Antifungal Activity of Chitosan against Histoplasma capsulatum in Planktonic and Biofilm Forms: A Therapeutic Strategy in the Future?

Histoplasmosis is a respiratory disease caused by Histoplasma capsulatum, a dimorphic fungus, with high mortality and morbidity rates, especially in immunocompromised patients. Considering the small existing therapeutic arsenal, new treatment approaches are still required. Chitosan, a linear polysaccharide obtained from partial chitin deacetylation, has anti-inflammatory, antimicrobial, biocompatibility, biodegradability, and non-toxicity properties. Chitosan with different deacetylation degrees and molecular weights has been explored as a potential agent against fungal pathogens. In this study, the chitosan antifungal activity against H. capsulatum was evaluated using the broth microdilution assay, obtaining minimum inhibitory concentrations (MIC) ranging from 32 to 128 µg/mL in the filamentous phase and 8 to 64 µg/mL in the yeast phase. Chitosan combined with classical antifungal drugs showed a synergic effect, reducing chitosan's MICs by 32 times, demonstrating that there were no antagonistic interactions relating to any of the strains tested. A synergism between chitosan and amphotericin B or itraconazole was detected in the yeast-like form for all strains tested. For H. capsulatum biofilms, chitosan reduced biomass and metabolic activity by about 40% at 512 µg/mL. In conclusion, studying chitosan as a therapeutic strategy against Histoplasma capsulatum is promising, mainly considering its numerous possible applications, including its combination with other compounds.

Improving Drug Delivery on Candida Albicans Using Geraniol Nanoemulsion

Geraniol (GE) is a monoterpene alcohol with excellent antifungal activity. However, its low solubility and high volatility impair its use. Nanoemulsions (NE) are excellent delivery systems for poorly soluble and volatile drugs, achieving controlled release of the active ingredient. The aim of this study was to improve the delivery of geraniol (GE) incorporated in NE against Candida albicans in order to evaluate the antibiofilm effect and cytotoxicity. Nanoemulsion containing 10% oil phase (cholesterol) (w/w), 10% surfactant (mixture of soy phosphatidylcholine and Brij 58; 1:2) (w/w), and 80% aqueous phase (phosphate buffer) (w/w) was synthesized. Incorporation of GE was carried out by sonication and the final compounds were characterized by hydrodynamic diameter, polydispersity index (PDI), and zeta potential (ZP), in addition to evaluation of physicochemical stability after 6 months and 1 year. The GE-NE effect was evaluated on Candida albicans biofilms and cytotoxic effect was evaluated on immortalized normal oral cell line NOK-Si. The diameter of GE-NE was 232.3 ± 2.7 nm and PDI 0.155 with exhibited homogeneity and stability in solution. GE-NE showed antibiofilm activity at a concentration of 75 μg/mL with reduction of >6.0 log10, and no cytotoxicity against NOK-Si cells at concentrations below 150 μg/mL was observed. GE-NE proved to be a promising candidate for prevention and treatment of fungal diseases.

Essential Oils in Respiratory Mycosis: A Review

Respiratory mycosis is a major health concern, due to the expanding population of immunosuppressed and immunocompromised patients and the increasing resistance to conventional antifungals and their undesired side-effects, thus justifying the development of new therapeutic strategies. Plant metabolites, namely essential oils, represent promising preventive/therapeutic strategies due to their widely reported antifungal potential. However, regarding fungal infections of the respiratory tract, information is disperse and no updated compilation on current knowledge is available. Therefore, the present review aims to gather and systematize relevant information on the antifungal effects of several essential oils and volatile compounds against the main type of respiratory mycosis that impact health care systems. Particular attention is paid to Aspergillus fumigatus, the main pathogen involved in aspergillosis, Candida auris, currently emerging as a major pathogen in certain parts of the world, and Cryptococcus neoformans, one of the main pathogens involved in pulmonary cryptococcosis. Furthermore, the main mechanisms of action underlying essential oils’ antifungal effects and current limitations in clinical translation are presented. Overall, essential oils rich in phenolic compounds seem to be very effective but clinical translation requires more comprehensive in vivo studies and human trials to assess the efficacy and tolerability of these compounds in respiratory mycosis.

