Paracoccidioides spp.: the structural characterization of extracellular matrix, expression of glucan synthesis and associated genes and adhesins during biofilm formation

The genus Paracoccidioides includes Paracoccidioides lutzii and the Paracoccidioides brasiliensis complex, which comprises four phylogenetic species. A key feature distinguishing planktonic growth from biofilm is the presence of a 3D extracellular matrix (ECM). Therefore, in this study, we analyzed biofilm formation in different species of Paracoccidioides yeast phase, characterized the structural elements of the matrix of P. brasiliensis (Pb18), P. lutzii (Pl01 and 8334) and P. restrepiensis (339 and 192) and evaluated the expression of glucan genes, according to the stage of biofilm evolution for P. brasiliensis. The strains were cultivated in planktonic and biofilm form for 24-144 h. The fungi biomass and metabolic activity were determined by crystal violet and tetrazolium salt reduction (XTT) tests and colony-forming unit (CFU) by plating. The biofilm structure was designed using scanning electron microscopy and confocal laser scanning microscopy techniques. The extracellular matrix of P. brasiliensis and P. lutzii biofilms was extracted by sonication, and polysaccharides, proteins, and extracellular DNA (eDNA) were quantified. The RNA was extracted with the Trizol® reagent and quantified; then, the cDNA was synthesized to analyze the enolase expression, 14-3-3, FKS1, AGS1, GEL3, and KRE6 genes by real-time PCR. All strains of Paracoccidioides studied form a biofilm with more significant metabolic activity and biomass values in 144 h. The extracellular matrix of P. brasiliensis and P. lutzii had a higher content of polysaccharides in their composition, followed by proteins and eDNA in smaller quantities. The P. brasiliensis biofilm kinetics of formation showed greater expression of genes related to glucan's synthesis and its delivery to the external environment in addition adhesins during the biofilm's adhesion, initiation, and maturation. The GEL3 and enolase genes increased in expression within 24 h and during the biofilm maturation period, there was an increase in 14-3-3, AGS1, and FKS1. Furthermore, at 144 h, there was a decrease in KRE6 expression and an increase in GEL3. This study highlights the potential for biofilm formation for three species of Paracoccidioides and the main components of the extracellular matrix that can contribute to a better understanding of biofilm organization.

Polypeptides Targeting Paracoccidioides brasiliensis Drk1

Considering the toxicity of conventional therapeutic approaches and the importance of precise mechanistic targets, it is important to explore signaling pathways implicated in fungal pathobiology. Moreover, treatment of paracoccidioidomycosis, a systemic mycosis caused by a dimorphic fungus, requires prolonged therapeutic regimens. Among the numerous factors underpinning the establishment of Paracoccidioides spp. infection, the capacity to transition from the mycelial to the yeast form is of pivotal importance. The Drk1 protein of Paracoccidioides brasiliensis likely plays a decisive role in this morphological shift and subsequent virulence. We identified peptides with affinity for the PbDrk1 protein using the phage-display method and assessed the effects of these peptides on P. brasiliensis. The peptides were found to inhibit the phase transition of P. brasiliensis. Furthermore, a substantial proportion of these peptides prevented adhesion to pneumocytes. Although these peptides may not possess inherent antifungal properties, they can augment the effects of certain antifungal agents. Notably, the cell wall architecture of P. brasiliensis appears to be modulated by peptide intervention, resulting in a reduced abundance of glycosylated proteins and lipids. These peptides were also evaluated for their efficacy in a Galleria mellonella model and shown to contribute to enhanced larval survival rates. The role of PbDrk1, which is notably absent in mammals, should be further investigated to improve the understanding of its functional role in P. brasiliensis, which may be helpful for designing novel therapeutic modalities.

Alternative Non-Mammalian Animal and Cellular Methods for the Study of Host-Fungal Interactions

In the study of fungal pathogenesis, alternative methods have gained prominence due to recent global legislation restricting the use of mammalian animals in research. The principle of the 3 Rs (replacement, reduction, and refinement) is integrated into regulations and guidelines governing animal experimentation in nearly all countries. This principle advocates substituting vertebrate animals with other invertebrate organisms, embryos, microorganisms, or cell cultures. This review addresses host-fungus interactions by employing three-dimensional (3D) cultures, which offer more faithful replication of the in vivo environment, and by utilizing alternative animal models to replace traditional mammals. Among these alternative models, species like Caenorhabditis elegans and Danio rerio share approximately 75% of their genes with humans. Furthermore, models such as Galleria mellonella and Tenebrio molitor demonstrate similarities in their innate immune systems as well as anatomical and physiological barriers, resembling those found in mammalian organisms.

Green Chromatographic Methods and in Vitro Pharmacological Analysis of Varronia curassavica Leaf Derivatives

Varronia curassavica displays anti-inflammatory, antiulcerogenic, and antioxidant activities. Herein, we employed new UHPLC -UV green chromatographic methods for the analysis of in vitro antioxidant and anti-inflammatory activities of V. curassavica and its embryotoxicity in Zebrafish. Cordialin A, brickellin, and artemetin were purified from the ethanol (EtOH) extract of V. Curassavica leaves and identified using spectrometric techniques. In line with Green Analytical Chemistry principles, the proposed UHPLC methods involve the use of ethanol as organic modifier with low mobile phase consumption, and without sample pretreatment (OLE-UHPLC-UV). The application of the Agree and HPLC-EAT tools for greenness assessment yielded this pattern: HPLC-UV (reference) Collapse

Key Words

• Varronia curassavica
• anti-inflammatory
• antioxidant
• embryotoxicity
• green chemistry

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MESH Headings

• Animals
• Plant Extracts/chemistry
• Antioxidants/chemistry
• Zebrafish
• Anti-Inflammatory Agents/pharmacology
• Plant Leaves/chemistry
• Ethanol

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Grants

• Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES)
• #465637/2014-0 National Institute of Science and Technology on Biodiversity and Natural Products - INCT-BioNat

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Affiliation(s)

Isabela Jacob Moro Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Flávio Alexandre Carvalho Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Juhan Augusto Scardelato Pereira Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Gabriela Brasil Romão Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
André Faibicher Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Winner Duque Rodrigues Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Renata Pires Assis Department of Clinical Analysis, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Iguatemy Lourenço Brunetti Department of Clinical Analysis, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Junya de Lacorte Singulani Department of Clinical Analysis, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
Ana Marisa Fusco-Almeida Department of Clinical Analysis, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil
André Gonzaga Dos Santos Department of Drugs and Medicines, São Paulo State University (Unesp), School of Pharmaceutical Sciences, Araraquara-Jaú Road, Km 01, s/n, 14.801-903, Araraquara, SP, Brazil

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Alginate-Based 3D A549 Cell Culture Model to Study Paracoccidioides Infection

A three-dimensional (3D) lung aggregate model based on sodium alginate scaffolds was developed to study the interactions between Paracoccidioides brasiliensis (Pb) and lung epithelial cells. The suitability of the 3D aggregate as an infection model was examined using cell viability (cytotoxicity), metabolic activity, and proliferation assays. Several studies exemplify the similarity between 3D cell cultures and living organisms, which can generate complementary data due to the greater complexity observed in these designed models, compared to 2D cell cultures. A 3D cell culture system of human A549 lung cell line plus sodium alginate was used to create the scaffolds that were infected with Pb18. Our results showed low cytotoxicity, evidence of increased cell density (indicative of cell proliferation), and the maintenance of cell viability for seven days. The confocal analysis revealed viable yeast within the 3D scaffold, as demonstrated in the solid BHI Agar medium cultivation. Moreover, when ECM proteins were added to the alginate scaffolds, the number of retrieved fungi was significantly higher. Our results highlight that this 3D model may be promising for in vitro studies of host-pathogen interactions.

