Melanization and morphological effects on antifungal susceptibility of Penicillium marneffei

The biosynthesis of melanin has been linked with virulence in diverse pathogenic fungi. Penicillium marneffei, a dimorphic fungus, is capable of melanization in both mycelial and yeast phases, and the pigment may be produced during infection to protect the fungus from the host immune system. To investigate the impact of yeast morphological transformation on antifungal susceptibility, P. marneffei was cultured on various media including minimal medium, 1 % tryptone, brain heart infusion broth, and malt extract broth by using the standardized susceptibility protocol (the M27-A protocol, RPMI medium) for yeasts. We also investigated whether P. marneffei melanization affected its susceptibility to antifungal drugs by adding l-DOPA into culture broths. There were no differences in the minimum inhibitory concentrations of P. marneffei yeast cells previously grown in various culture broths with or without l-DOPA using the M27A protocol (into which no melanin substrate can be added due to a rapid colour change of the RPMI medium to black) for testing amphotericin B, clotrimazole, fluconazole, itraconazole and ketoconazole. However, both melanized and non-melanized P. marneffei displayed increased resistance to antifungal drugs when l-DOPA was added into a selected assay medium, 0.17 % yeast nitrogen base, 2 % glucose, and 1.5 % agar. Hence, active melanin formation appears to protect P. marneffei by enhancing its resistance to antifungal drugs.     

Intracellular melanization of the larvae of Dirofilaria immitis in the malpighian tubules of the mosquito, Aedes sollicitans

Frequent melanization of larvae of the nematode Dirofilaria immitis parasitizing the Malpighian tubules of the mosquito, Aedes sollicitans, has been observed. Melanized and nonmelanized larvae in the Malpighian tubules were examined using light and electron microscopy. The results indicate that the pattern of melanin deposition and the ultrastructural characteristics of the pigment around the worms are identical to that observed on nematodes which have undergone humoral melanization in other dipteran insects. In the Malpighian tubules, no contact between the intracellular melanized nematodes and the hemolymph or hemocytes was observed. The results suggest that the Malpighian tubules of this species of mosquito are capable of inducing a melanotic response to invading nematode parasites. It is proposed that this is an example of “humoral” melanization at an intracellular site.     

Importance of complement 3 and mannose receptors in phagocytosis of Paracoccidioides brasiliensis conidia by Nramp1 congenic macrophages lines

Genetic factors influence susceptibility to Paracoccidioidomycosis, a Latin American endemic mycosis. The pattern of susceptibility of congenic mouse strains infected with Paracoccidioides brasiliensis resembles the pattern of the Nramp1 gene. Thus, congenic murine bone-marrow-derived macrophage lines B10R (Nramp1rGly169) and B10S (null Nramp1 protein expression, Nramp1sAsp169) were infected with P. brasiliensis conidia and compared, under opsonic and nonopsonic conditions. Opsonization increased the percentage of phagocytosis by both cell lines. B10R macrophages exhibited a higher percentage of cells with associated conidia and higher number of conidia per macrophage than B10S. Heat-inactivation and EDTA treatment of serum used for opsonization, and treatment of macrophages with anti-complement receptor 3 (CR3) decreased phagocytosis by both cell lines. alpha-methyl-d-mannoside reduced phagocytosis by B10R macrophages, suggesting that the mannose receptor participates in phagocytosis by these cells. The CR3 expression was similar on both cell lines and B10R expressed more mannose receptors, but neither cell line expressed CR1. IFNgamma decreased the conversion of conidia to the yeast form of P. brasiliensis in B10R, but not in B10S macrophages.     

Effects of Pimenta pseudocaryophyllus (Gomes) L. R. Landrum, on Melanized and Non-melanized Cryptococcus neoformans

In the present study, the in vitro susceptibility and capsular width from both melanized and non-melanized Cryptococcus neoformans cells in the presence of Pimenta pseudocaryophyllus crude extract were determined. The results were compared with those obtained for voriconazole and amphotericin B. Melanization was obtained in minimal medium broth with the addition of L-dopa, and the antifungal susceptibility tests were performed using the broth microdilution method. Capsular width of 30 cells of each one of the isolates in medium with crude extracts of P. pseudocaryophyllus or voriconazole or amphotericin B at a concentration corresponding to 0.5?times the minimal inhibitory concentration (MIC) was measured, and the mean was calculated. The MICs and minimal fungicidal concentrations (MFCs) for plant extract and voriconazole were identical for both melanized and non-melanized C. neoformans isolates, but for amphotericin, the MFCs for melanized cells were up to 8?times higher than for non-melanized cells. The capsular width of C. neoformans cells was smaller (p?<?0.001) in the presence crude extract of P. pseudocaryophyllus and of voriconazole regardless melanization. The findings of capsule alterations of C. neoformans verified in this study provide fertile ways for future research into the effects of antifungal agents on the pathogenesis of cryptococcosis.     

