Introduction to Fungal Stuff Flashcards
Describe fungi morphology and composition
Fungi are eukaryotic, aerobic, unicellular or filamentous, heterotrophic organisms encased in a rigid cell wall.
All these cell walls contains chitin, mannans and glucans and a cell membrane containing ergosterol.
Most aren’t motile expect chytridiomycota.
what are the most common fungal infections?
Dermatophytes: utilize keratin as a substrate for growth.
Candida: non-dermatophyte yeast that prefers the glucose of interstitial fluids for growth.
Pityrosporum – prefers breakdown products of sebum for growth
Deed mycoses
Characterized by their ability to cause systemic infection.
Many begin in the lungs like inhalation through arthrospores and disseminate widely to a variety of tissues.
Describe means of categorizing fungi
The Linnean -> Fungi (Mycota) are a separate kingdom, are wholly unrelated to bacteria or protozoa.
Also subclassified as saprobes, symbionts, commensals or parasites.
Saprobes live upon dead and decaying organic matter.
Symbiots live upon another organism to the mutual advantage of both!
Commensals live upon another organism with no detriments to the host.
Parasites live upon another organism with clear detriment to the host.
Also subclassified in respect to their sexual reproduction:
Chutridiomycota
Zygomycota -> mucor, rhizomucor, rhizopus
Ascomucotina -> dermaphytes
Basidomucotina -> Cryptococcus
Deuteromyoctina -> asexual/imperfect fungi
Describe yeast forms of fungi and list some medically relevant types
A unicellular growth from where the fungus reproduces via budding to form blastoconidia or by diving in half through fission.
Colonies of yeast are usually moist or mucoid in appearance.
Medically relevant types : Cryptococcus neoformas and candida albicans.
Describe mold forms of fungi and list medically relevant types
A filamentous growth form where the fungus reproduces via formation of spores or condidia. These filamentous elements are called hyphae. (are MULTICELLULAR)
A mass of hyphae is called collectively mycelium. Are often branches and grow by apical extension.
Medically relevant molds include dermatophytes and aspergillosis.
What are septate and non-septate hyphae?
Hyphae may be septate (with internal divisions) or NON-septate.
Septa divide hyphae into compartments but do not strictly divide the fungus into cells, as cytoplasm or organelles can flow freely between compartments via pores within the septa.
Pseudohyphae
Incomplete budding -> no true septa
Elongated yeast linked together like sausages. DO NOT HAVE CYTOPLASMIC CONNECTIONS.
Candida is a common organism that forms these.
Dimorphic fungi
Dimorphic – fungi that do not have a fixed morphology but may exist in a yeast or hyphal form
Typically an environmental change can trigger a transition from one form of another.
All medically relevant fungi are asexual spores. Name them yo
CONIDIA – borne off of specialized aerial hyphae called conidophores. A conidium may be large and multinucleated or small and unicellular.
SPORANGIA – similar to macroconidia, except spores are enclosed in a membranous sac that breaks and the entire structure is bound by a sporangiophore.
CHLAMYDOSPORES – thick walled, round spores, highly resistant to adverse environmental conditions. Terminal chlamydospores form the ends of hyphae, while intercalary chlamydospores form along and within hyphae.
ARTHROSPORES – develop along the hyphae, are numerous and elongated, and often shaped like a barrel.
SPHERULES – large spores that develop during the yeast phase of some organism growth. The yeast form of the dimorphic fungus coccidiodes immitis forms spherules in tissue that are filled with endospores.
BLASTOCONIDIA – yeasts that bud asymmetrically are said to form blastoconidia.
SCLEROTIC BODIES – thick walled environmentally protective forms of yeast that are produced by some fungi that reproduce by fission.
Endospores
conidia enclosed within a sporangium sac
Cryptococcus - what is it? How is it diagnosed?
Systemic infection prevalent in HIV/AIDS patients.
This yeast has a thick, mucoid capsule surrounding it.
If cryptococcosis is suspected, the CSF from a lumbar puncture may be identified by mixing the fluid w/ India ink which stains everything except the mucoid capsule, thereby highlighting the organism.
Direct microscopic observation of fungi
scraping of epithelium from affected skin or mucosa
A drop of KOH or surfactant DMSO may be added, which denatures human material and leaves the chitinous walls of fungi more visible.
Allows for direct observation of yeast. Stains it a green-grey color.
Sabouraud’s agar
is the most sensitive to fungi culturing – growth of both dermatophytes and non-dermatophytes.
Unrelated contaminants also grow.
Mycosel media
fungal media impregnated w/ chloramphenicol and chlorohexamide to inhibit the growth of bacteria and saprobes.
