Lipid-Like Biofilm from a Clinical Brain Isolate of Aspergillus terreus: Quantification, Structural Characterization and Stages of the Formation Cycle

Invasive infections caused by filamentous fungi have increased considerably due to the alteration of the host's immune response. Aspergillus terreus is considered an emerging pathogen and has shown resistance to amphotericin B treatment, resulting in high mortality. The development of fungal biofilm is a virulence factor, and it has been described in some cases of invasive aspergillosis. In addition, although the general composition of fungal biofilms is known, findings related to biofilms of a lipid nature are rarely reported. In this study, we present the identification of a clinical strain of A. terreus by microbiological and molecular tools, also its in vitro biofilm development capacity: (i) Biofilm formation was quantified by Crystal Violet and reduction of tetrazolium salts assays, and simultaneously the stages of biofilm development were described by Scanning Electron Microscopy in High Resolution (SEM-HR). (ii) Characterization of the organizational structure of the biofilm was performed by SEM-HR. The hyphal networks developed on the surface, the abundant air channels created between the ECM (extracellular matrix) and the hyphae fused in anastomosis were described. Also, the presence of microhyphae is reported. (iii) The chemical composition of the ECM was analyzed by SEM-HR and CLSM (Confocal Laser Scanning Microscopy). Proteins, carbohydrates, nucleic acids and a relevant presence of lipid components were identified. Some structures of apparent waxy appearance were highlighted by SEM-HR and backscatter-electron diffraction, for which CLSM was previously performed. To our knowledge, this work is the first description of a lipid-type biofilm in filamentous fungi, specifically of the species A. terreus from a clinical isolate.

Construction of a fusion protein consisting of α-1,3-glucan-binding domains and tetrameric red fluorescent protein, which is involved in the aggregation of α-1,3-glucan and inhibition of fungal biofilm formation

Agl-KA, an α-1,3-glucan-hydrolyzing enzyme from Bacillus circulans KA-304, has three α-1,3-glucan-binding domains DS1, CB6, and DS2 (DCD). While their individual binding activities toward insoluble α-1,3-glucan and fungal cell-wall are weak, the three domains in combination bind strongly to the α-1,3-glucan and the cell-wall. In this study, we constructed DCD-tetraRFP by fusing DCD with DsRed-Express2, a tetrameric red fluorescent protein. DCD-tetraRFP forms a tetramer in an aqueous solution and contains twelve substrate-binding domains in one complex. We also constructed DCD-monoGFP by fusing DCD with AcGFP1, a monomeric green fluorescent protein. The molecular weight of DCD-tetraRFP and DCD-monoGFP were compared. The results of gel filtration chromatography and dynamic light scattering indicated that DCD-tetraRFP was larger than DCD-monoGFP, suggesting that DCD-tetraRFP had a tetrameric structure. In addition, DCD-tetraRFP bound to insoluble α-1,3-glucan strongly, and the amount of DCD-tetraRFP binding to 0.01% α-1,3-glucan was about twice of DCD-monoGFP. The Kd values of DCD-tetraRFP (measurements per subunit) and DCD-monoGFP were 0.16 and 0.84 μM, respectively. Adding DCD-tetraRFP to a suspension of α-1,3-glucan caused glucan aggregation; however, adding DCD-monoGFP did not. These data suggested that DCD-tetraRFP had four DCDs sterically arranged in different directions so that DCD-tetraRFP cross-linked with the substrate, causing aggregation. Lastly, the aggregates of DCD-tetraRFP and α-1,3-glucan captured Aspergillus oryzae conidia and decreased their biofilm formation by 80% in a 24-well dish.

