofilm communities to produce matrix, which confers environmental protection and modulates community dispersion. Infections are increasingly due to diverse Candida species, such as the emerging pathogen Candida auris, as well as mixed Candida communities. Here, we define the composition and function of biofilm-associated vesicles among five species across the Candida genus. We find similarities in vesicle size and release over the biofilm lifespan. Whereas overall cargo proteomes differ dramatically among species, a group of 36 common proteins is enriched for orthologs of C. albicans biofilm mediators. To understand the function of this set of proteins, we asked whether mutants in select components were important for key biofilm processes, including drug tolerance and dispersion. We found that the majority of these cargo components impact one or both biofilm processes across all five species. Exogenous delivery of wild-type vesicle cargo returned mutant phenotypes toward wild type. To assess the impact of vesicle cargo on interspecies interactions, we performed cross-species vesicle addition and observed functional complementation for both biofilm phenotypes. We explored the biologic relevance of this cross-species biofilm interaction in mixed species and mutant studies examining the drug-resistance phenotype. We found a majority of biofilm interactions among species restored the community’s wild-type behavior. Our studies indicate that vesicles influence the development of protective monomicrobial and mixed microbial biofilm communities.

Production and Isolation of the Candida Species Biofilm Extracellular Matrix

The extracellular matrix (ECM) is a dynamic structure comprising of all four classes of macromolecules. In the biofilm setting, this matrix is key to the survival of microbial communities by conferring to biofilms both structural integrity and protection against diverse environmental insults. In Candida spp., this matrix contributes to pathogenesis by conferring to biofilms both drug resistance and protection against immune attack. Understanding the biochemical nature of the matrix and its individual components is critical to the development of novel diagnostics and antifungal strategies against persistent Candida biofilm infections. Therefore, efficient methods for ECM isolation are required. The two matrix isolation protocols described herein are adapted for both small- and large-scale isolation of biofilm matrix. Both procedures involve seeding of biofilms in either 6-well plates or large-surface-area roller bottles, followed by cell adhesion and biofilm maturation for 2 days with continuous motion. In both cases, the matrix is separated from the biomass via sonication, a step which gently and effectively removes the matrix without disturbing the fungal cell wall. The large-scale protocol includes additional filtration, lyophilization, and dialysis steps to yield purified matrix material sufficient for numerous biochemical, structural, and functional assays. Small-scale isolation yields enough matrix for gas chromatography (GC), total carbohydrate quantification via the phenol-sulfuric acid method, and total protein quantification via the bicinchoninic acid (BCA) assay. Large-scale isolation yields enough matrix to perform NMR spectroscopy, liquid chromatography, mass spectrometry, and nucleic acid sequencing. These protocols have been adapted for use in Candida species but may be adapted for other biofilm-forming fungal species and bacteria.

Coordination of fungal biofilm development by extracellular vesicle cargo

The fungal pathogen Candida albicans can form biofilms that protect it from drugs and the immune system. The biofilm cells release extracellular vesicles (EVs) that promote extracellular matrix formation and resistance to antifungal drugs. Here, we define functions for numerous EV cargo proteins in biofilm matrix assembly and drug resistance, as well as in fungal cell adhesion and dissemination. We use a machine-learning analysis of cargo proteomic data from mutants with EV production defects to identify 63 candidate gene products for which we construct mutant and complemented strains for study. Among these, 17 mutants display reduced biofilm matrix accumulation and antifungal drug resistance. An additional subset of 8 cargo mutants exhibit defects in adhesion and/or dispersion. Representative cargo proteins are shown to function as EV cargo through the ability of exogenous wild-type EVs to complement mutant phenotypic defects. Most functionally assigned cargo proteins have roles in two or more of the biofilm phases. Our results support that EVs provide community coordination throughout biofilm development in C. albicans.

The fungal pathogen Candida albicans can release extracellular vesicles that promote biofilm formation and antifungal resistance. Here, Zarnowski et al. define functions for numerous vesicle cargo proteins in biofilm matrix assembly and drug resistance, as well as in fungal cell adhesion and dissemination.

