Fungal pathogens Flashcards
Fungi
- Eukaryotic
- Equal in rank to plants and animals
- Fewer antifungals because the essential functions targeted by them are the same as in host cells
- Specificity to kill a fungus is difficult
- Produce secreted hydrolytic enzymes which they secrete into the environment that breaks down complex organic materials into simple molecules which they can then take up
Types of fungi
- Filamentous fungi Mould Eg. Aspergillus sp. - Yeasts Unicellular Eg. Saccharomyces cerevisiae - A subgroup of yeasts are dimorphic/ polymorphic Eg. Candida albicans
Human disease
- Superficial mycoses
- Subcutaneous mycoses
- Systemic mycoses
Superficial mycoses
- Dermatophytes Eg. tinea pedis
- Candida sp. Eg. thrush
- Malassezia sp. Eg. dandruff
Subcutaneous mycoses
- Rare infections
- Black moulds
- Madurella mycetomatis
Invasive mycoses
- Primary pathogens
- Oppurtunistic pathogens
Superficial mycoses
Dermaptophytes
- Superficial infection of the skin, hair and nails
Eg. tinea pedis + tinea corporis
Caused by 3 genera, all filamentous fungi:
- Microsporum sp.
- Epidermophyton sp.
- Trichophyton sp.
- It is from soil, animals and people
- It produces keratinase, digests keratin as a growth substrate. Infects keratin rich tissues
Non mycophogical classification, divided into 3 groups on habitat: - Anthrophilic Host is man Eg. Trichophyton rubrum - Zoophilic In animals They give the most severe inflammatory response Eg. Microsporum canis - Geophilic Found in soil
Superficial mycoses
Candida albicans
- Commensal organism
- Present in the mouth, GI tract and in women in genital tract
Superficial mycoses
Candida infections
Sites:
- Mouth
- Vagina
- Skin
Predisposing factors:
- Antibitotics, pregnancy
- Occurance
75% have 1+ vaginal infection - Causes thrush
Candidiasis
- A fungal infection due to any type of Candida
- When it affects the mouth it is commonly called thrush
- When it affects the vagina, it is called a yeast infection
Subcutaneous mycoses
- Geographically limited
- Wide range of causative species
- Affects subcutaneous tissue
Introduced by puncture wounds - Disease develops slowly
- Challenge to treat
Limited facilities (locally)
Poor response to treatment (chronic)
Eg.
- Chromoblastomycosis
Invasive mycoses
Primary pathogens: - Histoplasma capsulatum - Blastomyces dermatidis - Parracoccoidiodes brasiliensis Infect healthy individuals Route of infection; inhalation of spores
Oppurtunistic pathogens:
- Candida sp.
- Aspergillus sp.
- Cryptococcus sp.
- 90% of all reported fungal- related deaths are from:
Cryptococcus, Candida, Aspergillus + Pneunmocystis
Invasive mycoses
Primary fungal pathogens
- All thermally dimorphic
Saphrophytic filamentous form at 25
Parisitic yeast form at 37 - Types of disease
Asymptomatic
Mild respiratory infection
Can progress to serious pulmonary infection
Oppurtunistic pathogen
Candida auris
- An emerging pathogen
Key concerns:
- multidrug resistance (azoles, polyenes + echinocandins)
- misdiagnosis
- hospital outbreaks
Oppurtunistic pathogen
Aspergillosis
Causative organisms:
- Most Aspergillosis species do not cause disease
- Causative organisms limited to, A. fumigatus + A. flavus
Route of infection:
- Inhalation of spores
Type of disease:
- Allergy
- Toxins
- Invasive bronchopulmonary Aspergillosis
- Disseminated Aspergillosis
Oppurtunistic pathogen
Cryptococcus organisms
Causative organisms:
- Cryptococcus neoformans + Cryptococcus gatti
- Dimorphic
- In clincal= caspsulate yeast
- Found in soil and avian habitats
Route of infection:
- Inhalation
- Sexual cycle produces small spores
Disease: - Pulmonary Cryptococcosis Often asymptomatic Chronic Cryptococcus can become an intracellular pathogen and therefore persist
- Meningitis
Can occur in ‘normal’ individuals
High mortality
Pneumocytisis jirovecii
- Non culturable in vitro
- Obligate parasite
- Lacks genes for amino acid biosynthesis
- It scavenges amino acids from the host