Membranolytic Activity Profile of Nonyl 3,4-Dihydroxybenzoate: A New Anti-Biofilm Compound for the Treatment of Dermatophytosis

The ability of dermatophytes to live in communities and resist antifungal drugs may explain treatment recurrence, especially in onychomycosis. Therefore, new molecules with reduced toxicity that target dermatophyte biofilms should be investigated. This study evaluated nonyl 3,4-dihydroxybenzoate (nonyl) susceptibility and mechanism of action on planktonic cells and biofilms of T. rubrum and T. mentagrophytes. Metabolic activities, ergosterol, and reactive oxygen species (ROS) were quantified, and the expression of genes encoding ergosterol was determined by real-time PCR. The effects on the biofilm structure were visualized using confocal electron microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). T. rubrum and T. mentagrophytes biofilms were susceptible to nonyl and resistant to fluconazole, griseofulvin (all strains), and terbinafine (two strains). The SEM results revealed that nonyl groups seriously damaged the biofilms, whereas synthetic drugs caused little or no damage and, in some cases, stimulated the development of resistance structures. Confocal microscopy showed a drastic reduction in biofilm thickness, and transmission electron microscopy results indicated that the compound promoted the derangement and formation of pores in the plasma membrane. Biochemical and molecular assays indicated that fungal membrane ergosterol is a nonyl target. These findings show that nonyl 3,4-dihydroxybenzoate is a promising antifungal compound.

Nanotechnology-Based Approaches for Voriconazole Delivery Applied to Invasive Fungal Infections

Invasive fungal infections increase mortality and morbidity rates worldwide. The treatment of these infections is still limited due to the low bioavailability and toxicity, requiring therapeutic monitoring, especially in the most severe cases. Voriconazole is an azole widely used to treat invasive aspergillosis, other hyaline molds, many dematiaceous molds, Candida spp., including those resistant to fluconazole, and for infections caused by endemic mycoses, in addition to those that occur in the central nervous system. However, despite its broad activity, using voriconazole has limitations related to its non-linear pharmacokinetics, leading to supratherapeutic doses and increased toxicity according to individual polymorphisms during its metabolism. In this sense, nanotechnology-based drug delivery systems have successfully improved the physicochemical and biological aspects of different classes of drugs, including antifungals. In this review, we highlighted recent work that has applied nanotechnology to deliver voriconazole. These systems allowed increased permeation and deposition of voriconazole in target tissues from a controlled and sustained release in different routes of administration such as ocular, pulmonary, oral, topical, and parenteral. Thus, nanotechnology application aiming to delivery voriconazole becomes a more effective and safer therapeutic alternative in the treatment of fungal infections.

Multiple Tolerization Subtractive Immunization (MTSI) Protocol: Effects on Mice and Monoclonal Antibody Specificity

Monoclonal antibodies (mAbs) have been a valuable tool to elucidate several biological processes, such as stem cell differentiation and cancer, and contributed to virtually all areas of biomedical sciences. Yet, it remains a challenge to obtain mAbs specific to poorly expressed epitopes, or to epitopes that are actually involved in important biological phenomena, such as cell differentiation and metastasis. Drug-induced subtractive immunization, and recently the multiple tolerization subtractive immunization (MTSI) technique, reported by our group, have the potential to level up the field, as they direct the host´s immune response towards these epitopes. However, due to cyclophosphamide (CY) treatment, high mice mortality can be observed, and only a few data are available on how these techniques affect the immune system of mice. Tolerogen and immunogen cells, RWPE-1 and PC-3 cells, respectively, were individually seeded at 2 × 104 cells/cm2, and then adjusted to 2 × 106 cells per mouse before immunization, which was conducted in a subtractive approach (MTSI) with CY. Immunosuppression of mice was recorded via total white blood counting, as well the reactivity of circulating polyclonal antibodies (pAbs). General parameters, including weight, physical appearance, and behavior on mice subjected to three different concentrations of CY were recorded. mAbs were obtained using classical hybridoma techniques, using the spleen of immunized mice. After purification, antibodies were characterized by Western blotting, and Indirect immunofluorescence. In conclusion, all CY dosage were efficient in creating an immunosuppression state, but only the 100 mg/kg body weight was feasible, as the others resulted in extensive mice mortality. pAbs obtained in the peripheral blood of mice showed more reactivity towards tumor cells. MAbs 2-7A50 and 2-5C11 recognized antigens from tumor cells, but not from their non-tumor counterparts, as shown in western blotting and immunofluorescence assays. MTSI technique was successful in generating mAbs that recognize tumor-specific antigens.

Mycobacterium tuberculosis and Paracoccidioides brasiliensis Formation and Treatment of Mixed Biofilm In Vitro

Co-infection of Mycobacterium tuberculosis and Paracoccidioides brasiliensis, present in 20% in Latin America, is a public health problem due to a lack of adequate diagnosis. These microorganisms are capable of forming biofilms, mainly in immunocompromised patients, which can lead to death due to the lack of effective treatment for both diseases. The present research aims to show for the first time the formation of mixed biofilms of M. tuberculosis and P. brasiliensis (Pb18) in vitro, as well as to evaluate the action of 3’hydroxychalcone (3’chalc) -loaded nanoemulsion (NE) (NE3’chalc) against monospecies and mixed biofilms, the formation of mixed biofilms of M. tuberculosis H37Rv (ATCC 27294), 40Rv (clinical strains) and P. brasiliensis (Pb18) (ATCC 32069), and the first condition of formation (H37Rv +Pb18) and (40Rv + Pb18) and second condition of formation (Pb18 + H37Rv) with 45 days of total formation time under both conditions. The results of mixed biofilms (H37Rv + Pb18) and (40Rv + Pb18), showed an organized network of M. tuberculosis bacilli in which P. brasiliensis yeasts are connected with a highly extracellular polysaccharide matrix. The (Pb18 + H37Rv) showed a dense biofilm with an apparent predominance of P. brasiliensis and fragments of M. tuberculosis. PCR assays confirmed the presence of the microorganisms involved in this formation. The characterization of NE and NE3’chalc displayed sizes from 145.00 ± 1.05 and 151.25 ± 0.60, a polydispersity index (PDI) from 0.20± 0.01 to 0.16± 0.01, and zeta potential -58.20 ± 0.92 mV and -56.10 ± 0.71 mV, respectively. The atomic force microscopy (AFM) results showed lamellar structures characteristic of NE. The minimum inhibitory concentration (MIC) values of 3’hidroxychalcone (3’chalc) range from 0.97- 7.8 µg/mL and NE3’chalc from 0.24 - 3.9 µg/mL improved the antibacterial activity when compared with 3’chalc-free, no cytotoxicity. Antibiofilm assays proved the efficacy of 3’chalc-free incorporation in NE. These findings contribute to a greater understanding of the formation of M. tuberculosis and P. brasiliensis in the mixed biofilm. In addition, the findings present a new possible NE3’chalc treatment alternative for the mixed biofilms of these microorganisms, with a high degree of relevance due to the lack of other treatments for these comorbidities.

Drk1, a Dimorphism Histidine Kinase, Contributes to Morphology, Virulence, and Stress Adaptation in Paracoccidioides brasiliensis

P. brasiliensis is a thermally dimorphic fungus belonging to Paracoccidioides complex, causative of a systemic, endemic mycosis limited to Latin American countries. Signal transduction pathways related to important aspects as surviving, proliferation according to the biological niches are linked to the fungal pathogenicity in many species, but its elucidation in P. brasiliensis remains poorly explored. As Drk1, a hybrid histidine kinase, plays regulators functions in other dimorphic fungi species, mainly in dimorphism and virulence, here we investigated its importance in P. brasilensis. We, therefore generated the respective recombinant protein, anti-PbDrk1 polyclonal antibody and a silenced strain. The Drk1 protein shows a random distribution including cell wall location that change its pattern during osmotic stress condition; moreover the P. brasiliensis treatment with anti-PbDrk1 antibody, which does not modify the fungus's viability, resulted in decreased virulence in G. mellonella model and reduced interaction with pneumocytes. Down-regulating PbDRK1 yielded phenotypic alterations such as yeast cells with more elongated morphology, virulence attenuation in G. mellonella infection model, lower amount of chitin content, increased resistance to osmotic and cell wall stresses, and also caspofungin, and finally increased sensitivity to itraconazole. These observations highlight the importance of PbDrk1 to P. brasiliensis virulence, stress adaptation, morphology, and cell wall organization, and therefore it an interesting target that could help develop new antifungals.

