Typing of Histoplasma capsulatum strains by fatty acid profile analysis

A Langmuir-Blodgett Study of the Interaction between Amphotericin B and Lipids of Histoplasma capsulatum

Histoplasma capsulatum is a dimorphic, thermal, and nutritional fungus. In the environment and at an average temperature of 28 °C, it develops as a mold that is composed of infecting particles. Once in the host or in cultures at 37 °C, it undergoes a transition into the parasitic form. In the present work, we performed chemical extraction and characterization using chromatography techniques of the associated lipid composition of the external surface of the cell wall of the mycelial phase of two isolates of the H. capsulatum: one clinical and one environmental. Several differences were evidenced in the fatty acids in the phospholipid composition. Surface pressure–area isotherms and compression module curves of the Amphotericin B and lipid extract monolayers, as well as (AmB)-lipid extract mixed monolayers were recorded. Results show a high affinity of AmB towards lipid extracts. The most stable monolayers were formed by AmB + environmental with a mass ratio of 1:3 and AmB + clinical with a mass ratio of 1:2. Knowledge of the AmB aggregation processes at a molecular level and the characterization of the lipid extracts allows the possibility to understand the interaction between the AmB and the lipid fractions of H. capsulatum.

Metabolism of Gluconeogenic Substrates by an Intracellular Fungal Pathogen Circumvents Nutritional Limitations within Macrophages

Microbial pathogens exploit host nutrients to proliferate and cause disease. Intracellular pathogens, particularly those exclusively living in the phagosome such as Histoplasma capsulatum, must adapt and acquire nutrients within the nutrient-limited phagosomal environment. In this study, we investigated which host nutrients could be utilized by Histoplasma as carbon sources to proliferate within macrophages. Histoplasma yeasts can grow on hexoses and amino acids but not fatty acids as the carbon source in vitro Transcriptional analysis and metabolism profiling showed that Histoplasma yeasts downregulate glycolysis and fatty acid utilization but upregulate gluconeogenesis within macrophages. Depletion of glycolysis or fatty acid utilization pathways does not prevent Histoplasma growth within macrophages or impair virulence in vivo However, loss of function in Pck1, the enzyme catalyzing the first committed step of gluconeogenesis, impairs Histoplasma growth within macrophages and severely attenuates virulence in vivo, indicating that Histoplasma yeasts rely on catabolism of gluconeogenic substrates (e.g., amino acids) to proliferate within macrophages.IMPORTANCEHistoplasma is a primary human fungal pathogen that survives and proliferates within host immune cells, particularly within the macrophage phagosome compartment. The phagosome compartment is a nutrient-limited environment, requiring Histoplasma yeasts to be able to assimilate available carbon sources within the phagosome to meet their nutritional needs. In this study, we showed that Histoplasma yeasts do not utilize fatty acids or hexoses for growth within macrophages. Instead, Histoplasma yeasts consume gluconeogenic substrates to proliferate in macrophages. These findings reveal the phagosome composition from a nutrient standpoint and highlight essential metabolic pathways that are required for a phagosomal pathogen to proliferate in this intracellular environment.

Thermotolerance of Histoplasma capsulatum at 40 °C predominates among clinical isolates from different Latin American regions

The yeast phase of 22 Histoplasma capsulatum clinical isolates from Mexico, Argentina, Colombia, and Guatemala and three reference strains, one from Panama and two from the United States of America (USA), were screened for thermosensitivity characteristics using different analyses. Growth curves at 0, 3, 6, 12, 24, and 30 h of incubation at 37 and 40 °C, the growth inhibition percentage at 40 °C, and the doubling time at 37 and 40 °C were determined for all yeasts studied. Most of the isolates examined exhibited thermotolerant phenotypes at 40 °C, whereas a thermosensitive phenotype at 40 °C was only detected in the Downs reference strain from the USA. Growth inhibition values lower than 33.8% supported the predominance of the thermotolerant phenotype at 40 °C. The doubling time means found for the different isolates were 5.14 h ± 1.47 h at 37 °C and 5.55 h ± 1.87 h at 40 °C. This is the first report to underscore the predominance of thermotolerant and delayed doubling time phenotypes in H. capsulatum clinical isolates from different regions of Latin America.

Improved Diagnosis of Acute Pulmonary Histoplasmosis by Combining Antigen and Antibody Detection

BACKGROUND

Acute pulmonary histoplasmosis can be severe, especially following heavy inoculum exposure. Rapid diagnosis is critical and often possible by detection of antigen, but this test may be falsely negative in 17% of such cases. Antibody detection by enzyme immunoassay (EIA) may increase sensitivity and permit the measurement of immunoglobulin M (IgM) and immunoglobulin G (IgG) classes of antibodies separately.

