Mycology Flashcards
Fungus morphology
Eukaryotic (nuclear membranes and organelles) Larger, more complex than bacteria Has a cell wall with ergosterol Lacks chlorophyll Sexual and asexual repro Biochemically distinct pathways
Classification of fungi is based on…
Structures formed during sexual repro
Deuteromycetes
Human pathogens that do not form sexual structures
Yeasts
Single celled
Elongate to form chains called pseudohyphae
Reproduce by budding to form daughter cells/blastospores
Some are commensal and some are pathogens
Pseudohyphae
Chains of yeast
Moulds
Multicellular
Form hyphae than may be septate or aseptate
Many hyphae form a mycelium
Specialized structures produce asexual spores
Some hyphae fragment to form spores
Hypae
Tubular mould structure
Maybe be septate (have cross walls) or aseptate (no cross walls)
Mycelium
Mass of hyphae
Mould
Conidiophores give rise to…
Conidia
In mould
Arthrospores
The spores formed from the fragmenting of hyphae
Dimorphic fungi
Fungi behaving as yeasts or molds
Grows at mould at room temperature (found in environment, limited distribution, produce infectious spores)
Grow at yeast at elevated temperatures (in the body, not transmissible between people)
How do fungi cause disease?
Growth on body surfaces
Invasion of the body (rare, have to be profoundly immunosuppressed)
Allergic reactions
Toxins released after ingestion
Candida albicans
Often commensal on mucus membranes in GI tract
Rapidly colonizes damaged skin
Chief fungal pathogen
Can cause oral, skin and vaginal infections
3 systemic candida infections
Urinary tract (from foley catheters usually) Endocarditis (esp in prosthetic heart valves or IV drug use) Septicemia (immunosuppressed)
3 ways to diagnose candida infections
Clinical suspicion
Microscopy (KOH, gram stain)
Culture (takes several days)
Why do you need to add KOH when looking at Candida under the microscope?
It will dissolve the host tissue so you can see the fungi much easier
Cryptococcus neoformans/gattii
Encapsulated yeast
Neoformans from bird droppings, gattii from douglas firs
Clinical disease usually in partly immunosuppressed
Pneumonia (subclinical), meningitis (chronic), disseminated (for immunosuppressed)
Pneumocystis jirovecii
Yeast
Widely distributed geographically
Caused pneumonia in immunosuppressed patients, esp HIV
Dermatophytes
Closely related group of keratolytic fungi
Attack skin, hair, nails
Minor trauma to skin allows initial infection, then fungal penetration balances turn over of superficial squamous cells
3 predisposing factors to Dermatophyte infection
Minor trauma
Occlusion
Moisture
Clinical features of Dermatophyte infection
Red, scaly, rash may have pustules, with central clearing and migrating margin
Called ringworm, athlete’s foot, or jock itch
Transmission of Dermatophytes
Skin squames contaminating fomites
Rarely by direct (person to person) transmission
Tinea pedis
Dermatophyte infection of the feet
Tinea versicolor
caused by, location, presentation
Caused by Malassezia furfur
Widespread skin commensal that flourishes on skin fatty acids
Infection is superficial, and manifests as hyper or hypo pigmented lesions with itching and occasional pustules
2 groups of fungi that can cause invasive fungal infections
- Opportunistic fungi (that occur widely)
2. Geographically defined dimorphic fungi
Aspergillus fumigatus
location, risk factors, presentations
Widespread, grows on rotting vegetation
Spores commonly present in the air
Immunosuppression is risk factor
Presentations: allergic bronchiopulmonary aspergillosis (asthma like symptoms), fungal ball (in cavities), and invasive disease (tissue destruction, pneumonia)
Histoplasma capsulatum
Dimorphic fungus
Infection occurs when spores are inhaled and germinate in the lung
Only a small proportion of people get disease (most others just fight it off with antibodies - can detect)
4 dimorphic fungi
Histoplasma capsulatum
Blastomyces
Sporothrix
Coccidiodes
