Mycology Flashcards
Dematiaceous molds can be broadly separated into two major groups: agents of chromomycosis and clinically insignificant commensals or contaminants. Which of the following statements is true
a) Agents of chromomycosis typically grow slower than clinically insignificant commensals or contaminants
b) Agents of chromomycosis grow faster than clinically insignificant commensals or contaminants
c) Agents of chromomycosis grow at the same rate as clinically insignificant commensals or contaminants
d) Agents of chromomycosis don’t grow in vitro, where clinically insignificant commensals and contaminants do
A - Agents of chromomycosis typically grow slower than clinically insignificant commensals or contaminants
The agents of chromomycosis grow more slowly, maturing only after seven days or more of incubation
Clinically insignificant commensals or contaminants are more rapidly growing species that are commonly recovered from clinical specimens, but in rare situations may cause opportunistic infections called phaeohyphomycosis
Both with grow in vitro, just with varying amounts of time needed to mature
A tech has a 4 day growth of a fungus colony on SABDEX agar. It has a cottony to woolly surface and a distinctive lavender, pink pigmentation. A lactophenol cotton blue slide shows narrow multi-celled macro-conidia that are sickle-shaped. Based on these observations, select the genus identification of this isolate
a) Curvularia
b) Acremonium
c) Fusarium
d) Paecilomyces
C - Fusarium
These colonies are distinctive for the lavender pink to reddish pigmentation and the production of long, sickle shaped (canoe/banana) segmented macro-conidia
Identification is important as infections may result in mycotic keratitis
Which Aspergillus species show biseriate with phialides covering the entire surface of a spherical vesicle with black conidia as microscopic morphological features
a) Aspergillus flavus
b) Aspergillus niger
c) Aspergillus fumigatus
d) Aspergillus terreus
B - Aspergillus niger
Which of the following morphological features would correspond to Phialophora verrucosum
a) Polar germ tubes
b) Transverse and longitudinal septations
c) Urn or vase shaped phialides
d) Black yeast colony
C - Urn or vase shaped phialides
After three days of incubation at 25 degrees Celsius, a sputum specimen placed on SABDEX with chloramphenicol and cycloheximide produced moist, graying growth, with a white aerial mycelium. The patient had a history of travel to national parks in California. The questionable organism is MOST likely
a) Histoplasma capsulatum
b) Blastomyces dermatitidis
c) Coccidioides immitis
d) Paracoccidioides brasiliensis
C - Coccidioides immitis
All of the dimorphic fungi listed here may cause pulmonary disease through inhalation of conidia. Although macroscopic morphology may be difficult to distinguish, the growth rates differ, with C. immitis growing faster than the others listed
A tech observed a yellow-brown colony growing on SABDEX after 72 hours incubation at 30 degrees Celsius, as recovered from a subcutaneous abscess following a traumatic injury in an immunocompromised host. The microscopic appearance shows relatively large conidia arranged in long chains. Based on these features, select the fungus genus from the following choices
a) Paecilomyces
b) Fusarium
c) Scopulariopsis
d) Penicillium
C - Scopulariopsis
Scopulariopsis colonies are characteristically yellow-brown to buff with a finely granular surface, with radial rugae emanating from the center to the periphery
Identification can be observed microscopically from observation of the size and morphology of the conidia being spherical (except for a distinct flat or lemon-shaped base) arranged in chains
In tissues infected with Histoplasma capsulatum, which of the following is usually true
a) Hyphae usually invade blood vessells
b) Encapsulated yeast cells are typical
c) Conidiophores with metulae and phialides are typical
d) Fungus is usually intracellular
D - Fungus is usually intracellular
H. capsulatum is found within mononuclear cells as small, round, to oval yeast cells. It also invades the reticuloendothelial system, which is the primary site of dissemination through the lymph nodes, liver, spleen, and bone marrow
This yeast has been found in respiratory secretions, the vagina, urine, gastric washings, and the oropharynx, but is mainly thought to cause vaginitis and UTI. Growth on Cornmeal Tween 80 agar demonstrates elongated blastoconidia that lie parallel to pseudohyphae (like logs on a stream)
a) Rhodotorula rubra
b) Geotrichum candidum
c) Saccharomyces spp.
d) Candida kefyr (pseudotropicalis)
D - Candida kefyr (pseudotropicalis)
Elongated blastoconidia that lie next to each other, similar to logs in a stream is characteristic of Candida kefyr as observed in cornmeal agar preparations
Rhodotorula rubra reproduces by successively budding, producing multilateral, oval yeast cells that may form short chains and causes fungemia, endocarditis and mycotic keratitis
Arthroconidia are produced by Geotrichum candidum that may resemble a hockey stick, particularly when grown on cornmeal agar. The “handle” represents a germ tube that emanates from one corner of an arthroconidium. It causes bronchitis, skin infections, colitis, conjunctivitis, thrush and wound infections
Saccharomyces is found in endocarditis and rarely in pulmonary infections. Arthroconidia are long and spherical and rudimentary hyphae are sometimes found
