Fumigatus Biofilm Research Articles

A fast and quantitative evaluation of the Aspergillus fumigatus biofilm adhesion properties by means of digital pulsed force mode

The opportunistic pathogenic mould Aspergillus fumigatus (A. fumigatus) is an increasing cause of morbidity and mortality in immunocompromised and in part immunocompetent patients. A. fumigatus can grow in multicellular communities by the formation of a hyphal network embedded in an extracellular matrix (ECM) meanly composed by polysaccharides, melanin, proteins. Because adhesion properties is one primary factor affecting the balance between growth, detachment and biofilm formation, its quantification is essential in understanding, predicting, and modelling biofilm development.Atomic force microscopy (AFM) imaging and force spectroscopy have recently opened a range of novel applications in microbiology including the imaging and manipulation of membrane proteins at the subnanometer level, the observation of the surface of living cells at high resolution, the mapping of local properties such as surface charges, the measurement of elastic properties of cell-surface constituents and the probing of cellular interactions using functionalized probes. Nevertheless, the principal disadvantage of this approach is the relatively slow acquisition rate that makes AFM is not able to detect fast dynamics.In this study we demonstrated that digital pulsed force mode (DPFM) atomic force microscopy can be used to obtain high-resolution topographical images and to quantify the adhesion properties of the A. fumigatus biofilm with an high acquisition rate.Here we show by means of DPFM-AFM that Alginate Lyase (AlgL), an enzyme known to reduce negatively charged alginate levels in microbial biofilm, is able to reduce the biofilm adhesion forces forming several nano-fractures in the ECM. These results suggest that the AlgL could used to enhance the antifungal drugs transit through the ECM.

Investigation of Aspergillus fumigatus biofilm formation by various omics approaches

Investigation of Aspergillus fumigatus biofilm formation by various omics approaches

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

Aspergillus fumigatus has been shown to form biofilms that are associated with adaptive antifungal resistance mechanisms. These include multidrug efflux pumps, heat shock proteins, and extracellular matrix (ECM). ECM is a key structural and protective component of microbial biofilms and in bacteria has been shown to contain extracellular DNA (eDNA). We therefore hypothesized that A. fumigatus biofilms also possess eDNA as part of the ECM, conferring a functional role. Fluorescence microscopy and quantitative PCR analyses demonstrated the presence of eDNA, which was released phase dependently (8 < 12 < 24 < 48 h). Random amplification of polymorphic DNA (RAPD) PCR showed that eDNA was identical to genomic DNA. Biofilm architectural integrity was destabilized by DNase treatment. Biochemical and transcriptional analyses showed that chitinase activity and mRNA levels of chitinase, a marker of autolysis, were significantly upregulated as the biofilm matured and that inhibition of chitinases affected biofilm growth and stability, indicating mechanistically that autolysis was possibly involved. Finally, using checkerboard assays, it was shown that combinational treatment of biofilms with DNase plus amphotericin B and caspofungin significantly improved antifungal susceptibility. Collectively, these data show that eDNA is an important structural component of A. fumigatus ECM that is released through autolysis, which is important for protection from environmental stresses, including antifungal therapy.

