Microbiology of Fungal Infections

Question 1

What is an eukaryotic organism?

Answer 1

Cells that have membrane-bound nucleus which contain mitochondria, golgi bodies and other organelles

Question 2

What is fungi?

Answer 2

Eukaryotic organism with plasma membrane and a rigid cell wall external to membrane

Question 3

What are the two basic growth forms of fungi?

Answer 3

Yeasts = unicellular

Filamentous/Hyphal = multicellular structures

Question 4

Describe the four main components making up the structure of fungi

Answer 4

Vacuoles
Organelles
Plasma Membrane
External Cell Wall

Question 5

What does the plasma membrane in fungus consist of?

Answer 5

Phospholipid bilayer

Sterols - Ergosterol usually

Embedded proteins (channels etc.)

Synthases (specialised protein enzymes to build cell wall)

Question 6

Describe the structure of the external cell wall

Answer 6

Consists of:

• carbohydrate polymers (beta-glucans, chitins, mannose)
• mannoproteins

Question 7

What is a true pathogen?

Answer 7

A pathogen able to cause disease in all exposed individuals

- note: very few fungi are true pathogens

Question 8

What is an opportunistic pathogen?

Answer 8

only able to cause disease in an immunocompromised host

Question 9

State the regional classifications for fungal infections

Answer 9

Superficial and cutaneous

Subcutaneus

Systemic

Question 10

List four travel-associated true fungal pathogens that cause systemic infection?

Answer 10

Histoplasmosis

Coccidiomycosis

Blastomycosis

Paracoccidioidomycosis

Question 11

What is dermatophytosis (a.k.a. Tinea/Ringworm)?

Answer 11

Superficial, localised infection of keratinised tissue

- skin, hair, nails

Question 12

Describe the transmission of dermatophytosis

Answer 12

Via direct or indirect contact
- sharing towels, bedsheets

Need moisture and trauma

Question 13

What is pityriasis versicolor?

Answer 13

Superficial infection of the stratum corneum

- produces hyperpigmented/depigmented macules on trunk and proximal limbs

Question 14

What causes pityriasis versicolor?

Answer 14

Malassezia furfur

Question 15

What is superficial candidiasis?

Answer 15

Superficial infection most commonly of mucous membranes

- also skin and nails

Question 16

What most commonly causes superficial candidiasis?

Answer 16

Candida albicans (90%) - normal commensal which canges to pseudohyphal form (yeast-like)

Question 17

How can candidiasis become invasive?

Answer 17

Usually due to immunodeficiency (e.g. neurtopenia, ABX, indwelling lines)
- candida species invade bloodstream

Question 18

What causes Cryptococcosis?

Answer 18

Caused by Cryptococcus neoformans - encapsulated yeast (commensal) in the environment, esp. in soil

Normally associated with immunodeficiency

Usually presents as a CNS infection

Question 19

What causes Pneumocystosis?

Answer 19

Pneumocystis Jiroveci which causes infection of lungs

- very common in AIDS patients

Question 20

What is the treatment for pneumocystosis?

Answer 20

Co-Trimoxazole (due to protazoan-like tendencies)

Question 21

What do histoplasmosis and coccidiomycosis have in common?

Answer 21

They both usually cause asymptomatic pulmonary infection in most

Question 22

What is the significance of using a wood’s lamp?

Answer 22

Useful since many fungi are fluorescent

- not all, also some bacteria are fluorescent

Question 23

When would serology be used instead of culture?

Answer 23

In systemic infections when no time for full culturing and need rapid identification of fungi