An aberrant variant of Histoplasma capsulatum var. capsulatum.

We studied an aberrant culture of Histoplasma capsulatum var. capsulatum isolated from synovial fluid collected from the right elbow of a patient from Kansas. Colonies on Sabouraud glucose agar and other routine mycological media were glabrous to soft, moist, heaped, deeply folded or convoluted, and orange-brown with a white, irregular margin. Microscopically, hyphae were hyaline, septate, and branched and remained totally devoid of conidiation over a period of 2 years on all mycological media. Conversion to the yeast form was achieved on Pine's medium at 37 degrees C. Colonies at early stages of growth were smooth, moist, pasty, shiny, and orange-brown but soon became wrinkled and slightly raised and produced oval, thin-walled cells measuring 2 to 3 by to 4.5 microns which multiplied by polar budding. The identity of the isolate was further confirmed by utilizing the Accuprobe DNA and the exoantigen test for H. capsulatum var. capsulatum.     

Histoplasma capsulatum sinusitis.

Sinusitis is commonly reported in patients with AIDS. In addition to the usual bacterial pathogens isolated from immunocompetent patients, sinusitis in patients with AIDS may be caused by a variety of unusual bacteria, viruses, fungi, parasites, and mycobacteria. Histoplasma capsulatum has not typically been associated with sinusitis in either group of patients. We report a case of sinusitis caused by H. capsulatum in a patient with AIDS.     

Hydroxamate siderophores of Histoplasma capsulatum

The zoopathogenic fungus Histoplasma capsulatum, like other eukaryotic aerobic microorganisms, requires iron for growth. Under conditions of low iron availability, the fungus secretes hydroxamates that function as siderophores (iron chelators). The experiments to be reported were designed to gather further information on the hydroxamate siderophores of H. capsulatum. The fungus was grown in a synthetic medium deferrated with the cationic exchange resin Chelex 100. Siderophores were detected after 4 days of incubation at 37 degrees C in media containing 0.3 to 1.0 microM iron. The secretion was suppressed by 10 microM iron. The hydroxamates were purified by reverse-phase and size-exclusion chromatography. On the basis of ions observed during electrospray mass spectroscopy, five hydroxamate siderophores were tentatively identified: dimerum acid, acetyl dimerum acid, coprogen B, methyl coprogen B, and fusarinine (monomeric). A polyclonal antibody to dimerum acid was generated. This reagent cross-reacted with coprogen B and fusarinine. Thus, the antibody detects hydroxamates in all three families of siderophores excreted by H. capsulatum.     

Histoplasma capsulatum var. capsulatum occurring in an HIV-positive Ghanaian immigrant to Italy. Identification of H. capsulatum DNA by PCR from paraffin sample

Histoplasmosis, which is highly endemic in the United States, is rare in Europe, usually imported but sometimes autochthonous. In Africa, histoplasmosis capsulati coexists with "African histoplasmosis", a characteristic skin infection caused by H. capsulatum var. duboisii. Histoplamosis due to H. capsulatum is one of the 12 secondary infections listed in the surveillance definitions of AIDS. We report the case of a 36-year-old black man with acquired immunodeficiency syndrome (AIDS) who was living in Italy but originally came from Ghana. Histoplasmosis was disseminated with fever and cutaneous manifestations. The diagnosis was demonstrated morphologically based on the presence of yeast, observed by light microscopy, in skin lesions and by identification of H. capsulatum var. capsulatum DNA by nested PCR from a paraffin sample. No clinical reports of histoplamosis capsulati in Ghana have been published until now. The present case stresses the role of immigration of subjects from outside Europe who have been infected in their native country.     

A complementary tool for management of disseminated Histoplasma capsulatum var. capsulatum infections in AIDS patients

In South America, disseminated histoplasmosis due to Histoplasma capsulatum var. capsulatum (H. capsulatum), is a severe and frequent opportunistic infection in AIDS patients. In areas outside the USA where specific-Histoplasma antigen detection is not available, the diagnosis is difficult. With the galactomannan antigen (GM) detection, a test commonly used for invasive aspergillosis diagnosis, there is a cross-reactivity with H. capsulatum that can be helpful for the diagnosis of histoplasmosis. The aim of this study was to evaluate the GM detection for the diagnosis of disseminated histoplasmosis in AIDS patients. The performance of the GM detection was evaluated with serum collected in French Guiana where H. capsulatum is highly endemic. Sera from AIDS patients with disseminated histoplasmosis occurring from 2002 to 2009 and from control HIV-positive patients without histoplasmosis were tested with the GM detection and Histoplasma-specific antibody detection (IEP). In 39 AIDS patients with proven disseminated histoplasmosis, the sensitivity of the Histoplasma IEP was only 35.9% and was linked to the TCD4+ lymphocyte level. For the GM detection, the sensitivity (Se) was 76.9% and specificity (Sp) was 100% with the recommended threshold for aspergillosis diagnosis (0.5). The test was more efficient with a threshold of 0.4 (Se: 0.82 [95% CI: 0.66–0.92], Sp: 1.00 [95% CI: 0.86–1.00], LR+: >10, LR−: 0.18). This study confirms that the GM detection can be a surrogate marker for the diagnosis of disseminated histoplasmosis in AIDS patients in endemic areas where Histoplasma EIA is not available.     

