Fungal Structure, Function, and Antifungals

Question 1

Which of the following are defining properties of fungi: eukaryotic, 70S ribosome, peptidoglycan cell wall, ergosterol in cell membrane, LPS in cell membrane

Answer 1

Eukaryotic and ergosterol in cell membrane.
Fungi have 80S ribosomes and chitin + beta-glucan in their cell walls. These 2 features make them resistant to most antibiotics! They also lack endotoxin.

Question 2

Are most fungi obligate aerobes, obligate anaerobes, or facultative anaerobes; and are they autotrophs or heterotrophs?

Answer 2

Obligate aerobes, some are facultative anaerobes; heterotrophs

Question 3

Name the only commensal fungus.

Answer 3

Candida albicans

Question 4

Name 3 environments in which fungi survive better than bacteria.

Answer 4

Dry, acidic, and high-osmotic pressure environments

Question 5

How do yeasts and molds reproduce?

Answer 5

Yeasts - budding; molds - spores (can be sexual or asexual)

Question 6

What kind of fungi reproduce by budding, and how does the size of the daughter cell compare to the mother’s?

Answer 6

Yeast; daughter cell is smaller than mother

Question 7

What term describes the filamentous, long multinucleated cells that make up molds?

Answer 7

Hyphae

Question 8

What term describes the mat-like appearance of some molds?

Answer 8

Mycelium

Question 9

Zygospores, ascospores, and basidiospores are what kind of fungi, and how do they reproduce?

Answer 9

Molds; reproduce by forming sexual spores

Question 10

What are conidia, and what kind of fungi reproduce by this method?

Answer 10

Asexual spores; fungi imperfecti

Question 11

What does it mean to say that yeast reproduce by “closed mitosis”?

Answer 11

The nuclear envelope doesn’t disappear during yeast mitosis

Question 12

In thermal dimorphism, what form do fungi take at 37°C vs. 24°C?

Answer 12

37°C - yeasts, 24°C - molds

Question 13

Describe the 2 main immune responses to fungi.

Answer 13

Granuloma formation and acute suppuration

Question 14

Immune review: what cells are involved in granuloma vs. pus formation?

Answer 14

Granulomas: T cells and macrophages
Pus: mainly neutrophils

Question 15

PPD-type skin tests can sometimes be used to detect what kind of fungal reaction?

Answer 15

Delayed hypersensitivity

Question 16

What is mycotoxicosis?

Answer 16

Toxigenic disease caused by ingestion - not an infection (ex. eating amanita mushrooms)

Question 17

What condition is caused by eating grain contaminated with Claviceps purpura, which produces LSD?

Answer 17

Ergotism

Question 18

What fungus, found in spoiled grains, produces aflatoxins, which may be linked to p53 mutation and hepatic carcinoma?

Answer 18

Aspergillus flavus

Question 19

Immediate hypersensitivity leading to asthmatic reaction (bronchoconstriction), eosinophilia, and “wheal and flare” reactions (like mosquito bites) can all be caused by what kind of response to fungi?

Answer 19

Allergic response

Question 20

What is a KOH mount?

Answer 20

A method of breaking down human tissue with KOH while leaving the fungi intact for microscopy

Question 21

What fungus, which may be isolated from CSF, has a characteristically thick capsule and can be stained with India ink?

Answer 21

Cryptococcus

Question 22

What fungus, also know as the cause of “valley fever,” can be detected by spherules in the sputum?

Answer 22

Coccidioidomycosis

Question 23

Fungi can be cultured on what type of low pH, antibiotic-containing agar?

Answer 23

Sabouraud’s agar

Question 24

Name 2 other methods of fungal identification besides direct microscopy and culture.

Answer 24

DNA probe tests/PCR and serology

Question 25

Name the 3 major classes of anti fungal agents.

Answer 25

Polyenes, azoles, and echinocandins

Question 26

Which is the only polyene that can be used systemically (because all the others are too toxic), and what is its major toxicity?

Answer 26

Amphotericin B - is nephrotoxic

Question 27

What is only non-teratogenic, systemic anti-fungal, and thus the only one that can be used on pregnant women?

Answer 27

Amphotericin B

Question 28

Describe how amphotericin B and its cousin nystatin work.

Answer 28

They bind ergosterol, disrupting and making pores in the fungal membrane

Question 29

How does the liposomal preparation of amphotericin B compare to the normal solution in terms of efficacy, side effects, and cost?

Answer 29

Both are highly effective and broad spectrum. The liposomal prep is less toxic, but more expensive

Question 30

Describe how azoles like Fluconazole/Diflucan, Itraconazole, and Ketoconazole work.

Answer 30

They inhibit ergosterol synthesis

Question 31

What class of antifungals does Flucanazole/Diflucan belong to, and what 2 fungi is it used on?

Answer 31

Azoles; candida and cryptococcus

Question 32

Describe how the lipopeptide echinocandins work against fungi.

Answer 32

They inhibit beta-glucan synthesis

Question 33

What 2 fungi are targeted by the echinocandins, such as mycafungin and caspofungin?

Answer 33

Candida and Aspergillus (not cryptococcus or mucormycosis)

Question 34

What is a significant side effect of ketoconazole, and what cancer is it therefore used to treat?

Answer 34

Decreases synthesis of gonadal steroids; can occasionally be used to treat prostate cancer