Introduction to fungal pathogens

Question 1

Describe the characteristics of fungi with respect to morphology, cell composition, and biochemical functioning and explain why fungi differ from bacteria, plants, and animals

Answer 1

Fungi are eukaryotic, aerobic, unicellular or filamentous, heterotrophic organisms encased in a rigid cell wall. Fungi may reproduce by sexual and/or asexual means, and the nature reproduction is used in classification.

• contain membrane bound organelles but lack chlorophyll and are not photosynthetic.
• cell walls contain chitin
• cell membrane contains ergosterol
• only few are motile

Question 2

Saprobes

Answer 2

live upon dead and decaying organic matter

Question 3

Symbionts

Answer 3

live upon another organism to the mutual advantage of both

Question 4

Commensals

Answer 4

live upon another organism with no detriment to the host

Question 5

Parasites

Answer 5

live upon another organism with clear detriment to the host

Question 6

Linnean categorization:

Answer 6

method of sexual reproduction, sexual vs. asexual. Fungi are one (Mycota) of the five kingdoms at the top of the phylogenetic classification scheme, as opposed to bacteria (Monera) or protozoa (Protista)

Question 7

functional categorization: where fungi are found

Answer 7

i. Geophilic: found in soil
ii. Anthrophilic: found in humans
iii. Zoophilic: found in animals
iv. Dematiaceous: produces its own pigment (usually melanin)

Question 8

functional categorization: superficial vs. deep

Answer 8

i. Superficial fungal infections
1. Tinea (dermatophytes, dermatophytosis, “ringworm”)
2. Candida (candidiasis, thrush, “yeast infections”)
3. Pityrosporum (pityrosporum versicolor/tinea versicolor)
ii. Deep fungal infections
1. Sporotrichosis, Cryptococcosis, Coccidioidomycosis, North American Blastomycosis, Histoplasmosis, Lobomycosis, Mucormycosis

Question 9

Yeast:

Answer 9

unicellular growth form, reproduces by budding to form blastoconidia or by dividing through fission. Yeast colonies are moist or mucoid in appearance. Medical examples: Cryptococcus neoformans and Candida albicans

Question 10

Hyphal foms of fungi (molds):

Answer 10

filamentous growth form, reproduces by formation of spores or conidia, filamentous elements are called hyphae, a mass of hyphae=mycelium. Medical example: dermatophytes and Aspergillosis. Hyphae may be septate (with internal divisions) or nonseptate. Septa divide hyphae into compartments, but not into “cells”, cytoplasm + organelles flow between

Question 11

Pseudohyphae:

Answer 11

elongated YEAST linked together like sausage. They do not have cytoplasmic connections between the compartments. Do NOT get confused!

Question 12

Rhizoids:

Answer 12

specialized form of hyphal elements that grow like roots from larger hyphae

Question 13

Dimorphic:

Answer 13

May exist in a yeast OR hypheal form, environmental change (atmosphere, temperature, food supply) will trigger a transition from one form to another. Thermal dimorphism is dictated by temperature. Example: Histoplasmosis is mold at ambient temperature, but inhaled into body it transformed into parasitic yeast of macrophages