Atypical chlamydoconidium-producing Trichophyton tonsurans strains from Ceará State, Northeast Brazil: investigation of taxonomy by phylogenetic analysis and biofilm susceptibility

Chlamydoconidium-producing Trichophyton tonsurans strains isolated in Northeastern Brazil have morphological features different from the classic description of this dermatophyte species. This study investigated the phylogenetic relationship of chlamydoconidium-producing T. tonsurans strains isolated in Northeastern Brazil. Also, the effect of terbinafine and farnesol on mature biofilms of T. tonsurans strains was evaluated. The mass spectra of T. tonsurans strains were investigated by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The ITS and LSU loci regions of rDNA and the partial β-tubulin gene were sequenced and the phylogenetic tree was analysed. The effects of terbinafine and farnesol on mature T. tonsurans biofilms were evaluated through the analysis of metabolic activity, quantification of biomass and observation by scanning electron microscopy. MALDI-TOF MS spectra of the chlamydoconidium-producing T. tonsurans strains differed from the spectrum of the control strain (ATCC 28942), presenting an intense ion peak at m/z 4155 Da. Phylogenetic tree analysis showed that the chlamydoconidium-producing strains isolated in Northeastern Brazil are allocated to a single cluster, differing from strains isolated from other countries. As for mature T. tonsurans biofilms, farnesol reduced biomass and metabolic activity by 64.4 and 65.9 %, respectively, while terbinafine reduced the biomass by 66.5 % and the metabolic activity by 69 %. Atypical morphological characteristics presented by chlamydoconidium-producing T. tonsurans strains result from phenotypic plasticity, possibly for adaptation to environmental stressors. Also, farnesol had inhibitory activity against T. tonsurans biofilms, demonstrating this substance can be explored for development of promising anti-biofilm drugs against dermatophytes.

Biofilm formation in clinically relevant filamentous fungi: a therapeutic challenge

Biofilms are highly-organized microbial communities attached to a biotic or an abiotic surface, surrounded by an extracellular matrix secreted by the biofilm-forming cells. The majority of fungal pathogens contribute to biofilm formation within tissues or biomedical devices, leading to serious and persistent infections. The clinical significance of biofilms relies on the increased resistance to conventional antifungal therapies and suppression of the host immune system, which leads to invasive and recurrent fungal infections. While different features of yeast biofilms are well-described in the literature, the structural and molecular basis of biofilm formation of clinically related filamentous fungi has not been fully addressed. This review aimed to address biofilm formation in clinically relevant filamentous fungi.

Farnesol: An approach on biofilms and nanotechnology

Biofilms are important virulence factor in infections caused by microorganisms because of its complex structure, which provide resistance to conventional antimicrobials. Strategies involving the use of molecules capable of inhibiting their formation and also act synergistically with conventional drugs have been explored. Farnesol is a molecule present in essential oils and produced by Candida albicans as a quorum sensing component. This sesquiterpene presents inhibitory properties in the formation of microbial biofilms and synergism with antimicrobials used in clinical practice, and can be exploited even for eradication of biofilms formed by drug-resistant microorganisms. Despite this, farnesol has physical and chemical characteristics that can limit its use, such as high hydrophobicity and volatility. Therefore, nanotechnology may represent an option to improve the efficiency of this molecule in high complex environments such as biofilms. Nanostructured systems present important results in the improvement of treatment with different commercial drugs and molecules with therapeutic or preventive potential. The formation of nanoparticles offers advantages such as protection of the incorporated drugs against degradation, improved biodistribution and residence time in specific treatment sites. The combination of farnesol with nanotechnology may be promising for the development of more effective antibiofilm therapies, as it can improve its solubility, reduce volatility, and increase bioavailability. This review summarizes existing data about farnesol, its action on biofilms, and discusses its encapsulation in nanostructured systems.

LAY SUMMARY

Farnesol is a natural compound that inhibits the formation of biofilms from different microbial species. The encapsulation of this molecule in nanoparticles is a promising alternative for the development of more effective therapies against biofilms.