A surface 75-kDa protein with acid phosphatase activity recognized by monoclonal antibodies that inhibit Paracoccidioides brasiliensis growth

Paracoccidioides brasiliensis is a thermo-dimorphic fungus responsible for paracoccidioidomycosis (PCM), a systemic granulomatous mycosis prevalent in Latin America. The fungus releases many antigens which may be transiently bound to its cell surface. Some of them may show enzymatic functions essential for maintaining many cell processes and survival of the microorganism at different conditions. In this study, we report the characterization of a secreted 75kDa protein from P. brasiliensis with phosphatase activity. Biologic function of the molecule was demonstrated using two specific mAbs produced and characterized as IgM and IgG isotypes. Confocal microscopy and flow cytometry analysis demonstrated that both mAbs recognized the protein on the fungus surface, mainly in its budding sites. In vitro experiments showed that fungal growth was inhibited by blocking the protein with mAbs. In addition, opsonized yeast cells with both mAbs facilitated phagocytosis by murine peritoneal macrophages. Passive immunization using mAbs before P. brasiliensis mice infection reduced colony-forming units (CFU) in the lungs as compared with controls. Histopathology showed smaller inflammation, absence of yeast cells and no granuloma formation.     

Interference of melanin in the susceptibility profile of Sporothrix species to amphotericin B

BackgroundThe presence of melanin in the fungal cell is a major virulence factor of the genus Sporothrix since it protects the fungal cells against the defense systems.AimsThe present study aimed to investigate the interference of melanin in the susceptibility of Sporothrix brasiliensis and Sporothrix schenckii sensu stricto to amphotericin B and itraconazole, drugs recommended as therapy for disseminated and subcutaneous sporotrichosis, respectively.MethodsYeast cells were cultivated in minimal medium with or without l-DOPA in order to induce the production of melanin. Microdilution and killing assay methods were used to determine the antifungal activity against yeast cells with different amounts of melanin.ResultsThe killing assay showed that melanization protected isolates within the S. schenckii complex from amphotericin B, particularly in the lower concentrations tested.ConclusionsStudies combining amphotericin B and inhibitors of melanin are required in order to avoid this effect.     

Influence of N-glycosylation on the morphogenesis and growth of Paracoccidioides brasiliensis and on the biological activities of yeast proteins

The fungus Paracoccidioides brasiliensis is a human pathogen that causes paracoccidioidomycosis, the most prevalent systemic mycosis in Latin America. The cell wall of P. brasiliensis is a network of glycoproteins and polysaccharides, such as chitin, that perform several functions. N-linked glycans are involved in glycoprotein folding, intracellular transport, secretion, and protection from proteolytic degradation. Here, we report the effects of tunicamycin (TM)-mediated inhibition of N-linked glycosylation on P. brasiliensis yeast cells. The underglycosylated yeasts were smaller than their fully glycosylated counterparts and exhibited a drastic reduction of cell budding, reflecting impairment of growth and morphogenesis by TM treatment. The intracellular distribution in TM-treated yeasts of the P. brasiliensis glycoprotein paracoccin was investigated using highly specific antibodies. Paracoccin was observed to accumulate at intracellular locations, far from the yeast wall. Paracoccin derived from TM-treated yeasts retained the ability to bind to laminin despite their underglycosylation. As paracoccin has N-acetyl-β-d-glucosaminidase (NAGase) activity and induces the production of TNF-α and nitric oxide (NO) by macrophages, we compared these properties between glycosylated and underglycosylated yeast proteins. Paracoccin demonstrated lower NAGase activity when underglycosylated, although no difference was detected between the pH and temperature optimums of the two forms. Murine macrophages stimulated with underglycosylated yeast proteins produced significantly lower levels of TNF-α and NO. Taken together, the impaired growth and morphogenesis of tunicamycin-treated yeasts and the decreased biological activities of underglycosylated fungal components suggest that N-glycans play important roles in P. brasiliensis yeast biology.     