A sticky situation: extracellular DNA shapes Aspergillus fumigatus biofilms

Multicellular stages play an important role for microbial communities as well as during infections. For one of the major fungal pathogens, the environmental mold Aspergillus fumigatus, an interesting and relevant morphotype beyond the conidial and hyphal stages has gained increasing attention: the multicellular biofilm. Such hyphal communities were first described for A. fumigatus in 2007 (Mowat et al., 2007) and are nowadays recognized to be relevant in the clinic (Muller et al., 2011). A. fumigatus is environmentally omnipresent and its airborne conidia are constantly inhaled to become eliminated by the functional host immune system. In case of immune response failure, these infectious propagules germinate and invade the infected tissue to cause forms of aspergillosis (Dagenais and Keller, 2009). Treatment options for this disease are still inadequate, based on the limited number of antifungal drugs and their side effects. Resistance of A. fumigatus to antifungal treatment is influenced by several factors, among them biofilm formation (Seidler et al., 2008). In these structures, a dense network of hyphae becomes embedded in an extracellular matrix (ECM) that is mainly composed of polysaccharides. The ECM of such biofilms grown in vitro further contains melanin, proteins like hydrophobins or antigens, polyols, and monosaccharides (Beauvais et al., 2007). A. fumigatus biofilms are also formed in vivo during invasive aspergillosis or aspergilloma and have been characterized to slightly differ from their in vitro counterparts with respect to ECM composition (Loussert et al., 2010). Recent evidence has identified extracellular DNA (eDNA) as important component of A. fumigatus biofilms, either derived from fungal autolysis (Rajendran et al., 2013) or, as elegantly demonstrated in a recent publication by Brakhage, Hillmann, and colleagues, when externally supplied (Shopova et al., 2013). Probably supported by a high affinity of nucleic acids to the cell wall of A. fumigatus (Jochl et al., 2009) that is based on electrostatic interactions, extrinsic eDNA promotes adhesion of the conidia in the initial phase of biofilm formation, triggers polysaccharide formation and becomes incorporated in the biofilm, thereby shaping its overall structure. Accordingly, DNA contributes to the structural integrity of mature A. fumigatus biofilms, a finding that has been described for several bacterial biofilm formers before (Flemming and Wingender, 2010) and that highlights the structural conservation of microbial biofilms. Considering that A. fumigatus commonly colonizes patients suffering from cystic fibrosis and that the mucus of such patients contains extrinsic DNA at high concentrations that may stem from of neutrophil extracellular traps (NETs) (Brinkmann et al., 2004; Bruns et al., 2010), which are released by a special form of cell death termed NETosis (Remijsen et al., 2011; Almyroudis et al., 2013), from necrotic tissue, or from competing microorganisms, the formation of biofilms is of special significance in this particular host group. In the light of the clinical as well as industrial relevance of Aspergillus biofilms (Ramage et al., 2011), the newly presented data and insights not only sharpen our image of this multicellular stage within the Aspergillus lifestyle but also provide perspective for improvement and new avenues in antifungal therapy or biotechnological applications.

Investigation of Aspergillus fumigatus biofilm formation by various “omics” approaches

In the lung, Aspergillus fumigatus usually forms a dense colony of filaments embedded in a polymeric extracellular matrix called biofilm (BF). This extracellular matrix embeds and glues hyphae together and protects the fungus from an outside hostile environment. This extracellular matrix is absent in fungal colonies grown under classical liquid shake conditions (PL), which were historically used to understand A. fumigatus pathobiology. Recent works have shown that the fungus in this aerial grown BF-like state exhibits reduced susceptibility to antifungal drugs and undergoes major metabolic changes that are thought to be associated to virulence. These differences in pathological and physiological characteristics between BF and liquid shake conditions suggest that the PL condition is a poor in vitro disease model. In the laboratory, A. fumigatus mycelium embedded by the extracellular matrix can be produced in vitro in aerial condition using an agar-based medium. To provide a global and accurate understanding of A. fumigatus in vitro BF growth, we utilized microarray, RNA-sequencing, and proteomic analysis to compare the global gene and protein expression profiles of A. fumigatus grown under BF and PL conditions. In this review, we will present the different signatures obtained with these three “omics” methods. We will discuss the advantages and limitations of each method and their complementarity.

