Fungal infections (Mycology & Antifungals) Flashcards
What are features of fungi?
- Eukaryotic
- Chitinous cell wall
- Heterotrophic
- Can’t synthesise their own carbon molecules from inorganic sources
- Move by means of growth or through the generation of spores (conidia), which are carried through air or water
What is yeast?
- Yeasts are small single celled organisms that divide by budding
- Account for <1% of fungal species but include several highly medically relevant ones
What is mould?
Moulds form multicellular hyphae and spores
What is dimorphic fungi?
Some fungi exist as both yeasts and moulds switching between the two when conditions suit (usually based on temperature)
Why do only a few hundred species of fungi cause human infection?
- Inability to grow at 37 degrees
- Innate and adaptive immune response of body
Why is it different to treat bacteria rather than fungi?
- Fungi have some components similar to humans
- Generally much more different for fungi than bacteria because they are eukaryotic
What is the main target of antifungals?
Plasma membrane
What is the main component of plasma membrane in fungi?
Ergosterol
What’s the difference between human plasma walls and fungi plasma walls?
Human plasma walls have cholesterol and fungi plasma walls have ergosterol
What is similar between mammalians and fungi?
DNA/RNA synthesis, protein synthesis
What components of fungi cell wall aren’t present in humans?
Mannoproteins
B1,3 glucan
B1,6 glucan
Chitin
What 3 classes of drugs target the plasma membrane?
- Polyenes - can form pores in fungal cell membrane → leakage of cations and disrupt membrane proteins
- Azoles
- Allylamines
- Both inhibit ergosterol synthetic pathway
What is the aim of antimicrobial drug therapy?
to achieve inhibitory levels of agent at the site of infection without host cell toxicity
Relies upon identifying molecules with selective toxicity for organism targets
What features should an antimicrobial drug have?
- Target does not exist in humans
- Target is significantly different to human analogue
- Drug is concentrated in organism cell with respect to humans
- Increased permeability to compound
- Modification of compound in organism or human cellular environment
- Human cells are ‘rescued’ from toxicity by alternative metabolic pathways
Can a fungal infection be life threatening in a healthy host?
Yes but rare
What is a common and recurrent disease caused by fungal infection?
Mucosal candidiasis
What are risk factors for Mucosal candidiasis?
immunosuppression, diabetes antibacterial therapy and mucosal disruption
What would you treat Mucosal candidiasis with?
topical or oral azoles
How are dermatophytes spread?
Human-human or animal-human transmission
What temperature are dimorphic fungi mould?
Mould at ambient temperature (25-30C)
What temperature are dimorphic fungi yeast?
Convert to yeast form at 37C
What is a true pathogen?
infect healthy hosts
What is the containment level or dimorphic fungi?
Containment level 3 (especially in mould form)
What can cause infection from dimorphic fungi?
Infection via inhalation of conidia from soil or implantation
What are examples of dimorphic fungi?
Coccidioides, Invasive candidiasis, cryptococcus
What infection could a cannula cause?
Invasive candidiasis
What is an infective differential diagnosis of sub-acute/ chronic meningitis?
- Tuberculosis
- Cryptococcus
- Dimorphic fungi – Histoplasma, Coccidioides, Blastomyces
- Lyme
- Brucella
- Syphilis
What is a non-infective differential diagnosis of sub-acute/ chronic meningitis?
- Sarcoidosis
- Behçets’s
- SLE
- Malignant
- Drug induced
Who is severe disease caused in by a small number of fungi?
Immunocompromised
