Thursday, November 19, 2015

Mycology Questions Set #2 with Text

Mycology Questions Set #2 with Text ANSWERS
6. A 70 yo male presents to a clinic visit with shortness of breath and fatigue.  He is 6 months status post left lung transplant.  A CT scan shows consolidation in the left lower lobe in addition to nodules throughout the left lobe.  Serial serum 1-3-Beta-D-glucan and Aspergillus galactomannan testing is negative.  Bronchcoscopy is ordered with biopsy.  Histological examination of the biopsy shows the following on Gomori Methanamine stain (GMS).  What is the most likely fungal organism in the tissue:
a. Spergillus
b.  Scedosporium   
c.  Mucor
d.  Candida
f.  Fusarium
7.  A 27 year-old man from Missouri presents to his physician with shortness of breath, fever and fatigue.  In addition to his job as an accountant, he enjoys spelunking and trout fishing. A sputum was submitted for fungal culture and a white mold grew after 14 days of incubation at 30*C.  An adhesive tape prep revealed thin septate hyphae with both microconidia and large tuberculate macroconidia.  The mold is identified as:
rounded tuberculate macroconidia
a. Coccidioides immitis
b. Blastomyces dermatitidis
c. Histoplasma capsulatum
d. Fusarium species
e. Sporothrix schenckii

8.  A 43 year-old female experienced fever and shortness of breath.  She lived in the northwestern part of the US and spent time trekking through the forested areas of the region.  Her sputum culture grew a mucoid yeast colony on Sabouraud’s agar, the yeast was 8 – 10um in size, growth turned brown on birdseed agar, and blue on L-canavanine glycine brom-thymol blue medium.  This yeast can be identified as:
a. Cryptococcus neoformans
b. Candida albicans
c. Cryptococcus gattii
d. Cryptococcus albidus
e. Candida dublinensis

9. A 32 year-old female presents to her physician with a hypo-pigmented skin lesion.  A skin scraping was submitted to the laboratory for KOH preparation and fungal culture.  The KOH examination was described as hyphae with yeast like structures in a spaghetti and meatball arrangement.  The yeast did not grow on Sabouraud’s agar after 72 hours of incubation but grew after the addition of oil to the culture plate.  This infection is most likely due to:
10% KOH with Parker ink mount

a. Candida albicans 

b. Malassezia furfur

c. Trichophyton rubrum

d. Microsporum canis

e. Prototheca species

10.  A yeast was isolated on Sabourauds agar after 24 hrs incubation at 30°C. The yeast produced chlamydospores on cornmeal agar, germ tubes were produced with incubation in serum at 35°C for 4 hours, and green pigmentation was produced on chromogenic agar.  These reactions identify the yeast:
a. Candida dublinensis
b. Candida tropicalis
c. Candida glabrata
d. Candida albicans
e. Candida lusitaniae


