Fungi Flashcards
What are 5 features of the fungi kingdom?
- Eukaryotic
- Larger and more complex than bacteria
- Cell wall (ergosterol present)
- lack chlorophyl
- reproduce asexually or sexually
How are fungi classified?
based on structures formed during sexual reproduction
What class of fungi do not form sexual structures?
The deuteromycetes
Are yeasts multi or single celled?
single celled
What are chains of yeast cells called?
pseudohyphae
How do yeast reproduce?
By budding to form daughter cells/blastopores
Are yeast commensal or pathogenic?
there are some of both
Are moulds multi or single celled?
multicellular
What structures do moulds form?
Tubular structures called hyphae which have either cross walls (called septate) or lack cross walls (aseptate)
What are asexual spores formed by moulds called? what do they give rise to?
conidiophores giving rise to conidia
What are arthrospores?
Fragmented hyphae that form spores
What are dimorphic fungi?
fungi that can behave as either yeast or mould depending on the temperature
What is the temperature differential for mould vs. yeast in dimorphic fungi?
grow as mould at RT
Yeast at elevated temps
What form of dimorphic fungi is typically found in the body vs the environment?
mould in the environment
yeast in the body
Can dimorphic fungi be passed person to person?
no because the form in the body is yeast which doesnt produce spores
What tends to limit the mould form of dimorphic fungi?
geographical distribution
Where can the yeast form of dimorphic fungi sometimes be seen ?
stained tissue samples
What are 4 ways in which fungi cause disease?
- growth on body surfaces
- Invasion of the body
- Allergic reactions by the body
- Toxins released after ingestion
What fungi is often a commensal of mucous membranes in the GI tract but can rapidly colonize damaged skin
Candida albicans
the sites of Candida infections by C. albicans tend to be?
mucocutaneous
What are two common forms of candidiasis?
oral and vaginal
What are 3 possible presentations of oral candidiasis?
- thrush
- Stomatitis: denture sore mouth
- Chelitis: angular erosions with pustules
What is the vaginal presentation of candidiasis like?
similar to thrush
What are 3 presentations of skin infections by Candida albicans?
Interigo: between toes
Diaper rash: due to ammonia from urine irritating the skin and allowing the candida in
Nail
What are 3 systemic infections that candida are often associated with?
- Urinary tract
- due to use of foley catheters - Endocarditis
- especially with prosthetic heart valves or IV drug use - Septicemia in immunosuppressed patients
What are two lab methods of diagnosing candida infections
- Microscopy
- KOH or gram stain - Culture
What is an encapsulated yeast endemic to BC and found in bird droppings?
Cryptococcus neoformans and C. gattii
What 2 things does infection with C. neoformans/gattii cause ?
- Pneumonia
- subclinical - Meningitis
- chronic
What widely distributed yeast causes pneumonia in immunosuppressed patients?
Pneumocystis jirovecii
What is the closely related group of keratolytic (attack skin, hair, nails) fungi
Dermatophytes
What is the pathogenesis for an infection with a dermatophyte?
- minor trauma to skin = initial infection
2. Fungal penetration balances turnover of superficial skin squamous cells
What 2 factors predispose someone to develop a dermatophyte infection?
- Minor trauma
2. Occlusion: no drying of skin. Moisture reduces harshness of skin environment
What are some clinical features/presentations of a dermatophyte infection?
- Red, scaly, rash with pustules (maybe)
2. Central clearing and migrating margin
How are dermatophyte infections passes?
Infected skin squames that contaminate fomites
- rarely by direct contact
What is the name given to skin infections typically caused by dermatophytes?
Tinea (capitis, pedis…)
How are dermatophyte infections identified?
- culture - looking for pigment of colonies
2. growth on plates - looking for macro and microconidia
What fungi is the cause of tinea versicolor?
Malassezia furfur
What is M. furfur?
A widepread skin commensal that flourishes by feeding on skin fatty acids
What is the presentation of Tinea versicolor?
Infection is superficial, and manifests as hyper- or hypo- pigmented lesions with itching, and occasional pustules.
How is an infection with M. furfur often identified?
through microscopy - looking for the characteristic spaghetti and meatballs pattern of yeast cells
Invasive infection causing fungi can often be divided into two groups… give some examples
- Opportunistic fungi (widely occurring)
- Aspergillus spp., Pneumocystis jirovecii, Candida spp. - Geographically defined - dimorphic fungi
- Histoplasma capsulatum
Where can Aspergillus fumigatus be found?
pretty widespread on rotting vegetation
spores are commonly present in the air
What is an important predisposing factor to disease being caused by A. fumigatus?
immunosuppression
What are 3 clinical presentations of Aspergillus fumigatus?
- Allergic bronchiopulmonary
- Asthma-like symptoms. - Fungus grows in bronchial secretions. - Fungal ball in cavities of lungs and sinuses
- Invasive disease
- tissue destruction and pneumonia
What lab techniques are used to diagnose invasive fungal infections?
Microscopy
- secretions/KOH
- histology
Culture but multiple positives may occur due to contamination
What kind of fungus is Histoplasma capsulatum? Morphology?
dimorphic fungus
doesn’t actually have a capsule!
Where is Histoplasma capsulatum found
Central United States, especially the Mississippi river valley and Southern States, north to Ontario, Montreal.
How does an infection with H. capsulatum occur?
Spores are inhaled and germinate in the lung
What proportion of people infected with Histoplasma capsulatum develop disease? how is it detected?
only a small portion
identification by serology
What is characteristic of Histoplama capsulatum in culture?
Growth of cells with extensions
