Microbiology - 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 (dimorphic)
What are moulds?
Multicellular hyphae
Give 3 examples of moulds that are clinically important
Dermatophytes
Aspergillus
mucormycetes.
what drug to treat Candida albicans
fluconazole
amphetricin B for invasive disease
2 principles of candidiasis management
serology for B-D-glucan
antifungals
Recall the different types of cryptococcus, and which of these infect immunodeficient vs immunocompetent hosts
Serotypes A and D = cryptococcus neoformans (immunodeficient hosts)
Serotypes B and C = cryptococcus gatti (immunocompetent hosts)
Which type of cryptococcus can cause meningitis?
Cryptococcus gatti
What ink can be used to stain for cryptococcus?
India Ink (all black apart form distinct capsule around yeast)
How should cryptococcus infection be managed?
- Induction: 2/52 of amphotericin B + flucytosine
2. Consolidation: 8/52 of high dose oral fluconazole
Which type of aspergillus disease is an allergic disease?
ABPA - Allergic bronchopulmonary aspergillosis
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
What is the typical history for PCP pneumonia?
Desaturating on exertion
What are the clinical features of mucormycoses?
Orbital/facial cellulitis with discharge of black pus from nose/ palate
How are mucormycoses managed?
LONG duration of ambisone (amphotericin B)
Recall 2 examples of a dermatophyte
tinea
ringworm
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
Azoles - membrane
Polyenes - membrane
Echinocandins -inhibit glucan synthase (cell wall)
Pyrimidine analogues - dna synthesis
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
Give 2 examples of polyene medications
Amphotericin B
Nystatin
Which 2 types of fungus are echinocandins particularly useful for?
Candida
Aspergillus
What class of antifungal is flucytosine? mechanism?
Pyrimidine analogue - INHIBITS dna SYNTHESIS
what stain for candida
periodic acid schiff (PAS)
most common candida
Candida albicans
what’s the germ tube test? what so you see for what organism
Germ tube test is a screening test for the presumptive identification of Candida albicans
only albicans has pseudohyphae
what can candida cause in the eyes & in mouth
candida endophthlamitis
angular chelitis
what agar to detect candida
sabouraud agar
can also detect w beta-d glutan assay
what is the management of candidiasis
eco and fundoscopy
if albicans - fluconazole
if not - echinocandin
Cryptococcus gatti grows in which plant
eucalyptus
what crypotocccus is common in those w AIDS
neoformans
2nd most common cause of death in AIDS
cryptococcal meningitis can cause what in the brain
hydrocephalus
in LP CSF isn’t mixed w CSF in brain
what stain to diagnose aspergillosis
Grocott methenamine silver (GMS)
treatment of aspergillosis
amphoetrcin B
not fluconazole for moulds as poor activity
what causes pityriasis versicolour
looks like vitiligo
caused by malassezia fur
mucormycosis happens in which 2 patients
imunocompromised
poorly controlle diabetics
cellulitis of orbit and black pus = what disease
mucormycosis
severe brain consequence of mucormycosis
rhinocerebral mucormycosis
murco. is caused by rhizopum and rhizomucor spp
management of mucormycosis
ENT referral as surgical emergency
high dose amphotericin B
tines pedis, tinea cruris, tinea capatis and onchomycosis (fungal nail) are all caused by?
trichophyton rubrum
many other too but this is common to all
which anti fungal works for virtually all fungi
amphotericin B
what fungi are resistant to echinocandins
Cryptococcus
give an example of an echinocandin
micafungin
mechanism of polyenes
bind ergosterol in cell membrane, creating channels
mechanism of azoles
inhibit enzyme in cell membrane (lanosterol 14 a demythelyase)
mechanism of echinocandins
inhibit beta d glucan synthase
