Mycology

Question 1

Fungus morphology

Answer 1

Eukaryotic (nuclear membranes and organelles)
Larger, more complex than bacteria
Has a cell wall with ergosterol
Lacks chlorophyll
Sexual and asexual repro
Biochemically distinct pathways

Question 2

Classification of fungi is based on…

Answer 2

Structures formed during sexual repro

Question 3

Deuteromycetes

Answer 3

Human pathogens that do not form sexual structures

Question 4

Yeasts

Answer 4

Single celled
Elongate to form chains called pseudohyphae
Reproduce by budding to form daughter cells/blastospores
Some are commensal and some are pathogens

Question 5

Pseudohyphae

Answer 5

Chains of yeast

Question 6

Moulds

Answer 6

Multicellular
Form hyphae than may be septate or aseptate
Many hyphae form a mycelium
Specialized structures produce asexual spores
Some hyphae fragment to form spores

Question 7

Hypae

Answer 7

Tubular mould structure

Maybe be septate (have cross walls) or aseptate (no cross walls)

Question 8

Mycelium

Answer 8

Mass of hyphae

Mould

Question 9

Conidiophores give rise to…

Answer 9

Conidia

In mould

Question 10

Arthrospores

Answer 10

The spores formed from the fragmenting of hyphae

Question 11

Dimorphic fungi

Answer 11

Fungi behaving as yeasts or molds
Grows at mould at room temperature (found in environment, limited distribution, produce infectious spores)
Grow at yeast at elevated temperatures (in the body, not transmissible between people)

Question 12

How do fungi cause disease?

Answer 12

Growth on body surfaces
Invasion of the body (rare, have to be profoundly immunosuppressed)
Allergic reactions
Toxins released after ingestion

Question 13

Candida albicans

Answer 13

Often commensal on mucus membranes in GI tract
Rapidly colonizes damaged skin
Chief fungal pathogen
Can cause oral, skin and vaginal infections

Question 14

3 systemic candida infections

Answer 14

Urinary tract (from foley catheters usually)
Endocarditis (esp in prosthetic heart valves or IV drug use)
Septicemia (immunosuppressed)

Question 15

3 ways to diagnose candida infections

Answer 15

Clinical suspicion
Microscopy (KOH, gram stain)
Culture (takes several days)

Question 16

Why do you need to add KOH when looking at Candida under the microscope?

Answer 16

It will dissolve the host tissue so you can see the fungi much easier

Question 17

Cryptococcus neoformans/gattii

Answer 17

Encapsulated yeast
Neoformans from bird droppings, gattii from douglas firs
Clinical disease usually in partly immunosuppressed
Pneumonia (subclinical), meningitis (chronic), disseminated (for immunosuppressed)

Question 18

Pneumocystis jirovecii

Answer 18

Yeast
Widely distributed geographically
Caused pneumonia in immunosuppressed patients, esp HIV

Question 19

Dermatophytes

Answer 19

Closely related group of keratolytic fungi
Attack skin, hair, nails
Minor trauma to skin allows initial infection, then fungal penetration balances turn over of superficial squamous cells

Question 20

3 predisposing factors to Dermatophyte infection

Answer 20

Minor trauma
Occlusion
Moisture

Question 21

Clinical features of Dermatophyte infection

Answer 21

Red, scaly, rash may have pustules, with central clearing and migrating margin
Called ringworm, athlete’s foot, or jock itch

Question 22

Transmission of Dermatophytes

Answer 22

Skin squames contaminating fomites

Rarely by direct (person to person) transmission

Question 23

Tinea pedis

Answer 23

Dermatophyte infection of the feet

Question 24

Tinea versicolor

caused by, location, presentation

Answer 24

Caused by Malassezia furfur
Widespread skin commensal that flourishes on skin fatty acids
Infection is superficial, and manifests as hyper or hypo pigmented lesions with itching and occasional pustules

Question 25

2 groups of fungi that can cause invasive fungal infections

Answer 25

1. Opportunistic fungi (that occur widely)

2. Geographically defined dimorphic fungi

Question 26

Aspergillus fumigatus

location, risk factors, presentations

Answer 26

Widespread, grows on rotting vegetation
Spores commonly present in the air
Immunosuppression is risk factor
Presentations: allergic bronchiopulmonary aspergillosis (asthma like symptoms), fungal ball (in cavities), and invasive disease (tissue destruction, pneumonia)

Question 27

Histoplasma capsulatum

Answer 27

Dimorphic fungus
Infection occurs when spores are inhaled and germinate in the lung
Only a small proportion of people get disease (most others just fight it off with antibodies - can detect)

Question 28

4 dimorphic fungi

Answer 28

Histoplasma capsulatum
Blastomyces
Sporothrix
Coccidiodes