Specific and rapid identification of medically important fungi by exoantigen detection

Development of Indirect Competitive Enzyme-Linked Immunosorbent Assay to Detect Fusarium verticillioides in Poultry Feed Samples

Fumonisins are a group of toxic secondary metabolites that are produced by Fusarium verticillioides which are associated with poultry health hazard and great economic losses. The objective of the present study was to develop an immunological method to detect F. verticillioides in poultry feed samples. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on a polyclonal antibody against 67 kDa protein of the F. verticillioides 97K exoantigen was developed to detect this fungus. Antibody anti-67 kDa protein showed cross-reactivity against F. graminearum (2⁻7%) and F. sporotrichioides (10%), but no or low cross-reactivity against Aspergillus sp. and Penicillium sp. exoantigens. The detection limit for the 67 kDa protein of F. verticillioides was 29 ng/mL. Eighty-one poultry feed samples were analyzed for Fusarium sp. count, 67 kDa protein of F. verticillioides and fumonisin concentrations. Eighty of the 81 feed samples (98.6%) showed Fusarium sp. contamination (mean 6.2 x 10⁴ CFU/g). Mean 67 kDa protein and fumonisin concentration in the poultry feed samples was 21.0 µg/g and 1.02 µg/g, respectively. The concentration of 67 kDa protein, as determined by ic-ELISA correlated positively (p < 0.05) with fumonisin levels (r = 0.76). These results suggest that this ic-ELISA has potential to detect F. verticillioides and predict fumonisin contamination in poultry feed samples.

Molecular characterization of Histoplasma capsulatum isolated from an outbreak in treasure hunters Histoplasma capsulatum in treasure hunters

Background

In Mexico, primary pulmonary histoplasmosis is the most relevant clinical form of the disease. The geographical distribution of specific strains of Histoplasma capsulatum circulating in Mexico has not been fully established. Outbreaks must be reported in order to have current, updated information on this disease, identifying new endemic areas, manner of exposure to the fungi, and molecular characterization of the causative agents. We report a recent outbreak of histoplasmosis in treasure hunters and the molecular characterization of two isolates obtained from these patients.

Methods

Six patients admitted to the National Institute of Respiratory Diseases (INER) in Mexico City presented severe respiratory symptoms suggestive of histoplasmosis. They acquired the infection in the Veracruz (VZ) endemic zone. Diagnosis was made by X-ray and Computed tomography (CT), liver function, immunological techniques, and culture. Identification of H. capsulatum isolates was confirmed by using Polymerase chain reaction (PCR) was conducted with a probe from the M antigen, and the isolates were characterized by means of Random amplification of polymorphic DNA (RAPD)-PCR employed the 1253 oligonucleotide and a mixture of oligonucleotides 1281 and 1283. These were compared to eight reference strain isolates from neighboring areas.

Results

X-ray and CT revealed disseminated micronodular images throughout lung parenchyma, as well as bilateral retrocaval, prevascular, subcarinal, and hilar adenopathies, hepatosplenomegaly, and altered liver function tests. Five of the six patients developed disseminated histoplasmosis. Two H. capsulatum strains were isolated. The same band profile was detected in both strains, indicating that both isolates corresponded to the sole H. capsulatum strain. Molecular characterization of the isolates was similar in 100% with the EH-53 Hidalgo human (HG) strain (reference strain integrated into the LAm A clade described for Latin America).

Conclusions

The two isolates appeared to possess the same polymorphic pattern; they are indistinguishable from each other and from EH-53. It is important to remain updated on recent outbreaks of histoplasmosis, the manner of exposure to the fungi, as well as the molecular characterization of the isolates. The severity of cases indicates that this strain is highly virulent and that it is probably prevalent in Hidalgo and Veracruz states.

Guedes HL, Nosanchuk JD, Zancopé-Oliveira RM. Biological function and molecular mapping of M antigen in yeast phase of Histoplasma capsulatum

Histoplasmosis, due to the intracellular fungus Histoplasma capsulatum, can be diagnosed by demonstrating the presence of antibodies specific to the immunodominant M antigen. However, the role of this protein in the pathogenesis of histoplasmosis has not been elucidated. We sought to structurally and immunologically characterize the protein, determine yeast cell surface expression, and confirm catalase activity. A 3D-rendering of the M antigen by homology modeling revealed that the structures and domains closely resemble characterized fungal catalases. We generated monoclonal antibodies (mAbs) to the protein and determined that the M antigen is present on the yeast cell surface and in cell wall/cell membrane preparations. Similarly, we found that the majority of catalase activity was in extracts containing fungal surface antigens and that the M antigen is not significantly secreted by live yeast cells. The mAbs also identified unique epitopes on the M antigen. The localization of the M antigen to the cell surface of H. capsulatum yeast and the characterization of the protein's major epitopes have important implications since it demonstrates that although the protein may participate in protecting the fungus against oxidative stress it is also accessible to host immune cells and antibody.

