Microbiology - Mycology

Question 1

Fungi

Answer 1

Eukaryotic (unlike bacteria)
Heterotrophic (unlike plants and algae)
Unicellular or filamentous
Rigid cell wall –> non-motile (unlike protista)
Reproduce by both sexual and asexual means

Question 2

Saprophytes

Answer 2

Living on dead tissue

Question 3

Parasites

Answer 3

utilising living tissue

Question 4

Types of disease caused by fungi

Answer 4

Mycotoxicosis - ingestion of preformed toxins produced by fungi
Mycetismus - ingestion of fungi that contain toxic substances
Mycosis - infection of people or animals caused by fungal organism

Question 5

What are the two morphologic types of fungi?

Answer 5

Yeasts
- Unicellular, oval or spherical cells
- Reproduce asexually to form blastoconidia
- Some produce pseudophyphae - elongated cells that remain attached to each other and resemble hyphae
- Colonies are moist or mucoid
Moulds
- Hypha - branching, tubular structure
- When hypha are present, colony is called a thallus
- Hypha in the centre of the thallus are often necrotic due to deprivation of O2 and nutrients

Question 6

Septate hyphae

Answer 6

• Cross walls along the hypha divide it into compartments

- Cytoplasm and/or nuclei can flow through pores in septae

Question 7

Vegetative hyphae

Answer 7

Hyphae which project into the substrate for nutrients

Question 8

Aerial hyphae

Answer 8

Project into the air - often contain reproductive cells or pores

Question 9

Dimorphic fungi

Answer 9

Grow as either yeasts or moulds depending on the on the cultural conditions
Body temp - yeast form
Room temp - mould form

Question 10

Visualisation of fungal elements by direct examination of exudate or tissues

Answer 10

DIFFQUIK - does not differentially stain
bacteria, useful in examining inflammatory cells in fluids

Gram stain - used to divide bacteria into two broad categories: Gram positive
(retain crystal violet and iodine –> purple) or Gram negative (decolourised –> pink) based on their cell wall structure.

Question 11

KOH preparation

Answer 11

‘Optically clears’ surrounding tissue - acts to hydrolyse proteins, fats and many polysaccharides in tissues, leaving the fungi intact

Question 12

Visualising fungal elements in histologic sections

Answer 12

Haemotoxylin & eosin - tissue response to invading fungi

Periodic acid-Schiff (PAS) - fungi stained intense pink

Gomori methenamine silver - stains fungal elements brown/black and provides good contrast

Question 13

Fungal culture

Answer 13

• More slowly than bacteria - must be maintained for longer periods
• Inhibit bacterial growth - lower pH, lower temps, various antibiotics
• Sabouraud’s dextrose agar - composed mainly of peptones and dextrose
• Antimicrobial agents added to inhibit growth of contaminating organisms