Exam 6 - (CH 27) Medically Significant Fungi Textbook Review Questions

Question 1

This type of hyphae are characteristically hyaline (nonpigmented) or only lightly-pigmented.
A. Dematiaceous
B. Moniliaceous
C. Phaeoid
D. Mycelia

Answer 1

B. Moniliaceous

Question 2

This genus often has both yeast and mold forms in the same culture despite growth conditions.
A. Polymorphic Exophiala spp.
B. Dimorphic Pseudallescheria spp.
C. Thermally dimorphic Sporothrix spp.
D. Polymorphic Histoplasma spp.

Answer 2

A. Polymorphic Exophiala spp.

Question 3

These conidia are formed by fragmentation of fertile hyphae.
A. Phialoconidia
B. Annelloconidia
C. Blastoconidia
D. Arthroconidia

Answer 3

D. Arthroconidia

Question 4

This is a sac-like structure in which sexual spores are produced.
A. Sporangium
B. Rhizoid
C. Ascus
D. Annellide

Answer 4

C. Ascus

Question 5

This fungi is associated with tinea versicolor and dandruff and requires lipids for growth.
A. Coccidioides immitis
B. Blastomyces dermatitidis
C. Sporothrix schenckii
D. Malassezia furfur

Answer 5

D. Malassezia furfur

Question 6

This fungi is associated with black nonscaly macules on the palms of the hands and brown-olive colored colonies.
A. Hortaea werneckii
B. Histoplasma capsulatum
C. Trichosporon beigelii
D. Piedraia hortae

Answer 6

A. Hortaea werneckii

Question 7

This dermatophyte has spindle-shaped, spiny macroconidia.
A. Epidermophyton floccosum
B. Microsporum canis
C. Microsporum gypseum
D. Trichophyton rubrum

Answer 7

B. Microsporum canis

Question 8

To induce mycelia conversion to yeast in the dimorphic fungi Sporothrix schenckii
A. the fungus is inoculated onto Tinsdale agar supplemented with iron and incubated at 37°C in a CO2 incubator.
B. the fungus is inoculated onto brain–heart infusion agar supplemented with cyclohexamide and incubated at 37°C in a CO2 incubator.
C. the fungus is inoculated onto brain–heart infusion agar supplemented with sheep red blood cells and incubated at 37°C in a CO2 incubator.
D. the fungus is inoculated onto brain–heart infusion agar supplemented with sorbitol and incubated at 42°C in a CO2 incubator.

Answer 8

C. the fungus is inoculated onto brain–heart infusion agar supplemented with sheep red blood cells and incubated at 37°C in a CO2 incubator.

Question 9

Reticuloendothelial cytomycosis is caused by the inhalation of microconidia of
A. Coccidioides immitis.
B. Blastomyces dermatitidis.
C. Histoplasma capsulatum.
D. Cryptococcus neoformans.

Answer 9

C. Histoplasma capsulatum.

Question 10

Rhizopus is most often associated with
A. thrombosis.
B. patients with AIDs and tuberculosis.
C. tap water and indwelling catheter-associated infections.
D. diabetic patients with ketoacidosis.

Answer 10

D. diabetic patients with ketoacidosis.

Question 11

Alternaria spp. have this type of conidia.
A. Tapered multicelled conidia with angular cross-walls
B. Clustered in balls at the phialide tips
C. Canoe-shaped in clusters
D. Extremely tapered sympoduloconidia with a significantly swollen base

Answer 11

A. Tapered multicelled conidia with angular cross-walls

Question 12

Which organism is most likely given the following results?
1. Pseudohyphae present
2. No growth at 45°C, but growth at 37°C and 42°C
3. Sensitive to cyclohexamide
4. Nitrate negative
A. Candida albicans
B. Cryptococcus neoformans
C. Trichosporon beigelii
D. Candida krusei

Answer 12

D. Candida krusei

Question 13

Hairs infected with Microsporum audouinii fluoresce:
A. Orange at 250 nm using a illuminator
B. With a Wood’s ultraviolet lamp
C. When treated with potassium hydroxide (KOH)
D. Under a black light

Answer 13

B. With a Wood’s ultraviolet lamp

Question 14

This organism forms perpendicular penetration pegs in the hair shafts in a hair perforation test.
A. Trichophyton mentagrophytes
B. Trichophyton rubrum
C. Epidermophyton floccosum
D. Rhodotorula spp.