Aspergillus tubingensis Endocarditis: A Case Report and Review of the Literature

Aspergillus endocarditis is a rare infection that may affect immunocompetent patients following heart valve replacement or heart surgery. We report the case of a 39 year old woman with a history of intravenous drug use who developed endocarditis with direct examination of the resected valve and vegetation showing the presence of mycelia. Cultures were positive for an Aspergillus of section Nigri, which was subsequently identified as Aspergillus tubingensis by sequencing. The clinical course was favorable following surgery and prolonged antifungal therapy (8 months in total). Antifungal susceptibility testing showed good in vitro activity of amphotericin B, voriconazole and echinocandins against planktonic cells of this A. tubingensis isolate. However, only amphotericin B displayed significant activity against biofilms. In vitro combinations of voriconazole or amphotericin B with echinocandins did not meet the criteria of synergism. Our review of the literature identified 17 other cases of endocarditis attributed to Aspergillus of section Nigri with an overall mortality rate of 57% (100% in the absence of surgery). Endocarditis caused by Aspergillus niger and related cryptic species are rare events, for which surgical management appears to be crucial for outcome. While amphotericin B was the only antifungal drug displaying significant anti-biofilm activity, the type and duration of antifungal therapy remain to be determined.

Activity of antifungal drugs and Brazilian red and green propolis extracted with different methodologies against oral isolates of Candida spp

Background

Oral candidiasis is an opportunistic disease caused by fungi of the Candida genus. The occurrence of Candida spp. resistance to the commercial antifungal drugs points to the search for alternative treatments. Propolis has been successfully used in the treatment of infectious diseases for centuries. It has been proposed that an ultrasound pretreatment in the propolis extraction protocol can enhance the concentrations of molecules with antimicrobial activities in the final extract. Thus, this study aimed to compare the antifungal activity against oral Candida spp. isolates of green and red propolis extracts submitted or not to an ultrasound pretreatment before the extraction procedure.

Methods

Candida spp. were isolated from denture stomatitis lesions and identified by sequencing. Oral Candida spp. isolates and reference strains were submitted to broth microdilution assays using commercial antifungals and Brazilian green and red propolis extracts submitted or not to an ultrasound pretreatment. Minimal Inhibitory Concentrations (MIC) and Minimal Fungicide Concentrations (MFC) were determined and biofilm formation interference was evaluated for resistant isolates.

Results

C. albicans, Candida tropicalis and Candida dubliniensis were isolated from denture stomatitis lesions. Growth inhibition was observed in all Candida isolates incubated with all green and red propolis extracts. At lower doses, red propolis extracts presented significant antifungal activity. The ultrasound pretreatment did not promote an increase in the antifungal activity of green or red propolis. Three isolates, which were highly resistant to fluconazole and itraconazole, were susceptible to low doses of red propolis extracts. These same three specimens had their biofilm formation inhibted by red propolis ethanolic extract.

Conclusions

Thus, red propolis can be faced as a promising natural product to be used in the auxiliary antifungal therapy of denture stomatitis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03445-5.

Biofilms and the Nail Unit

Recent studies have shown that a superficial fungal infection such as onychomycosis may form complex biofilms. Although most individuals susceptible to documented fungal biofilm infections are immunocompromised, physical damage to the nail or concurrent infection with other organisms is also a common risk factor in developing nail biofilm. The complex nature of the biofilm, which includes efflux pumps and the formation of a virulent extracellular matrix, helps it evade the immune system. Although there is no standardized treatment for fungal biofilms in onychomycosis, various studies using antimicrobials and lasers have shown some efficacy in treating human fingernails.

Expression of F-actin and β-tubulin genes in free mycelia and robust biofilms of the filamentous fungus Aspergillus niger

The morphology and growth of the filamentous fungi are influenced by different factors as the culture conditions and the type of fermentative process. The production and secretion of metabolites by these organisms present a direct relationship with their morphology. The organization of the microtubules and actin in the cytoskeleton is determinant for both the fungal growth and morphology. In this context, this study aimed to analyze the expression of the β-tubulin, F-actin, and glucan synthase in the A. niger mycelia obtained from submerged fermentation and biofilm fermentation through qPCR, as well as the analysis of the nucleus distribution in the hypha. Herein, we showed that β-tubulin and the F-actin gene were more expressed in the biofilm condition, while the glucan synthase was in the submerged condition. No significant difference was observed in the nucleus distribution between the mycelia obtained from both the fermentative processes. In conclusion, the different morphologies observed for the mycelia from submerged fermentation and biofilm fermentation might be influenced by the differential modulation of genes that codify cytoskeleton proteins, which seems to be potentially regulated by mechanosensing during fungal contact with solid supports.

