Question

7. Give the one most obvious morphological, cultural, or other character that would allow one to clea distinguish between the following pathogens. Assume you are growing them in culture:

a. Histoplasma capsulatum (filamentous phase) and Blastomyces dermatitidis (filamentous phase)

b. Aspergillus spp. and Rhinopus spp.

Answer 1

a) Histoplasma capsulatum possesses hyphae like conidiophores which are perpendicular to the parent hyphae. These are thermally dimorphic fungus and thus grow in two temperatures i.e., at 25 degrees Cand at 37 degree C. At 25 degree C they are septate and hyaline and possess both micro-conidia and macro-conidia. The former (micro-conidia) are unicellular, hyaline, round along with smooth or rough wall whereas the latter (macro-conidia) are thick-walled, round, unicellular, hyaline, large and often possess fingerlike projections on the surface.

Blastomyces dermatitis: It is also thermally dimorphic and resembles Histoplasma capsulatum in the two tempeartues of existence i.e., at 25 and 37 degree C and is mostly found in decaying wood materials. Blastomyces dermatidis is a pathogenic fungus and is responsible to cause blastomycosis. They also contain septate hyaline hyphae and unbranched short conidiophores and these conidiophores are perpendicular to vegetative hyphae. The conidia are unicellular and hyaline and remain singular with a globose structure.

b) Aspergillus species: Aspergillus is a genus of fungi which inhabits in various environments of the earth and mostly in aquatic environments. They are small, columnous,  and globose in structure with a smooth surface and gray stipes all around the apex. They produce conidia of size 200-400 mm which can vary from being smooth to spiny in appearance.

Rhizopus species: Rhizopus is also a fungi which can be characterized by a body of branching mycelia consisting of hyphae, stolons and rhizoids and unbranching sporangiophores. Black sporangia at the tips of sporangiophores are round in structure and produces numerous non-motile multinucleate spores for asexual reproduction. Rhizopus are ccoenocytic i.e., lack cross walls, and filamentous in structure. They reproduce by both sexual and asexual spores and grow well at 37 degree C and possess whitish colour which changes to pale yellowish brown with time.