Answer 14

A. Trichophyton mentagrophytes

Question 15

This species is positive for the germ tube test but cannot grow at 42°C or 45°C.
A. Candida dubliniensis
B. Candida tropicalis
C. Candida albicans
D. Candida glabrata

Answer 15

A. Candida dubliniensis

Question 16

Which fungi is most associated with the Mississippi and Ohio River valleys, primary lung disease, and large, broad based yeasts?
A. Histoplasma capsulatum
B. Blastomyces dermatitidis
C. Coccidioides immitis
D. Paracoccidioides brasiliensis

Answer 16

B. Blastomyces dermatitidis

Question 17

For each of the following dimorphic fungi, describe the characteristic microscopic appearance when grown at 22 or 35 ° C:

a. Blastomyces dermatitidis
b. Coccidioides immitis and C. posadasii
c. Histoplasma capsulatum
d. Sporothrix schenckii species complex

Answer 17

a. Blastomyces dermatitidis: Microscopic examination of cultures grown at 35 ° C reveals large, broad-based budding yeast. At 22 ° C, the microscopic examination of the mold reveals conidia borne on short lateral branches that are ovoid to dumbbell-shaped, and varying in diameter from 2 to 10 µm.

b. Coccidioides immitis and C. posadasii: Microscopic examination of secretions may reveal spherules containing endospores. At 22 ° C, the microscopic examination of the mold reveals alternating (separated by a disjunctor cell) hyaline arthroconidia.

c. Histoplasma capsulatum: Microscopic examination of cultures grown at 35 ° C reveals small yeast cells. The yeast cells measure 2 to 3 µm by 4 to 5 µm. At 22 ° C, the microscopic examination of the mold reveals nondescript spherical microconidia and characteristic tuberculate macroconidia.

d. Sporothrix schenckii: Microscopic examination of cultures grown at 35 ° C reveals small, cigar-shaped yeast. Microscopic examination of the mold phase reveals conidia developing in a rosette pattern at the ends of delicate conidiophores in addition to dark-walled conidia being produced along the sides of the hyphae.

Question 18

Describe the microscopic morphology for each of the following organisms:

a. Microsporum gypseum
b. Microsporum canis
c. Trichophyton rubrum
d. Trichophyton mentagrophytes

Answer 18

a. Microsporum gypseum: Microscopic examination reveals fusiform, moderately thick-walled conidia measuring 8 to 15 µm by 25 to 60 µm, with as many as six cells. In some isolates, the distal end of the macroconidium may bear a thin, filamentous tail.

b. Microsporum canis: Microscopic examination reveals spindle-shaped macroconidia with echinulate, thick walls measuring 12 to 25 µm by 35 to 110 µm with 3 to 15 cells. The tapering, sometimes elongated, spiny distal ends of macroconidia are key features that distinguish this species.

c. Trichophyton rubrum: Microscopic examination reveals clavate or peg-shaped microconidia formed along undifferentiated hyphae. Rare macroconidia may be formed.

d. Trichophyton mentagrophytes: Globose microconidia are found primarily in clusters described as grapelike or engrape. Macroconidia are thin-walled, smooth, and cigar-shaped, with four to five cells separated by parallel cross walls.

Question 19

Compare the results of the urease test and the hair perforation test for T. rubrum and T. mentagrophytes.

Answer 19

Trichophyton rubrum is urease-positive, whereas T. mentagrophytes is typically urease-negative. Wedge-shaped perforations in the hair shaft (positive) are characteristic of T. mentagrophytes as well as M. canis and M. gypseum. Species negative for hair perforation include T. rubrum, M. audouinii, and M. praecox.

Question 20

Describe the significance of isolating a saprobe from an infection in an immunocompromised patient.

Answer 20

Saprobes are usually environmental contaminants and are not considered human pathogens. However, saprobes may cause disease in individuals with impaired immune systems. When a saprobe is recovered from an immunocompromised patient, the laboratory should work closely with the physician to help determine if the isolate is an environmental contaminant, or if it is possibly causing disease.

Question 21

Compare the macroscopic and microscopic morphology of the following saprobes: Penicillium spp., Aspergillus fumigatus, Fusarium spp., and Curvularia spp.