DIAGNOSIS OF HISTOPLASMOSIS

Endemic mycoses can be challenging to diagnose and accurate interpretation of laboratory data is important to ensure the most appropriate treatment for the patients. Although the definitive diagnosis of histoplasmosis (HP), one of the most frequent endemic mycoses in the world, is achieved by direct diagnosis performed by micro and/or macroscopic observation of Histoplasma capsulatum (H. capsulatum), serologic evidence of this fungal infection is important since the isolation of the etiologic agents is time-consuming and insensitive. A variety of immunoassays have been used to detect specific antibodies to H. capsulatum. The most applied technique for antibody detection is immunodiffusion with sensitivity between 70 to 100 % and specificity of 100%, depending on the clinical form. The complement fixation (CF) test, a methodology extensively used on the past, is less specific (60 to 90%). Detecting fungal antigens by immunoassays is valuable in immunocompromised individuals where such assays achieve positive predictive values of 96-98%. Most current tests in diagnostic laboratories still utilize unpurified antigenic complexes from either whole fungal cells or their culture filtrates. Emphasis has shifted, however, to clinical immunoassays using highly purified and well-characterized antigens including recombinant antigens. In this paper, we review the current conventional diagnostic tools, such as complement fixation and immunodiffusion, outline the development of novel diagnostic reagents and methods, and discuss their relative merits and disadvantages to the immunodiagnostic of this mycosis.

Molecular and immunochemical phylogeny of Verticillium species

21 strains with all typical morphological characteristics of eight Verticillium species (Phyllachorales) were studied in this work, together with representatives from four Hypocreales species (11 strains), that were previously classified as members of the genus. The PCR products from two nuclear genes, i.e. the ITS1-5.8S-ITS2 region and RNA polymerase II largest subunit gene (rpb1), together with four mitochondrial genes, i.e. the small ribosomal rRNA subunit (rns), the two NADH dehydrogenase subunit genes (nad1 and nad3), and the cytochrome oxidase subunit III gene (cox3) were sequenced and analyzed. Similarly, antibodies raised against one strain of each of the species examined (V. nubilum and V. theobromae excluded) were used against the proteins of all other strains. The number and relative area of precipitates formed after crossed electrophoreses served to estimate the degree of immunochemical relatedness. Combined molecular and immunochemical data clarified the phylogenetic relationships of all true Verticillium species and provided a convincing insight into the evolutionary relation of the sect. Nigrescentia with members of the sect. Verticillium and sect. Prostrata that until recently were included in Verticillium.

Identification of the infectious source of an unusual outbreak of histoplasmosis, in a hotel in Acapulco, state of Guerrero, Mexico

Three isolates of Histoplasma capsulatum were identified from mice lung, liver, and spleen inoculated with soil samples of the X hotel's ornamental potted plants that had been fertilized with organic material known as compost. The presence of H. capsulatum in the original compost was detected using the dot-enzyme-linked immunosorbent assay. Nested-PCR, using a specific protein Hcp100 coding gene sequence, confirmed the fungal identification associated with an unusual histoplasmosis outbreak in Acapulco. Although, diversity between the H. capsulatum isolate from the hotel and some clinical isolates from Guerrero (positive controls) was observed using random amplification of polymorphic DNA based-PCR, sequence analyses of H-anti and ole fragment genes revealed a high homology (92-99%) between them.

Diagnosis of fungal diseases

In this chapter, we focus on diagnostic laboratory methods that are necessary and suitable for providing physicians with a timely and accurate diagnosis of fungal diseases. After discussing some pre-analytical aspects, the complete set of methods, i.e., microscopy, histopathology, culture, antigen detection, DNA detection, and antibody detection, is concisely described. Identification techniques depend on the fungal group involved. Therefore, separate paragraphs are dedicated to the identification of yeasts and filamentous fungi, which include moulds, dermatophytes, and dimorphic fungi.

Blastomycosis

Blastomycosis is an endemic mycoses in the central United States caused by a dimorphic fungus, Blastomyces dermatitidis, that exists in nature in mycelial phase and converts to yeast phase at body temperature. The organism may produce epidemics of infection following a point source of infection or sporadic endemic infection. Blastomycosis can be a subclinical illness with subsequent protection against progressive infection afforded by cellular immune mechanisms, but it may present with progressive disease with either pulmonary or extrapulmonary disease or both. Itraconazole has been shown to be the drug of choice for both infections, except in cases of life-threatening infection when amphotericin B should be used.

Antigen detection assay for identification of Penicillium marneffei infection

Two recently produced monoclonal antibodies were used to develop an antigen capture enzyme-linked immunosorbent assay (ELISA) for rapid diagnosis of Penicillium marneffei. The method was evaluated with 53 patients with culture-confirmed penicilliosis and 240 controls. The diagnostic sensitivity, specificity, and accuracy of the ELISA were 92.45, 97.5, and 96.59%, respectively.