In Vitro Interaction between Alginate Lyase and Amphotericin B against Aspergillus fumigatus Biofilm Determined by Different Methods

Aspergillus fumigatus biofilms represent a problematic clinical entity, especially because of their recalcitrance to antifungal drugs, which poses a number of therapeutic implications for invasive aspergillosis, the most difficult-to-treat Aspergillus-related disease. While the antibiofilm activities of amphotericin B (AMB) deoxycholate and its lipid formulations (e.g., liposomal AMB [LAMB]) are well documented, the effectiveness of these drugs in combination with nonantifungal agents is poorly understood. In the present study, in vitro interactions between polyene antifungals (AMB and LAMB) and alginate lyase (AlgL), an enzyme degrading the polysaccharides produced as extracellular polymeric substances (EPSs) within the biofilm matrix, against A. fumigatus biofilms were evaluated by using the checkerboard microdilution and the time-kill assays. Furthermore, atomic force microscopy (AFM) was used to image and quantify the effects of AlgL-antifungal combinations on biofilm-growing hyphal cells. On the basis of fractional inhibitory concentration index values, synergy was found between both AMB formulations and AlgL, and this finding was also confirmed by the time-kill test. Finally, AFM analysis showed that when A. fumigatus biofilms were treated with AlgL or polyene alone, as well as with their combination, both a reduction of hyphal thicknesses and an increase of adhesive forces were observed compared to the findings for untreated controls, probably owing to the different action by the enzyme or the antifungal compounds. Interestingly, marked physical changes were noticed in A. fumigatus biofilms exposed to the AlgL-antifungal combinations compared with the physical characteristics detected after exposure to the antifungals alone, indicating that AlgL may enhance the antibiofilm activity of both AMB and LAMB, perhaps by disrupting the hypha-embedding EPSs and thus facilitating the drugs to reach biofilm cells. Taken together, our results suggest that a combination of AlgL and a polyene antifungal may prove to be a new therapeutic strategy for invasive aspergillosis, while reinforcing the EPS as a valuable antibiofilm drug target.

Aspergillus Fumigatus Biofilm on Primary Human Sinonasal Epithelial Culture

Bacterial biofilms have been implicated in chronic rhinosinusitis (CRS). However, direct evidence in support of fungal biofilms in sinus disease is lacking in the literature. This study was designed to develop and characterize an in vitro Aspergillus fumigatus biofilm model on primary human sinonasal epithelial cell culture. Sinonasal biopsy specimens harvested during endoscopic sinus surgery of six CRS patients and three pituitary tumor (control) patients were cultured in Dulbecco's modified Eagle media (DMEM; Invitrogen)/Hams F12 airway media to encourage epithelial cell proliferation. Epithelial cells separated by immunomagnetic beads were seeded in tissue culture-treated Y-shaped microslides. At confluence the primary cultures were inoculated with A. fumigatus spores. Fungus was allowed to germinate and form biofilms under two in vitro conditions: (1) static (no flow through of media) and (2) continuous flow coculture (continuous flow movement of media). At regular intervals cocultures were stained with FUN-1, concanavalin A-alexa fluor 488, and examined by confocal scanning laser microscopy. Comstat software was used to assess biomass and thickness. A. fumigatus formed three-dimensional biofilm structures with parallel-packed, cross-linked hyphae and channels/passages. Metabolically active hyphae showed orange-red fluorescing intravacuolar structures. Extracellular matrix (ECM) between/around the hyphae fluoresced intense green. A. fumigatus biofilms development occurred in five stages: (1) conidial attachment to epithelial cells, (2) hyphal proliferation, (3) ECM production, (4) hyphal parallel packing and cross-linking, and (5) channel/pores formation. Mature biofilms showed basal conidial, middle hyphal, and superficial ECM layers. Biofilms formed under flow conditions displayed more robust and faster growth kinetics when compared with that under static conditions, with a thick, stocky, wrinkly/undulating hyphal growth and extensive ECM production. The differences in biomass and average thickness of the cocultures under static and flow conditions were statistically significant after similar periods of incubation (p = 0.0002; p < 0.0001, respectively). To our knowledge, this is the first article of an in vitro model characterizing A. fumigatus biofilm formation using primary human sinonasal epithelium under different growth conditions.

