Microbiology 16 - Fungal infections Flashcards
What is the main conponent of fungal cell walls?
Chitin
What is the main component of fungal cell membranes?
Ergosterol
What is the reproductive method of yeats?
Budding
Recall 3 examples of yeasts that are clinically important
Candida
Cryptococcus
Histoplasma
What are moulds?
Multicellular hyphae
Give 2 examples of moulds that are clinically important
Dermatophytes
Aspergillus
Recall the empiric treatment for oral, vulvovaginal and cutaneous candida infection
Oral candidiasis: nystatin suspension/fluconazole
Vulvovaginal and cutaneous: fluconazole/clotrimazole pessary if oral not tolerated/topical imidazole
Advise patient that topical treatments like imidazole may damage latex condoms/diaphragms
Recall the principles of candidaemia management
- Look for source and signs of dissemination:
- Imaging
- Serology for beta-D-glucan
- echocardiogram/fundoscopy (candida is sticky- likes to stick to surfaces) - Antifungals for at least 2/52 from date of first negative blood culture - repeat BCs every 48 hours
Grown on Sabouraud agar
If there are any central lines/catheters remove them
Recall the different types of cryptococcus, and which of these infect immunocompetent vs immunocompromised hosts
Serotypes A and D = cryptococcus neoformans (immunocompromised hosts)
Serotypes B and C = cryptococcus gatti (immunocompetent hosts)
Cryptococcus can cause pulmonary infection and meningitis
Which type of cryptococcus can cause meningitis?
Cryptococcus gatti (serotype B/C-immunoCompetent hosts)
What ink can be used to stain for cryptococcus?
India Ink
How should cryptococcus infection be managed?
- Induction: 2/52 of amphotericin B + flucytosine
- Consolidation: 8/52 of high dose fluconazole
- Maintenance: 1 year low-dose fluconazole
Resistant to echinocandins
Which type of aspergillus disease is an allergic disease?
Allergic Bronchopulmonary Aspergillosis (ABPA)
How does aspergillus appear under the microscope?
Fluffy colonies
What parts of the body can be infected by aspergillus?
Pre-formed cavities (eg. by TB) - so treated pulmonary TB may be in the history
What is a galactomannan assay used for?
Aspergillosis diagnosis
Why is pneumocystis jirovecii an unusual fungus?
No ergosterol wall
What is the typical history for PCP pneumonia?
Desaturating on exertion
Walking 10m and feeling breathless
What are the clinical features of mycormycoses?
Orbital/facial cellulitis with discharge of black pus from nose/ palate
Typically only affects immunocompromised/diabetics
How are mycormycoses managed?
Surgical management-very invasive disease
Early referral to ENT
Strong dose of ambisone (amphotericin B)- MOA- polyene-target cell membrane
Caused by moulds starting with “rhizo… smth”
Recall an example of a dermatophyte
tinea
Where does tinea cruris infect?
Groin
How is tinea diagnosed?
Often clinically, but can be confirmed via skin scrapings for MC&S
Recall 4 classes of antifungal medications
Polyenes- Amphotericin B (Ambisone)- cell membrane- Nephrotoxic
Azoles- Fluconazole, Clotrimazole- cell membrane- Abnormal LFTs
Echinocandins- Caspofungin- cell wall- no side effects
Pyrimidine analogues- flucytosine- DNA/RNA synthesis- Blood disorders
Recall the side effect profile of each class of antifungal
Azoles - abnormal LFTs
PolyeNes - Nephrotoxicity
Echinocandins - relatively innocuous
Pyrimidine analogues - blood disorders
What is the mechanism of action of azoles?
Inhibit ergosterol synthesis
What is the mechanism of action of polyenes?
Bind sterols in membranes to create leakage of electrolytes
E.g Amphotericin B/Ambisome
Give 2 examples of polyene medications
Amphotericin B
Nystatin
Which 2 types of fungus are echinocandins particularly useful for?
Candida
Aspergillus
NOT useful for cryptococcus
Examples: Micafungin, Caspofungin
What class of antifungal is flucytosine?
Pyrimidine analogue
What antifungal is cryptococcus resistant to?
Echinocandins (E.g- Caspofungin-affects cell wall)
Echinocandins are useful for candida/aspergillus
What is a pathognomonic sign seen on microscopy of Candida albicans to differentiate it from the other candida species
Germ tubes
How to identify the different aspergillus species?
Cannot tell based on hyphae, have to look at spores.
Treatment of aspergillosis?
At least 6weeks of amphotericin