Immunochemical detection of molds: a review

Molds are widely distributed in nature and cause deterioration of foods and feeds. Their mycotoxins can adversely affect human and animal health. Suitable assays for molds, therefore, are required to implement control and regulatory strategies and to develop appropriate feeding regimens for mold-infested feeds. Many different types of mold assays have been used, most of which are not reproducible or accurate. However, the immunoassays, particularly enzyme-linked immunosorbent assays (ELISAs), can be especially useful. Among these, assays that detect the water-soluble extracellular secretions of fungi, the exoantigens, are generally able to detect fungi at the genus or species level, whereas the heat-stable polysaccharides tend to be specific for one or more genus of fungi. Several species and genus (genera)-specific ELISAs have been developed using monoclonal or polyclonal antibodies against exoantigens and heat-stable polysaccharides from a wide range of fungi, including Aspergillus, Penicillium, and Fusarium species. Other assays have been developed that nonspecifically detect mold in food or feed, some using antibodies against a mixture of antigens from different fungi. These assays are highly sensitive, are easy to perform, and provide an index of the amount of mold present in the sample. Further refinement of these assays should facilitate their widespread use by food and feed processors, regulatory agencies, taxonomists, and research scientists.

Atypical disseminated cutaneous histoplasmosis in an immunocompetent child, caused by an "aberrant" variant of histoplasma capsulatum var. capsulatum

A case of atypical disseminated cutaneous histoplasmosis in a five-year old, otherwise healthy child, native and resident in Sao Paulo metropolitan area is reported. Cutaneous lesions were clinically atypical. Histologic examination disclosed a granulomatous reaction but no fungal structures could be demonstrated by specific staining nor by immunohistochemical reaction. The fungus was isolated from biopsy material on two different occasions, confirming diagnosis of an unusual fungal infection. The fungus, originally thought to be a Sepedonium sp. due to the large sized, hyaline or brownish colored tuberculated macroconidia and to lack of dimorphism (yeast form at 37 degrees C) produce H and M antigens, visualized by the immunodiffusion with rabbit anti-Histoplasma capsulatum hyperimmune serum. Patient's serum sample was non reactive with H. capsulatum antigen by immunodiffusion, counterimmunoelectrophoresis and complement fixation tests, and immunoenzymatic assay failed to detect the specific circulating antigen. This serum was tested negative by double immunodiffusion when antigen obtained from one of the isolated samples was used. Both cultures were sent to Dr. Leo Kaufman, Ph.D. (Mycoses Immunodiagnostic Laboratory, CDC-Atlanta/USA), who identified them as H. capsulatum by the exoantigen and gen-probe tests. Both clinic and mycologic characteristics of the present case were atypical, suggesting the fungus isolated is an "aberrant variant" of H. capsulatum var. capsulatum, as described by SUTTON et al. in 1997. Treatment with itraconazole 100 mg/day led to cure within 90 days

Relatedness analyses of Histoplasma capsulatum isolates from Mexican patients with AIDS-associated histoplasmosis by using histoplasmin electrophoretic profiles and randomly amplified polymorphic DNA patterns

The present paper analyzes the histoplasmin electrophoretic profiles and the randomly amplified polymorphic DNA (RAPD) patterns of the fungus Histoplasma capsulatum isolated from Mexican patients with AIDS-associated histoplasmosis. Clinical isolates from Guatemala, Colombia, and Panama, as well as H. capsulatum isolates from different sources in nature, were also processed. All histoplasmin samples shared four antigenic fractions of 200, 49, 10.5, and 8.5 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). According to their percentage of relatedness, based on SDS-PAGE histoplasmin electrophoretic image analysis, H. capsulatum isolates were divided in two groups: group A contained all AIDS-associated isolates studied and two human reference strains from Mexican histoplasmosis patients without AIDS; group B included bat guano, infected bat, and cock excreta isolates from the State of Guerrero, Mexico, plus three human histoplasmosis strains from Guatemala, Panama, and Colombia. Polymorphic DNA patterns evaluated by RAPD-PCR showed three major bands of 4.4, 3.2, and 2.3 kb in most H. capsulatum isolates studied. Four groups were related by DNA polymorphisms: group I was formed by most of the AIDS-associated H. capsulatum isolates studied, one human histoplasmosis strain from Colombia, two human reference strains from Mexican patients without AIDS, and one human histoplasmosis strain from Guatemala. Group II consisted of only a single strain from Panama. Group III included three strains: one from a Mexican patient with AIDS and two isolated from nature in Guerrero (cock excreta and bat guano). The last, group IV, consisted of only one strain isolated from an infected bat, captured in Guerrero. A tight relationship between phenotypic and genotypic characterization was observed, and both analyses could be useful tools for typing H. capsulatum from different sources and geographic origins.