A Label-Free Cellular Proteomics Approach to Decipher the Antifungal Action of DiMIQ, a Potent Indolo[2,3-b]Quinoline Agent, against Candida albicans Biofilms

Candida albicans forms extremely drug-resistant biofilms, which present a serious threat to public health globally. Biofilm-based infections are difficult to treat due to the lack of efficient antifungal therapeutics, resulting in an urgent demand for the development of novel antibiofilm strategies. In this study, the antibiofilm activity of DiMIQ (5,11-dimethyl-5H-indolo[2,3-b]quinoline) was evaluated against C. albicans biofilms. DiMIQ is a synthetic derivative of indoquinoline alkaloid neocryptolepine isolated from a medicinal African plant, Cryptolepis sanguinolenta. Antifungal activity of DiMIQ was determined using the XTT assay, followed by cell wall and extracellular matrix profiling and cellular proteomes. Here, we demonstrated that DiMIQ inhibited C. albicans biofilm formation and altered fungal cell walls and the extracellular matrix. Cellular proteomics revealed inhibitory action against numerous translation-involved ribosomal proteins, enzymes involved in general energy producing processes and select amino acid metabolic pathways including alanine, aspartate, glutamate, valine, leucine and isoleucine. DiMIQ also stimulated pathways of cellular oxidation, metabolism of carbohydrates, amino acids (glycine, serine, threonine, arginine, phenylalanine, tyrosine, tryptophan) and nucleic acids (aminoacyl-tRNA biosynthesis, RNA transport, nucleotide metabolism). Our findings suggest that DiMIQ inhibits C. albicans biofilms by arresting translation and multidirectional pathway reshaping of cellular metabolism. Overall, this agent may provide a potent alternative to treating biofilm-associated Candida infections.

The Role of Candida albicans Secreted Polysaccharides in Augmenting Streptococcus mutans Adherence and Mixed Biofilm Formation: In vitro and in vivo Studies

The oral cavity is a complex environment harboring diverse microbial species that often co-exist within biofilms formed on oral surfaces. Within a biofilm, inter-species interactions can be synergistic in that the presence of one organism generates a niche for another enhancing colonization. Among these species are the opportunistic fungal pathogen Candida albicans and the bacterial species Streptococcus mutans, the etiologic agents of oral candidiasis and dental caries, respectively. Recent studies have reported enhanced prevalence of C. albicans in children with caries indicating potential clinical implications for this fungal-bacterial interaction. In this study, we aimed to specifically elucidate the role of C. albicans-derived polysaccharide biofilm matrix components in augmenting S. mutans colonization and mixed biofilm formation. Comparative evaluations of single and mixed species biofilms demonstrated significantly enhanced S. mutans retention in mixed biofilms with C. albicans. Further, S. mutans single species biofilms were enhanced upon exogenous supplementation with purified matrix material derived from C. albicans biofilms. Similarly, growth in C. albicans cell-free spent biofilm culture media enhanced S. mutans single species biofilm formation, however, the observed increase in S. mutans biofilms was significantly affected upon enzymatic digestion of polysaccharides in spent media, identifying C. albicans secreted polysaccharides as a key factor in mediating mixed biofilm formation. The enhanced S. mutans biofilms mediated by the various C. albicans effectors was also demonstrated using confocal laser scanning microscopy. Importantly, a clinically relevant mouse model of oral co-infection was adapted to demonstrate the C. albicans-mediated enhanced S. mutans colonization in a host. Analyses of harvested tissue and scanning electron microscopy demonstrated significantly higher S. mutans retention on teeth and tongues of co-infected mice compared to mice infected only with S. mutans. Collectively, the findings from this study strongly indicate that the secretion of polysacharides from C. albicans in the oral environment may impact the development of S. mutans biofilms, ultimately increasing dental caries and, therefore, Candida oral colonization should be considered as a factor in evaluating the risk of caries.