2-Hydroxychalcone as a Potent Compound and Photosensitizer Against Dermatophyte Biofilms

Dermatophytes, fungi that cause dermatophytosis, can invade keratinized tissues in humans and animals. The biofilm-forming ability of these fungi was described recently, and it may be correlated with the long treatment period and common recurrences of this mycosis. In this study, we evaluated the anti-dermatophytic and anti-biofilm activity of 2-hydroxychalcone (2-chalcone) in the dark and photodynamic therapy (PDT)-mediated and to determine its mechanism of action. Trichophyton rubrum and Trichophyton mentagrophytes strains were used in the study. The antifungal susceptibility test of planktonic cells, early-stage biofilms, and mature biofilms were performed using colorimetric methods. Topographies were visualized by scanning electron microscopy (SEM). Human skin keratinocyte (HaCat) monolayers were also used in the cytotoxicity assays. The mechanisms of action of 2-chalcone in the dark and under photoexcitation were investigated using confocal microscopy and the quantification of ergosterol, reactive oxygen species (ROS), and death induction by apoptosis/necrosis. All strains, in the planktonic form, were inhibited after treatment with 2-chalcone (minimum inhibitory concentration (MIC) = 7.8-15.6 mg/L), terbinafine (TRB) (MIC = 0.008–0.03 mg/L), and fluconazole (FLZ) (1–512 mg/L). Early-stage biofilm and mature biofilms were inhibited by 2-chalcone at concentrations of 15.6 mg/L and 31.2 mg/L in all tested strains. However, mature biofilms were resistant to all the antifungal drugs tested. When planktonic cells and biofilms (early-stage and mature) were treated with 2-chalcone-mediated PDT, the inhibitory concentrations were reduced by four times (2–7.8 mg/L). SEM images of biofilms treated with 2-chalcone showed cell wall collapse, resulting from a probable extravasation of cytoplasmic content. The toxicity of 2-chalcone in HaCat cells showed higher IC₅₀ values in the dark than under photoexcitation. Further, 2-chalcone targets ergosterol in the cell and promotes the generation of ROS, resulting in cell death by apoptosis and necrosis. Overall, 2-chalcone-mediated PDT is a promising and safe drug candidate against dermatophytes, particularly in anti-biofilm treatment.

Understanding the mechanism of action of peptide (p-BthTX-I)2 derived from C-terminal region of phospholipase A2 (PLA2)-like bothropstoxin-I on Gram-positive and Gram-negative bacteria

Based on the antimicrobial activity of bothropstoxin-I (BthTX-I) and on the premise that a C-terminal peptide of Lys49 myotoxin can reproduce the antimicrobial activity of the parent protein, we aimed to study the mechanism of action of a peptide derived from the C-terminal region of the myotoxin BthTX-I [(p-BthTX-I)₂, sequence: KKYRYHLKPFCKK, disulfide-linked dimer] against Gram-positive and Gram-negative bacteria. Fluorescence quenching technique showed that the carboxyfluorescein labeled-peptide [CF-(p-BthTX-I)₂] when incubated with E. coli displayed a superior penetration activity than when incubated with S. aureus. Cell death induced by the peptide (p-BthTX-I)₂ showed a loss of membrane integrity in E. coli and S. aureus; however, the mechanisms of cell death were different, characterized by the presence of necrosis-like and apoptosis-like deaths, respectively. Scanning electron microscopy studies in E. coli and S. aureus showed morphological changes in the cells, with superficial deformities, appearance of wrinkles and bubbles, and formation of vesicles. Our results demonstrate that the mechanism of action of the peptide (p-BthTX-I)₂ is different in Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. Knowledge of the mechanism of action of these peptides is important, since they are promising prototypes for new antimicrobial drugs.

Rhamnolipid-Based Liposomes as Promising Nano-Carriers for Enhancing the Antibacterial Activity of Peptides Derived from Bacterial Toxin-Antitoxin Systems

Background

Antimicrobial resistance poses substantial risks to human health. Thus, there is an urgent need for novel antimicrobial agents, including alternative compounds, such as peptides derived from bacterial toxin-antitoxin (TA) systems. ParELC3 is a synthetic peptide derived from the ParE toxin reported to be a good inhibitor of bacterial topoisomerases and is therefore a potential antibacterial agent. However, ParELC3 is inactive against bacteria due to its inability to cross the bacterial membranes. To circumvent this limitation we prepared and used rhamnolipid-based liposomes to carry and facilitate the passage of ParELC3 through the bacterial membrane to reach its intracellular target - the topoisomerases.

Methods and Results

Small unilamellar liposome vesicles were prepared by sonication from three formulations that included 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and cholesterol. ParELC3 was loaded with high efficiency into the liposomes. Characterization by DLS and TEM revealed the appropriate size, zeta potential, polydispersity index, and morphology. In vitro microbiological experiments showed that ParELC3 loaded-liposomes are more efficient (29 to 11 µmol·L⁻¹) compared to the free peptide (>100 µmol·L⁻¹) at inhibiting the growth of standard E. coli and S. aureus strains. RL liposomes showed high hemolytic activity but when prepared with POPC and Chol this activity had a significant reduction. Independently of the formulation, the vesicles had no detectable cytotoxicity to HepG2 cells, even at the highest concentrations tested (1.3 mmol·L⁻¹ and 50 µmol·L⁻¹ for rhamnolipid and ParELC3, respectively).

Conclusion

The present findings suggest the potential use of rhamnolipid-based liposomes as nanocarrier systems to enhance the bioactivity of peptides.

Heat Shock Protein 60, Insights to Its Importance in Histoplasma capsulatum: From Biofilm Formation to Host-Interaction

Heat shock proteins (Hsps) are among the most widely distributed and evolutionary conserved proteins, acting as essential regulators of diverse constitutive metabolic processes. The Hsp60 of the dimorphic fungal Histoplasma capsulatum is the major surface adhesin to mammalian macrophages and studies of antibody-mediated protection against H. capsulatum have provided insight into the complexity involving Hsp60. However, nothing is known about the role of Hsp60 regarding biofilms, a mechanism of virulence exhibited by H. capsulatum. Considering this, the present study aimed to investigate the influence of the Hsp60 on biofilm features of H. capsulatum. Also, the non-conventional model Galleria mellonella was used to verify the effect of this protein during in vivo interaction. The use of invertebrate models such as G. mellonella is highly proposed for the evaluation of pathogenesis, immune response, virulence mechanisms, and antimicrobial compounds. For that purpose, we used a monoclonal antibody (7B6) against Hsp60 and characterized the biofilm of two H. capsulatum strains by metabolic activity, biomass content, and images from scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). We also evaluated the survival rate of G. mellonella infected with both strains under blockage of Hsp60. The results showed that mAb 7B6 was effective to reduce the metabolic activity and biomass of both H. capsulatum strains. Furthermore, the biofilms of cells treated with the antibody were thinner as well as presented a lower amount of cells and extracellular polymeric matrix compared to its non-treated controls. The blockage of Hsp60 before fungal infection of G. mellonella larvae also resulted in a significant increase of the larvae survival compared to controls. Our results highlight for the first time the importance of the Hsp60 protein to the establishment of the H. capsulatum biofilms and the G. mellonella larvae infection. Interestingly, the results with Hsp60 mAb 7B6 in this invertebrate model suggest a pattern of fungus-host interaction different from those previously found in a murine model, which can be due to the different features between insect and mammalian immune cells such as the absence of Fc receptors in hemocytes. However further studies are needed to support this hypothesis