Misleading manifestations of Coccidioides immitis in vivo

We describe a case of coccidioidomycosis in which several unusual morphologic forms of Coccidioides immitis occurred in biopsy tissue from the right lower lung of a patient. To our knowledge, this is the first case where so many diverse morphologic forms were manifested in a single patient in the absence of typical endosporulating spherules. Immature spherules demonstrating segmentation mimicked morula forms of Prototheca spp. Certain elements resembled budding cells of Blastomyces dermatitidis. These consisted of juxtaposed immature spherules without endospores, a germinating endospore, or thick-walled hyphal cells. Branched, septate hyphae and moniliform hyphae consisting of chains of thick-walled arthroconidia or immature spherules were also present. Complement fixation and immunodiffusion tests performed on the patient's serum were negative for C. immitis, B. dermatitidis, and Histoplasma capsulatum antibodies. Fluorescent-antibody studies were carried out with a specific C. immitis conjugate. All of the diverse fungal tissue elements stained positive with a moderate to strong (2 to 3+) intensity.

Purification and characterization of beta-N-acetylhexosaminidase from the phytopathogenic fungus Bipolaris sorokiniana

N-acetylhexosaminidase (HEX) from the phytopathogenic fungus Bipolaris sorokiniana was isolated and characterized. The production of HEX by B. sorokiniana was not altered by growing on different carbon sources. Enzyme purification was carried out by sequential liquid chromatography on Sephacryl S-200 HR, and p-aminobenzyl-2-acetamido-2-deoxy-beta-D-thioglucopyranoside agarose. The purification was about 70-fold, with a yield of 41%, determined with p-nitrophenyl-N-acetylglucosaminide as substrate. The enzyme had pH and temperature optima of 4.5 and 55 degrees C, respectively. The molecular weight of non-denatured enzyme was estimated as 120,000 Da by gel filtration chromatography, and about 55,000 Da by SDS-PAGE. The fungal HEX had glycosylated residues as evidenced by binding to Concanavalin-A. Bipolaris sorokiniana enzyme was also active with p-nitrophenyl-chitobioside and p-nitrophenyl-N-acetylgalactosaminide as substrates.

Antigenic relationships among pathogenic Beauveria bassiana with Engyodontium album (= B. alba) and non-pathogenic species of the genus Beauveria

Exoantigenic extracts of 15 isolates belonging to hyalohyphomycosis-causing Beauveria bassiana (1), and Engyodontium album (1), as well as other species of the genus Beauveria (one isolate each of B. brogniartii, B. densa, B. stephanoderis, B. velata, B. vermiconia and six isolates of unknown Beauveria species) were studied. Aqueous-merthiolated extracts derived from 10-day-old Sabouraud's dextrose agar slant cultures (25 degrees C) were concentrated (25X), and reacted against rabbit anti-B. bassiana serum in the presence of partially purified homologous antigen (20X) prepared from 5-week-old shaken cultures (30 degrees C), using a microimmunodiffusion procedure. Beauveria bassiana reference antigen and antiserum reacted to produce four bands of identity. With the exception of E. album, which was negative, extracts of the isolates of B. brogniartii, B. densa, B. stephanoderis, B. velata, B. vermiconia and the unknown Beauveria species all produced 2-4 lines of identity against the homologous anti-B. bassiana serum. These results suggested that all the species of the genus Beauveria tested were antigenically related to B. bassiana. Engyodontium album demonstrated antigenic distinctness, however, from B. bassiana and thus supported the validity of this taxon.

The characterization of chicken antibodies raised against Fusarium spp. by enzyme-linked immunosorbent assay and immunoblotting

Immunoassays for the detection of three Fusarium species have been developed. Chickens were immunized with the soluble antigens from within the mycelia (mycelia-soluble antigens) and the exoantigens of Fusarium sporotrichioides, Fusarium poae and Fusarium graminearum and the antigens were characterized using enzyme-linked immunosorbent assays, immunoblotting and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The cross-reactivities of antisera with eleven species of Fusarium, eleven species of fungi from other genera and the buffer-extracts of grain were determined. Antisera to the exoantigens and mycelia-soluble antigens did not cross-react with buffer-extracts of grain. The antisera against the mycelia-soluble antigens tended to cross-react with the antigens from other genera whereas the antisera against the exoantigens were genus specific. The antiserum raised against exoantigens from F. poae was species specific. The molecular weights of the immunodominant antigens from the Fusaria were above 28 kilodaltons. Antigens from Fusaria showed specific bands in SDS-PAGE gel that can be used to produce more specific antibodies. The results suggest that exoantigen immunoassay can be developed to identify Fusarium genus, whereas mycelia-soluble antigens are not suitable for immunoidentification among genus.

Immunoreactivity of a 38-kilodalton Penicillium marneffei antigen with human immunodeficiency virus-positive sera

Penicillium marneffei produced and secreted a 38-kDa antigen that appeared to be specific for this dimorphic fungus. This component could not be detected in antigenic extracts of Histoplasma capsulatum, Cryptococcus neoformans, Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, Candida albicans, and two other species of Penicillium by immunoblot analysis against the sera from patients with culture-confirmed penicilliosis marneffei. Antibody reactive with this antigen was found in a large proportion of human immunodeficiency virus (HIV)-positive patients, indicating a presumptive diagnosis of P. marneffei infection. A small number of asymptomatic HIV-seropositive patients and HIV-seropositive patients with other fungal infections were also found to be positive by this analysis, suggesting that subclinical or mixed fungal infections involving P. marneffei are not uncommon.