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

Differential miRNA Expression in Human Macrophage-Like Cells Infected with Histoplasma capsulatum Yeasts Cultured in Planktonic and Biofilm Forms

Histoplasma capsulatum affects healthy and immunocompromised individuals, sometimes causing a severe disease. This fungus has two morphotypes, the mycelial (infective) and the yeast (parasitic) phases. MicroRNAs (miRNAs) are small RNAs involved in the regulation of several cellular processes, and their differential expression has been associated with many disease states. To investigate miRNA expression in host cells during H. capsulatum infection, we studied the changes in the miRNA profiles of differentiated human macrophages infected with yeasts from two fungal strains with different virulence, EH-315 (high virulence) and 60I (low virulence) grown in planktonic cultures, and EH-315 grown in biofilm form. MiRNA profiles were evaluated by means of reverse transcription-quantitative polymerase chain reaction using a commercial human miRNome panel. The target genes of the differentially expressed miRNAs and their corresponding signaling pathways were predicted using bioinformatics analyses. Here, we confirmed biofilm structures were present in the EH-315 culture whose conditions facilitated producing insoluble exopolysaccharide and intracellular polysaccharides. In infected macrophages, bioinformatics analyses revealed especially increased (hsa-miR-99b-3p) or decreased (hsa-miR-342-3p) miRNAs expression levels in response to infection with biofilms or both growth forms of H. capsulatum yeasts, respectively. The results of miRNAs suggested that infection by H. capsulatum can affect important biological pathways of the host cell, targeting two genes: one encoding a protein that is important in the cortical cytoskeleton; the other, a protein involved in the formation of stress granules. Expressed miRNAs in the host’s response could be proposed as new therapeutic and/or diagnostic tools for histoplasmosis.

Essential oils encapsulated in chitosan microparticles against Candida albicans biofilms

The aim of the study was to produce and characterize chitosan microparticles loaded with essential oils (CMEOs), evaluate the essential oil (EO) release profile and the CMEOs' anti-Candida activity. The chitosan microparticles (CMs) loaded with lemongrass essential oil (LEO) and geranium essential oil (GEO) were produced by the spray-drying method and characterized regarding CMEO morphological and physicochemical parameters and EO encapsulation efficiency (EE) and release profile. The planktonic activity was quantified by broth microdilution, and the activity against biofilm was quantified by biomass formation measurement. The LEO and GEO compositions were analyzed by gas chromatography combined with mass spectrometry (GC/MS), finding the main components citral (83.17%) and citronellol (24.53%). The CMs and CMEOs showed regular distribution and spherical shape (1 to 15 μm), without any morphological and physical modifications after EO incorporation. EE% ranged from 12 to 39%. In vitro release tests demonstrated the EO release rates, after 144 h, were 33% and 55% in PBS and HCl media, respectively. The minimum inhibitory concentration (MIC) values for CMEOs were lower than for CMs and pure EOs (P < 0.05). The higher CMEO biofilm inhibition percentage demonstrates the efficiency of microparticles against Candida biofilm. These results indicate that CMEOs are promising compounds that have antibiofilm activity against C. albicans.

Exogenous fungal quorum sensing molecules inhibit planktonic cell growth and modulate filamentation and biofilm formation in the Sporothrix schenckii complex

This study investigated the effect of the quorum sensing molecules (QSMs) farnesol, 2-phenylehtanol, tyrosol and tryptophol against planktonic cells, filamentation and biofilms of Sporothrix spp. The antifungal activity of QSMs was evaluated by broth microdilution. QSMs showed MICs in the ranges of 0.01-1 µM (farnesol), 1-8 mM (2-phenylehtanol and tyrosol), and >16 mM (tryptophol). Filamentous biofilm formation was inhibited by farnesol and 2-phenylehtanol and stimulated by tyrosol. Yeast biofilm formation was inhibited by 2-phenylehtanol and tyrosol. Tryptophol did not affect Sporothrix biofilm formation. QSMs showed MICs against mature biofilms of 8-32 µM (farnesol), 8-32 mM (2-phenylehtanol) and 64-128 mM (tyrosol). In conclusion, farnesol, 2-phenylethanol and tyrosol have antifungal activity against planktonic and sessile cells and modulate filamentation and biofilm formation in Sporothrix spp.

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.