In Vitro and In Vivo Effect of Peptides Derived from 14-3-3 Paracoccidioides spp. Protein

Background: Paracoccidioidomycosis (PCM) is a chronic disease that causes sequelae and requires prolonged treatment; therefore, new therapeutic approaches are necessary. In view of this, three peptides from Paracoccidioides brasiliensis 14-3-3 protein were selected based on its immunogenicity and therapeutic potential. Methods: The in vitro antifungal activity and cytotoxicity of the 14-3-3 peptides were evaluated. The influence of the peptides in immunological and survival aspects was evaluated in vivo, using Galleria mellonella and the expression of antimicrobial peptide genes in Caenorhabditis elegans. Results: None of the peptides were toxic to HaCaT (skin keratinocyte), MRC-5 (lung fibroblast), and A549 (pneumocyte) cell lines, and only P1 exhibited antifungal activity against Paracoccidioides spp. The peptides could induce an immune response in G. mellonella. Moreover, the peptides caused a delay in the death of Paracoccidioides spp. infected larvae. Regarding C. elegans, the three peptides were able to increase the expression of the antimicrobial peptides. These peptides had essential effects on different aspects of Paracoccidioides spp. infection showing potential for a therapeutic vaccine. Future studies using mammalian methods are necessary to validate our findings.

Dynamics of Mono- and Dual-Species Biofilm Formation and Interactions Between Paracoccidioides brasiliensis and Candida albicans

The oral cavity is a highly diverse microbial environment in which microorganisms interact with each other, growing as biofilms on biotic and abiotic surfaces. Understanding the interaction among oral microbiota counterparts is pivotal for clarifying the pathogenesis of oral diseases. Candida spp. is one of the most abundant fungi in the oral mycobiome with the ability to cause severe soft tissue lesions under certain conditions. Paracoccidioides spp., the causative agent of paracoccidioidomycosis, may also colonize the oral cavity leading to soft tissue damage. It was hypothesized that both fungi can interact with each other, increasing the growth of the biofilm and its virulence, which in turn can lead to a more aggressive infectivity. Therefore, this study aimed to evaluate the dynamics of mono- and dual-species biofilm growth of Paracoccidioides brasiliensis and Candida albicans and their infectivity using the Galleria mellonella model. Biomass and fungi metabolic activity were determined by the crystal violet and the tetrazolium salt reduction tests (XTT), respectively, and the colony-forming unit (CFU) was obtained by plating. Biofilm structure was characterized by both scanning electronic- and confocal laser scanning- microscopy techniques. Survival analysis of G. mellonella was evaluated to assess infectivity. Our results showed that dual-species biofilm with P. brasiliensis plus C. albicans presented a higher biomass, higher metabolic activity and CFU than their mono-species biofilms. Furthermore, G. mellonella larvae infected with P. brasiliensis plus C. albicans presented a decrease in the survival rate compared to those infected with P. brasiliensis or C. albicans, mainly in the form of biofilms. Our data indicate that P. brasiliensis and C. albicans co-existence is likely to occur on oral mucosal biofilms, as per in vitro and in vivo analysis. These data further widen the knowledge associated with the dynamics of fungal biofilm growth that can potentially lead to the discovery of new therapeutic strategies for these infections.

A Two-Way Road: Antagonistic Interaction Between Dual-Species Biofilms Formed by Candida albicans/Candida parapsilosis and Trichophyton rubrum

Dermatomycoses include superficial fungal infections of the skin and its appendages. Trichophyton rubrum, Candida albicans, and Candida parapsilosis are some of the most prevalent species that cause dermatomycoses. Several studies show a variable predominance of Candida spp. in relation to dermatophytes, especially in onychomycosis and the possibility of isolating both from the same site. The ability of dermatophytes to form biofilms recently been explored and there is currently no evidence on the involvement of these filamentous fungi in multi-species biofilms. Thus, this study aims to investigate the probable dual-species interaction between T. rubrum and C. albicans and T. rubrum and C. parapsilosis biofilms, considering variable formation conditions, as well as the susceptibility of these dual-species biofilms against terbinafine and efinaconazole. Three conditions of formation of dual-species biofilms were tested: (a) the suspensions of T. rubrum and Candida albicans or C. parapsilosis placed together; (b) suspensions of C. albicans and C. parapsilosis added the pre-adhesion of T. rubrum biofilms; (c) after the maturation of T. rubrum sessile cells. In the first and second conditions, the quantification of metabolic activities, biomass, and polysaccharide materials of mixed biofilms tended to resemble Candida monospecies biofilms. In the third condition, the profiles were modified after the addition of Candida, suggesting that T. rubrum biofilms served as substrate for the development of Candida biofilms. Scanning electron microscopy showed Candida predominance, however, numerous blastoconidia were noted, most evident in the conditions under which Candida was added after the pre-adhesion and maturation of T. rubrum biofilms. Despite the predominance of Candida, the presence of T. rubrum appears to inhibit C. albicans filamentation and C. parapsilosis development, confirming an antagonistic interaction. Fungal burden assays performed when the biofilms were formed together confirmed Candida predominance, as well as susceptibility to antifungals. Further studies will be needed to identify the components of the Candida and T. rubrum biofilm supernatants responsible for inhibiting dermatophyte growth and C. albicans filamentation.

Fungal-host interactions: insights into microRNA in response to Paracoccidioides species

BACKGROUND

Paracoccidioides spp. causes paracoccidioidomycosis (PCM), an important and frequent systemic mycosis that occurs in Latin America. The infectious process begins with contact between the fungus and lung cells, and the molecular pattern of this interaction is currently poorly understood. MicroRNAs (miRNAs) are small non-coding RNAs that regulate the gene expression in many biological processes, including in the infections.

OBJECTIVE

This study aimed to analyse the expression of miRNAs in lung cells as response to infection by Paracoccidioides spp.

METHODS

A quantitative real-time polymerase chain reaction (RT-qPCR) based screening was employed to verify differentially expressed miRNAs in human lung cells infected with three different species; Paracoccidioides lutzii, Paracoccidioides americana, and Paracoccidioides brasiliensis. Furthermore, the in silico predictions of target genes and pathways for miRNAs were obtained.

FINDINGS

The results showed that miRNAs identified in the lung cells were different according to the species studied. However, based on the predicted targets, the potential signaling pathways regulated by miRNAs are common and related to adhesion, actin cytoskeleton rearrangement, apoptosis, and immune response mediated by T cells and TGF-β.

MAIN CONCLUSIONS

In summary, this study showed the miRNAs pattern of epithelial cells in response to infection by Paracoccidioides species and the potential role of these molecules in the regulation of key pathogenesis mechanisms of PCM.