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.

Molecular and biochemical characterization of a Coccidioides immitis-specific antigen

Results of earlier investigations have indicated that the saprobic phase of Coccidioides immitis produces a heat-stable, 19-kDa antigen with serine proteinase activity which has been suggested to be specific for this pathogenic fungus. In the present study we have determined the N-terminal and partial internal amino acid sequences of the purified, 19-kDa antigen, cloned the gene which encodes this polypeptide, and confirmed that the secreted proteinase is a Coccidioides-specific antigen (CS-Ag). Both the genomic and cDNA sequences are reported and reveal that the csa gene which encodes this antigen has no introns. A 543-bp open reading frame encodes a 181-amino-acid-containing protein with a predicted molecular mass of 19.8 kDa and an isoelectric point of 8.3. The csa gene was localized on chromosome I of three representative C. immitis clinical isolates on the basis of Southern hybridizations. Expression of the csa gene in Escherichia coli using the pET21a plasmid vector yielded a recombinant protein that was recognized in immunoblot assays by antibody raised to the purified 19-kDa CS-Ag. Secretion of the native antigen is suggested to occur by cleavage of a putative 23-residue signal peptide. The native CS-Ag showed a low degree of glycosylation. Analysis of the carbohydrate composition of the CS-Ag revealed xylose, mannose, galactose, and glucose. However, the purified antigen showed no affinity for concanavalin A. A PCR method with specificity and high sensitivity for detection of C. immitis genomic DNA, using a pair of synthetic oligonucleotide primers whose sequences were based on that of the csa gene, was developed. A 520-bp product was amplified only when C. immitis genomic DNA was used as the template. The lower limits of DNA detection using this PCR method were 1 pg of C. immitis genomic DNA by ethidium bromide staining and 100 fg after Southern hybridization. The csa gene-based PCR method for detection of C. immitis DNA is useful for culture identification and may have clinical applications for the diagnosis of coccidioidal infections.

Occurrence of Penicillium marneffei infections among wild bamboo rats in Thailand

Penicilliosis marneffei has emerged as an endemic systemic mycosis in Southeast Asia among humans and wild bamboo rats. To gain an insight into the epidemiology of this life-threatening disease, a survey of bamboo rats for natural infections by Penicillium marneffei was carried out in the central plains of Thailand during June-September, 1987. Thirty-one lesser bamboo rats (Cannomys badius) and eight hoary bamboo rats (Rhizomys pruinosus) were trapped. Portions of their internal organs were cultured to determine if they had been infected by P. marneffei. Six each of C. badius (19.4%) and R. pruinosus (75%) yielded cultures of this unique, dimorphic Penicillium species. All of the isolates were readily converted to their unicellular form that multiplies by the process of schizogony by incubating them at 37 degrees C on plates of brain heart infusion agar. Their identity was further confirmed by a specific immunological test. Among the internal organs of the positive rats, the lungs had the highest positivity (83.3%), next in decreased order of frequency were the liver (33.3%) and the pancreas (33.3%). The use and value of domestic and wild animals in locating and demarcating endemic areas of geophilic fungal pathogens are discussed. Penicilliosis marneffei is considered to be a zooanthroponosis--a disease that occurs in lower animals, as well as, humans.

Immunochemical identification of fungi using polyclonal antibodies raised in rabbits to exoantigens from Aspergillus ochraceus

Aspergillus ochraceus Wilhelm is a producer of highly toxic mycotoxin, ochratoxin A, and is known to contribute to the damage of grain on storage. Rabbit antibodies were produced against the exoantigens of A. ochraceus, and ELISA and immunoblotting procedures were used to characterize their reactivity towards fungal exoantigens of four Aspergillus, seven Penicillium, three Fusarium, one Mucor and one Alternaria species. The antibodies were specific for A. ochraceus and essentially cross-reacted neither with other fungi nor with the water-soluble grain components. These antibodies, therefore, have the potential of being utilized for the discriminative monitoring of A. ochraceus in foodstuffs and feeds.