A serendipitous isolate of Histoplasma capsulatum

This is a report of an unexpected laboratory diagnosis of Histoplasma capsulatum. The fungus was isolated from an acute cellulitic lesion on the forearm of an elderly male patient with a functioning renal transplant. The patient resides within the environs of Brisbane and has not travelled outside Australia. We consider the isolation of H. capsulatum from a rare site in a patient resident in a non-endemic area indicative of a latent opportunistic infection in an immunocompromised patient.     

Comparison of radioimmunoassay and enzyme-linked immunoassay methods for detection of Histoplasma capsulatum var. capsulatum antigen.

The purpose of this study was to compare the conventional radioimmunoassay (RIA) to an enzyme-linked immunoassay (EIA) for the measurement of Histoplasma antigen in banked urine specimens. A correlation between the two methods would allow the EIA to be used as a nonradioactive alternative to the established 125I RIA. The study used stored urine from patients diagnosed with histoplasmosis during an outbreak in Indianapolis which began in 1988. Control specimens from healthy adults, patients with other fungal infections, urinary tract infections, or nonfungal pneumonia were also tested. Both the RIA and EIA were run concurrently. The RIA system measured antigen levels of 0.4 to 27.0 RIA units, while the EIA measured antigen levels of 0.6 to 20.1 units. Both the EIA and RIA detected measurable antigen levels in urine from 50 of 56 patients (89%) with disseminated disease and 11 of 30 patients (37%) with self-limiting disease. One of 96 control specimens, from a patient with paracoccidioidomycosis, was positive with both systems. Antigen levels measured by EIA correlated well with those measured by the established RIA method (correlation coefficient, 0.974). The EIA is an acceptable alternative to the RIA for measuring Histoplasma antigen levels in urine specimens.     

Immunological studies on Histoplasma capsulatum.

Alveolar macrophages freshly harvested from normal and immunized rabbits were parasitized with yeast cells and protoplasts of Histoplasma capsulatum. Macrophages obtained from either normal or sensitized rabbits failed to phagocytize protoplasts, whereas, the yeast cells were actively ingested. There was no detectable intracellular killing by macrophages. A serological similarity was found between the whole yeast cell, the purified isolated cell wall, and the protoplasts of the fungus. Aprecipitin test of the protoplasts of the fungus gave a postive band, whereas immunodiffusion in agar was negative. Addition of immune sera activated phagocytosis, the immune sera against cell walls being the most active.     

Morphogenesis and pathogenicity of Histoplasma capsulatum.

The sulfhydryl blocking agent p-chloromercuriphenylsulfonic acid (PCMS) irreversibly inhibited the mycelium-to-yeast transitions of two virulent strains of Histoplasma capsulatum, G184A and G222B, when the temperature of incubation was raised to 37 degrees C, and the block persisted even after the cultures were washed free of PCMS. Instead of transforming to yeast cells, PCMS-treated mycelia continued to grow as mycelia at the elevated temperatures. A less virulent strain (Downs) was more temperature sensitive, but it showed a similar irreversible effect at 34 degrees C. Therefore, the mycelium-to-yeast transition of H. capsulatum is not required for the adaptation of mycelia to elevated temperatures but probably results from the temperature-dependent activation of yeast-specific genes. The transition to yeast is inferred to be obligate for pathogenicity in mice because PCMS-treated mycelia failed to cause infection, and no fungi were seen in tissues after PCMS-treated mycelia were injected into mice.     

Disseminated infection by Histoplasma capsulatum with AIDS

Histoplasmosis is an illness which occurs very rarely in Europe and it is especially rare in Germany. A generalised infection with Histoplasma capsulatum, a systemic mycosis of the mononuclear phagocyte system (MPS), occurs only in individuals with weakened immune systems. Within the framework of diagnostics, a pathologist can be confronted with histoplasmosis since there has been an increase in travel to and from endemic regions, as well as an increase in the number of diseases of the immune system. The presented case reports the histological intravital and post-mortem diagnostics of disseminated histoplasmosis in existing HIV-infection in the stage of manifest AIDS.     

Histoplasma capsulatum infection in nude mice.

Congenitally athymic nude (nu/nu) mice, when injected intraperitoneally with Histoplasma capsulatum, developed a rapidly fatal disseminated infection characterized by heavy parasitization of reticuloendothelial tissues. In contrast, their heterozygous (nu/X) littermates, which possessed a functioning thymus, developed only a low-grade infection which was apparently self-limited and rarely fatal. Transplantation of thymic tissue into nu/nu mice diminished greatly the severity of infection and reduced mortality by about 50%. These studies emphasize the importance of cell-mediated immunity in host defense against histoplasmosis and suggest that the nude mouse may be a valuable model for the study of this chronic intracellular infection.     