Potassium iodide and miltefosine inhibit biofilms of Sporothrix schenckii species complex in yeast and filamentous forms

This study aimed to evaluate the yeast biofilm growth kinetics and ultrastructure of Sporothrix schenckii complex and assess their mature biofilm susceptibility in filamentous and yeast forms to potassium iodide (KI) and miltefosine (MIL). Yeast biofilms were evaluated by crystal violet staining, XTT reduction assay and microscopic techniques. Susceptibility of planktonic and sessile cells was analyzed by broth microdilution. S. schenckii complex in yeast form produced biofilms, with an optimum maturation at 96 h, showing multilayered blastoconidia embedded in extracellular matrix. KI and MIL minimum inhibitory concentration (MIC) ranges against planktonic cells were 62,500-250,000 μg/ml and 0.125-4 μg/ml, respectively. KI and MIL reduced biofilm metabolic activity by 75.4% and 67.7% for filamentous form and 55.1% and 51.6% for yeast form, respectively. This study demonstrated that S. schenckii complex forms biofilms in vitro, and potassium iodide and miltefosine inhibit Sporothrix spp. biofilms in both filamentous and yeast forms.

Antifungal susceptibility of Sporothrix schenckii complex biofilms

Sporotrichosis, caused by species of Sporothrix schenckii complex, is the most prevalent subcutaneous mycosis in many areas of Latin America. The aim of this study was to evaluate the ability of Sporothrix spp. to form biofilms in vitro and to characterize the growth kinetics, morphology, and antifungal susceptibility of biofilms against classical antifungals. We investigated the ability of strains to produce biofilms in vitro and determined the effects of exposure to amphotericin B, itraconazole, caspofungin, ketoconazole, voriconazole, and fluconazole at minimum inhibitory concentration (MIC) against planktonic form and at 10× MIC and 50× MIC on the biomass and metabolic activity of these biofilms. Biofilm structure was analyzed by optical microscopy using Congo-red staining, confocal and scanning electron microscopy. Strains were classified for biofilm-forming ability, through the analysis of absorbance of crystal violet retained by biomass of mature biofilms. We found that all S. brasiliensis (n = 10), S. schenckii sensu stricto (n = 2), S. globosa (n = 2), and S. mexicana (n = 4) strains were strong biofilm-producers. The analyzed biofilms had dense network of hyphae and conidia immersed in extracellular matrix, with presence of water channels. Antifungal drugs at the three tested concentrations showed different effects on biomass and metabolic activity of biofilms. However, the best inhibitory response was observed with 50× MIC of amphotericin B and caspofungin, which reduced these parameters. Furthermore, high drug concentrations, especially amphotericin B and caspofungin, showed antifungal activity against these biofilms, probably because they damaged the architecture and extracellular matrix, allowing diffusion of the drugs.

Farnesol inhibits planktonic cells and antifungal-tolerant biofilms of Trichosporon asahii and Trichosporon inkin

Trichosporon species have been considered important agents of opportunistic systemic infections, mainly among immunocompromised patients. Infections by Trichosporon spp. are generally associated with biofilm formation in invasive medical devices. These communities are resistant to therapeutic antifungals, and therefore the search for anti-biofilm molecules is necessary. This study evaluated the inhibitory effect of farnesol against planktonic and sessile cells of clinical Trichosporon asahii (n = 3) andTrichosporon inkin (n = 7) strains. Biofilms were evaluated during adhesion, development stages and after maturation for metabolic activity, biomass and protease activity, as well as regarding morphology and ultrastructure by optical microscopy, confocal laser scanning microscopy, and scanning electron microscopy. Farnesol inhibited Trichosporon planktonic growth by 80% at concentrations ranging from 600 to 1200 μM for T. asahii and from 75 to 600 μM for T. inkin. Farnesol was able to reduce cell adhesion by 80% at 300 μM for T. asahii and T. inkin at 600 μM, while biofilm development of both species was inhibited by 80% at concentration of 150 μM, altering their structure. After biofilm maturation, farnesol decreased T. asahii biofilm formation by 50% at 600 μM concentration and T. inkin formation at 300 μM. Farnesol inhibited gradual filamentation in a concentration range between 600 and 1200 μM. Farnesol caused reduction of filament structures of Trichosporon spp. at every stage of biofilm development analyzed. These data show the potential of farnesol as an anti-biofilm molecule.

Quantitative and structural analyses of the in vitro and ex vivo biofilm-forming ability of dermatophytes

PURPOSE

The aim of this study was to evaluate the in vitro and ex vivo biofilm-forming ability of dermatophytes on a nail fragment.