Comparative evaluation of chemiluminescent DNA probe assays and exoantigen tests for rapid identification of Blastomyces dermatitidis and Coccidioides immitis

Chemiluminescent DNA probe (Accuprobe) assays developed by Gen-Probe, Inc. (San Diego, Calif.), for the rapid identification of Blastomyces dermatitidis and Coccidioides immitis were evaluated and compared with the exoantigen test by using 74 mycelial cultures of B. dermatitidis and 72 mycelial cultures of C. immitis. Seventeen isolates of the dimorphic pathogen Paracoccidioides brasiliensis were included because of their gross morphologic and antigenic relatedness to B. dermatitidis. The heterologous fungi, namely, species of Chrysosporium, which are often confused with B. dermatitidis, and species of Malbranchea, which morphologically resemble C. immitis, were tested. All 74 of the B. dermatitidis mycelial isolates were correctly identified by the Accuprobe assay for B. dermatitidis within 2 h. However, the B. dermatitidis probe cross-hybridized with rRNA extracts of 10 of the 17 P. brasiliensis isolates, misidentifying them as B. dermatitidis. All 72 of the C. immitis isolates were identified correctly with the C. immitis probe. None of the other heterologous fungi belonging to Chrysosporium spp., Malbranchea spp., Onychocola canadensis, and Geotrichum sp. were cross-reactive with the B. dermatitidis and C. immitis probes. The exoantigen tests specifically identified 74 B. dermatitidis, 72 C. immitis, and 17 P. brasiliensis isolates within 48 to 72 h and differentiated the related heterologous fungi from the three dimorphic fungal pathogens.

Chemiluminescent immunoassays: discrimination between the reactivities of natural and human patient antibodies with antigens from eukaryotic pathogens, Trypanosoma cruzi and Paracoccidioides brasiliensis

Quantitative chemiluminescent enzyme-linked immunosorbent assay (ELISA) and dot-blotting procedures were developed to evaluate the reactivity of human antibodies with crude antigens and purified molecules of parasites and fungi, mainly Trypanosoma cruzi and Paracoccidioides brasiliensis. Reproducible, highly sensitive, and strictly dose-responding results were obtained, with the specificity depending on the kind of antigen used. Mixed antigens (epimastigote membrane and HIV-1 heptapeptide) applied in dots could be independently recognized by specific sera. Purified antigens (T. cruzi F2/3 and P. brasiliensis gp43) at very small concentrations gave specific reactions with patients' sera diluted > or = 1:1,000 and were very poorly reactive or unreactive with natural antibodies using the chemiluminescent immunoassays. P. brasiliensis crude antigen Fava Netto polysaccharide antigen (FNPA) contained peptide epitopes recognized by natural antibodies and carbohydrate epitopes reactive with sera from histoplasmosis patients. It is very important that sensitive chemiluminescence immunoassays be used with purified antigenic molecules to ensure specificity for the diagnosis and follow-up of parasitic and fungal infections.

Oral histoplasmosis in India: a case report and an overview of cases reported during 1968-92

Oral histoplasmosis in a 30-year-old male with no history of travel outside India is described. An ulcerating lesion was located on the hard palate. A chest X-ray was normal. Based on physical examination, regional lymph nodes, liver and spleen were not involved. The diagnosis was established by demonstrating yeast-like budding cells in a biopsy of the lesion and by isolating Histoplasma capsulatum in pure culture. The identity of the isolate was confirmed by a chemiluminescent DNA-probe assay and the exoantigen test. A review of the Indian literature from 1968 to 1992 revealed the occurrence of 25 authentic cases of histoplasmosis in India. In 19 cases, lesions were confined to the oral cavity confirming prior observation that histoplasmosis in Indian patients tends to occur primarily in extrapulmonary sites, particularly the oral cavity.

Aberrant Histoplasma capsulatum. Confirmation of identity by a chemiluminescence-labeled DNA probe

A cottony, light tan, filamentous fungus with pear-shaped microconidia and lacking tuberculated macroconidia was isolated from a bronchial lavage specimen. Subculture on several media at 37 degrees C failed to convert the fungus to a yeast form after several weeks; attempts at in vivo conversion in mice were also unsuccessful. Sera obtained several months apart showed M bands with Histoplasma capsulatum (HC) antigen by immunodiffusion and an increase in complement fixation titers with mycelial and yeast phase antigens of HC. Parallel identity was obtained on two occasions with exoantigen culture confirmation reagents for HC from Immuno-Mycologics as well as one of identity with Nolan reagents. Extracts from four Chrysosporium spp. strains had no identity reactions with HC with either kit. The fungus was identified as HC by the Accuprobe Histoplasma chemiluminescence-labeled DNA probe directed at ribosomal RNA, whereas all four Chrysosporium spp. isolates tested negative. DNA probes are a fast and accurate method to confirm the identity of aberrant fungal isolates.

