Kinzy - Intro To Fungi Flashcards
What are some important. Genera characteristics of fungi?
They are eukaryotic - makes it difficult to selectively target fungi in the body.
Thick, rigid, cell walls - make it difficult to get drugs in.
Source of many allergies
Saprophytic - secrete enzymes that break down organic matter around them and then transport the molecules into their cells.
Form spores
Our defense is usually via neutrophils - neutropenic patients are very susceptible.
Ergosterol replaces cholesterol in membranes
5-fluorocytosine
Gets converted to FdUMP, a dTMP analogue. This is toxic for the fungus.
Membrane inhibitors
Take advantage of the fact that fungi have ergosterol whereas mammalian cells have cholesterol.
Polyenes
Bind to ergosterol in the membrane and increase membrane permeability. This allows for the loss of small molecules from the cell.
- amphotericin - systemic infections
- Nystatin - used only topically due to toxicity
Azoles
Interfere with synthesis of ergosterol.
- end in “Azole”
Echinocandins
Block synthesis of cell-wall polysaccharides
Pentamidine
Used against pneumocystis carinii which is common in AIDS patients.
What are the four major groups of fungi?
Zygomycetes
Ascomycetes
Basidiomycetes
Fungi imperfecti
Zygomyces
Forms a sporangium, which is essentially a big bag full of haploid spores formed by meiosis.
Ascomyces
Starts with a single cell that undergoes meiosis and the resulting four haploid spores are contained in a sac derived from the wall of the original diploid cell.
- Think that A is the first letter in the alphabet and it starts from 1 cell.
Basidiomycete
Sexual spores bud from tip of club-shaped terminal cell.
Fungi imperfecti
No meiotic stage known. Also known as deuteromycete.
How to identify fungi?
- in a culture they are not fastidious so they will grow on pretty much anything
- typically though we grow them on what is called a Saboraud agar, which is broth based and has glucose.
- whether it is pigmented (dematiciaceous) or not (hyaline) is a big deal
- serology is important - seeing which antibodies we have circulating around. This isn’t always useful because we may have antibodies anyway in our body for some of these
- therefore treatment is usually more dependent on site than on species.
What is the name of the agar that we grow fungi on generally?
Saboraud
How do Yeast multiply?
Budding
What do yeast look like in culture?
Smooth and creamy colonies
How do molds multiply?
They elongate and form a filament called a hypha. A mass of hyphae is called a mycelium.
Hypha
Filament of mold
Mycelium
Mass of hyphae
What does mold look like in culture?
Large, fuzzy, colonies that are often pigmented.
How do pseudohyphae multiply?
Basically is multiplies like a yeast but they stay attached. This causes them to look a lot like a hyphae
Chlammydospores
Large, round, terminal cells with thick walls. They form by differentiation of the terminal cell of a hypha.
Conidia
Resting/dispersal stage
Thick walled
Asexual spores
Macrocondia
Large and contain multiple cells. Form by differentiation of a length of hypha. Have a septa between cells though
Arthoconidia
Form by fragmentation of hyphae at septal planes. Alternate cells from thick walls. Later hyphae break apart at septa.
Phiaoloconidia
Chains of Conidia bud from specialized terminal cells of hyphae
What are the 5 different classifications of fungal infections? And what are they classified based off of?
Classified based off of location of infection.
Superficial Cutaneous Sub-cutaneous Systemic Primary pathogens vs. opportunistic
Piedra
A type of superficial infection that attacks the hair.
Tinea
A type of cutaneous infection of the skin.
- lesion of inflamed rim of active infection and central clearing.
- take the specimen from the rim of the infection!
- usually found in soil, animals, and humans
If patient has a superficial infection of the skin where should you take your sample?
The rim
Subcutaneous mycoses
Fungi introduced by local trauma
Three important genera of dermatophytes
EMT
Epidermophyton, microsporum, Tricophyton
What is a common cause of subcutaneous infection?
Sporothrix schenkii - cigar shaped in tissue but hyphae conida in culture.
Systemic mycoses
Endemic to specific areas
Infect all people, not just immonocomprimised people
Infection is usually in the lung but can spread
Exposure is often occupational so more frequent in males than females
Most infections are asymptomatic
Dimorphic - they are yeasts in 37 degrees but hyphae in standard culture at 30 degrees.
How do you diagnose a fungal infection?
Microscopy Skin testing (similar to TB) Serology PCR Culture Exoantigen test
Blastomyces dermatidis
Large yeast with broad-based buds.
Use a KOH mount to destroy everything other than the fungus, which has cell walls.
Histoplasma capsulatum
Tuberculate conida in culture but tiny intracellular yeast in clinical material.
Coccidioides immitis
Large spherules in the lung
Paracoccidioides brazilienses
Yeasts with multiple buds. Looks like a ship wheel
Candida albicans
Budding yeast, hyphae, pseudohyphae, microconidia, chlamydospores
- borderline between true pathogen and opportunist
- normal flora
- causes vaginal infections, GI and skin infections in infants
- causes oral infections (thrush)
- forms “germ tubes” while other Candida’s don’t.
Cryptococcus neoformans
Heavily-encapsulated yeast.
- causes infections of the lung, which then go to the brain or meninges.
- similar presentation as strep Neumo, H. Influenzae, N. Menigiditis
Aspergillus
Opportunist Especially in neutropenic patients Can start in lung and then go to heart or great vessels Use cytokines to treat Ubiquitous in soil and plants
Zygomyces - Nucor and rhizopus
Nasopharyngeal infections
Upper or lower respiratory tract disease
Tendency to branch at right angles
Can spread to brain
Pneumocystis carinii
Usually infected in childhood
Rare causes of disease until the AIDS epidemic
Not possible to culture in clinical labs