Candida albicans cell wall integrity transcription factors regulate polymicrobial biofilm formation with Streptococcus gordonii

Polymicrobial biofilms play important roles in oral and systemic infections. The oral plaque bacterium Streptococcus gordonii is known to attach to the hyphal cell wall of the fungus Candida albicans to form corn-cob like structures in biofilms. However, the role of C. albicans in formation of polymicrobial biofilms is not completely understood. The objective of this study was to determine the role of C. albicans transcription factors in regulation of polymicrobial biofilms and antibiotic tolerance of S. gordonii. The proteins secreted by C. albicans and S. gordonii in mixed planktonic cultures were determined using mass spectrometry. Antibiotic tolerance of S. gordonii to ampicillin and erythromycin was determined in mixed cultures and mixed biofilms with C. albicans. Additionally, biofilm formation of S. gordonii with C. albicans knock-out mutants of 45 transcription factors that affect cell wall integrity, filamentous growth and biofilm formation was determined. Furthermore, these mutants were also screened for antibiotic tolerance in mixed biofilms with S. gordonii. Analysis of secreted proteomes resulted in the identification of proteins being secreted exclusively in mixed cultures. Antibiotic testing showed that S. gordonii had significantly increased survival in mixed planktonic cultures with antibiotics as compared to single cultures. C. albicans mutants of transcription factors Sfl2, Brg1, Leu3, Cas5, Cta4, Tec1, Tup1, Rim101 and Efg1 were significantly affected in mixed biofilm formation. Also mixed biofilms of S. gordonii with mutants of C. albicans transcription factors, Tec1 and Sfl2, had significantly reduced antibiotic tolerance as compared to control cultures. Our data indicates that C. albicans may have an important role in mixed biofilm formation as well as antibiotic tolerance of S. gordonii in polymicrobial biofilms. C. albicans may play a facilitating role than being just an innocent bystander in oral biofilms and infections.

The effect of isoflavaspidic acid PB extracted from Dryopteris fragrans (L.) Schott on planktonic and biofilm growth of dermatophytes and the possible mechanism of antibiofilm

ETHNOPHARMACOLOGICAL RELEVANCE

Dryopteris fragrans (L.) Schott (D. fragrans), a deciduous perennial herb, has been traditionally used for treatment of various skin diseases in Heilongjiang province of China for many years. Phloroglucinol derivatives extracted from D. fragrans were the most effective fraction against dermatophytes. Isoflavaspidic acid PB is a typically phloroglucinol derivative which extracted from D. fragrans and has been reported to exert anti-fungal activities against several dermatophytes.

AIM OF THE STUDY

This study aimed to evaluate anti-fungal and anti-biofilm activity of isoflavaspidic acid PB on planktonic and biofilm growth of dermatophytes and explore possible mechanisms of anti-biofilm.

MATERIALS AND METHODS

Minimal inhibitory concentrations (MIC) and minimal fungicidal concentrations (MFC) of isoflavaspidic acid PB against 25 isolates of dermatophytes were determined by the Clinical and Laboratory Standards Institute (CLSI) M38-A2 method. The effects of isoflavaspidic acid PB on dermatophytes biofilm formation and pre-formed biofilm were assessed by 2.3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[carbonyl (phenylamino)]-2H-tetrazolium hydroxide (XTT) assay. Morphology of mature biofilm were observed by Scanning Electron Microscope (SEM). Biomass, exopolysaccharide and ergosterol content of mature biofilm were analyzed by gravimetric analysis, anthranone sulfuric acid method and Ultra Performance Liquid Chromatography (UPLC) assay respectively.

RESULT

The MIC and MFC ranges of isoflavaspidic acid PB against 25 isolates of dermatophytes were 20-80 μg/mL and 40-80 μg/mL respectively. Isoflavaspidic acid PB (2 MIC) inhibited not only Trichophyton biofilm formation (54.8% ∼ 81.2%) but also the metabolic activity of mature biofilm (20.7% ∼ 44.2%). The result of SEM showed that isoflavaspidic acid PB (8 MIC) could destroy the morphology of hyphae seriously. Comparing with control group, biomass, exopolysaccharide and ergosterol content of the mature biofilm under isoflavaspidic acid PB (8 MIC) were significantly decreased (P < 0.01).

