Question 1

Tinea versicolor is a skin infection characterized by superficial brownish scaly areas most often on the trunk,arms,or shoulders.Which type of replacement therapy places patients at risk for developing this type of skin infection?

Accepted Answer

Malassezia furfur causes tinea versicolor,a skin infection that is characterized by superficial brownish scaly areas on light-skinned persons and lighter areas on dark-skinned persons.The lesions occur on the smooth surfaces of the body,specifically,the trunk,arms,shoulders,and face.It has a worldwide distribution.M.furfur is also a cause of disseminated infection in infants and young children and in adults taking lipid replacement therapy.

Question 2

A fungal infection found mostly in the tropics and temperate regions is characterized by the development of soft,yellow or pale-brown aggregations around hair shafts in the axillary,facial,genital,and scalp regions.The fungus that would most likely be isolated is:

Accepted Answer

White piedra caused by Trichosporon spp.is an uncommon fungal infection in patients who are immunocompetent and is found in both tropical and temperate regions of the world.It is characterized by the development of soft,yellow or pale-brown aggregations around hair shafts in the axillary,facial,genital,and scalp regions of the body.The Trichosporon spp.that causes this disease frequently invades the cortex of the hair and causes damage.

Question 3

A patient with leukemia is diagnosed with a Candida infection after receiving several doses of chemotherapy.The most likely yeast causing the infection is:

Accepted Answer

C.tropicalis has been shown to be prevalent in patients with hematologic malignancies,especially those with neutropenia.

Question 4

Cryptococcus neoformans is widely distributed in nature,and aerosolization is a prerequisite to most infections.This organism is most often associated with exposure to:

Accepted Answer

C.neoformans exists as a saprobe in nature and is most often found associated with avian excreta,particularly that of pigeons.Numerous reports substantiate the hypothesis that pigeon habitats serve as reservoirs for human infection.The pigeon manure apparently serves as an enrichment factor for C.neoformans because of its composition.C.neoformans is believed to be widely distributed in nature,and aerosolization is a prerequisite to most infections.

Question 5

If cornmeal agar is set up and chlamydoconidia are produced,the organism is most likely:

Accepted Answer

Cornmeal agar may be successfully used for the detection of characteristic chlamydoconidia produced by C.albicans.This method is currently satisfactory for the definitive identification of C.albicans when the germ tube test is negative.

Question 6

Match the organism with its characteristics.
-Polysaccharide capsule

Accepted Answer

Polysaccharide capsule is a characteristic of C. neoformans.

Answer: A 
 Trichosporon spp. do not have a polysaccharide capsule.

Answer: B 
 Although C. albicans has a cell wall composed of polysaccharides, it does not have a polysaccharide capsule.

Answer: C 
 M. furfur does not have a polysaccharide capsule.

Question 7

Match the organism with its characteristics.
-"Spaghetti and meatball" morphologic appearance

Accepted Answer

The "spaghetti and meatball" morphologic appearance is characteristic of Malassezia furfur, which causes tinea versicolor. This description refers to the mix of hyphae (spaghetti) and yeast cells (meatballs) seen under the microscope.

Question 8

A patient with acquired immunodeficiency syndrome (AIDS)notices skin lesions on his back that have begun to ulcerate.Upon physical examination,his physician also notices hepatomegaly that is most likely caused by hepatitis.The physician prescribes antifungal therapy to prevent the dissemination of which of the following yeasts?

Accepted Answer

In the patient who is immunocompromised,disseminated disease with meningitis caused by C.neoformans is common.Disseminated cryptococcosis and cryptococcal meningitis became well recognized in patients with AIDS,and both infections remain important causes of morbidity and mortality in patients in resource-poor countries who do not have access to highly active antiretroviral therapy (HAART).Patients with disseminated infection may exhibit painless papular skin lesions that may ulcerate.Other less common manifestations of cryptococcosis include endocarditis,hepatitis,renal infection,and pleural effusion.

Question 9

Blood cultures are drawn on a patient suspected of having a fungemia.Positive cultures reveal the presence of chlamydoconidia on cornmeal agar.In addition,the yeast is germ tube positive.The most likely identification of the fungal agent is:

Accepted Answer

One method of identification of C.albicans and the differentiation from other Candida spp.is made on the basis of the presence of chlamydoconidia on cornmeal agar containing 1% Tween 80 and trypan blue incubated at room temperature for 24 to 48 hours.

