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1.20.1.12 - An Introduction to Fungi - Coggle Diagram
1.20.1.12 - An Introduction to Fungi
what are fungi?
eukaryotic
widely distributed in the environment
grow at 25º (some at 37º)
non-photosythetic, aerobic
cell walls contain chitin and other polysaccharides
heterotrophic nutrition
obtain nutrients from dead organic matter (decomposers) or living organisms (parasites)
uses exoenzymes to digest outside and then absorbs nutrients
can reproduce sexually and asexually
tolerate high osmolality and low pH
resistant to antibacterial drugs
moulds
yeasts
fungal structure
cell walls contain chiting and other polysaccharied
eukaryotic - possess membrane-bound organelles
fungal growth
moulds: hyphal growth
form large colonies
can produce asexual spored in different ways
sexual spores (acospores, basidiospores, zygospores) are important in taxonomy
yeast cells: divison/budding
asexual division by budding
can also have a sexual reporduction
morphological forms
yeast
oval/spherical appreance
mould
filamentous fungi
hyphal forms
dimorphic fungi
will grow in yeast or hyphal forms
dependent on temp of growth
reproduction
reproduction is complex
many can reporduce both sexually and asexually
sporulation bodies can be used for clinical identification
pores are relatively resistant and can survive and spread infection
spores germinate where conditions are favourable
two main types of asexual spores
sporangiospores formed on sporangiophores
conidia formed on conidiophores
in dermatophytes (skin infecting fungi) you get macroconidia and microconidia)
culture
sabouraud dextrose media
slightly acidic pH (5.6)
They are not considered negative for growth until after 4 weeks of incubation
The cultures are examined macroscopically and microscopically.
Cyclohexamide, penicillin, streptomycin or other inhibitory antibiotics are often added to prevent bacterial contamination and overgrowth.
in 1st opinion practice, culture is only really used if infection is recurrent or results of other clinical tests are not conclusive
to identify if fungi is dimporhic, grow at two temperatures
differentiation of fungi
colony characteristics
other patterns
colour both sides
size appearance after set time
surface eleveltion depresssions
examination of spore structures from culture or clinical sample
presence of vegetative hyphae
presencee/absence of septa
hyaline (colourless) or dermatiaceous (pigmented)
hyphal structures (spiral/racket shaped)
tissue invading fungi
serology
may be helpful - similar problems to any serology
microscopy
Infected tissue mounted in potassium hydroxide (KOH) on a slide and examined directly under the microscope.
Chitin in the cell wall is resistant to KOH cells are not.
Typical stain: Periodic acid-Schiff reaction (PAS).
Stains polysaccharides
Fluorescent microscopy may be used for identification, even on non-viable cultures or on fixed tissue sections. (The reagents for this test are difficult to obtain).
The common tissue H&E stain does not always stain the organism.
biopsy and histopathology
May be very useful for the identification of tissue-invading fungi.
clinical examples
Malassezia pachydermat
yeast - unicellular bottle shaped cell
commensal on skin
associated with canine skin and ear infection
opportunistic
Aspergillus
rapidly growing pigmented colonies
respiratory pathgoen aquired by inhalation of spores, most common animal pathogen
ubiquitous (soil, poor hay etc.)
invasive
filamentous mould with septated hyaline hyphae and conidia formed on conidiophores
ringworm
circular skin lesions caused by dermatophytes
colonise and invade skin hair and nails
spores shed from infected animals remain infective for many moths
zoonotic
transmission by contact or contaminated surfaces
very often under straps of things due to rubbing