METHODS

Microplates coated with Histoplasma antigen were used for testing of serum from patients with acute pulmonary histoplasmosis and controls in the MVista Histoplasma antibody EIA. Results for IgG and IgM were reported independently.

RESULTS

IgG antibodies were detected in 87.5%, IgM antibodies in 67.5%, and IgG and/or IgM antibodies in 88.8% of patients with acute pulmonary histoplasmosis in this assay, while immunodiffusion, complement fixation, and antigen testing showed sensitivities of 55.0%, 73.1%, and 67.5%, respectively (n = 80). Combining antigen and antibody detection increased the sensitivity to 96.3%.

CONCLUSIONS

The MVista Histoplasma antibody EIA offers increased sensitivity over current antibody tests while also allowing separate detection of IgG and IgM antibodies and complementing antigen detection. Combining antigen and EIA antibody testing provides an optimal method for diagnosis of acute pulmonary histoplasmosis.

Fungal Morphology, Iron Homeostasis, and Lipid Metabolism Regulated by a GATA Transcription Factor in Blastomyces dermatitidis

In response to temperature, Blastomyces dermatitidis converts between yeast and mold forms. Knowledge of the mechanism(s) underlying this response to temperature remains limited. In B. dermatitidis, we identified a GATA transcription factor, SREB, important for the transition to mold. Null mutants (SREBΔ) fail to fully complete the conversion to mold and cannot properly regulate siderophore biosynthesis. To capture the transcriptional response regulated by SREB early in the phase transition (0–48 hours), gene expression microarrays were used to compare SREB∆ to an isogenic wild type isolate. Analysis of the time course microarray data demonstrated SREB functioned as a transcriptional regulator at 37°C and 22°C. Bioinformatic and biochemical analyses indicated SREB was involved in diverse biological processes including iron homeostasis, biosynthesis of triacylglycerol and ergosterol, and lipid droplet formation. Integration of microarray data, bioinformatics, and chromatin immunoprecipitation identified a subset of genes directly bound and regulated by SREB in vivo in yeast (37°C) and during the phase transition to mold (22°C). This included genes involved with siderophore biosynthesis and uptake, iron homeostasis, and genes unrelated to iron assimilation. Functional analysis suggested that lipid droplets were actively metabolized during the phase transition and lipid metabolism may contribute to filamentous growth at 22°C. Chromatin immunoprecipitation, RNA interference, and overexpression analyses suggested that SREB was in a negative regulatory circuit with the bZIP transcription factor encoded by HAPX. Both SREB and HAPX affected morphogenesis at 22°C; however, large changes in transcript abundance by gene deletion for SREB or strong overexpression for HAPX were required to alter the phase transition.

Blastomyces dermatitidis belongs to a group of human pathogenic fungi that convert between two forms, mold and yeast, in response to temperature. Growth as yeast (37°C) in tissue facilitates immune evasion, whereas growth as mold (22°C) promotes environmental survival, sexual reproduction, and generation of transmissible spores. Despite the importance of dimorphism, how fungi regulate temperature adaptation is poorly understood. We identified SREB, a transcription factor that regulates disparate processes including dimorphism. SREB null mutants, which lack SREB, fail to fully complete the conversion to mold at 22°C. The goal of our research was to characterize how SREB regulates transcription during the switch to mold. Gene expression microarray along with chromatin binding and biochemical analyses indicated that SREB affected several processes including iron homeostasis, lipid biosynthesis, and lipid droplet formation. In vivo, SREB directly bound and regulated genes involved with iron uptake, lipid biosynthesis, and transcription. Functional analysis suggested that lipid metabolism may influence filamentous growth at 22°C. In addition, SREB interacted with another transcription factor, HAPX.

African histoplasmosis: the first report of an indigenous case in India

OBJECTIVES

African histoplasmosis, caused by Histoplasma capsulatum var. duboisii, is an invasive fungal infection endemic in Central and West Africa. Cases seen outside Africa are generally imported. We report a disseminated purely cutaneous form of this infection in an otherwise healthy person from Kerala, in southern India.

METHODS

A 59-year-old farmer presented with asymptomatic, generalized, reddish skin lesions of five months in duration. Dermatologic examination revealed multiple erythematous papules and plaques of varying sizes, predominantly over the trunk and upper limbs. The patient was otherwise in good health. Systemic examination including the pulmonary and musculoskeletal systems revealed no abnormalities.

RESULTS

Skin biopsy was performed from a lesion on the thigh. Histopathologic examination revealed epithelioid and suppurative granulomas in the upper dermis, with lymphocytes, neutrophils, and plenty of giant cells. Fite-Faraco staining for Mycobacterium leprae was negative. Fungus cultured from the specimen was identified as H. capsulatum var. duboisii, the rarer variant of H. capsulatum. The patient was treated with ketoconazole 200 mg/day for four months and attained complete clearance. No relapse has been detected over two years of follow-up.