6. (c) Mucor.  This patient has an invasive infection with Mucor species.  Mucor is a member of the of the rapidly growing fungi known as the Zygomycetes  (most commonly Mucor, Rhizopus, Absidia, Cunnignhamella species) that are ubiquitous in the environment. These fungi grow rapidly on most fungal media producing aerial mycelia. They can produce have a wide range of clinical manifestations in humans, from cutaneous infection to sinusitis to pneumonia. The presence of a black necrotic eschar either in the nasopharynx or palate is a useful clue for this type of fungal infection.  In disseminated infections the prognosis is very poor as these are rapidly growing and incredibly invasive pathogens.  Major risk factors include diabetes and receipt of solid organ or stem cell transplant.  In transplant recipients, incidence occurs late in the post-transplant stage (usually greater than 3 months), as was the case for this patient
Based on the appearance on GMS and lack of positivity on serial 1-3-Beta-D-glucan testing, the only possible correct choice for part one was Mucormycosis.  The other infections listed should be positive for 1-3-Beta-D-glucan.  Further, the appearance of wide, ribbon-like hyphal elements on GMS is also characteristic of Mucormycosis.  This GMS appearance would also be consistent with the other member of the Zygomycetes, which include Rhizopus and Absidia species.
7. (c) Histoplasma capsulatum exhibits thermal dimorphism by growing in tissue or in culture at 37C as a budding yeast or in soil or culture at temperatures below 30C as a mold. On Sabouraud's agar at 30°C, colonies are slow growing, white or buff-brown, suede-like to cottony. Microscopic morphology shows the presence of characteristic large (8-14 um in diameter), rounded, single-celled, tuberculate macroconidia formed on hyaline hyphae. Microconidia, if present, are small (2-4 um in diameter), round and on short branches of the hyphae.  On brain heart infusion (BHI) blood agar incubated at 37°C, colonies are smooth, moist, white and yeast-like. Microscopically, numerous small round to oval budding yeast cells, 3-4 x 2-3 um in size are observed.
The fungus lives in the environment, particularly in soil that contains large amounts of bird or bat droppings. In the United States, Histoplasma mainly lives in the central and eastern states, especially areas around the Ohio and Mississippi River valleys. The fungus also lives in parts of Central and South America, Africa, Asia, and Australia. Infection occurs from breathing in the microscopic fungal spores from the air. Although most who breathe in the spores don’t become infected (95%), those who do may develop a fever, cough, and fatigue. Many infected recover on their own without medication, but those with weakened immune systems can develop pulmonary infection or disseminate to organs of the reticuloendothelial system.
8. (c) Cryptococcus gattii is a yeast that lives in the environment in many tropical and sub-tropical areas of the world as well as British Columbia and the U.S. Pacific Northwest. Cases have also been reported in California. C. gattii cryptococcosis is a rare infection, occurong from breathing in the yeast cell from nature.  The natural reservoir of C. gattii has yet to be fully revealed but some evidence points to forested areas and trees and possibility. It is not associated with pigeon excreta like C. neoformans.  The infection can affect both the lungs, where it can produce a cryptococcoma, and the central nervous system.  Both C. neoformans and C. gattii turn brown with growth on bird seed agar but only C. gattii will turn blue on L-canavanine glycine brom-thymol blue medium.

9. (b) Malassezia furfur is the causative agent of Pityriasis versicolor, Pityriasis folliculitis and it has recently been implicated as a causative agent of seborrhoeic dermatitis and dandruff. It has also been recovered in blood cultures from neonate and adult patients undergoing lipid replacement therapy. M. furfur is a lipophilic yeast. Pityriasis versicolor is a chronic, superficial fungal disease of the skin characterized by white, pink, or brownish lesions,and covered with thin furfuraceous scales. Lesions occur on the trunk, shoulders and arms, rarely on the neck and face, and fluorescent pale greenish color under Wood's ultra-violet light. Young adults are affected most often, but the disease may occur in childhood and old age.
Skin scrapings taken from patients with Pityriasis versicolor when mounted in 10% KOH show characteristic clusters of thick-walled round, budding yeast-like cells with collarettes and short angular hyphal forms. These microscopic features are diagnostic for Malassezia furfur and culture preparations are usually not necessary.  If culture is performed, oil must be added to the culture media to promote growth.
GMS stained skin biopsy showing characteristic spherical yeast cells and short pseudohyphal elements typical of M. furfur that have been described as spaghetti and meatballs.
10. (d) Candida albicans is one of nine species of Candida which most commonly cause human infections.  It can be found in soil, inanimate objects, and foods.  It is also found as normal flora of the human GI tract, vagina, and skin and it is considered an opportunistic human pathogen.  
C. albicans grow well on many different agars and colonies are smooth, creamy white colonies.  Identification of C. albicans can be made by the observation of germ tubes, produced when C. albicans grows in serum.  C. albicans can also be differentiated from other yeast based on the microscopic morphology on corn meal agar.  C. albicans produce chlamydospores, large round structures produced along the pseudohyphae.  C. albicans produces a green pigment when grown on ChromAgar for Candida species. C-albicans Germ tube LAb11D-6b 2012

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