Analyses of the genetic diversity and population structures of Histoplasma capsulatum clinical isolates from Mexico, Guatemala, Colombia and Argentina, using a randomly amplified polymorphic DNA-PCR assay.

We studied the genetic diversity and the population structure of human isolates of Histoplasma capsulatum, the causative agent of histoplasmosis, using a randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) assay to identify associations with the geographic distribution of isolates from Mexico, Guatemala, Colombia and Argentina. The RAPD-PCR pattern analyses revealed the genetic diversity by estimating the percentage of polymorphic loci, effective number of alleles, Shannon's index and heterozygosity. Population structure was identified by the index of association (IA) test. Thirty-seven isolates were studied and clustered into three groups by the unweighted pair-group method with arithmetic mean (UPGMA). Group I contained five subgroups based on geographic origin. The consistency of the UPGMA dendrogram was estimated by the cophenetic correlation coefficient (CCCr = 0.94, P = 0.001). Isolates from Mexico and Colombia presented higher genetic diversity than isolates from Argentina. Isolates from Guatemala grouped together with the reference strains from the United States of America and Panama. The IA values suggest the presence of a clonal population structure in the Argentinian H. capsulatum isolates and also validate the presence of recombining populations in the Colombian and Mexican isolates. These data contribute to the knowledge on the molecular epidemiology of histoplasmosis in Latin America.

Identification of Aspergillus tubingensis in a primary skin infection.

OBJECTIVE: Aspergillus section Nigri comprises a group of related species that include Aspergillus niger, A. welwitschiae, A. carbonarius, A. brasiliensis and A. tubingensis. Some of these species are morphologically very similar to A. niger but exhibit different patterns of susceptibility to antifungal agents; such is the case for A. tubingensis. Therefore, when diagnosing aspergillosis, it is important to identify the pathogen at the species level. This study aimed to identify the species of an Aspergillus spp. isolate (MM-82) obtained from a patient with a dermatosis localized to the right leg. MATERIALS AND METHODS: The MM-82 isolate was examined for macro- and microscopic morphology, conidia size and thermotolerance, and a phylogenetic analysis of a benA gene segment was performed for molecular identification. Susceptibility to antifungals was determined using antifungal microdilution according to the methodology of European Society of Clinical Microbiology and Infectious Diseases (EUCAST). RESULTS: Based on its phenotypic characteristics and the phylogenetic analysis of the sequence of a benA gene segment, the MM-82 isolate was identified as A. tubingensis. This fungus did not show resistance to antifungal agents commonly used for treatment. CONCLUSION: This study demonstrated that A. tubingensis can cause skin infection; this constitutes the first report of a case of aspergillosis caused by A. tubingensis in Mexico.

Histoplasma capsulatum yeast cells attach and agglutinate human erythrocytes.

The ability of yeast cells of Histoplasma capsulatum to attach and agglutinate human erythrocytes has been described. This is the first report involving these yeasts in the hemagglutination phenomenon. Results revealed that the yeast cells were able to bind to erythrocytes irrespective of blood groups and to agglutinate them when a high density of yeast cells was used. Assays on the inhibition of yeast attachment to erythrocytes were also performed, using sugar-treated yeast cells. Results indicate that galactose (Gal), mainly the beta-anomer, specially inhibited yeast attachment. Disaccharides (Gal-derivatives) and glycosaminoglycans containing Gal residues, mainly chondroitin sulfate C, promote this type of inhibition. In addition, preliminary data of inhibition assays also involved a probable ionic strength driven mechanism mediated by sialic acid and heparan sulfate, suggesting that yeast binding to erythrocytes could be associated with negative charges of both molecules.

Interaction of murine macrophage-membrane proteins with components of the pathogenic fungus Histoplasma capsulatum.

The interaction of macrophage-membrane proteins and histoplasmin, a crude antigen of the pathogenic fungus Histoplasma capsulatum, was studied using murine peritoneal macrophages. Membrane proteins were purified via membrane attachment to polycationic beads and solubilized in Tris-HCl/SDS/DTT/glycerol for protein extraction; afterwards they were adsorbed or not with H. capsulatum yeast or lectin binding-enriched by affinity chromatography. Membrane proteins and histoplasmin interactions were detected by ELISA and immunoblotting assays using anti-H. capsulatum human or mouse serum and biotinylated goat anti-human or anti-mouse IgG/streptavidin-peroxidase system to reveal the interaction. Results indicate that macrophage-membrane proteins and histoplasmin components interact in a dose-dependent reaction, and adsorption of macrophage-membrane proteins by yeast cells induces a critical decrease in the interaction. Macrophage-membrane glycoproteins with terminal D-galactosyl residues, purified by chromatography with Abrus precatorius lectin, bound to histoplasmin; and two bands of 68kD and 180kD of transferred membrane protein samples interacted with histoplasmin components, as revealed by immunoblot assays. Specificity for beta-galactoside residues on the macrophage-membrane was confirmed by galactose inhibition of the interaction between macrophage-membrane proteins and histoplasmin components, in competitive ELISA using sugars, as well as by enzymatic cleavage of the galactoside residues.

[Strategies of Histoplasma capsulatum for evading the cytocidal mechanisms of phagocytes]. / Estrategias del Histoplasma capsulatum para evadir los mecanismos citocidas de los fagocitos.

Although proliferation of Histoplasma capsulatum within the macrophage is restricted by cell mediated immunity and, that there is no apparent deficiency in the fungicidal power of the macrophage, H. capsulatum can prosper in this intracellular microenvironment in some circumstances, which provides special nutritional advantages to intracellular growth for H. capsulatum, and access to other organs via the bloodstream and lymphatics. Nevertheless the environment within professional phagocytes is complex and generally hostile to microorganisms. Intracellular pathogens must avoid or overcome a series of obstacles in order to prevent their destruction. We present the strategies used by H. capsulatum to escape the host cell aggressiveness from the moment it reaches the cell surface up to its survival inside the phagocyte. Our aim is to discuss the advances on the escape mechanisms used by H. capsulatum to survive in the intracellular environment.