Fungal infections Flashcards
Bacteria:
- unicellular
- prokaryote
- circular chromosomes
- no membrane bound organelles
- 70s ribosomes
- asexual reproduction
- peptidoglycan cell wall
Fungi:
- can be multicellular
- eukaryote
- distinct nucleus
- DNA on several chromosomes
- membrane-bound organelles
- 80s ribisomes
- sexual or asexual reproduction
- chitin cell wall
How many known species of fungi are there?
250,000
Saprophytes =
organisms that live in the environment
Why are fungi infections so rare?
- Not well adapted to 37 degrees, redox poTentials, human nutirents
- host defence mechanisms
- slow growing
- already highly successful in environment
Fungal infections are most common in:
Immunocompromised
Ex of immunocompromised patients:
- HIV
- Chemotherapy
- Diabetes mellitus
- Pregnancy
- Leukemia, lymphoma
- Steroids
Fungal infections in the immunocompromised may..
- more common
- disseminate
- more severe
- be a type that doesn’t occur in immunocompetent
3 types of fungi:
- moulds
- yeasts
- dimorphic
Moulds:
Grow by formation of filaments (hyphae) which form mycelium
In moulds, what is visible to the naked eye?
Mycelium
Reproduction of moulds:
- sexual
- asexual
Ex of moulds:
Apergillus
Yeasts:
Single-celled organisms, round.
Reproduction of yeasts:
Budding, asexual
ex of pathogenic yeasts:
Candida species
Cryptococcus neoformans
Candida albicans has:
Pseudohyphae and true hyphae
Dimorphic fungi:
Can grow as yeasts or mould. Yeast = infection, Mould = saprophytic
Ex of dimorphic fungi:
Coccidiodes immitis (coccidiodomycoses)
Toxic substance produced by fungus:
Mycotoxins
Mycotoxins can cause conditions such as:
Ergotism
Ex of hypersensitivity to fungi:
Asthma, farmer’s lung
2 kinds of superficial mycoses:
- no tissue invaded, no cellular response
2. no tissue invaded, cellular response
Ex no tissue invaded, no cellular response:
Tinea versicolour = painless scaling of skin
Tinea versicolor is caused by:
Yeast Malasezzia furfur
Malasezzia furfur:
- yeasts
- feeds on keratin but doesn’t produce host immune response
Ex No tissue invaded but host response elicited:
Ringworm/tinea/dermatophytosis.
Ringworm =
Use keratin as a nutrient (via production of keratinase). Ellicits a host response
3 groups of ringworms:
- geophillic
- zoophillic
- anthropophillic
Athletes foot =
tinea pedis
Ringworm vs eczema:
Ringworm: doesn’t itch as much, anywhere, circular ring with raised borers and clear center
Eczema: itches, elbows and behind knees, flat borders.
Subcutaneous mycoses are a result of:
Direct penetration of fungus into dermis and subcutaneous tissue through traumatic injury
Most common deep/systemic mycoses:
Aspergillus fumigatus.
Aspergillus fumigatus:
Deep infection followed by inhalation of spores resulting in pulmonary aspergillosis.
Can form a aspergilloma
Can invade blood vessels and cause pulmonary haemorrhage or infarction
Excepting to ‘fungi grow slow’ rule:
Murcomycoses
Murcomycoses:
- start in sinuses
- fast growing
- don’t respond to anti-fungals
Ex of invasive yeast:
Candida
Deep Candida:
Oesophagitis, candidaemia, endocarditis, hepatosplenic candidiasis
Superficial candida:
Trush (mucus), cadiosis of skin (rash)
Most common cause of thrush:
Candida albicans
Coccidiodomycoses
Deep dimorphic mycoses. Respiratory symptoms, rash, fibrosis.
How many classes of antifungals are there?
3
Polyene =
Amphotericin
Amphotericin B =
Binds to ergosterol
Very broad spectrum anti-fungal =
Amphotericin B
The most toxic drug used to treat infection =
Amphotericin B
Toxicity of amphotericin:
- Renal damage
- Chills/fever during infusion
Ex of Azoles
Flycoazole, voriconazole
MoA of azoles
Inhibit enzyme lansosterol 14 a-demethylase.
Lansosterol 14 a-demthylase:
converts lanosterol to ergosterol
Ergosterol =
Fungi cholesterol
Ex of exhinocandins:
Caspofugin
MoA of echinocandins:
Inhibits glucan synthase so inhibits cell wall synthesis
Use of echinocandins:
Invasive aspergillosis, invasive candida
