Week 4 Mycology

Question 1

Are fungi prokaryotes or eukaryotes?

Answer 1

• Eukaryotes (multicellular)
• Bacteria (prokaryotes)
• Plants (eukaryotes)
• Viruses (neither)

Question 2

What forms can fungi exist in?

Answer 2

• Yeasts
  ~ Single-cell form
• Mould
  ~ Filamentous/hyphal form
  ~ Disseminated via airbone conidia (asexual reproduction from fungi)
• Dimorphic fungi
  ~ Exists in both forms

Question 3

What are the superficial infections caused by fungi?

Answer 3

• Candidiasis
• Dermatophytes
• Pityriasis versicolor

Question 4

What are the subcutaneous infections caused by fungi?

Answer 4

• Subcutaneous mycoses

Question 5

What are the systemic infections caused by fungi? (7)

Answer 5

• Systemic candidiasis
• Systemic mycoses
• Aspergillosis
• Cryptococcus
• Penicillium marnefeii
• Mucomycosis
• Pneumocystis jirovecii/carinii

Question 6

What are the common types of candida causing superficial candidiasis?

Answer 6

• Yeast form
• C. albicans
  ~ Most common
• C. glabrata
  ~ Common
  ~ Less susceptible to azoles (Abx class)
• C. auris
  ~ Rare but often resistant to antifungals

Question 7

Where does candidiasis usually affect?

Answer 7

• Normal flora overgrowth in mucous membranes (throat, GIT, vagina)
• Skin and nails (nappy rash, skin folds)
• Recurrent infections in HIV/AIDS

Question 8

How is candidiasis managed?

Answer 8

• Address precipitating factors
  ~ Stop Abx
  ~ Reduce steroids
  ~ Test for HIV
  ~ Practice good hygiene
• Topical/systemic antifungal drugs
  ~ Echinocandins/anidulafungin (often first-line as many people are not resistant)
  ~ Clotrimazole
  ~ Azoles

Question 9

What are dermatophytes?

Answer 9

• Filamentous fungi
• Found in humans, animals or environment

Question 10

Where are dermatophytes found?

Answer 10

• Scaly skin, broken hair shafts, white opaque brittle nails (to digest keratin)
• Foot (tinea pedis/athlete’s foot)
• Head (tinea capitis)
• Nail (tinea unguium)

Question 11

How do you identify dermatophytes?

Answer 11

• Microscopy
• Potassium hydroxide clarifies the keratin in skin scrapings
• Culture

Question 12

What is pityriasis versicolor caused by?

Answer 12

• Malassezia furfur
• Dimorphic
• Common in hot, humid climates

Question 13

What are the causes of subcutaneous mycoses?

Answer 13

• By a variety of fungi and bacteria
• Found in environment (i.e. not endogenous)
  ~ Inoculation injuries

Question 14

How to diagnose subcutaneous mycoses?

Answer 14

• Tease out granules or biopsy for microscopy and culture

Question 15

Difference between superficial and systemic candidiasis?

Answer 15

• Systemic candidiasis has similar but more extensive predisposing factors
  ~ GIT perforation/surgery
  ~ IV line
  ~ In preterm neonates

Question 16

What is the treatment for systemic candidiasis?

Answer 16

• Stop Abx
• Remove central lines
• Treat despite possible negative blood cultures (insensitive to candida)
• Treat early especially in ICU

Question 17

What is the cause of aspergillosis?

Answer 17

• Aspergillus fumigatus (most common)
• A filamentous fungus

Question 18

What happens in invasive aspergillus? (IMPT)

Answer 18

• Neutropenia may occur in immunocompromised patients
• Cultures become less predictive
• Biopsy more specific
• May go to her lung and brain

Question 19

What are the cryptococcus spp that can cause infections?

Answer 19

• Cryptococcus neoformans and C gattii
• Capsulated yeasts

Question 20

How are cryptococcus spread?

Answer 20

• Inhaled or skin lesions
• May appear in immunocompromised px

Question 21

How are cryptococcus infections diagnosed?

Answer 21

• Antigen test of CSF (more sensitive)
• Culture of CSF, blood, BAL or biopsy (but slow growth)
• Microscopy (India ink shows yeast cell in a capsule)

Question 22

What are the s/s of talaromyces/ penicillium marnefeii infection?

Answer 22

• Cough
• Skin lesions
• Systemic symptoms (weight loss, fever, lymphadenopathy)

Question 23

What are talaromyces/penicillium marnefeii?

Answer 23

• Thermally dimorphic fungus
• Will have red pigment on culture

Question 24

What is mucormycosis and what is it caused by?

Answer 24

• By Mucor and related species
• Infections only in immunocompromised people (esp w/ DM)

Question 25

What is the diagnosis and treatment for mucormycosis?

Answer 25

• Microscopy and culture of biopsy
• Surgical debridement
• Antifungals

Question 26

Brief on pneumocystis jiroveci/carinii?

Answer 26

• Causes lung infections in immunocompromised px (common in HIV/AIDS px with low CD4)
• Use microscopy or PCR to diagnose (culture is hard to do)
• Does not respond to antifungal drugs
• Treat with co-trimoxazole

Question 27

What are the diagnostic methods for fungi?

Answer 27

• On human samples:
  ~ Microscopy and culture
  ~ Antigen tests
  ~ Nucleic acid tests
• From fungal culture (but will take weeks)
  ~ Microscopy
  ~ MALDI TOS Mass spectrometry
  ~ Nucleic acid tests
• From susceptibility testing
  ~ For invasive Candida spp
  ~ For filamentous fungi

Question 28

How to culture fungi?

Answer 28

• In Sabouraud Dextrose agar
• Take days-weeks
• May need supplements (eg Abx) for dirtier sites to prevent overgrowth of fast-growing bacteria

Question 29

What are the microscopic/macroscopic features of Aspergillus/some filamentous fungi?

Answer 29

• Conidia (spores)
• Phialides (holds spores)
• Vesicle (holds phialides)
• Conidiophore (holds vesicle)
• Fluffy colonies (like mould)

Question 30

What are some microscopic/macroscopic features of yeast?

Answer 30

• Germ tubes (only for albicans)
• Capsules (neoformans)
  ~ For antigen test
• Chrom agar
  ~ Different species show different colours

Question 31

How is gene sequencing carried out?

Answer 31

1) Use PCR to amplify the target gene
2) Use gel to see if the expected band is present
3) Sequence the DNA in the band
40 Use bioinformatics to analyse sequence and find a match