Week 4 Mycology Flashcards
Are fungi prokaryotes or eukaryotes?
- Eukaryotes (multicellular)
- Bacteria (prokaryotes)
- Plants (eukaryotes)
- Viruses (neither)
What forms can fungi exist in?
- Yeasts
~ Single-cell form - Mould
~ Filamentous/hyphal form
~ Disseminated via airbone conidia (asexual reproduction from fungi) - Dimorphic fungi
~ Exists in both forms
What are the superficial infections caused by fungi?
- Candidiasis
- Dermatophytes
- Pityriasis versicolor
What are the subcutaneous infections caused by fungi?
- Subcutaneous mycoses
What are the systemic infections caused by fungi? (7)
- Systemic candidiasis
- Systemic mycoses
- Aspergillosis
- Cryptococcus
- Penicillium marnefeii
- Mucomycosis
- Pneumocystis jirovecii/carinii
What are the common types of candida causing superficial candidiasis?
- Yeast form
- C. albicans
~ Most common - C. glabrata
~ Common
~ Less susceptible to azoles (Abx class) - C. auris
~ Rare but often resistant to antifungals
Where does candidiasis usually affect?
- Normal flora overgrowth in mucous membranes (throat, GIT, vagina)
- Skin and nails (nappy rash, skin folds)
- Recurrent infections in HIV/AIDS
How is candidiasis managed?
- 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
What are dermatophytes?
- Filamentous fungi
- Found in humans, animals or environment
Where are dermatophytes found?
- Scaly skin, broken hair shafts, white opaque brittle nails (to digest keratin)
- Foot (tinea pedis/athlete’s foot)
- Head (tinea capitis)
- Nail (tinea unguium)
How do you identify dermatophytes?
- Microscopy
- Potassium hydroxide clarifies the keratin in skin scrapings
- Culture
What is pityriasis versicolor caused by?
- Malassezia furfur
- Dimorphic
- Common in hot, humid climates
What are the causes of subcutaneous mycoses?
- By a variety of fungi and bacteria
- Found in environment (i.e. not endogenous)
~ Inoculation injuries
How to diagnose subcutaneous mycoses?
- Tease out granules or biopsy for microscopy and culture
Difference between superficial and systemic candidiasis?
- Systemic candidiasis has similar but more extensive predisposing factors
~ GIT perforation/surgery
~ IV line
~ In preterm neonates
What is the treatment for systemic candidiasis?
- Stop Abx
- Remove central lines
- Treat despite possible negative blood cultures (insensitive to candida)
- Treat early especially in ICU
What is the cause of aspergillosis?
- Aspergillus fumigatus (most common)
- A filamentous fungus
What happens in invasive aspergillus? (IMPT)
- Neutropenia may occur in immunocompromised patients
- Cultures become less predictive
- Biopsy more specific
- May go to her lung and brain
What are the cryptococcus spp that can cause infections?
- Cryptococcus neoformans and C gattii
- Capsulated yeasts
How are cryptococcus spread?
- Inhaled or skin lesions
- May appear in immunocompromised px
How are cryptococcus infections diagnosed?
- 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)
What are the s/s of talaromyces/ penicillium marnefeii infection?
- Cough
- Skin lesions
- Systemic symptoms (weight loss, fever, lymphadenopathy)
What are talaromyces/penicillium marnefeii?
- Thermally dimorphic fungus
- Will have red pigment on culture
What is mucormycosis and what is it caused by?
- By Mucor and related species
- Infections only in immunocompromised people (esp w/ DM)
What is the diagnosis and treatment for mucormycosis?
- Microscopy and culture of biopsy
- Surgical debridement
- Antifungals
Brief on pneumocystis jiroveci/carinii?
- 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
What are the diagnostic methods for fungi?
- 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
How to culture fungi?
- In Sabouraud Dextrose agar
- Take days-weeks
- May need supplements (eg Abx) for dirtier sites to prevent overgrowth of fast-growing bacteria
What are the microscopic/macroscopic features of Aspergillus/some filamentous fungi?
- Conidia (spores)
- Phialides (holds spores)
- Vesicle (holds phialides)
- Conidiophore (holds vesicle)
- Fluffy colonies (like mould)
What are some microscopic/macroscopic features of yeast?
- Germ tubes (only for albicans)
- Capsules (neoformans)
~ For antigen test - Chrom agar
~ Different species show different colours
How is gene sequencing carried out?
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