CONCLUSIONS

To the best of our knowledge, this case represents the first instance of African histoplasmosis to be reported from India. The occurrence of such a rare infection in an immunocompetent individual, who had not travelled elsewhere, raises the possibility of the indigenous existence of H. capsulatum var. duboisii in Kerala. Further studies of the ecology and epidemiology of this rare infection are essential.

An unusual cutaneous tumor: African histoplasmosis following mudbaths: case report and review

African histoplasmosis, caused by Histoplasma capsulatum var. duboisii, is endemic in Africa. The disease usually involves the skin, subcutaneous tissue, and bones. A case of African histoplasmosis presenting as a cutaneous tumor and non-healing wound in a 66-year-old immunocompetent male residing in Africa, the first ever reported following mudbaths and acupuncture, is hereby reported. Diagnosis was confirmed by means of polymerase chain reaction performed on tissue material. The patient was started on long-term itraconazole therapy and he responded well. African histoplasmosis should be included in the differential diagnosis of non-healing wounds or tumor-like lesions, especially in the context of mudbaths in an endemic area.

Fatty acid profile and influence of oxythiamine on fatty acid content in Malassezia pachydermatis, Candida albicans and Saccharomyces cerevisiae

Malassezia pachydermatis and Candida albicans are fungi involved in the skin diseases and systemic infections. The therapy of such infections is difficult due to relapses and problems with pathogen identification. In our study, we compare the fatty acids profile of M. pachydermatis, C. albicans and S. cerevisiae to identify diagnostic markers and to investigate the effect of oxythiamine (OT) on the lipid composition of these species. Total fatty acid content is threefold higher in C. albicans and M. pachydermatis compared with S. cerevisiae. These two species have also increased level of polyunsaturated fatty acids (PUFA) and decreased content of monounsaturated fatty acids (MUFA). We noted differences in the content of longer chain (>18) fatty acids between studied species (for example a lack of 20 : 1 in S. cerevisiae and 22 : 0 in M. pachydermatis and C. albicans). OT reduces total fatty acids content in M. pachydermatis by 50%. In S. cerevisiae, OT increased PUFA whereas it decreased MUFA content. In C. albicans, OT decreased PUFA and increased MUFA and SFA content. The results show that the MUFA to PUFA ratio and the fatty acid profile could be useful diagnostic tests to distinguish C. albicans, M. pachydermatis and S. cerevisiae, and OT affected the lipid metabolism of the investigated species, especially M. pachydermatis.

Histoplasma mechanisms of pathogenesis--one portfolio doesn't fit all

Histoplasma capsulatum is the leading cause of endemic mycosis in the world. Analyses of clinical isolates from different endemic regions show important diversity within the species. Recent molecular studies of two isolates, the Chemotype I NAm2 strain G217B and the Chemotype II Panamanian strain G186A, reveal significant genetic, structural, and molecular differences between these representative Histoplasma strains. Some of these variations have functional consequences, representing distinct molecular mechanisms that facilitate Histoplasma pathogenesis. The realization of Histoplasma strain diversity highlights the importance of characterizing Histoplasma virulence factors in the context of specific clinical strain isolates.

Comparison of different DNA-based methods for molecular typing of Histoplasma capsulatum

Histoplasma capsulatum is very prevalent in the environment and is one of the most common causes of mycoses in humans and diverse animals in Brazil. Multiple typing methods have been developed to study H. capsulatum epidemiology; however, there is limited information concerning comparisons of results obtained with different methods using the same set of isolates. To explore the diversity of H. capsulatum in Brazil and to determine correlations between the results of three different molecular typing techniques, we examined 51 environmental, animal, and human isolates by M13 PCR fingerprinting, PCR-restriction fragment length polymorphism (RFLP) analysis of the internal transcribed region 1 (ITS1)-5.8S-ITS2 region of the rDNA locus, and DNA sequencing and phylogenetic analysis of parts of four protein-encoding genes, the Arf (ADP ribosylation factor), H-anti (H antigen precursor), Ole (delta-9 fatty acid desaturase), and Tub1 (alpha-tubulin) genes. Each method identified three major genetic clusters, and there was a high level of concordance between the results of the typing techniques. The M13 PCR fingerprinting and PCR-RFLP analyses produced very similar results and separated the H. capsulatum isolates included in this study into three major groups. An additional approach used was comparison of our Brazilian ITS1-5.8S-ITS2 sequences with the sequences deposited previously in NCBI data banks. Our analyses suggest that H. capsulatum can be divided into different molecular types that are dispersed around the world. Our results indicate that the three methods used in this study are reliable and reproducible and that they have similar sensitivities. However, M13 PCR fingerprinting has some advantages over the other two methods as it is faster, cheaper, and more user friendly, which especially increases its utility for molecular typing of Histoplasma in situations where laboratory facilities are relatively limited.