Paracoccin, an N-acetyl-glucosamine-binding lectin of Paracoccidioides brasiliensis, is involved in fungal growth

Paracoccin is an N-acetyl-glucosamine-binding lectin from Paracoccidioides brasiliensis, which can be obtained in small amounts either from culture supernatants or yeast cell extracts. In the present work, immunoelectron microscopy with mouse anti-paracoccin IgG localized the antigen to the cell wall of P. brasiliensis yeast forms. Paracoccin interacted with chitin, and colocalized with beta-1,4-homopolymer of GlcNAc to the budding sites of P. brasiliensis yeast cell. In order to evaluate the role of paracoccin on fungal growth, yeast cells were cultivated in the presence of anti-paracoccin antibodies. A significant reduction of both colony forming units and individual yeast cells was observed as well as morphological alterations such as smaller colonies and cells more loosely aggregated than in control cultures without the antibody. A role of paracoccin on the cell wall organization was reinforced by alterations in the labeling pattern of chitin when yeasts were treated with anti-paracoccin antibodies. Binding of specific antibodies to paracoccin may disrupt the paracoccin/chitin interactions, resulting in the inhibition of P. brasiliensis growth.     

Growth conditions influence melanization of Brazilian clinical Sporothrix schenckii isolates

Sporothrix schenckii is known to produce DHN melanin on both conidial and yeast cells, however little information is available regarding the factors inducing fungal melanization. We evaluated whether culture conditions influenced melanization of 25 Brazilian S. schenckii strains and one control strain (ATCC 10212). Tested conditions included different media, pH, temperature, incubation time, glucose concentrations, and presence or absence of tricyclazole or L-DOPA. Melanization was reduced on Sabouraud compared to defined chemical medium. The majority of strains produced small amounts of melanin at 37 °C and none melanized at basic pH. Increased glucose concentrations did not inhibit melanization, rather increasing glucose enhanced pigment production in 27% of strains. Melanin synthesis was also enhanced by the addition of L-DOPA and its addition to medium with tricyclazole, an inhibitor of melanin synthesis, resulted in fungal melanization, including hyphal melanin production. Our results suggest that different S. schenckii strains have distinct control of melanization and that this fungus can use phenolic compounds to enhance melanization in vitro.     

Decreased susceptibility of melanized Cryptococcus neoformans to UV light.

Melanized Cryptococcus neoformans cells were less susceptible than nonmelanized cells to the fungicidal effects of UV light. Phenoloxidase-catalyzed production of melanin-like pigments may serve to protect the fungus against ionizing radiation.     

Fungal melanin detection by the use of copper sulfide-silver

Silver-staining procedures were investigated for their effectiveness in identifying cell wall-based fungal melanins in live and fixed plastic embedded samples, particularly 1,8-dihydroxynaphthalene (DHN) based polyketide melanins. We developed a simple and reliable melanin-staining technique based on a silver accumulation method originally published for histological demonstration of heavy metal sulfides in mammalian tissues. Copper is bound to fungal melanin followed by formation of the copper sulfide at melanin sites in fungal cell walls, which then are amplified into vivid black stains using a silver enhancement step. The method demonstrates patterns of melanization in a range of fungal hyphae and is suitable for light and electron microscopy. Albino mutant fungi and normally nonmelanized fungi do not stain with the sulfide-silver technique. Mammalian melanocytes also were labeled by the technique, indicating its universality as a melanin probe.     

In vivo and in vitro activation of pulmonary macrophages by IFN-gamma for enhanced killing of Paracoccidioides brasiliensis or Blastomyces dermatitidis

The fungicidal capacity of murine pulmonary macrophages (PuM) activated in vitro with IFN or lymphokines or in vivo with IFN was studied. PuM treated overnight with IFN (1000 U/ml), Con A-stimulated spleen cell culture supernatants, or lymph node cells plus Con A significantly killed yeast cells of the Gar w isolate of Paracoccidioides brasiliensis 45.5 +/- 2.1%, 72.0 +/- 4.2%, and 51.5 +/- 0.7% respectively. Two other isolates of P. brasiliensis (Ru and LA) were also killed (45 and 34%) by PuM activated by lymph node cells plus Con A. Control PuM had lesser but significant capacity for killing of P. brasiliensis isolates, ranging from 15 to 22%. Killing of P. brasiliensis by PuM activated by Con A-stimulated spleen cell culture supernatants could not be significantly inhibited by superoxide dismutase, catalase, or azide. When mice were treated in vivo with 4 X 10(5) IFN U i.p. and PuM isolated 24 h later, the PuM had significantly enhanced ability to kill P. brasiliensis (47.0 +/- 6.3%) compared with PuM from control mice (25.0 +/- 4.2%). PuM thus activated also showed enhanced killing (43%) of a second isolate compared with control PuM (22%). PuM from IFN-treated mice were able to significantly kill Blastomyces dermatitidis (37.5 +/- 0.7%) compared with control PuM (4.5 +/- 6.3%). These results show that PuM can be activated in vitro and in vivo by IFN for enhanced fungicidal activity against two pulmonary fungal pathogens and suggests that immunologic production of IFN could be an important factor in host defenses against these diseases.     