Partial purification and characterization of mold antigens commonly found in foods

Rapid methods are needed for detection of molds in foods; therefore, an enzyme-linked immunosorbent assay was developed. The extracellular and mycelial antigens for Mucor, Aspergillus, Cladosporium, and Geotrichum species were partially purified and characterized. The molecular masses of the mycelial and extracellular antigens, as determined by size exclusion chromatography, ranged from 4.5 x 10(5) to 6.7 x 10(5) Da. There was only one main antigenic peak separated by Sepharose CL-4B and concanavalin A-Sepharose columns for Mucor, Cladosporium, and Geotrichum mycelial and extracellular antigens, but there were two for Aspergillus mycelial antigens and three for Aspergillus extracellular antigens. These antigens contained 10 to 50% protein which was part of the active site since protease digestion significantly decreased antigenic activity. Neutral sugars, ranging from 13 to 75%, made up the rest of the active site, and < 1% phosphate was detected in mycelial antigens. Geotrichum, Cladosporium, and Aspergillus antigens contained mainly glucose, galactose, and mannose. Mucor antigens contained these sugars plus fucose. The percentage of sugars differed between the mycelia and extracellular antigens. Enzymatic digestion and competitive inhibition tests using different sugar derivatives showed that galactosyl residues with beta linkages were immunodominant for Aspergillus, Geotrichum, and Cladosporium antigens and mannosyl residues with alpha linkages were immunodominant for Mucor antigens.

Evaluation of Gen-Probe's Histoplasma capsulatum and Cryptococcus neoformans AccuProbes

Gen-Probe's DNA probes were evaluated for use in the identification of clinical isolates of Histoplasma capsulatum var. capsulatum and Cryptococcus neoformans. Ninety-five mould-phase fungi were probed, including 41 isolates of H. capsulatum var. capsulatum. Similarly, 98 yeasts, including 42 C. neoformans isolates, were examined by using the C. neoformans DNA probe. In the study, both probes demonstrated 100% specificity and 100% sensitivity. Their use in the clinical laboratory may significantly reduce the time required for definitive identification of fungi.

Comparative evaluation of a chemiluminescent DNA probe and an exoantigen test for rapid identification of Histoplasma capsulatum

A chemiluminescent DNA probe (Accuprobe) assay developed by Gen Probe, Inc., for the rapid identification of Histoplasma capsulatum was evaluated and compared with the exoantigen test by using 162 coded cultures including Histoplasma capsulatum var. capsulatum, Histoplasma capsulatum var. duboisii, Histoplasma capsulatum var. farciminosum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides brasiliensis, and morphologically related saprobic fungi. Each test uses a chemiluminescent, acridinium ester-labeled, single-stranded DNA probe that is complementary to the rRNA of the target organism. Lysates of the test cultures were prepared by sonication with glass beads and heat treated. After the rRNA was released from the target organism, the labeled DNA probe combined with the target H. capsulatum rRNA to form a stable DNA-RNA hybrid. A hybridization protection assay was used, and the chemiluminescence of hybrids was measured initially with a Leader 1 luminometer as relative light units and later during the investigation with a probe assay luminometer as probe light units. Of the 162 coded mycelial cultures tested by the Accuprobe assay, 105 were identified as H. capsulatum. The test could be performed with an inoculum of a few square millimeters (1 to 2 mm2) of growth. In the primary evaluation, the Accuprobe identified 103 of the 105 cultures as H. capsulatum within 2 h. The remaining two cultures, contaminated with bacteria, had to be purified before the Accuprobe assay identified them correctly as H. capsulatum. Since each coded culture was concurrently tested for H. capsulatum, B. dermatitidis, and C. immitis exoantigens, the identification of all three dimorphic pathogens was provided simultaneously. Of the 162 coded cultures tested, 105 were identified by the exoantigen test as H. capsulatum, 12 were identified as B. dermatitidis, 13 were identified as C. immitis, and 32 were negative for H. capsulatum, B. dermatitidis, and C. immitis. The bacterial contamination in two isolates did not interfere with the exoantigen testing. The exoantigen test required 7- to 10-day-old colonies and required 48 to 72 h of incubation before definitive identification was obtained.

Evaluation of a chemiluminescent probe assay for identification of Histoplasma capsulatum isolates

Fifty-three of 54 isolates of fungi were correctly identified with an acridinium ester-labelled probe for Histoplasma capsulatum (Accuprobe; Gen-Probe, San Diego, Calif.). One isolate of Aspergillus niger was incorrectly identified as H. capsulatum. Age of the culture, medium for isolation, and morphologic state did not affect the results.

[The sources of histoplasmosis infection on the Isla de la Juventud, Cuba]

The purpose of this work is to report the isolation of Histoplasma capsulatum, etiologic agent of histoplasmosis, from soil in sites inhabited by bats and chicken in the Island of Youth, Cuba. The fungus was cultured from four species of cave dwelling bats too. The identification of H. capsulatum was done by mycelial to yeast conversion and exoantigen test. It is pointed out the epidemiological value of some of these isolations in caves of great importance from the archaeological, speleological or tourist point of view, and the potential risk that they represent to human health. The authors conclude with some recommendation to prevent the infection with H. capsulatum in people who have to keep in contact with those environments.