Ferrous, but not ferric, iron maintains homeostasis in Histoplasma capsulatum triacylglycerides

Iron is an indispensable micronutrient for virtually all microorganisms, where it acts as a cofactor of many enzymes involved in regulation of multiple cellular and physiological functions. This metal is also considered an important determinant contributing to the pathogenesis of fungal infectious diseases, and therefore the identification of iron-regulated metabolic processes occurring within the invading fungal cell can help the development of new antifungal therapeutic strategies. In this study, we examined relationships between iron availability and neutral storage lipids in Histoplasma capsulatum, a dimorphic fungus responsible for the most common respiratory and systemic mycosis in humans. Yeast cells were grown in a defined minimal medium supplemented with or without iron. Lipids were extracted from cells at the log and late stationary growth phases, then separated by thin-layer chromatography, and fatty acids were analyzed by gas chromatography. A culture age-related decrease in the unsaturated fatty acid content was observed in all four neutral lipid classes examined. Iron-related alterations could be seen in relation to triacylglycerol and free fatty acid pools, whereas no iron-dependent effects were detected in diacylglycerol and steryl ester fractions. Regarding triacylglycerols, the presence of iron positively affected the content of unsaturated fatty acids, and this stabilizing action of iron was notably increased when ferrous ions were added. Subsequent iron uptake studies showed a definite preference of H. capsulatum to acquire iron in its reduced, more soluble, ferrous form, and therefore, the availability of iron may be the underlying reason for the observed iron-maintained homeostasis in H. capsulatum triacylglycerols.

Neutral storage lipids of Histoplasma capsulatum: effect of culture age

Lipids contribute significantly to the pathogenesis of fungal infectious diseases and an understanding of lipid metabolism occurring in fungal pathogens can help the development of more efficient antifungal therapeutic strategies. In this study, the effect of culture age on the distribution of fatty acids among different neutral lipid (NL) classes in the dimorphic fungus Histoplasma capsulatum was investigated. Yeast cells of the G217B strain grown in two different media were collected after 4 and 7 days of growth, which roughly correspond to log and stationary culture growth phases, respectively. Neither culture age nor medium type had any influence on qualitative fatty acid (FA) profiles; however, the FA percentage composition varied with culture growth. A culture age-related decrease in the content of unsaturated FAs could be observed in all four of the NL classes examined, but the most intensive changes were detected in diacylglycerol and free FA fractions. Conversely, an increase in saturated FAs was observed. The transcriptional analysis of two major delta 9- and delta 12-FA desaturase genes, ode1 and sde1, showed no differences in their expression levels under experimental conditions. These results showing the dynamics of changes in FA composition in the NL fraction were concomitant with nutrient exhaustion in aging H. capsulatum cultures. Overall, the results presented in this work not only have implications for our knowledge of basic lipid biochemistry of H. capsulatum, but also will contribute to better understanding of biology and pathogenesis of this fungus and, consequently, can help in the discovery of more effective antifungal drugs.

Production of extracellular proteolytic activity by Histoplasma capsulatum grown in Histoplasma-macrophage medium is limited to restriction fragment length polymorphism class 1 isolates

Extracellular proteolytic activity was studied for 28 strains of Histoplasma capsulatum var. capsulatum and 2 strains of H. capsulatum var. duboisii. Secreted protease activity assessed by skim milk agarose clearance was limited solely to H. capsulatum var. capsulatum restriction fragment length polymorphism (RFLP) class 1 strains. There was a difference in proteolytic activity levels among class 1 strains. Extracellular proteolytic activity was further determined during growth of those strains in liquid medium using azodye-impregnated protein substrates. In general, the highest activities were measured when azocollagen was used, whereas azocasein and azoalbumin were cleaved less efficiently. The activity was inhibited by phenylmethylsulfonyl fluoride, 4-(2-aminoethyl) benzenesulfonyl fluoride, antipain, and chymostatin, indicating, thereby, the presence of chymotrypsin-like serine proteases. Chromatographic analyses as well as variable substrate use at different culture times revealed production of at least 2 different enzyme pools of the same serine-like protease family. Our results demonstrate a distinctive ability of RFLP class 1 isolates to produce and secrete serine proteinase-type activity. This peculiarity may be relevant to the biology and pathogenesis of this particular clade of H. capsulatum isolates. Overall, the feature of extracellular proteolytic activity production enables a convenient and unequivocal identification of RFLP class 1 isolates and, thereby, can be used in H. capsulatum strain differentiation and typing.