Answer 21

Penicillium spp. and A. fumigatus can form blue-green colonies, but they may be differentiated microscopically in that conidia in the aspergilli are formed from phialides attached to a vesicle or metula, whereas conidia in the genus Penicillium are formed from branched conidiophores bearing phialides at their tips. Fusarium spp. are typically white to pink to purple colonies that produce large, hyaline, thin canoe- to green bean– shaped macroconidia. Curvularia spp. have black colonies that produce wide, phaeoid (dematiaceous), crescent to half circle– shaped conidia.

Question 22

Describe the differences between chromoblastomycosis and eumycotic mycetoma.

Answer 22

Lesions of chromoblastomycosis most often appear as verrucous nodules that may become ulcerated and crusted. Long-standing lesions have a cauliflower-like surface. Brown, round, sclerotic bodies, which are nonbudding structures occurring singly or in clusters, are seen in tissues. These sclerotic bodies reproduce by dividing in various planes, resulting in multicellular forms. Lesions of mycetoma are characterized by tumefaction, draining sinuses, and granules. Mycetomas are localized infections that involve the cutaneous and subcutaneous tissue, and possibly bone. Granules are released through the draining sinus tracts.

Question 23

Discuss the differences between bacteria and fungi.

Answer 23

Fungi are eukaryotic and possess a true nucleus, with a nuclear membrane and organelles like mitochondria. Bacteria are prokaryotic and lack these structures. Unlike plants, fungi lack chlorophyll and do not undergo photosynthesis and must absorb nutrients from the environment. In addition, fungal cell walls are made of chitin, whereas those of plants contain cellulose.

Question 24

Discuss the differences between hyaline and phaeoid fungi.

Answer 24

Fungal colonies, although occurring in many colors, may be generally divided as hyaline or phaeoid. Hyaline molds are light-colored, whereas phaeoid fungi are darkly pigmented. This pigmentation is a result of melanin in the cell wall of the organism. The Fontana-Masson stain will detect phaeoid hyphae in the tissues because it stains melanin.

Question 25

Define teleomorph, anamorph, and synanamorph.

Answer 25

Teleomorph is the sexual stage of a fungus, whereas the anamorph is the stage that reproduces asexually. In certain species, more than one asexual stage is associated with the same teleomorph. When more than one anamorph exists, they are termed synanamorphs.

Question 26

You suspect that a yeast isolated from the oral cavity of a patient with HIV infection is C. albicans. Describe the results of the germ tube test. What morphology would you see if you inoculated the colony onto cornmeal agar?

Answer 26

The germ tube test would be positive within 2.5 to 3 hours, and the cornmeal agar would result in true hyphae and pseudohyphae, with rare chlamydoconidia.

Question 27

Points to Remember

Answer 27

■ Yeasts typically reproduce by budding, whereas molds often reproduce by forming spores.
■ A large array of fungi produce human infections.
■ Fungi can be isolated from almost any type of clinical specimen.
■ Fungal identification is based on a variety of characteristics, including macroscopic appearance, microscopic appearance, ability to grow at various temperatures, and biochemical reactions.
■ Phaeoid fungi produce dark pigments.
■ Dermatophytoses are caused by Trichophyton, Microsporum, and Epidermophyton species.
■ The thermally dimorphic fungi Blastomyces dermatitidis, Coccidioides immitis, Coccidioides posadasii, Histoplasma capsulatum, Paracoccidioides brasiliensis, Sporothrix schenckii species complex, and Talaromyces (Penicillium) marneffei are often associated with systemic mycoses.
■ Clinically important Mucorales include Rhizopus, Mucor, Lichtheimia, Cunninghamella, and Syncephalastrum.
■ Because of its microscopic morphology, Geotrichum is a mold that is often initially mistaken for a yeast. ■ Saprobic fungi are most problematic in the immunocompromised host.
■ Candida albicans is the most commonly isolated yeast.
■ Pneumocystis jirovecii is an important pathogen of patients with AIDS.
■ Extreme care should be taken when working with dimorphic fungi and in the laboratory. Cultures for all molds should be processed in a biological safety cabinet.
■ Antifungal therapy is frequently ineffective when diagnosis is delayed.