Azole Resistance of Aspergillus fumigatus Biofilms Is Partly Associated with Efflux Pump Activity

This study investigated the phase-dependent expression and activity of efflux pumps in Aspergillus fumigatus treated with voriconazole. Fourteen strains were shown to become increasingly resistant in the 12-h (16- to 128-fold) and 24-h (>512-fold) phases compared to 8-h germlings. An Ala-Nap uptake assay demonstrated a significant increase in efflux pump activity in the 12-h and 24-h phases (P<0.0001). The efflux pump activity of the 8-h germling cells was also significantly induced by voriconazole (P<0.001) after 24 h of treatment. Inhibition of efflux pump activity with the competitive substrate MC-207,110 reduced the voriconazole MIC values for the A. fumigatus germling cells by 2- to 8-fold. Quantitative expression analysis of AfuMDR4 mRNA transcripts showed a phase-dependent increase as the mycelial complexity increased, which was coincidental with a strain-dependent increase in azole resistance. Voriconazole also significantly induced this in a time-dependent manner (P<0.001). Finally, an in vivo mouse biofilm model was used to evaluate efflux pump expression, and it was shown that AfuMDR4 was constitutively expressed and significantly induced by treatment with voriconazole after 24 h (P<0.01). Our results demonstrate that efflux pumps are expressed in complex A. fumigatus biofilm populations and that this contributes to azole resistance. Moreover, voriconazole treatment induces efflux pump expression. Collectively, these data may provide evidence for azole treatment failures in clinical cases of aspergillosis.

Pseudomonas aeruginosa and their small diffusible extracellular molecules inhibit Aspergillus fumigatus biofilm formation

Aspergillus fumigatus is often isolated from the lungs of cystic fibrosis (CF) patients, but unlike in severely immunocompromised individuals, the mortality rates are low. This suggests that competition from bacteria within the CF lung may be inhibitory. The purpose of this study was to investigate how Pseudomonas aeruginosa influences A. fumigatus conidial germination and biofilm formation. Aspergillus fumigatus biofilm formation was inhibited by direct contact with P. aeruginosa, but had no effect on preformed biofilm. A secreted heat-stable soluble factor was also shown to exhibit biofilm inhibition. Coculture of P. aeruginosa quorum-sensing mutants (PAO1:ΔLasI, PAO1:ΔLasR) did not significantly inhibit A. fumigatus biofilms (52.6-58.8%) to the same extent as that of the PA01 wild type (22.9-30.1%), both by direct and by indirect interaction (P<0.001). Planktonic and sessile inhibition assays with a series of short carbon chain molecules (decanol, decanoic acid and dodecanol) demonstrated that these molecules could both inhibit and disrupt biofilms in a concentration-dependent manner. Overall, this suggests that small diffusible and heat-stable molecules may be responsible for the competitive inhibition of filamentous fungal growth in polymicrobial environments such as the CF lung.

Aspergillus fumigatus forms biofilms with reduced antifungal drug susceptibility on bronchial epithelial cells.

Aspergillus fumigatus is a leading cause of death in immunocompromised patients and a frequent colonizer of the respiratory tracts of asthma and cystic fibrosis (CF) patients. Biofilms enable bacteria and yeasts to persist in infections and can contribute to antimicrobial resistance. We investigated the ability of A. fumigatus to form biofilms on polystyrene (PS) and human bronchial epithelial (HBE) and CF bronchial epithelial (CFBE) cells. We developed a novel in vitro coculture model of A. fumigatus biofilm formation on HBE and CFBE cells. Biofilm formation was documented by dry weight, scanning electron microscopy (SEM), and confocal scanning laser microscopy (CSLM). The in vitro antifungal activities of seven antifungal drugs were tested by comparing planktonic and sessile A. fumigatus strains. A. fumigatus formed an extracellular matrix on PS and HBE and CFBE cells as evidenced by increased dry weight, SEM, and CSLM. These biofilms exhibited decreased antifungal drug susceptibility and were adherent to the epithelial cells, with fungi remaining viable throughout 3 days. These observations might have implications for treatment of A. fumigatus colonization in chronic lung diseases and for its potential impact on airway inflammation, damage, and infection.

P630 Aspergillus fumigatus biofilms are refractory to antifungal challenge

P630 Aspergillus fumigatus biofilms are refractory to antifungal challenge