Biofilm Formation by Histoplasma capsulatum in Different Culture Media and Oxygen Atmospheres

Histoplasma capsulatum is a dimorphic fungus that causes an important systemic mycosis called histoplasmosis. It is an infectious disease with high prevalence and morbidity that affects the general population. Recently, the ability of these fungi to form biofilms, a phenotype that can induce resistance and enhance virulence, has been described. Despite some efforts, data regarding the impact of nutrients and culture media that affect the H. capsulatum biofilm development in vitro are not yet available. This work aimed to study H. capsulatum biofilms, by checking the influence of different culture media and oxygen atmospheres in the development of these communities. The biofilm formation by two strains (EH-315 and G186A) was characterized under different culture media: [Brain and Heart Infusion (BHI), Roswell Park Memorial Institute (RPMI) with 2% glucose, Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% fetal bovine serum and nutrient medium HAM-F12 (HAM-F12) supplemented with glucose (18.2 g/L), glutamic acid (1 g/L), HEPES (6 g/L) and L-cysteine (8.4 mg/L)] and oxygen atmospheres (aerobiosis and microaerophilia), using the XTT reduction assay to quantify metabolic activities, crystal violet staining for biomass, safranin staining for the quantification of polysaccharide material and scanning electron microscopy (SEM) for the observation of topographies. Results indicated that although all culture mediums have stimulated the maturation of the communities, HAM-F12 provided the best development of biomass and polysaccharide material when compared to others. Regarding the oxygen atmospheres, both stimulated an excellent development of the communities, however in low oxygen conditions an exuberant amount of extracellular matrix was observed when compared to biofilms formed in aerobiosis, mainly in the HAM-F12 media. SEM images showed yeasts embedded by an extracellular matrix in several points, corroborating the colorimetric assays. However, biofilms formed in BHI, RPMI, and DMEM significantly induced yeast to hyphae reversal, requiring further investigation. The results obtained so far contribute to in vitro study of biofilms formed by these fungi and show that nutrition promoted by different media modifies the development of these communities. These data represent advances in the field of biofilms and contribute to future studies that can prove the role of these communities in the fungi-host interaction.

Incorporation of Nonyl 3,4-Dihydroxybenzoate Into Nanostructured Lipid Systems: Effective Alternative for Maintaining Anti-Dermatophytic and Antibiofilm Activities and Reducing Toxicity at High Concentrations

Dermatophytosis is the most common mycosis worldwide, affecting approximately 20 to 25% of the population, regardless of gender, race, color, and age. Most antifungal agents used for the treatment of dermatophytosis belong to the azole and allylamine classes. Dermatophytes are reported to be resistant to most commercial drugs, especially microbial biofilms, in addition to their considerable toxicity. It should be emphasized the importance of looking for new molecules with reduced toxicity, as well as new targets and mechanisms of action. This work aims to incorporate nonyl 3,4-dihydroxybenzoate, a potent fungicide compound against planktonic cells and dermatophyte biofilms in nanostructured lipid systems (NLS), in order to reduce toxicity in high concentrations, improve its solubility and maintain its effectiveness. The compound was incorporated into NLS constituted by cholesterol, mixture of polyoxyethylene (23) lauryl ether (Brij^®98) and soybean phosphatidylcholine (Epikuron^® 200)], 2: 1 ratio and PBS (phosphate-buffered saline). The characterization of the incorporation was performed. Susceptibility tests were conducted according to document M38-A2 by CLSI (2008). The toxicity of the NLS compound was evaluated in HaCaT cell lines by the sulforhodamine B method and in alternative models Caenorhabditis elegans and zebrafish. Finally, its efficacy was evaluated against the mature Trichophyton rubrum and Trichophyton mentagrophytes biofilms. NLS and nonyl 3,4-dihydroxybenzoate loaded into NLS displayed sizes ranging from 137.8 ± 1.815 to 167.9 ± 4.070 nm; the polydispersity index (PDI) varying from 0.331 ± 0.020 to 0.377 ± 0.004 and zeta potential ranging from −1.46 ± 0.157 to −4.63 ± 0.398 mV, respectively. Polarized light microscopy results confirmed the formation of NLS of the microemulsion type. Nonyl incorporated into NLS showed minimum inhibitory concentration (MIC) values, ranging from 2 to 15.6 mg/L. The toxicity tests presented cell viability higher than 80% in all tested concentrations, as well as, a significantly increased of the survival of Caenorhabditis elegans and zebrafish models. Anti-biofilm tests proved the efficacy of the incorporation. These findings contribute significantly to the search for new antifungals and allow the systemic administration of the compound, since the incorporation can increase the solubility of non-polar compounds, improve bioavailability, effectiveness and reduce toxicity.

Paracoccidioides brasiliensis 14-3-3 protein is important for virulence in a murine model

The Paracoccidioides brasiliensis strain downregulated the expression of adhesin Pb14-3-3 (Pb14-3-3 aRNA) was evaluated in a murine model of paracoccidioidomycosis (PCM). Pb14-3-3 aRNA displays attenuated virulence and triggered the formation of fewer granulomas by lowering the fungal burden in the lungs. Additionally, the Pb14-3-3 aRNA showed more elongated yeast cells and less ability to induce pneumocytes apoptosis in vitro. Our results show that 14-3-3 is an important virulence factor in P. brasiliensis-induced pulmonary infection.

Methodologies and Applications of Proteomics for Study of Yeast Strains: An Update

Yeasts are one of the mostly used microorganisms as models in several studies. A wide range of applications in different processes can be attributed to their intrinsic characteristics. They are eukaryotes and therefore valuable expression hosts that require elaborate post-translational modifications. Their arsenal of proteins has become a valuable biochemical tool for the catalysis of several reactions of great value to the food (beverages), pharmaceutical and energy industries. Currently, the main challenge in systemic yeast biology is the understanding of the expression, function and regulation of the protein pool encoded by such microorganisms. In this review, we will provide an overview of the proteomic methodologies used in the analysis of yeasts. This research focuses on the advantages and improvements in their most recent applications with an understanding of the functionality of the proteins of these microorganisms, as well as an update of the advances of methodologies employed in mass spectrometry.

Applications of Invertebrate Animal Models to Dimorphic Fungal Infections

Dimorphic fungi can be found in the yeast form during infection and as hyphae in the environment and are responsible for a large number of infections worldwide. Invertebrate animals have been shown to be convenient models in the study of fungal infections. These models have the advantages of being low cost, have no ethical issues, and an ease of experimentation, time-efficiency, and the possibility of using a large number of animals per experiment compared to mammalian models. Invertebrate animal models such as Galleria mellonella, Caenorhabditis elegans, and Acanthamoebacastellanii have been used to study dimorphic fungal infections in the context of virulence, innate immune response, and the efficacy and toxicity of antifungal agents. In this review, we first summarize the features of these models. In this aspect, the growth temperature, genome sequence, availability of different strains, and body characteristics should be considered in the model choice. Finally, we discuss the contribution and advances of these models, with respect to dimorphic fungi Paracoccidioides spp., Histoplasma capsulatum, Blastomyces dermatitidis, Sporothrix spp., and Talaromyces marneffei (Penicillium marneffei).

Transcriptional profile of a bioethanol production contaminant Candida tropicalis

The fermentation process is widely used in the industry for bioethanol production. Even though it is widely used, microbial contamination is unpredictable and difficult to control. The problem of reduced productivity is directly linked to competition for nutrients during contamination. Yeasts representing the Candida species are frequently isolated contaminants. Elucidating the behavior of a contaminant during the fermentation cycle is essential for combatting the contamination. Consequently, the aim of the current study was to better understand the functional and transcriptional behavior of a contaminating yeast Candida tropicalis. We used a global RNA sequencing approach (RNA-seq/MiSeq) to analyze gene expression. Genes with significantly repressed or induced expression, and related to the fermentations process, such as sugar transport, pyruvate decarboxylase, amino acid metabolism, membrane, tolerance to high concentrations of ethanol and temperatures, nutrient suppression), and transcription-linked processes, were identified. The expression pattern suggested that the functional and transcriptional behavior of the contaminating yeast during fermentation for bioethanol production is similar to that of the standard yeast Saccharomyces cerevisiae. In addition, the analysis confirmed that C. tropicalis is an important contaminant of the alcoholic fermentation process, generating bioethanol and viability through its tolerance to all the adversities of a fermentation process essential for the production of bioethanol. According on the gene expression profile, many of these mechanisms are similar to those of S. cerevisiae strains currently used for bioethanol production. These mechanisms can inform studies on antimicrobials, to combat yeast contamination during industrial bioethanol production.

