Pathogenic Fungi

Question 1

What is fungus?

Answer 1

• eukaryotic organism
• hypertrophic, cannot make food
• consist of moulds, yeasts and mushrooms

Question 2

What are the 2 features of fungal cell structure?

Answer 2

• rigid cell wall containing lipopolysaccharides, usually made of chitin or cellulose
• cell membrane containing ergosterol

Question 3

What is a hypha?

Answer 3

A chain of fungal cells, the basic unit of a fungus

Question 4

What is mycelium?

Answer 4

The whole mass of hyphae, branches, and associated structures

Question 5

What are the main properties of yeast?

Answer 5

• mainly unicellular
• usually white in colour
• typically asexual reproduction via budding
• form smooth round colonies

Question 6

What are the main properties of moulds?

Answer 6

• multicellular, organised into hyphae
• large variety of colours
• reproduce typically via spore formation
• form fuzzy colonies

Question 7

How do fungi form biofilms?

Answer 7

Adherence: yeast cell adheres on surface
Initiation: hyphae begin extending with long protrusions, initiating development
Maturation: longer hyphae networks form
Dispersion: generate spores and disperse to restart cycle

Question 8

Main features of fungal cell wall?

Answer 8

• essential for growth and survival
• robust but flexible
• protective, yet porous to nutrients and membrane vesicles
• defines the shape of the fungus
• targeted by drugs

Question 9

Which phyla’s of fungi are pathogenic?

Answer 9

7 different phyla, only 3 are pathogenic - ascomycota, basidiomycota, and glomeromycota

Question 10

What are the 3 classifications of fungal infections?

Answer 10

• Superficial: keratinised tissue of hair, nails, and skin
• Subcutaneous: subcutaneous tissues, lymphatic vessels, and contiguous tissues, usually acquired via trauma
• Systemic: can involve any organ system, severity ranges from subclinical to progressive debilitating disease

Question 11

Examples of non-fatal disease?

Answer 11

• Athletes foot, caused by epidermiphyton, microsporum or trichophyton
• Thrush, caused by candida spp.

Question 12

Fatal diseases caused by fungi?

Answer 12

Candida spp. infection in organs of patients with various types of immune dysfunction
Aspergillus spp. infects organs of patients undergoing treatments like chemotherapy

Question 13

What host factors contribute to fungal pathogenicity?

Answer 13

• Favourable micro environments encourage growth
• broad spectrum antibacterial agents reduce competition for epithelial colonisation sites in the gut
• immunosuppression may create apparently for fungal infection

Question 14

What are dermatophytes and how are they spread?

Answer 14

Are fungi that degrade keratin as their nutrient source, are spread through direct contact from people, animals, soil, and indirectly from fomites

Question 15

Different growth forms of yeast and their benefits?

Answer 15

C.albicans is a yeast that can also form hyphae, and can switch reversible between the different growth forms

Yeast cells: good for dissemination
Hyphae: good for tissue invasion

Question 16

What is aspergillosis and how does it occur?

Answer 16

Moulds, infection occurs by inhaling conidia, which are strongly angio-invasive and penetrated walls of blood vessels

Question 17

How do polyenes work?

Answer 17

Bond to ergosterol in fungal cell membranes, cause fatal leakage of ions from the cell

Question 18

How do azoles work?

Answer 18

Target the enzyme lanosterol-a-demethylase in the ergosterol biosynthesis pathway

Question 19

How do echinocandins work?

Answer 19

Target enzyme Fks1p involved in the synthesis of b-glucan in the cell walls of some fungi