Question 10

Match the organism with its characteristics.
-White piedra

Accepted Answer

White piedra is a fungal infection caused by Trichosporon spp. It affects hair shafts, leading to the formation of small white nodules.

Answer: B, C
 Both C. albicans and M. furfur are types of fungi that can cause skin and mucosal infections in humans. However, they do not cause white piedra or other hair infections.

Answer: D
 C. neoformans is a type of yeast that can cause serious respiratory and neurological infections in humans. It is not associated with white piedra or other hair infections.

Question 11

Agar medium overlaid with olive oil will enhance the growth of which organism?

Accepted Answer

M.furfur is infrequently cultured in the clinical laboratory.Cultivation,for example,from a positive blood culture requires an agar medium overlaid with a long-chain fatty acid (olive oil).The colonies are small when compared with the colonies of C.albicans and are creamy and white to off white.

Question 12

The most commonly isolated yeast in clinical specimens is:

Accepted Answer

Candida infections are caused by a variety of species.Although C.albicans is the most commonly isolated yeast,other species are emerging such as Candida glabrata,Candida parapsilosis,C.tropicalis,C.dubliniensis,and C.krusei.The frequency with which these are isolated varies by institution.Until recently,C.albicans was the most common yeast isolated from infections,constituting at least 60% to 70% of the infections.In the last decade,epidemiologic data reveal a paradigm shift in Candida infections.Studies in the intensive care environment are now confirming an increase of C.glabrata and C.krusei isolated in approximately 25% of the infections and C.albicans in approximately 50% of the infections.

Question 13

Encapsulated yeast is identified in the cerebrospinal fluid (CSF)of a patient with AIDS.The most likely stain or reagent used to identify this organism is:

Accepted Answer

Traditionally,the India ink preparation has been the most widely used method for the rapid detection of C.neoformans in clinical specimens.This method delineates the large capsule of C.neoformans,because the ink particles cannot penetrate the capsular polysaccharide material.

Question 14

Determining urease activity and growth on niger seed agar is helpful in determining which type of yeast?

Accepted Answer

The rapid urease test (Procedure 62-2)is a most useful tool for screening for urease-producing yeast recovered from respiratory secretions and other clinical specimens.An alternative to traditional urease testing is the rapid selective urease test (Procedure 62-3).This method appears to be useful in rapidly detecting C.neoformans.Using these screening tests is helpful to make a presumptive identification of C.neoformans.In instances in which inoculum is limited,the laboratorian must use tests that can be performed and then prepare a subculture so that additional tests can be performed later.Often,inoculating the organism onto the surface of a plate of niger seed agar is just as fast;the results may be obtained during the same day of incubation at 25°C.This is discussed further in this section.

Question 15

In general,yeast reproduces asexually by the formation of:

Accepted Answer

In general,yeast reproduces asexually by blastoconidia formation (budding)and sexually by the production of ascospores or basidiospores.

Question 16

Match the organism with its characteristics.
-Creamy,white patches

Accepted Answer

Creamy, white patches are a characteristic of C. albicans, an opportunistic fungal pathogen that can cause infections such as oral thrush and vaginal yeast infections. Trichosporon spp. can cause skin and bloodstream infections, but they typically do not produce creamy, white patches. M. furfur is a yeast that can cause skin infections, but it does not typically produce creamy, white patches. C. neoformans is a fungal pathogen that can cause meningitis, but it does not typically produce creamy, white patches.

Question 17

Which yeast identification system uses chromogenic substrates to assess specific enzyme activity usually detected within 4 hours?

Accepted Answer

The MicroScan yeast identification panel (Siemens,Deerfield,IL)is a 96-well microtiter plate containing 27 dehydrated substrates;it was introduced as an alternative to the API-20C AUX yeast identification system.It uses chromogenic substrates to assess specific enzyme activity detected within 4 hours.

Question 18

A patient with diabetes is experiencing creamy patches on his tongue and mucous membranes.Cultures are performed,and yeast is recovered.His diagnosis is most likely:

Accepted Answer

Thrush is an infection of the mucous membranes in the mouth and is considered a localized infection.Thrush can be observed in newborns,in patients with human immunodeficiency virus or diabetes,and in patients who are receiving chemotherapy.Creamy patches or colonies will appear on the tongue and mucous membranes.Candida may be recovered from the oropharynx,gastrointestinal tract,genitourinary tract,and skin.

Quiz 61: The Yeasts