Evaluation of Caenorhabditis elegans as a host model for Paracoccidioides brasiliensis and Paracoccidioides lutzii

Paracoccidioidomycosis is a systemic fungal infection affecting mainly Latin American countries that is caused by Paracoccidioides brasiliensis and Paracoccidioides lutzii. During the study of fungal pathogenesis, in vivo studies are crucial to understand the overall mechanisms involving the infection as well as to search for new therapeutic treatments and diagnosis. Caenorhabditis elegans is described as an infection model for different fungi species and a well-characterized organism to study the innate immune response. This study evaluates C. elegans as an infection model for Paracoccidioides spp. It was observed that both species do not cause infection in C. elegans, as occurs with Candida albicans, and one possible explanation is that the irregular size and shape of Paracoccidioides spp. difficult the ingestion of these fungi by the nematode. Besides this difficulty in the infection, we could observe that the simple exposition of C. elegans to Paracoccidioides species was able to trigger a distinct pattern of expression of antimicrobial peptide genes. The expression of cnc-4, nlpl-27 and nlp-31 was superior after the exposure to P. brasiliensis in comparison to P. lutzii (P < 0.05), and these findings demonstrate important differences regarding innate immune response activation caused by the two species of the Paracoccidioides genus.

Evaluation of cytotoxicity features of antimicrobial peptides with potential to control bacterial diseases of citrus

Antimicrobial peptides (AMPs) can be found in various organisms, and could be considered an alternative for pesticides used to control plant pathogens, including those affecting citrus. Brazil is the largest producer and exporter of frozen concentrated orange juice in the world. However, the citrus industry has been affected by several diseases such as citrus canker and huanglongbing (HLB), caused by the bacteria Xanthomonas citri subsp. citri (X.citri) and Candidatus Liberibacter asiaticus (CaLas), respectively. In order to control these pathogens, putative AMPs were prospected in databases containing citrus sequences. Furthermore, AMPs already reported in the literature were also used for in vitro and in vivo assays against X.citri. Since CaLas cannot be cultivated in vitro, surrogates as Sinorhizobium meliloti and Agrobacterium tumefaciens were used. This study reports the evaluation of six AMPs obtained from different sources, two of them from Citrus spp. (citrus-amp1 and citrus-amp2), three from amphibians (Hylin-a1, K⁰-W⁶-Hy-a1 and Ocellatin 4-analogue) and one from porcine (Tritrpticin). Peptides K⁰-W⁶-Hy-a1, Ocellatin 4-analogue, and citrus-amp1 showed bactericidal activity against X.citri and S. meliloti and bacteriostatic effect on A. tumefaciens. These results were confirmed for X.citri in planta. In addition cytotoxicity evaluations of these molecules were performed. The AMPs that showed the lowest hemolytic activities were Triptrpticin, citrus-amp1 and citrus-amp2. Citrus-amp1 and citrus-amp2 not presented toxicity in experiments using in vivo model, G. mellonella and U87 MG cells. To verify the interaction of these AMPs with bacteria and erythrocyte cell membranes, vesicles mimicking these cells were built. Citrus-amp1 and Tritrpticin exhibited higher affinity to bacterial membranes, while Ocellatin 4-analogue and Hylin-a1 showed higher affinity to erythrocyte membranes; exclude their use in citrus. This work demonstrates an essential alternative, trough AMPs obtained from Citrus spp., which can be feasibly used to control bacterial pathogens.

Multiple Tolerization Reduces Antibody Binding Against Tolerogen Cells: Implications for the Production of Monoclonal Antibodies

We report an immunization technique that can update the production of monoclonal antibodies (mAbs): the multiple tolerization subtractive immunization (MTSI). A total of 10 BALB/C mice were used. Animals in group 1 received one inoculation of RWPE-1 cells (nontumoral), followed by cyclophosphamide, and then received serial inoculations of nonirradiated PC3 cells (tumoral). Animals in group 2 received our MTSI protocol, as follows: one inoculation of RWPE-1 cells, followed by cyclophosphamide (Cy). This whole tolerization step was repeated three other times, with 14-day intervals between the last Cy exposure and the next RWPE-1 cell inoculation. Finally, the animals received the same nonirradiated PC3 cell exposure as group 1. Blood was taken from each animal, and their polyclonal sera individually tested against the nontumoral RWPE-1 cells in flow cytometry. We found out that, after the MTSI was employed, the serum of the immunized animals, in group 2, contained considerably less antibodies that reacted against the tolerogenic cells, compared with the serum of the animals that underwent regular subtractive immunization. We showed that, by repeating the tolerization cycles, the polyclonal antibodies produced by mice have a reduced specificity toward common/immunodominant epitopes present at nontumoral cells, and thus this technique can be readily used by others in studies involving murine mAb protocols.

Can passage in Galleria mellonella activate virulence factors of Paracoccidioides brasiliensis as in the murine model?

Paracoccidioidomycosis (PCM) is a fungal disease restricted to Latin countries, and its etiologic agents derive from the Paracoccidioides genus. Attenuation or loss of virulence in Paracoccidioides spp. following successive subculturing has been described. However, virulence can be recovered by passage in mammalian host. In this study, the recovery of adhesion of P. brasiliensis through passage in mice was compared to that in the insect Galleria mellonella. Analysis of in vitro fungal-host cell interaction, gene expression of adhesins, and analysis of the survival curves revealed that Galleria mellonella is useful for the reactivation of P. brasiliensis adhesion.

Antifungal activity of fluconazole-loaded natural rubber latex against Candida albicans

Aim: This work aimed to produce a membrane based on fluconazole-loaded natural rubber latex (NRL), and study their interaction, drug release and antifungal susceptibility against Candida albicans. Materials & methods: Fluconazole-loaded NRL membrane was obtained by casting method. Results: The Fourier Transform Infrared Spectroscopy showed no modifications either in NRL or fluconazole after the incorporation. Mechanical test presented low Young's modulus and high strain, indicating the membranes have sufficient elasticity for biomedical application. The bio-membrane was able to release the drug and inhibit the growth of C. albicans as demonstrated by disk diffusion and macrodilution assays. Conclusion: The biomembrane was able to release fluconazole and inhibit the growth of C. albicans, representing a promising biomaterial for skin application.

Anti-apoptotic effects of decyl gallate on the induction of apoptosis in A549 pneumocytes by Paracoccidioides brasiliensis gp43

Apoptosis is considered an escape mechanism from the host immune system for the fungus Paracoccidioides spp, and it serves as a vehicle for entry into macrophages without stimulating microbicidal activities. Recently, gp43 of P. brasiliensis was demonstrated to be involved in this process. Therefore, as a new therapeutic alternative, it is very important to study compounds that could reduce the modulation of the induction of apoptosis caused by this fungus. Decyl gallate (G14) is a known antifungal compound, and we decided to investigate its anti-apoptotic properties. Our results demonstrate that G14 was effective against apoptosis induced by gp43, as observed in epithelial cells, and led to a reduction in DNA damage, Bak down-regulation and Bcl-2 up-regulation. Together, these data show that G14 presents promising anti-apoptotic activity.

Enhanced immunization techniques to obtain highly specific monoclonal antibodies

Despite fast advances in genomics and proteomics, monoclonal antibodies (mAbs) are still a valuable tool for areas such as the evolution of basic research in stem cells and cancer, for immunophenotyping cell populations, diagnosing and prognosis of diseases, and for immunotherapy. To summarize different subtractive immunization approaches successfully used for the production of highly specific antibodies, we identified scientific articles in NCBI PubMed using the following search terms: subtractive immunization, monoclonal antibody, tolerization, neonatal, high-zone tolerance, masking immunization. Patent records were also consulted. From the list of results, we included all available reports, from 1985 to present, that used any enhanced immunization technique to produce either polyclonal or monoclonal antibodies. Our examination yielded direct evidence that these enhanced immunization techniques are efficient in obtaining specific antibodies to rare epitopes, with different applications, such as to identify food contaminants or tumor cells.