Fosmid-based physical mapping of the Histoplasma capsulatum genome

A fosmid library representing 10-fold coverage of the Histoplasma capsulatum G217B genome was used to construct a restriction-based physical map. The data obtained from three restriction endonuclease fingerprints, generated from each clone using BamHI, HindIII, and PstI endonucleases, were combined and used in FPC for automatic and manual contig assembly builds. Concomitantly, a whole-genome shotgun (WGS) sequencing of paired-end reads from plasmids and fosmids were assembled with PCAP, providing a predicted genome size of up to 43.5 Mbp and 17% repetitive DNA. Fosmid paired-end sequences in the WGS assembly provide anchoring information to the physical map and result in joining of existing physical map contigs into 84 clusters containing 9551 fosmid clones. Here, we detail mapping the Histoplasma capsulatum genome comprehensively in fosmids, resulting in an efficient paradigm for de novo sequencing that uses a map-assisted whole genome shotgun approach.     

Histoplasma capsulatum in adrenal gland aspirate--a case report

We report a case of disseminated histoplasmosis in a 60-year-old non-immunocompromised patient who presented to us with fever and hepatosplenomegaly. Sonographic & CT examination of the abdomen showed bilateral adrenal masses. Cytological examination of the aspirated material from the mass showed yeast forms of H. capsulatum.     

Studies on the catalase of Histoplasma capsulatum.

Factors which control the levels of catalase within yeast cells of Histoplasma capsulatum were studied. Only a small fraction of the total catalase activity could be detected in whole cells. The bulk of the activity was revealed in cell-free extracts or in cells permeabilized with acetone. The formation of the enzyme was regulated by glucose and by oxygen. There were large, consistent differences in the levels of catalase among strains of H. capsulatum. The sensitivity of the strains to H2O2 toxicity also varied remarkably. Peroxidase activity could not be detected in cell-free extracts of the strains. Resistance to H2O2 did not correspond to levels of catalase. There was no obvious correlation of H2O2 sensitivity and virulence among the strains.     

DNA probe for the identification of Histoplasma capsulatum

A 1.85-kilobase HindIII nuclear DNA probe from Histoplasma capsulatum G217B detected polymorphic restriction fragments within whole-cell DNA from different clinical isolates of H. capsulatum, consistent with the previous system of classification. The probe failed to hybridize to DNA from Blastomyces dermatitidis, Candida spp., Saccharomyces cerevisiae, Sepedonium chrysospermum, and Chrysosporium keratinophilum under low-stringency conditions and therefore may have value as a diagnostic reagent to identify H. capsulatum.     

Incorporation of Cystine by Yeast Cells of Histoplasma capsulatum

This report deals with the incorporation of cystine into macromolecules by yeast cells of Histoplasma capsulatum. The results show that at saturating concentrations of cystine in a rich medium, total uptake of the cystine occurs in 10 hr, whereas the amount of label in the cold trichloroacetic acid-soluble material reaches a maximum at 3 to 4 hr and remains at this value. The amount of label in the cold acid-insoluble material accumulates linearly for 4 to 5 hr and reaches a plateau at 7 to 9 hr. A chemical fractionation of labeled cells shows that 25% of the cystine taken up remains as low-molecular-weight components, of which cystine comprises 60 to 75%. Approximately 30% of the total label incorporated is ethanol-soluble, and polyacrylamide gel electrophoresis of this material shows a rather uniform incorporation of the amino acid into many proteins. The combined hot KOH fractions account for 40% of the total label incorporated. The amount of hot KOH-insoluble material almost doubles in a 10-hr pulse, whereas there is an increase in hot KOH-soluble material. Hence, the greatest amount of label from cells pulsed with ¹⁴C-cystine is recovered from cell wall material.     

Molecular cell biology and molecular genetics of Histoplasma capsulatum

Histoplasma capsulatum is a dimorphic ascomycete which is capable of producing a broad spectrum of disease ranging from mild asymptomatic, pulmonary illness to severe, life-threatening systemic mycosis. Regulatory mechanisms that use temperature and other environmental cues are paramount to the successful adaptation of the organism as an effective intracellular pathogenic yeast. Although the biochemistry and phenomenology of reversible morphogenesis have been well examined in Histoplasma, the identification and functional characterization of genes and their products that are required for early establishment or maintenance of the parasitic yeast phase in intracellular host compartments have only recently been fruitful. Advances in the molecular biology of Histoplasma, including approaches to introduce telomeric plasmids, reporter fusion constructs, and gene disruption cassettes into the fungus are poised to solidify the pre-eminence of this fungus as a model system which can be applied to other dimorphic fungal pathogens that exhibit similar cellular and immunological complexities. This review centers on recent developments in the molecular cell biology and molecular genetics of Histoplasma capsulatum that provide important new avenues for examining the mold-to-yeast phase transition beyond the historical, binary view of dimorphism and the implications that these successful approaches may have on seminal issues in fungal pathogenesis.