Deck 57: Overview of Fungal Identification Methods and Strategies

Question 1

A 29-year-old patient with acquired immunodeficiency syndrome (AIDS)is suspected of having a C.neoformans infection in the cerebrospinal fluid (CSF).A CSF specimen is collected and set up on cycloheximide agar.In addition,an India ink stain is set up.The India ink stain reveals encapsulated yeast;however,3 weeks later,the cycloheximide agar is negative.Which one of the following statements explains this discrepancy?

A)The India ink result is most likely false positive.
B)The ingredients in the cycloheximide agar most likely inhibited the growth of the organism.
C)C.neoformans is rarely recovered from CSF;therefore the cycloheximide result is accurate.
D)The India ink stain is most likely contaminated.

Answer 1

B
Cycloheximide may be added to any of the media that contain or lack antibacterial antibiotics.However,if cycloheximide is included in the battery of culture media,then a medium lacking this ingredient should also be included.Pathogenic fungi,such as C.neoformans,Candida krusei,other Candida spp. ,Trichosporon cutaneum,Pseudallescheria boydii,and Aspergillus spp. ,are partially or completely inhibited by cycloheximide.

Question 2

A capsule and phenoloxidase melanin synthesis are virulence factors contributing to the pathogenicity of which of the following organisms?

A)Aspergillus spp.
B)P.brasiliensis
C)B.dermatitidis
D)C.neoformans

Answer 2

D
A capsule and phenoloxidase melanin synthesis are both virulence factors of C.neoformans.

Question 3

If a fungal colony is described as rugose,then it means that the colony:

A)is furrowed or convoluted.
B)is slightly raised in the center.
C)furrows radiate out from the center.
D)has a smooth surface with no aerial mycelium.

Answer 3

C
Topography can be described as verrucose (furrowed or convoluted),umbonate (slightly raised in the center),and rugose (furrows radiate out from the center).

Question 4

A 16-year-old male teenager is diagnosed with a fungal infection of his foot,which he acquired at the gym.This infection would most likely be classified as a(n)_______ mycosis.

A)superficial
B)subcutaneous
C)systemic
D)opportunistic

Question 5

Microscopically,this fungus appears barrel shaped with thick walls,which best describes which type of conidia?

A)Macroconidia
B)Chlamydoconidia
C)Arthroconidia
D)Blastoconidia

Question 6

Blood cultures are collected from a 36-year-old patient suspected of having a disseminated fungal infection.History reveals that she was exposed to bird droppings and may have inhaled the conidia.What is the best blood culture system to use to ensure optimal recovery of this pathogen?

A)BACTEC
B)BacT/ALERT
C)ESP system
D)Isolator system

Question 7

Colonies are isolated 4 days after incubation from a skin infection that disseminated in a burn victim.A fungal infection is suspected.Which of the following is a possible organism that may be identified?

A)Epidermophyton floccosum
B)Fusarium spp.
C)Cladosporium spp.
D)Microsporum audouinii

Question 8

The mode of transmission for most of the dimorphic fungi is:

A)inoculation.
B)inhalation.
C)arthropod.
D)blood.

Question 9

A septate hyphae is microscopically observed using lactophenol cotton blue.Which organism can be ruled out as the cause of infection on the basis of this information?

A)Aspergillus
B)Bipolaris
C)Microsporum
D)Rhizopus

Question 10

A 28-year-old woman was gardening when a rose thorn pricked her finger,which later became infected.A sample is taken of the exudate and sent to the microbiology laboratory.Small,round,cigar-shaped structures are microscopically observed.She is most likely infected with which type of fungi?

A)Malassezia furfur
B)H.capsulatum
C)S.schenckii
D)Fonsecaea pedrosoi

Question 11

An example of a dimorphic fungus is:

A)Candida albicans.
B)Coccidioides immitis.
C)Cryptococcus neoformans.
D)Aspergillus fumigatus.

Question 12

The optimal temperature and length of time to incubate a sample suspected of containing a dermatophyte is _____°C for _____ days.

A)25;10
B)25;14
C)30;7
D)30;21

Question 13

An example of a thermally monomorphic mold is:

A)P.marneffei.
B)S.schenckii.
C)Epidermophyton.
D)H.capsulatum.

Question 14

Which fungal media is ideal for the recovery of organisms such as Microsporum and Trichophyton?

A)Cornmeal agar with Tween 80
B)Niger seed agar
C)Cottonseed conversion agar
D)Mycosel agar

Question 15

A 59-year-old patient with cancer who was receiving high doses of chemotherapy developed a secondary lung infection that was identified as a fungus.The organism disseminated,which ultimately was fatal to the patient.The organism isolated from sputum exhibited septate hyphae that were dichotomous.The organism is most likely which of the following?

A)Candida
B)Cryptococcus
C)Aspergillus
D)Zygomycetes

Question 16

All mold cultures and clinical samples should always be handled in a Class _____ level biosafety cabinet.

A)I
B)II
C)III
D)IV

Question 17

Urea agar is set up for quality control purposes using two Trichophyton spp.-T.mentagrophytes and T.rubrum.After the appropriate amount of incubation,both organisms are negative.Which one of the following statements explains this discrepancy?

A)The medium is most likely expired.
B)These two Trichophyton spp.are poor choices for quality control.
C)The phenol red indicator is not working because both organisms are positive for urea.
D)No discrepancy is present;both organisms are negative for urease activity.

Question 18

Which stain requires the use of a fluorescent microscope?

A)Calcofluor white
B)India ink
C)Potassium hydroxide
D)Masson-Fontana

Question 19

Which phylum exhibits both a teleomorph and an anamorph form?

A)Ascomycota
B)Basidiomycota
C)Deuteromycota
D)Zygomycota

Question 20

Fungal infections are generally acquired via which route?

A)Person to person
B)Nosocomial
C)Vector
D)Inhalation of spores