Inkjet 3D Printing of Polymers Resistant to Fungal Attachment

Inkjet 3D printing is an additive manufacturing method that allows the user to produce a small batch of customized devices for comparative study versus commercial products. Here, we describe the use of a commercial 2D ink development system (Dimatix material printing) to manufacture small batches of 3D medical or other devices using a recently characterized fungal anti-attachment material. Such printed devices may resist problems that beset commercial medical products due to colonization by the fungal pathogen Candida albicans. By sequentially introducing the cross-section bitmaps of the product's CAD model and elevating the print head height using the auto-clicking script, we were able to create complex self-support geometries with the 2D ink development system. The use of this protocol allows researchers to produce a small batch of specimens for characterization from only a few grams of raw material. Additionally, we describe the testing of manufactured specimens for fungal anti-attachment. In comparison with most commercial AM systems, which require at least a few hundred grams of ink for printing trials, our protocol is well suited for smaller-scale production in material studies.

A new 1-nitro-9-aminoacridine derivative targeting yeast topoisomerase II able to overcome fluconazole-resistance

Fungal resistance remains a significant threat and a leading cause of death worldwide. Thus, overcoming microbial infections have again become a serious clinical problem. Although acridine derivatives are widely analyzed as anticancer agents, only a few reports have demonstrated their antifungal activity. In an effort to develop biologically active antifungals, twelve novel C-857 (9-(2'-hydroxyethylamino)-1-nitroacridine) and C-1748 (9-(2'-hydroxyethylamino)-4-methyl-1-nitroacridine) derivatives were synthesized. The evaluation of biological properties suggests that starting compounds: C-1748, C-857 and IE3 (2-[(4-methyl-1-nitroacridin-9-yl)amino]ethyl lysinate), IE4 (2-[(1-nitroacridin-9-yl)amino]ethyl lysinate) antifungal mode of action differ from that determined for IE5 (N'-{3-[(4-methyl-1-nitroacridin-9-yl)amino]propyl}lysinamide), IE6 (N'-{3-[(1-nitroacridin-9-yl)amino]propyl}lysinamide) and IE10 (3,3'-Bis-(1-nitroacridin-9-ylamino)-aminoethylaminoethylaminoethylamine). Although MIC values determined for the latter were higher, in contrast to C-857 and C-1748, newly synthesized IE5, IE6 and IE10 reduced C. albicans hyphal growth in different inducing media. Those compounds also exhibited antibiofilm activity, whereas IE10 was the most effective. Moreover, only IE6 exhibited antifungal activity against fluconazole resistant C. albicans strains with MICs values in the range of 16-64 μg mL^-1. Our results also indicate that, in contrast to other analyzed derivatives, novel synthetized compounds IE6 and IE10 with antifungal activity target yeast topoisomerase II activity.

Dissecting the anti-biofilm potency of kappa-carrageenan capped silver nanoparticles against Candida species

