mycology

• C. albicans

  produce germ tubes (95%), and a positive test is

  considered a presumptive identification.
• Cornmeal agar with Tween 80 (polysorbate) reduces

  the surface tension and allows for enhanced formation

  of hyphae, blastospores, and chlamydospores.
• Pseudohyphae are the result of a pinching-off

  process, blastoconidiation, with the growth of

  filaments with constrictions
• Arthrospores are the result of a breaking-off

  process of true septate hyphae resulting in square

  conidia
• A yeast isolated from the CSF producing

  blastospores is most likely to be C. neoformans,

  which is positive for urease and produces brown

  colonies on birdseed agar.
• S. cerevisiae produces

  ascospores when grown on ascospore agar for

  10 days at 25°C.
• Rhodotorula spp. produce pink- to coral-colored

  colonies on Sabouraud’s agar and cornmeal agar
• A positive

  germ tube is a presumptive identification along

  with the production of blastoconidia, terminal

  chlamydospores, and pseudohyphae. C. albicans
• Blastoconidia = + (arranged

  along pseudohyphae) Candida tropicalis
• Dimorphic molds are in the yeast form in infected

  tissues because they are in the yeast form at

  37°C.
• The mold form of C. immitis shows barrel-shaped

  arthroconidia
• S. schenckii is usually acquired by humans through

  thorns or splinters because it is commonly found on

  living or dead vegetation. It is called “rose gardener’s

  disease” cigar-shaped or oval
• The mycelial form of Histoplasma capsulatum seen

  on agar resembles: Sepodenium spp
• P. brasiliensis yeast forms are sometimes seen as

  a “mariner’s wheel” because multiple budding

  cells completely surround the periphery of the

  parent cell
• Zygomycetes commonly recovered from clinical

  specimens are Rhizopus spp. and Mucor spp. Both

  display aseptate hyphae
• Trichophyton spp. infect hair and nails as well as skin
• Microsporum

  are confined to the hair and skin
• Epidermophyton are seen only

  on the skin and nails.
• M. audouinii and T. tonsurans may both cause

  epidemic tinea capitis in children
• Epidermophyton spp. do not produce microconidia;

  this differentiates them from Trichophyton spp. and

  Microsporum spp
• Which Trichophyton species causes the favus

  type of tinea capitis seen in the Scandinavian

  countries and in the Appalachian region of the

  United States? T. schoenleinii
• A.niger is the only species listed producing black

  conidia, which causes a “pepper” effect as the colony

  grows
• Which dematiaceous mold forms flask-shaped

  phialides, each with a flask-shaped collarette? Phialophora spp.
• A.fumigatus is the most common cause of

  aspergillosis and produced

  colonies with a green surface on Sabouraud agar in

  5 days at 30°C.
• Thermally dimorphic Histoplasma capsulatum

  produce microconidia and hyphal fragments at 37°C

  (yeast phase), whereas at 25°C (mold phase) the

  organism displays large, thick-walled, round

  macroconidia with knobby or knoblike projections
• Pneumocystis jirovecii (carinii), is best

  recovered by bronchoalveolar lavage or induced

  sputum in immunocompromised patients. Gomori methenamine

  silver stain is used to identify the organism
• What is the most common cause of mucormycosis

  infection in humans ?

  Rhizopus spp.
• Which specimen is best for

  the initial identification of aspergillosis by soluble

  antigen testing? Serum or urine