CONCLUSION

Isoflavaspidic acid PB had anti-fungal and fungicidal activities against dermatophytes. Isoflavaspidic acid PB could inhibit the biofilm of Trichophyton. The mechanism might be related to the decline of the biofilm biomass, exopolysaccharide and ergosterol content. These results showed that isoflavaspidic acid PB could be explored for promising anti-biofilm drugs.

BIOF-HILO Assay: A New MALDI-TOF Mass Spectrometry Based Method for Discriminating Between High- and Low-Biofilm-Producing Candida parapsilosis Isolates

Candida parapsilosis is the most frequent cause of catheter-related candidemia among non-Candida albicans species. This may be related to intrinsic capabilities as adhering and forming a biofilm on abiotic surfaces such as on medical devices. As previously demonstrated, patients infected with high biofilm-producing C. parapsilosis isolates had a greater mortality risk compared to patients infected with low biofilm-producing C. parapsilosis isolates. We developed the BIOF–HILO assay, a MALDI–TOF mass spectrometry (MS)-based assay, which compares mass spectra obtained from attached and suspended isolate cells during the early (i.e., 3-h) adhesion phase of in vitro biofilm formation. The composite correlation index (CCI) analysis was used to discriminate between mass spectra differences of the two cell types, classifying all 50 C. parapsilosis clinical isolates, included in the study, after only 3-h of testing, in high or low biofilm producers. All high (n = 25) or low (n = 25) biofilm producers had, according to CCI mass spectra comparison values, higher or lower than one CCI ratios, which were obtained by dividing the CCI_{suspended cells} by the CCI_{attached cells}. In conclusion, the BIOF–HILO assay allows a rapid categorization of C. parapsilosis clinical isolates in high or low biofilm producers. This information, if timely provided to physicians, may improve treatment outcomes in patients with C. parapsilosis candidemia.

Extraction of Extracellular Matrix in Static and Dynamic Candida Biofilms Using Cation Exchange Resin and Untargeted Analysis of Matrix Metabolites by Ultra-High-Performance Liquid Chromatography-Tandem Quadrupole Time-of-Flight Mass Spectrometry (UPLC-Q-TOF-MS)

Fungal infections caused by Candida albicans poses a great threat to human health. The ability of biofilm formation is believed to be associated with resistance-related Candida infections. Currently, knowledge on extracellular matrix (EM) of C. albicans biofilm is limited. In this study, we introduced ion exchange resin, i.e., cation exchange resin (CER) and anion exchange resin (AER), in EM extraction of C. albicans biofilm as well as several non-albicans Candida (NAC) biofilms under static and dynamic states in combination with vortexing and ultrasonication (VU). The metabolites extracted from the dynamic C. albicans biofilm matrix using the CER-VU and VU were identified with ultra-high-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) via untargeted filtration. Compared with other physical and chemical extraction methods, CER-VU was demonstrated to be an ideal approach with high-yield acquisitions of EM constituents including proteins, triglycerides and carbohydrates and low-level damages on fungal cell viability and integrity. The untargeted MS analysis further showed the high efficacy of CER-VU, as a large quantity of metabolites (217 versus 198) was matched comprising a great number of lipids, carbohydrates, amino acids, nucleic acids and their derivatives together with a high involvement of signaling pathways compared with the VU alone. However, combining the results from both the CER-VU and VU methods could generate more metabolites. In summary, the EM analysis of the dynamic C. albicans biofilm expands our understanding upon a comprehensive depiction of matrix components and provides another effective approach for EM extraction.