Dual role for nitric oxide in paracoccidioidomycosis: essential for resistance, but overproduction associated with susceptibility

Using a murine model of susceptibility and resistance to paracoccidioidomycosis, we have previously demonstrated that immunosuppression occurs in susceptible (B10.A), but not in resistant (A/Sn), mouse strains. Accumulating evidence shows that NO is involved in the induction of T cell immunosuppression during infection as well as in the killing of Paracoccidioides brasiliensis. In the present work, we focused on NO and other macrophage products that could be associated with resistance or susceptibility to paracoccidioidomycosis. A striking difference was related to NO and TNF production. Macrophages from B10.A mice produced high and persistent NO levels, while in A/Sn animals, TNF production predominated. In in vitro cultures, P. brasiliensis-infected macrophages from A/Sn mice also produced large amounts of TNF, while B10.A macrophages only produced NO. TNF production by B10.A macrophages appeared to be suppressed by NO, because the addition of aminoguanidine sulfate, an inducible NO synthase (NOS2) inhibitor, resulted in TNF production. These results suggested that enhanced TNF or NO production is associated with resistance and susceptibility, respectively. However, regardless of the mouse strain, NOS2-deficient or aminoguanidine sulfate-treated mice presented extensive tissue lesions with increased fungal load in lungs and liver compared with their controls. We conclude that NOS2-derived NO is essential for resistance to paracoccidioidomycosis, but overproduction is associated with susceptibility.     

Effects of melanin upon susceptibility of Cryptococcus to antifungals

Melanin is a recognized virulence factor in Cryptococcus neoformans; several pathogenetic mechanisms have been suggested. We studied melanin as an antifungal resistance factor. The growth of laccase-active strains of C. neoformans and C. albidus in L-DOPA resulted in the production of black pigment. The formal minimal inhibitory concentrations (MICs) of amphotericin B and fluconazole were not changed by melanization. However, when we examined those wells which contained inhibited cells, we found live cells only in wells containing melanized C. neoformans. In contrast, melanization did not protect C. albidus from killing by amphotericin B. In an amphotericin B time-kill study of C. neoformans, significantly more melanized cells than non-melanized survived for the first few hours. Fluorescence microscopy and flow cytometry analyses showed that fewer melanized cells were stained with the fluorescent dye MitoRed. Incubation of MitoRed (the model) or amphotericin B with melanin extracted from C. neoformans decreased the free concentrations of these substances. Fluconazole, in contrast, was not removed from solution by melanin. This suggests that neoformans cryptococcal melanin deposited amphotericin B in the cell wall binds, reducing its effective concentrations.     

An association of actin isoforms with the expression of motile response in pigmentation variants induced from goldfish erythrophoroma cells

Comparison of actin isoforms in unpigmented goldfish cells (a normal dermal fibroblast-like cell line, and an unpigmented erythrophoroma cell line capable of being induced to undergo melanization) and in normal and neoplastic melanized goldfish cells shows that the melanized phenotype is accompanied by the presence of multiple actin isoforms. In contrast, the unpigmented cells have only beta-actin. The possible significance of this to pigment organelle translocation is discussed.     

Preliminary biological characterization of a melanization stimulating factor (MSF) from the dorsal skin of the channel catfish, Ictalurus punctatus.

A two step fractionation of conditioned media made from the darkly pigmented dorsal skin of the channel catfish, Ictalurus punctatus, has produced fractions that contain a melanization stimulating factor (MSF). Isolated neural tubes of Xenopus laevis embryos exposed to conditioned media and to specific fractions exhibit greater melanization (increased numbers of melanized cells and elevated percentages of melanized cells), a greater number of dendrites per melanized cell, and a greater number of emigrated neural crest cells than control neural tubes. The presence of MSF activity in the darkly pigmented dorsal integument suggests a role for a molecule or molecules in the development and maintenance of the dorsal/ventral pigment pattern of this piscine species and possibly of other vertebrates.