METHODOLOGY

Initially, four isolates of Trichophyton rubrum, six of Trichophyton tonsurans, three of Trichophyton mentagrophytes, ten of Microsporum canis and three of Microsporum gypseum were tested for production biomass by crystal violet assay. Then, one strain per species presenting the best biofilm production was chosen for further studies by optical microscopy (Congo red staining), confocal laser scanning (LIVE/DEAD staining) and scanning electron (secondary electron) microscopy.

RESULTS

Biomass quantification by crystal violet assay, optical microscope images of Congo red staining, confocal microscope and scanning electron microscope images revealed that all species studied are able to form biofilms both in vitro and ex vivo, with variable density and architecture. M. gypseum, T. rubrum and T. tonsurans produced robust biofilms, with abundant matrix and biomass, while M. canis produced the weakest biofilms compared to other species.

CONCLUSION

This study sheds light on biofilms of different dermatophyte species, which will contribute to a better understanding of the pathophysiology of dermatophytosis. Further studies of this type are necessary to investigate the processes involved in the formation and composition of dermatophyte biofilms.

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.

Selective photoinactivation of Histoplasma capsulatum by water-soluble derivatives chalcones

Histoplasmosis is a respiratory and systemic disease caused by the dimorphic fungus Histoplasma capsulatum. The clinical features may vary from asymptomatic infections to disseminated severe form depending of patient immunity. The treatment of histoplasmosis can be performed with itraconazole, fluconazole, and in the disseminated forms is used amphotericin B. However, the critical side effects of amphotericin B, the cases of itraconazole therapy failure and the appearance of fluconozole-resistant strains makes necessary the search of new strategies to treat this disease. Antimicrobial photodynamic therapy (aPDT) seems to be a potential candidate once have been show efficacy to inhibit others dimorphic fungi. Although the photosensitizer (PS) chalcone aggregates in biological medium, it has antifungal activity and show a high quantum yield of ROS formation. So, the aim of this study was to obtain the experimental parameters to achieve an acceptable selective chalcone water-soluble derivatives photoinactivation of H. capsulatum comparing with fibroblastic and keratinocytes cells which are the constituents of some potential host tissues. Yeast and cells were incubated with the same chalchones concentrations and short incubation time followed by irradiation with equal dose of light. The best conditions to kill H. capsulatum selectively were very low photosensitizers concentration (1.95μgmL^-1) incubated by 15min and irradiated with LED 450nm with 24Jcm^-2. Key words: chalcone, Histoplasma capsulatum, aPDT, selectivity.

Antifungal therapeutics for dimorphic fungal pathogens

Dimorphic fungi cause several endemic mycoses which range from subclinical respiratory infections to life-threatening systemic disease. Pathogenic-phase cells of Histoplasma, Blastomyces, Paracoccidioides and Coccidioides escape elimination by the innate immune response with control ultimately requiring activation of cell-mediated immunity. Clinical management of disease relies primarily on antifungal compounds; however, dimorphic fungal pathogens create a number of challenges for antifungal drug therapy. In addition to the drug toxicity issues known for current antifungals, barriers to efficient drug treatment of dimorphic fungal infections include natural resistance to the echinocandins, residence of fungal cells within immune cells, the requirement for systemic delivery of drugs, prolonged treatment times, potential for latent infections, and lack of optimized standardized methodology for in vitro testing of drug susceptibilities. This review will highlight recent advances, current therapeutic options, and new compounds on the horizon for treating infections by dimorphic fungal pathogens.

Fungal quorum sensing molecules: Role in fungal morphogenesis and pathogenicity

When microorganisms live together in high numbers, they need to communicate with each other. To achieve cell-cell communication, microorganisms secrete molecules called quorum-sensing molecules (QSMs) that control their biological activities and behaviors. Fungi secrete QSMs such as farnesol, tyrosol, phenylethanol, and tryptophol. The role of QSMs in fungi has been widely studied in both yeasts and filamentous fungi, for example in Candida albicans, C. dubliniensis, Aspergillus niger, A. nidulans, and Fusarium graminearum. QSMs impact fungal morphogenesis (yeast-to-hypha formation) and also play a role in the germination of macroconidia. QSMs cause fungal cells to initiate programmed cell death, or apoptosis, and play a role in fungal pathogenicity. Several types of QSMs are produced during stages of biofilm development to control cell population or morphology in biofilm communities. This review article emphasizes the role of fungal QSMs, especially in fungal morphogenesis, biofilm formation, and pathogenicity. Information about QSMs may lead to improved measures for controlling fungal infection.