The Significance of Lipids to Biofilm Formation in Candida albicans: An Emerging Perspective

Candida albicans, the dimorphic opportunistic human fungal pathogen, is capable of forming highly drug-resistant biofilms in the human host. Formation of biofilm is a multistep and multiregulatory process involving various adaptive mechanisms. The ability of cells in a biofilm to alter membrane lipid composition is one such adaptation crucial for biofilm development in C. albicans. Lipids modulate mixed species biofilm formation in vivo and inherent antifungal resistance associated with these organized communities. Cells in C. albicans biofilms display phase-dependent changes in phospholipid classes and in levels of lipid raft formation. Systematic studies with genetically modified strains in which the membrane phospholipid composition can be manipulated are limited in C. albicans. In this review, we summarize the knowledge accumulated on the impact that alterations in phospholipids may have on the biofilm forming ability of C. albicans in the human host. This review may provide the requisite impetus to analyze lipids from a therapeutic standpoint in managing C. albicans biofilms.

Candida albicans biofilm-induced vesicles confer drug resistance through matrix biogenesis

Cells from all kingdoms of life produce extracellular vesicles (EVs). Their cargo is protected from the environment by the surrounding lipid bilayer. EVs from many organisms have been shown to function in cell–cell communication, relaying signals that impact metazoan development, microbial quorum sensing, and pathogenic host–microbe interactions. Here, we have investigated the production and functional activities of EVs in a surface-associated microbial community or biofilm of the fungal pathogen Candida albicans. Crowded communities like biofilms are a context in which EVs are likely to function. Biofilms are noteworthy because they are encased in an extracellular polymeric matrix and because biofilm cells exhibit extreme tolerance to antimicrobial compounds. We found that biofilm EVs are distinct from those produced by free-living planktonic cells and display strong parallels in composition to biofilm matrix material. The functions of biofilm EVs were delineated with a panel of mutants defective in orthologs of endosomal sorting complexes required for transport (ESCRT) subunits, which are required for normal EV production in diverse eukaryotes. Most ESCRT-defective mutations caused reduced biofilm EV production, reduced matrix polysaccharide levels, and greatly increased sensitivity to the antifungal drug fluconazole. Matrix accumulation and drug hypersensitivity of ESCRT mutants were reversed by addition of wild-type (WT) biofilm EVs. Vesicle complementation showed that biofilm EV function derives from specific cargo proteins. Our studies indicate that C. albicans biofilm EVs have a pivotal role in matrix production and biofilm drug resistance. Biofilm matrix synthesis is a community enterprise; prior studies of mixed cell biofilms have demonstrated extracellular complementation. Therefore, EVs function not only in cell–cell communication but also in the sharing of microbial community resources.

Candida albicans—the most common fungal pathogen in humans—often grows as a biofilm, resulting in an infection that is difficult to treat. These adherent communities tolerate extraordinarily high concentrations of antifungals due in large part to the protective extracellular matrix. The present study identifies extracellular vesicles (EVs) that are distinct to biofilms. These EVs deliver the functional extracellular matrix and are essential for resistance to antifungals. Our findings not only reveal a coordinated mechanism by which the defining trait of the biofilm lifestyle arises but also identify a number of potential therapeutic targets.

Conservation and Divergence in the Candida Species Biofilm Matrix Mannan-Glucan Complex Structure, Function, and Genetic Control