Activity of 3'-hydroxychalcone against Cryptococcus gattii and toxicity, and efficacy in alternative animal models

AIM

This work aimed to evaluate the activity of 3'-hydroxychalcone against Cryptococcus gattii in planktonic and biofilm forms and their toxicity using alternative animal models.

MATERIALS & METHODS

Minimum inhibitory concentration and minimum fungicide concentration were determined. Biofilm formation and the susceptibility tests were performed by the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-5-[carbonyl(phenylamino)]-2H-tetrazolium hydroxide assay. Toxicity and efficacy were checked in Danio rerio and Galleria mellonella models.

RESULTS

The compound 3'-hydroxychalcone showed fungicidal activity against C. gattii in both planktonic and biofilm forms. The toxicity in zebrafish embryos revealed a low lethal concentration. In G. mellonella, the compound did not show antifungal activity and larvae toxicity.

CONCLUSION

Because of the activity of 3'-hydroxychalcone against C. gattii in vitro, molecular modifications should be made to improve efficacy and to reduce toxicity in vivo. [Formula: see text].

Fungal Biofilms and Polymicrobial Diseases

Biofilm formation is an important virulence factor for pathogenic fungi. Both yeasts and filamentous fungi can adhere to biotic and abiotic surfaces, developing into highly organized communities that are resistant to antimicrobials and environmental conditions. In recent years, new genera of fungi have been correlated with biofilm formation. However, Candida biofilms remain the most widely studied from the morphological and molecular perspectives. Biofilms formed by yeast and filamentous fungi present differences, and studies of polymicrobial communities have become increasingly important. A key feature of resistance is the extracellular matrix, which covers and protects biofilm cells from the surrounding environment. Furthermore, to achieve cell–cell communication, microorganisms secrete quorum-sensing molecules that control their biological activities and behaviors and play a role in fungal resistance and pathogenicity. Several in vitro techniques have been developed to study fungal biofilms, from colorimetric methods to omics approaches that aim to identify new therapeutic strategies by developing new compounds to combat these microbial communities as well as new diagnostic tools to identify these complex formations in vivo. In this review, recent advances related to pathogenic fungal biofilms are addressed.

Preliminary evaluation of circulating microRNAs as potential biomarkers in paracoccidioidomycosis

MicroRNAs (miRNAs) are small RNAs (length, 19-24 nucleotides) that regulate gene expression by either mRNA degradation or translational inhibition of proteins. Circulating miRNAs, which are extremely stable and protected from RNAse-mediated degradation in body fluids, have appeared as candidate biomarkers for numerous diseases. However, little is known about circulating miRNAs in fungal infections. Paracoccidioidomycosis (PCM) is caused by the Paracoccidioides species, and is endemic in Central and South America, with predominance in adult male workers from rural areas. The current study aimed to identify a serum miRNA expression profile that could serve as a novel diagnostic biomarker for PCM. Total RNA was isolated and the levels of circulating miRNAs were compared between patients with PCM and healthy control subjects using reverse transcription-quantitative polymerase chain reaction. Bioinformatic analysis was used to evaluate the potential roles of these miRNAs in PCM. Eight miRNAs were differentially expressed in serum samples from patients with PCM. These miRNAs are associated with apoptosis and immune response. The identified miRNAs facilitate with understanding the regulatory mechanisms involved in the host-parasite interaction of PCM. Furthermore, considering that the diagnosis of PCM presents difficulties, these miRNAs may serve as novel biomarkers for this disease.

Synergistic effect of pedalitin and amphotericin B against Cryptococcus neoformans by in vitro and in vivo evaluation

Cryptococcosis is an opportunistic fungal infection responsible for high morbidity and mortality in immunocompromised patients. Combination of antifungal substances is a promising way to increase the percentage of successful treatment. Pedalitin (PED) is a natural substance obtained from Pterogyne nitens. The aim of this study was to verify the efficacy of PED alone and in combination with amphotericin B (AmB) in vitro and in vivo against Cryptococcus spp. In the in vitro assay, minimum inhibitory concentrations (MICs) of 0.125 mg/L for AmB and 3.9 mg/L for PED were found when the substances were tested alone, whilst in the combination treatment the active concentration of both decreased, with MICs of 0.03 mg/L for AmB and 1 mg/L for PED. In the survival assay, fungal burden study and histopathological assays it was possible to study the efficacy of the substances alone and in combination. The efficacy of combination therapy was considered better than monotherapy as evaluated in a Galleria mellonella model and a murine model. Thus, the combination of PED and AmB is an interesting alternative for anticryptococcal fungal treatment. Moreover, a correlation was observed between the invertebrate and murine models for this antifungal treatment combination.

Metabolic profiles of planktonic and biofilm cells of Candida orthopsilosis

AIM

This study aims to understand which Candida orthopsilosis protein aids fungus adaptation upon its switching from planktonic growth to biofilm.

MATERIALS & METHODS

Ion mobility separation within mass spectrometry analysis combination were used.

RESULTS

Proteins mapped for different biosynthetic pathways showed that selective ribosome autophagy might occur in biofilms. Glucose, used as a carbon source in the glycolytic flux, changed to glycogen and trehalose.

CONCLUSION

Candida orthopsilosis expresses proteins that combine a variety of mechanisms to provide yeasts with the means to adjust the catalytic properties of enzymes. Adjustment of the enzymes helps modulate the biosynthesis/degradation rates of the available nutrients, in order to control and coordinate the metabolic pathways that enable cells to express an adequate response to nutrient availability.

Identification and characterisation of elongation factor Tu, a novel protein involved in Paracoccidioides brasiliensis-host interaction

Paracoccidioides spp., which are temperature-dependent dimorphic fungi, are responsible for the most prevalent human systemic mycosis in Latin America, the paracoccidioidomycosis. The aim of this study was to characterise the involvement of elongation factor Tu (EF-Tu) in Paracoccidioides brasiliensis-host interaction. Adhesive properties were examined using recombinant PbEF-Tu proteins and the respective polyclonal anti-rPbEF-Tu antibody. Immunogold analysis demonstrated the surface location of EF-Tu in P. brasiliensis. Moreover, PbEF-Tu was found to bind to fibronectin and plasminogen by enzyme-linked immunosorbent assay, and it was determined that the binding to plasminogen is at least partly dependent on lysine residues and ionic interactions. To verify the participation of EF-Tu in the interaction of P. brasiliensis with pneumocytes, we blocked the respective protein with an anti-rPbEF-Tu antibody and evaluated the consequences on the interaction index by flow cytometry. During the interaction, we observed a decrease of 2- and 3-fold at 8 and 24 h, respectively, suggesting the contribution of EF-Tu in fungal adhesion/invasion.

Fungal diseases: could nanostructured drug delivery systems be a novel paradigm for therapy?

Invasive mycoses are a major problem for immunocompromised individuals and patients in intensive care units. Morbidity and mortality rates of these infections are high because of late diagnosis and delayed treatment. Moreover, the number of available antifungal agents is low, and there are problems with toxicity and resistance. Alternatives for treating invasive fungal infections are necessary. Nanostructured systems could be excellent carriers for antifungal drugs, reducing toxicity and targeting their action. The use of nanostructured systems for antifungal therapy began in the 1990s, with the appearance of lipid formulations of amphotericin B. This review encompasses different antifungal drug delivery systems, such as liposomes, carriers based on solid lipids and nanostructure lipids, polymeric nanoparticles, dendrimers, and others. All these delivery systems have advantages and disadvantages. Main advantages are the improvement in the antifungal properties, such as bioavailability, reduction in toxicity, and target tissue, which facilitates innovative therapeutic techniques. Conversely, a major disadvantage is the high cost of production. In the near future, the use of nanosystems for drug delivery strategies can be used for delivering peptides, including mucoadhesive systems for the treatment of oral and vaginal candidiasis.