Global antimicrobial crisis and advent of drug resistant fungal strains has substantially distressed disease management for clinicians. Biodegradable silver nanoparticles (AgNps) emerge as an excellent alternative remedial option. In the current study, the anti-biofilm activity of microwave irradiated kappa-carrageenan (CRG) capped AgNps against Candida albicans, and Candida glabrata was investigated in terms of their effect on reactive oxygen species (ROS) generation, cellular morphology, biochemical composition, and the activity of enzymes of extracellular matrix. Minimum inhibitory concentration and fungicidal concentration value of CRG-AgNps against both Candida spp. ranged between 400 and 500 μg/mL. The 80% of Candida biofilm was inhibited and eradicated by CRG-AgNps at a concentration of ~300 μg/mL. Microscopic studies indicate that CRG-AgNps caused morphological damage through membrane disruption and pore formation. Further, CRG-AgNps generated ROS in a concentration-dependent manner and modulated the composition of Candida biofilm ECM by increasing the carbohydrate and eDNA content. CRG-AgNps also significantly inactivated the hydrolytic enzymes, thus hindering the biofilm forming ability. In conclusion, all these results suggest that the CRG-AgNps are potential antifungal agents against Candida biofilms, and they inhibit/eradicate the fungal biofilms through multiple signalling mechanisms.

Promising effect of in-situ lyticase enzyme therapy on peritoneal dialysis catheter obstruction from Acremonium fungal biofilm: A case report

We reported the first clinical use of lyticase enzyme in salvaging the peritoneal dialysis (PD) catheter obstruction from Acremonium fungal biofilm during the COVID-19 pandemic era with an impressive result in PD patient presenting with fungal peritonitis and ultrafiltration failure. The organism species was disclosed from PD effluent and catheter cultures. Adjuvant treatment with in-situ lyticase may be considered for catheter salvage therapy if the catheter could not promptly removed in time.

Bioactivity of magnesium oxide nanoparticles synthesized from cell filtrate of endobacterium Burkholderia rinojensis against Fusarium oxysporum

The present study was performed to synthesize, for the first time, the magnesium oxide nanoparticles (MgO NPs) using the cell filtrate of the endobacterium Burkholderia rinojensis. The MgO NPs were characterized by Ultraviolet-visible (UV-Vis), Fourier-transform infrared (FTIR), X-ray diffraction (XRD), Energy dispersive X-ray (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and zeta potential (ZP). The UV spectrum of the MgO NPs showed a sharp absorption peak at 330 nm. The FTIR results confirm that the bioactive compounds act as reducing and capping agents of synthesized MgO NPs. The XRD pattern showed three major peaks of the crystalline metallic MgO NPs. Presence of magnesium and oxygen were confirmed by EDX profile. Both SEM and TEM revealed the MgO NPs as roughly spherical granular structures, and the size was 26.70 nm. The zeta potential was -32.1 mV, which indicated the stability of the MgO NPs in suspension. The MgO NPs showed considerable antifungal and antibiofilm activities against Fusarium oxysporum f. sp. lycopersici. At the concentration of 15.36 μg/ml, the MgO NPs completely inhibited the mycelial growth of the fungus. The biofilm formation of the pathogen was completely suppressed by MgO NPs at 1.92 μg/ml. The MgO NPs caused severe morphological changes on the hyphal morphology and biofilm formation of the fungus with significant damage on the fungal membrane integrity.

Hybrid combinations containing natural products and antimicrobial drugs that interfere with bacterial and fungal biofilms

BACKGROUND

Biofilms contribute to the pathogenesis of many chronic and difficult-to eradicate infections whose treatment is complicated due to the intrinsic resistance to conventional antibiotics. As a consequence, there is an urgent need for strategies that can be used for the prevention and treatment of biofilm-associated infections. The combination therapy comprising an antimicrobial drug with a low molecular weight (MW) natural product and an antimicrobial drug (antifungal or antibacterial) appeared as a good alternative to eradicate biofilms.

PURPOSE

The aims of this review were to perform a literature search on the different natural products that have showed the ability of potentiating the antibiofilm capacity of antimicrobial drugs, to analyze which are the antimicrobial drugs most used in combination, and to have a look on the microbial species most used to prepare biofilms.