Candida biofilms resist the effects of available antifungal therapies. Prior studies with Candida albicans biofilms show that an extracellular matrix mannan-glucan complex (MGCx) contributes to antifungal sequestration, leading to drug resistance. Here we implement biochemical, pharmacological, and genetic approaches to explore a similar mechanism of resistance for the three most common clinically encountered non-albicansCandida species (NAC). Our findings reveal that each Candida species biofilm synthesizes a mannan-glucan complex and that the antifungal-protective function of this complex is conserved. Structural similarities extended primarily to the polysaccharide backbone (α-1,6-mannan and β-1,6-glucan). Surprisingly, biochemical analysis uncovered stark differences in the branching side chains of the MGCx among the species. Consistent with the structural analysis, similarities in the genetic control of MGCx production for each Candida species also appeared limited to the synthesis of the polysaccharide backbone. Each species appears to employ a unique subset of modification enzymes for MGCx synthesis, likely accounting for the observed side chain diversity. Our results argue for the conservation of matrix function among Candida spp. While biogenesis is preserved at the level of the mannan-glucan complex backbone, divergence emerges for construction of branching side chains. Thus, the MGCx backbone represents an ideal drug target for effective pan-Candida species biofilm therapy.IMPORTANCECandida species, the most common fungal pathogens, frequently grow as a biofilm. These adherent communities tolerate extremely high concentrations of antifungal agents, due in large part, to a protective extracellular matrix. The present studies define the structural, functional, and genetic similarities and differences in the biofilm matrix from the four most common Candida species. Each species synthesizes an extracellular mannan-glucan complex (MGCx) which contributes to sequestration of antifungal drug, shielding the fungus from this external assault. Synthesis of a common polysaccharide backbone appears conserved. However, subtle structural differences in the branching side chains likely rely upon unique modification enzymes, which are species specific. Our findings identify MGCx backbone synthesis as a potential pan-Candida biofilm therapeutic target.

Proteomics of Staphylococcus aureus biofilm matrix in a rat model of orthopedic implant-associated infection

The matrix proteins of Staphylococcus aureus biofilm have not been well defined. Previous efforts to identify these proteins were performed using in vitro systems. Here we use a proteomic approach to identify biofilm matrix proteins directly from infected bone implants using a rat model of orthopedic implant-associated S. aureus infection. Despite heavy presence of host proteins, a total of 28 and 105 S. aureus proteins were identified during acute infection and chronic infection, respectively. Our results show that biofilm matrix contains mostly intracellular cytoplasmic proteins and, to a much less extent, extracellular and cell surface-associated proteins. Significantly, leukocidins were identified in the biofilm matrix during chronic infection, suggesting S. aureus is actively attacking the host immune system even though they are protected within the biofilm. The presence of two surface-associated proteins, Ebh and SasF, in the infected bone tissue during acute infection was confirmed by immunohistochemistry. In addition, a large number of host proteins were found differentially expressed in response to S. aureus biofilm formed on bone implants.

The HIV aspartyl protease inhibitor ritonavir impairs planktonic growth, biofilm formation and proteolytic activity in Trichosporon spp

This study evaluated the effect of the protease inhibitor ritonavir (RIT) on Trichosporon asahii and Trichosporon inkin. Susceptibility to RIT was assessed by the broth microdilution assay and the effect of RIT on protease activity was evaluated using azoalbumin as substrate. RIT was tested for its anti-biofilm properties and RIT-treated biofilms were assessed regarding protease activity, ultrastructure and matrix composition. In addition, antifungal susceptibility, surface hydrophobicity and biofilm formation were evaluated after pre-incubation of planktonic cells with RIT for 15 days. RIT (200 μg ml^-1) inhibited Trichosporon growth. RIT (100 μg ml^-1) also reduced protease activity of planktonic and biofilm cells, decreased cell adhesion and biofilm formation, and altered the structure of the biofilm and the protein composition of the biofilm matrix. Pre-incubation with RIT (100 μg ml^-1) increased the susceptibility to amphotericin B, and reduced surface hydrophobicity and cell adhesion. These results highlight the importance of proteases as promising therapeutic targets and reinforce the antifungal potential of protease inhibitors.

The Candida albicans Biofilm Matrix: Composition, Structure and Function

A majority of infections caused by Candida albicans—the most frequent fungal pathogen—are associated with biofilm formation. A salient feature of C. albicans biofilms is the presence of the biofilm matrix. This matrix is composed of exopolymeric materials secreted by sessile cells within the biofilm, in which all classes of macromolecules are represented, and provides protection against environmental challenges. In this review, we summarize the knowledge accumulated during the last two decades on the composition, structure, and function of the C. albicans biofilm matrix. Knowledge of the matrix components, its structure, and function will help pave the way to novel strategies to combat C. albicans biofilm infections.