Mycology

Question 1

What is S.cerevisiae?

Answer 1

Baker’s yeast

Question 2

Describe the classification of fungi?

Answer 2

Unicellular (yeasts)

Filamentous (moulds)

Dimorphic

Question 3

Describe the basic properties of yeasts and moulds?

Answer 3

YEASTS

Unicellular, facultative anaerobes, reproduce asexually by budding, produce colonies on agar

MOULDS

Filamentous, aerobes, reproduce by conidia, produce mycelia on agar

Question 4

What is a conidium?

What is a mycelium?

Answer 4

Conidia: asexual spores

Mycelia: mass of branched, tubular filaments of fungi

Question 5

Describe the appearance of yeast cells on a Gram stain?

Answer 5

Larger than bacteria

Look like strange Gram positive cocci

Budding visible

Question 6

Describe the appearance of yeast culture on blood agar?

Answer 6

Non-descript, small colonies

Yeasty smell

Question 7

Describe the appearance of filamentous fungus on culture?

Answer 7

Filaments

Question 8

Describe the features of fungi visible in this picture?

Answer 8

Hyphae and conidia

Question 9

Rank the virulence fungi types?

Answer 9

Descending order of virulence:

Dimorphic fungi

Dermatophytes

Agents of subcutaneous mycoses

Opportunists

Toxic fungi

Question 10

Which types of fungi are primary pathogens?

Answer 10

Dimorphic fungi

Dermatophytes

Question 11

Describe why dimorphic fungi are so virulent?

Answer 11

Best adapted to grow in our tissues: can grow as moulds (filamentous) in the environment, and switch to yeast (unicellular)when they invade us

Question 12

Give an example of a dimorphic fungus?

Answer 12

Histoplasma capsulitin

Causes Cave’s disease

Question 13

Give an example of a dermatophyte?

Answer 13

Ringworm fungus

Question 14

Describe how dermatophytes colonise us?

Answer 14

Grow on skin, hair and nails

Don’t invade deeply

Question 15

What are agents of subcutaneous mycoses?

Answer 15

Low grade pathogens

Inoculated directly into skin

Question 16

Which patients do opportunistic fungi affect?

Answer 16

Immunocompromised patients

Question 17

Give an example of a toxic fungus?

Answer 17

Poisonous mushrooms

Question 18

Describe the behaviour of toxins released from fungi?

Answer 18

They diffuse

So, don’t just chop the mouldy bit off the cheese!

Question 19

What do dermatophytes cause in humans?

Answer 19

Tinea

Question 20

How are dermatophytes classified?

Answer 20

Three genera

Morphologically different, and have preferences for different tissues and hosts

Question 21

Give an example of a subcutaneous mycosis?

Answer 21

Mycetoma (maduromycosis)

Question 22

What are the causes of mycetoma?

Answer 22

Can be caused by bacteria (acintomycetoma, eg. nocardia spp.) or fungi (eumycetoma, eg. madurella spp.)

Question 23

Give three examples of opportunistic mycoses?

What are they caused by?

Answer 23

Candidiasis: candida albicans (yeast)

Cryptococcosis: c.neoformans or c.gattii (yeast)

Aspergillosis: aspergillus spp. (filamentous)

Question 24

Describe the types of candidiasis?

Answer 24

Mucocutaneous: infects mucous membranes

Chronic mucocutaneous: can’t get rid of it

Systemic: invasive, fatal

Question 25

In which patients does systemic candidiasis most commonly occur?

Answer 25

Neonates Advanced immunodeficiency

Question 26

Why can fungi reach such large numbers in the body?

Answer 26

Can reach large numbers before they kill a patient, because they don't activate the immune system as strongly as bacteria and viruses

Question 27

Which agent of cryptococcosis may cause infection in non-immunocompromised individuals? Why?

Answer 27

C.gattii More virulent than other agents

Question 28

What diseases areassociated with cryptococcosis?

Answer 28

Pulmonary infection (inhaled) Meningitis (if it spreads to blood or if casued by c.gattii)

Question 29

In which patients does meningitis due to cryptococcosis usually occur?

Answer 29

AIDS (AIDS defining illness) Lymphomas High dose steroids

Question 30

What are the different clinical forms of Aspergillosis?

Answer 30

Saprophytic (fungus ball) Allergic (can occur at distant site) Systemic

Question 31

What can saprophytic Aspergillosis be mistaken for?

Answer 31

Tumour Large fungus ball resembles a tumour

Question 32

Which methods can be used to diagnose fungal infections?

Answer 32

Microscopy Culture Antigen detection PCR Mass spec

Question 33

What is present in the microscopic image?

Answer 33

Tinea: hyphae in skin scraping

Question 34

Describe how c.albicans can be detected via culture?

Answer 34

One test to see if it is c.albicans If not \> do a whole lot of other biochemical tests

Question 35

Which fungus is this? How can we tell?

Answer 35

Macronidia: Epidermophyton sp. Unique appearance

Question 36

What is shown in this image?

Answer 36

Germ tubes (pseudohyphae) of c.albicans in vitro

Question 37

When is antigen detection often employed for fungi?

Answer 37

Used a lot for pseudococcus Used to see if treatment is working

Question 38

What are the two types of anti-fungal chemotherapy?

Answer 38

Systemic Topical

Question 39

List the systemic anti-fungal chemotherapies?

Answer 39

Polyenes Triazoles Echinocandins 5-fluorocytosine

Question 40

List the topical anti-fungal chemotherapies?

Answer 40

Polyenes Imidazoles

Question 41

What are the targets of anti-fungals?

Answer 41

Ergosterol in cytoplasmic membrane: polyenes affect integrity, allylamines trizoles and morpholines affect synthesis Nucleic acids: 5-fluorocytosine affects RNA and DNA synthesis

Question 42

Why must patients on anti-fungal therapies be hospitalised?

Answer 42

To monitor toxicity

Question 43

Describe the main treatment of the following systemic fungal infections: a) Candida spp. b) Cryptococcus c) Aspegillus d) Dimorphic fungi

Answer 43

a) Fluconazole b) Amphotericin B + 5-fluorocytosine c) Voriconazole d) Amphotericin B

Question 44

Which types of treatment can be employed for dermatophytosis?

Answer 44

Non-specific (to reduce fungal load) Topical Oral

Question 45

In which situation would oral treatment of dermatophytosis be used?

Answer 45

If it is difficult to treat topically If it is widely disseminated If it is under the nails