RESULTS

Seventeen papers, nine on combinations against antifungal biofilms and eight against antibacterial biofilms were collected. Within the text, the following topics have been developed: breaf history of the discovery of biofilms; stages in the development of a biofilm; the most used methodologies to assess antibiofilm-activity; the natural products with capacity of eradicating biofilms when acting alone; the combinations of low MW natural products with antibiotics or antifungal drugs as a strategy for eradicating microbial biofilms and a list of the low MW natural products that potentiate the inhibition capacity of antifungal and antibacterial drugs against biofilms.

CONCLUSIONS AND PERSPECTIVES

Regarding combinations against antifungal biofilms, eight over the nine collected works were carried out with in vitro studies while only one was performed with in vivo assays by using Caenorhabditis elegans nematode. All studies use biofilms of the Candida genus. A 67% of the potentiators were monoterpenes and sesquiterpenes and six over the nine works used FCZ as the antifungal drug. The activity of AmpB and Caspo was enhanced in one and two works respectively. Regarding combinations against bacterial biofilms, in vitro studies were performed in all works by using several different methods of higher variety than the used against fungal biofilms. Biofilms of both the gram (+) and gram (-) bacteria were prepared, although biofilm of Staphylococcus spp. were the most used in the collected works. Among the discovered potentiators of antibacterial drugs, 75% were terpenes, including mono, di- and triterpenes, and, among the atibacterial drugs, several structurally diverse types were used in the combinations: aminoglycosides, β-lactams, glucopeptides and fluoroquinolones. The potentiating capacity of natural products, mainly terpenes, on the antibiofilm effect of antimicrobial drugs opens a wide range of possibilities for the combination antimicrobial therapy. More in vivo studies on combinations of natural products with antimicrobial drugs acting against biofilms are highly required to cope the difficult to treat biofilm-associated infections.

Effect of yeasts on biodegradation potential of immobilized cultures of white rot fungi

The aim was to investigate the effect of yeast organisms on the degradation process by immobilized cultures of ligninolytic fungi. Immobilization was accomplished by 7-day colonization of polyamide mesh with mycelial fragments. Irpex lacteus decolorized >90% of the initial concentration of 150mgl^-1 of anthraquinone Remazol Brilliant Blue R dye in three subsequent decolorization cycles and the degradation capacity was not negatively affected by the presence of 10⁶Saccharomyces cerevisiae cells per ml in the mixed culture. The yeast was not able to degrade the dye. I. lacteus biofilm was also resistant to bacterial infection with E. coli. Inoculation of the yeast to pre-formed I. lacteus biofilm culture resulted in a reduction of fungal biomass by 27%. Levels of LiP, MnP and laccase of I. lacteus were not much influenced by S. cerevisiae or E. coli. Similar resilience of P. ostreatus biofilms was observed after exposure to yeast Issatchenkia occidentalis when the fungal degradation capacity measured with Reactive Orange 16 azo dye was maintained over two decolorization cycles. I. occidentalis did not degrade the dye under the conditions used. Formation of densely packed fungal biofilms with abundant extracellular polysaccharide was not impeded by the yeast. Increase of MnP and laccase levels attributable to the presence of I. occidentalis was observed.

Effect of selenite on the morphology and respiratory activity of Phanerochaete chrysosporium biofilms

The temporal and spatial effects of selenite (SeO3(2-)) on the physical properties and respiratory activity of Phanerochaete chrysosporium biofilms, grown in flow-cell reactors, were investigated using oxygen microsensors and confocal laser scanning microscopy (CLSM) imaging. Exposure of the biofilm to a SeO3(2-) load of 1.67mgSeL(-1)h(-1) (10mgSeL(-1) influent concentration), for 24h, resulted in a 20% reduction of the O2 flux, followed by a ∼10% decrease in the glucose consumption rate. Long-term exposure (4days) to SeO3(2-) influenced the architecture of the biofilm by creating a more compact and dense hyphal arrangement resulting in a decrease of biofilm thickness compared to fungal biofilms grown without SeO3(2-). To the best of our knowledge, this is the first time that the effect of SeO3(2-) on the aerobic respiratory activity on fungal biofilms is described.