DD 02-28-14 09-10am Introduction to Fungal Pathogens - High Flashcards
Basic Tenets of Medical Mycology - Linnaen system, Differences between Fungi & others
Divides living world into 5 kingdoms:
- Plantae
- Animalia
- Fungi (Mycota
- Protista (protozoa)
- Monera (bacteria)
Fungi are wholly unrelated to bacteria or protozoa
- these differences can be exploited therapeutically
- unaffected by antibacterial antibiotics
- instead use antifungal antibiotics
Fungi - basics of life / reproduction
- eukaryotic
- aerobic
- unicellular or filamentous
- heterotrophic
- encased in a rigid cell wall
- May reproduce sexually or asexually (nature of reproduction is used in classification)
Fungi as Eukaryotes
As Eukaryotes, have…
- contain membrane bound organelles (nuclei, mitochondria, Golgi, ER lysosomes)
Fungi as Heterotrophs
As Heterotrophs…
- lack chlorophyll
- NOT photosynthetic (autotrophic) like plants/algae
- obtain necessary organic substrates from surroundings
Fungi - Cell wall
Fungi have rigid cell wall
- like plants
- unlike animals
- contains chitin (as in exoskeleton of insects) and cellulose (as in plant matter)
Fungi - Cell membrane
- inside rigid cell wall
- contains ergosterol
Fungi - Motility
- Only a few specialized fungi (Chytridiomycota) are mobile
- NO medically-relevant species are motile
Subclassifications of Fungal Species
- saprobes
- symbionts
- commensals
- parasites
- This same system of classification applies to bacteria and protozoa.
Saprobes (subclassification of fungal species)
- live upon dead / decaying organic matter
Symbionts (subclassification of fungal species)
- live upon other organisms to the mutual advantage of both
Commensals (subclassification of fungal species)
- live upon another orangism with no detriment to the host
Parasites (subclassification of fungal species)
- live upon another organism w/clear detriment to the host
How fungi are sub-classified
Poses problem when fungus formerly thought to be “imperfect” (w/out a sexual state) is later discovered to be capable of sexual reproduction
–> thus, phyla recognized within mycology are in great flux
Cryptococcus classification & reproduction
Cryptococcus = fungal infection common in HIV/AIDS patients, caused by Cryptococcus neoformans
- 1st thought it was “imperfect” (w/out sexual state)
- Later discovery of sexual state prompted “re-naming” to Filobasidiella neoformans
- Clinicians have not embraced the change and, in the medical realm, the original name persists
Kingdom Fungi/Mycota - 6 Phyla
Chytridiomycota Zygomycota* Ascomycotina * Glomeromycota Basidomycotina* Deuteromyoctina*
*medially important
Zygomycota - reference species
Mucor, Rhizomucor, and Rhizopus
Ascomycotina - reference species
Dermatophytes
Basidomycotina - reference species
Cryptococcus
Deuteromyoctina - reference species
Asexual / imperfect fungi
2 Fungi Growth Forms
Yeasts - unicellular, round & oval
Molds - filamentous
Yeast growth form
- unicellular growth form
Fungus reproduces via…
- budding to form blastoconidia
- dividing in half through fission
Colonies of yeast are usually moist or mucoid in appearance
May form pseudohyphae (different than mold hyphae)
Yeast of medical relevance
Cryptococcus neoformans
Candida albicans
Mold growth form
- filamentous growth form
- Fungus reproduces via formation of spores or conidia
Filamentous elements = hyphae
Molds of medical relevance
common dermatophytes
Aspergillosis
Hyphae of Mold forms
- en mass = mycelium
- often branched
- grow by apical extension
- may be septate (w/internal divisions, like a cattail stalkca) or non-septate
Septa of Hyphae
Septa divide hyphae into compartment but do NOT strictly divide the fungus into “cells”
-cytoplasm or even organells may flow between compartments via pores w/in the septa
Pseudohyphae (vs. hyphae)
- formed by some yeasts (not the true hyphae of molds)
- simply elongated yest linked together like sausages
- typically demonstrate some degree of rounding
- DO NOT have cytoplasmic connections between compartments
- Candida albicans is an organism that often forms pseudohyphae
Dimorphic fungi
- Fungi that do not have fixed morphology but may exist in YEAST OR HYPHAL form
- Typically transition triggered by an environmental change (atmosphere, temperature, food supply)
*Thermal dimorphism refers to dimorphism that is dictated by temperature (most common context of “dimorphism”)
Histoplasmosis & Dimorphism
- disease caused by Histoplasmosa capsulatum
= thermally dimorphic fungi often found in bird/bat feces - at ambient temp in fecal material, exists mold and saprophyte
- if inhaled & at body temp, can transform into parasitic yeast of macrophages
Medically relevant thermally dimorphic organisms (w/pneumonic)
Some Can Have Both Phases S- Sporothrix schenckii C- Coccidioides immitis H- Histoplasmosa capsulatum B- Blastomyces dermatitidis P- Paracoccidioides brasiliensis
Hyphal Characteristics - Rhizoids
= specialized form of hyphal elements that grow like roots from larger hyphae
Medically-relevant fungi that form Rhizoids
- seen only in a few medically-relevant fungi (e.g. Rhizopus)
Hyphal Characteristics - Septa
- Septate hyphae are those that demonstrate complete cell walls that subdivide the hyphae into compartments
- These subdivisions are NOT equivalent to “cells,” as microscopic pores in septae allow for free exchange of cytoplasm & nuclei between compartments.
Medically-relevant SEPTATE fungi
Aspergillus fumigatus
Dermatophytes
Hyphal Characteristics - Non-septate
- Non-septate hyphae have no cell walls compartmentalizing the hyphae
- In truth, sometime very sparse or incomplete septae may be present, but fungus is still considered to be aseptate
Medically-relevant NON-SEPTATE fungi
Rhizopus
Spores & Fungal Reproduction
- Sexual & asexual fungi may reproduce via spore formation
- Yet at an introductory level, the spores useful to identify & classify medically-relevant fungi that are asexual spores
Examples of important types of asexual spores
Conidia Sporangia Chlamydospores Arthrospores Spherules Blastoconidia Sclerotic bodies
Conidia
- type of asexual spore of medical relevance
- usually borne off of specialized aerial hyphae (upward-projecting hyphae) called conidophores
- may macroconidia or microconidia
Microconidia vs. Macroconidia
Conidia may be…
- large & multinucleated (macroconidia)
- small & unicellular (microconidia)
(see pics in notes)
- Some fungal species may produce both macroconidia & microconidia
- Generally, macroconidia of certain shapes or with certain features are more useful in speciation than microconidia
Sporangia
– type of asexual spore of medical relevance
Similar to macroconidia
- BUT asexual spores (endospores) are enclosed in membranous sac
- sac that breaks & entire structure is borne by sporangiphore
(see pic in notes)
- Shapes / colors of sporangium may be useful in speciation