Evaluation of the efficacy of antifungal drugs against Paracoccidioides brasiliensis and Paracoccidioides lutzii in a Galleria mellonella model

Paracoccidioides brasiliensis and P. lutzii belong to a group of thermodimorphic fungi and cause paracoccidioidomycosis (PCM), which is a human systemic mycosis endemic in South and Central America. Patients with this mycosis are commonly treated with amphotericin B (AmB) and azoles. The study of fungal virulence and the efficacy and toxicity of antifungal drugs has been successfully performed in a Galleria mellonella infection model. In this work, G. mellonella larvae were infected with two Paracoccidioides spp. and the efficacy and toxicity of AmB and itraconazole were evaluated in this model for the first time. AmB and itraconazole treatments were effective in increasing larval survival and reducing the fungal burden. The fungicidal and fungistatic effects of AmB and itraconazole, respectively, were observed in the model. Furthermore, these effects were independent of changes in haemocyte number. G. mellonella can serve as a rapid model for the screening of new antifungal compounds against Paracoccidioides and can contribute to a reduction in experimental animal numbers in the study of PCM.

Transcriptomic Crosstalk between Fungal Invasive Pathogens and Their Host Cells: Opportunities and Challenges for Next-Generation Sequencing Methods

Fungal invasive infections are an increasing health problem. The intrinsic complexity of pathogenic fungi and the unmet clinical need for new and more effective treatments requires a detailed knowledge of the infection process. During infection, fungal pathogens are able to trigger a specific transcriptional program in their host cells. The detailed knowledge of this transcriptional program will allow for a better understanding of the infection process and consequently will help in the future design of more efficient therapeutic strategies. Simultaneous transcriptomic studies of pathogen and host by high-throughput sequencing (dual RNA-seq) is an unbiased protocol to understand the intricate regulatory networks underlying the infectious process. This protocol is starting to be applied to the study of the interactions between fungal pathogens and their hosts. To date, our knowledge of the molecular basis of infection for fungal pathogens is still very limited, and the putative role of regulatory players such as non-coding RNAs or epigenetic factors remains elusive. The wider application of high-throughput transcriptomics in the near future will help to understand the fungal mechanisms for colonization and survival, as well as to characterize the molecular responses of the host cell against a fungal infection.

Decreased expression of 14-3-3 in Paracoccidioides brasiliensis confirms its involvement in fungal pathogenesis

The interaction between the fungal pathogen Paracoccidioides brasiliensis and host cells is usually mediated by specific binding events between adhesins on the fungal surface and receptors on the host extracellular matrix or cell surface. One molecule implicated in the P. brasiliensis-host interaction is the 14-3-3 protein. The 14-3-3 protein belongs to a family of conserved regulatory molecules that are expressed in all eukaryotic cells and are involved in diverse cellular functions. Here, we investigated the relevance of the 14-3-3 protein to the virulence of P. brasiliensis. Using antisense RNA technology and Agrobacterium tumefaciens-mediated transformation, we generated a 14-3-3-silenced strain (expression reduced by ˜55%). This strain allowed us to investigate the interaction between 14-3-3 and the host and to correlate the functions of P. brasiliensis 14-3-3 with cellular features, such as morphological characteristics and virulence, that are important for pathogenesis.

Comparison of virulence between Paracoccidioides brasiliensis and Paracoccidioides lutzii using Galleria mellonella as a host model

Paracoccidioidomycosis is a systemic mycosis, endemic in Latin America. The etiologic agents of this mycosis are composed of 2 species: Paracoccidioides brasiliensis and P. lutzii. Murine animal models are the gold standard for in vivo studies; however, ethical, economical and logistical considerations limit their use. Galleria mellonella is a suitable model for in vivo studies of fungal infections. In this study, we compared the virulence of P. brasiliensis and P. lutzii in G. mellonella model. The deaths of larvae infected with P. brasiliensis or P. lutzii were similar, and both species were able to reduce the number of hemocytes, which were estimated by microscopy and flow cytometer. Additionally, the phagocytosis percentage was similar for both species, but when we analyze hemocyte-Paracoccidioides spp. interaction using flow cytometer, P. lutzii showed higher interactions with hemocytes. The gene expression of gp43 as well as this protein was higher for P. lutzii, and this expression may contribute to a greater adherence to hemocytes. These results helped us evaluate the behavior of Paracoccidioides spp in G. mellonella, which is a convenient model for investigating the host-Paracoccidioides spp. interaction.

Functional analysis of Paracoccidioides brasiliensis 14-3-3 adhesin expressed in Saccharomyces cerevisiae

BACKGROUND

14-3-3 proteins comprise a family of eukaryotic multifunctional proteins involved in several cellular processes. The Pb14-3-3 of Paracoccidioides brasiliensis seems to play an important role in the Paracoccidioides-host interaction. Paracoccidioides brasiliensis is an etiological agent of paracoccidioidomycosis, which is a systemic mycosis that is endemic in Latin America. In the initial steps of the infection, Paracoccidioides spp. synthetizes adhesins that allow it to adhere and invade host cells. Therefore, the aim of this work was to perform a functional analysis of Pb14-3-3 using Saccharomyces cerevisiae as a model.

RESULTS

The functional analysis of Pb14-3-3 was performed in S. cerevisiae, and it was found that Pb14-3-3 partially complemented S. cerevisiae proteins Bmh1p and Bmh2p, which are recognized as two yeast 14-3-3 homologues. When we evaluated the adhesion profile of S. cerevisiae transformants, Pb14-3-3 acted as an adhesin in S. cerevisiae; however, Bmh1p did not show this function. The influence of Pb14-3-3 in S. cerevisiae ergosterol pathway was also evaluated and our results showed that Pb14-3-3 up-regulates genes involved in ergosterol biosynthesis.

CONCLUSIONS

Our data showed that Pb14-3-3 was able to partially complement Bmh1p and Bmh2p proteins in S. cerevisiae; however, we suggest that Pb14-3-3 has a differential role as an adhesin. In addition, Pb-14-3-3 may be involved in Paracoccidioides spp. ergosterol biosynthesis which makes it an interest as a therapeutic target.

Advances and challenges in paracoccidioidomycosis serology caused by Paracoccidioides species complex: an update

Understanding the possible methodologies for the rapid and inexpensive identification of fungal infections is essential for disease diagnosis, but there are some limitations. To help with this problem, serological methods that detect antigens or antibodies are widely used and are useful for the diagnosis of paracoccidioidomycosis (PCM) through the detection of gp43, which is the main antigen employed for the immunodiagnosis of this disease caused by Paracoccidioides brasiliensis. However, the use of gp43 has become restricted because it was recently found that this marker is not identified in the infections caused by Paracoccidioides lutzii. Therefore, it is necessary to identify new antigens in both species or antigens specific for P. lutzii to decrease the morbidity and/or mortality associated with PCM. This review provides a discussion of new diagnostic challenges after the recent discoveries regarding the taxonomy of the Paracoccidioides genus.

In vitro characterization of Trichophyton rubrum and T. mentagrophytes biofilms

Dermatophytes are fungi responsible for a disease known as dermatophytosis. Biofilms are sessile microbial communities surrounded by extracellular polymeric substances (EPS) with increased resistance to antimicrobial agents and host defenses. This paper describes, for the first time, the characteristics of Trichophyton rubrum and T. mentagrophytes biofilms. Biofilm formation was analyzed by light microscopy, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) as well as by staining with crystal violet and safranin. Metabolic activity was determined using the XTT reduction assay. Both species were able to form mature biofilms in 72 h. T. rubrum biofilm produced more biomass and EPS and was denser than T. mentagrophytes biofilm. The SEM results demonstrated a coordinated network of hyphae in all directions, embedded within EPS in some areas. Research and characterization of biofilms formed by dermatophytes may contribute to the search of new drugs for the treatment of these mycoses and might inform future revisions with respect to the dose and duration of treatment of currently available antifungals.