Enzyme-linked immunosorbent assay for detection of molds in cheese and yogurt

An enzyme-linked immunosorbent assay was developed for the detection of molds in dairy products. New Zealand White female rabbits were immunized with .45 mg of partially purified extracellular antigen from freeze-dried culture filtrates of Aspergillus versicolor, Cladosporium herbarum, Geotrichum candidum, Mucor circinelloides, and Penicillium chrysogenum. Blood was drawn at various intervals, and antibodies were separated and purified. Antibody-peroxidase conjugates were prepared with the following ratios being the optimum ones: A. versicolor 10:20; C. herbarum 5:10; G. candidum 1:10; M. circinelloides 5:5; and P. chrysogenum 10:10. The assays were sensitive within a range of 1 ng to 1 microgram/ml, depending on the mold used. Inhibition tests were done for each mold with concentrations of 0 to 5000 micrograms/ml of antigen. The enzyme-linked immunosorbent assay tests for Cladosporium, Geotrichum, and Mucor were only inhibited by antigens from other species of the same genus; whereas there was crossreaction between antibodies and antigens of species of Penicillium and of Aspergillus. Citrate buffer was best for extracting the mold from cheese and yogurt. The extract was adjusted to pH 7.2 and ELISA was performed. Results showed that these molds can be detected in Cheddar and cottage cheeses and yogurt within 2 d, which is before mold growth is visible in these products.

Differentiation of medically important isolates of Bipolaris and Exserohilum with exoantigens

Soluble culture extracts of Bipolaris australiensis, B. hawaiiensis, B. spicifera, Exserohilum longirostratum, E. mcginnisii, E. rostratum, and Helminthosporium solani were used to prepare reference antisera in New Zealand White rabbits. The absorbed reference antisera were tested by a microimmunodiffusion method against concentrated culture filtrates prepared from 115 environmental and clinical isolates of Alternaria spp., Bipolaris spp., Curvularia spp., Dactylaria sp., Drechslera spp., Embellisia spp., Exserohilum spp., Fusarium sp., Helminthosporium sp., Microsporum sp., Scolecobasidium sp., and Scopulariopsis sp. Cross-reactivity did not occur between isolates of the genera tested except for some Bipolaris and Curvularia spp. Antigens shared by species of Bipolaris and Curvularia correlated with their morphologic similarity and phylogenetic closeness. Cross-reactivity was observed among isolates of B. australiensis, B. hawaiiensis, and B. spicifera and among isolates of E. longirostratum, E. mcginnisii, and E. rostratum. The exoantigen test is valuable for differentiating these fungi at the generic level.

Canine pythiosis--isolation and identification of Pythium insidiosum

Pythium insidiosum was isolated from the subcutaneous tissue of a 1-year-old tan crossbreed dog and from the intestinal tract of an 18-month-old Samoyed male. Gomori's methenamine silver stain was superior to hematoxylin and eosin in demonstrating the organism in tissue sections. The agent was identified as P. insidiosum by zoospore formation in an aqueous yeast extract solution containing grass blades. Exoantigens produced in culture were shown to be identical to known P. insidiosum antigens by microimmunodiffusion.

Isolation of antigens with proteolytic activity from Coccidioides immitis

Three antigens with proteolytic activity have been isolated from crude, water-soluble fractions of the saprobic phase of the fungal pathogen Coccidioides immitis. Two proteinases, identified in our immunoelectrophoresis reference system as Ag11 and AgCS, were isolated from the soluble conidial wall fraction (SCWF). Ag11 was previously shown to be a serine proteinase and was characterized in this study as a 60-kilodalton (kDa) fraction by gel filtration (GF). The purified proteinase demonstrated little or no reactivity with 21 serum samples from coccidioidomycosis patients in the enzyme-linked immunosorbent assay; this may be due to limited presentation of this antigen to the host during the course of coccidioidomycosis. AgCS was separated by GF chromatography into two fractions identified by molecular masses of 39 and 19 kDa. Most proteolytic activity was shown by substrate gel electrophoresis to be associated with the lower-molecular-mass fraction. AgCS was reactive with 18 of the 21 serum samples and shown to be the major component of a heat-stable antigen previously reported to be immunospecific for C. immitis. The third antigen with proteolytic activity was isolated from the 5-day mycelial culture filtrate and identified by GF as a 56-kDa fraction. Uniformly high levels of immunoreactivity between 18 of the 21 patient sera and the 56-kDa antigen were demonstrated. Antigens with proteolytic activity may play important roles in fungus-host interactions as well as morphogenesis of the pathogen.

Coccidioidomycosis

Coccidioidomycosis is a largely self-limited fungal respiratory illness. However, the infrequent case of progressive or disseminated disease can be devastating. As international travel to and from endemic areas increases, physicians unfamiliar with the disease may be called upon to recognize and treat serious coccidioidal infections. The major risk factors for dissemination are race and immunosuppression. The most common sites of dissemination are the skin, lymph nodes, bone and meninges. Diagnosis is aided by investigation of the patient's clinical history, delayed-type hypersensitivity skin test reaction, serologic testing, and recovery of organisms from infected tissue or secretions for direct examination and culture. Fungicidal agents are not available, fortunately, fungistatic therapy allows many patients to recover. The availability of both intravenous/intrathecal and oral agents now allows more therapeutic flexibility in the treatment of this disease.