Fungi Flashcards
Describe the fungi kingdom.
- Eukaryotic microorganisms
- Cytoplasm enclosed in cell wall
- Cell wall composed of complex carbohydrate polymers, including chitin
- Nutrition: absorption of organic molecules from the immediate surroundings
- Reproduction is both by sexual (meiosis) and asexual (mitosis) spores
- 2 main morphological forms – moulds and yeasts
Describe hyphae.
- The basic cell unit of the moulds
- An apically elongating cylinder capable of branching
- Membrane bound nuclei and mitochondria as main energy
- At intervals, cross walls or septa strengthen the tubular wall but as these have a central pore, the cytoplasm can stream through.
- The hypha is therefore acellular, often with several nuclei per segment.
- Burrow into things and can be huge.
What are mycelium?
- Network of hyphae, forming the body of the mould
- Can consist of submerged vegetative mycelium (in substrate growing on) and aerial mycelium (produce spores, like mushrooms), bearing asexual spore
- Conidia or sporangiospores
Describe yeasts.
- An alternative growth form to the hypha
- Consists of discrete, often ovoid cells
- Reproduce by budding (so have buds on one end, giving lemon shape)
- Much bigger than bacteria
What are dimorphic fungi?
Some can produce both yeasts and hyphae, depending on environmental conditions.
What are pseudo-myecelium?
Intermediate form a growth between hyphae and yeasts, in which elongated budding cells form pseudo hyphae.
Colony: in culture, a mycelium or mass of yeast cells, usually grown from a single hyphal fragment or yeast cell. Act of scratching will spread infection.
What are the fungi phylae?
Phylum: Zygomycota
Phylum: Ascomycota
Phylum: Basidiomycota
Phylum: Deuteromycota (Fungi imperfecti)
The yeasts are not a taxonomic group, but represent unicellular fungi which may be members of any of the above groups.
What is deuteromycota (fungi imperfecti)?
- An artificial assemblage of fungi which only produce conidia, there being no sexual reproductive state
- In many cases, these are known to have evolved from either Ascomycota or Basidiomycota
- Most of the pathogenic species fit here
What are arthrospores?
Conidia formed by simple fragmentation of hyphae in dermatophytes.
How are fungi pathogenic?
Mycosis (infection) – fungus growing in or on the animal
Allergy (inhaled spores) – chitin in then produce alcohols and other foreign substances that animals can become allergic too.
Toxicosis:
- Mycotoxicosis from spoiled feed
- Mycetism from ingested poisonous fungi
What are the sources of infection?
Endogenous – commensal flora, such as candida in GI tract. Oral thrush usually in low levels of the body has reduced competition after antibiotics course and has infection after course.
Exogenous – free living saprophytes, such as aspergillus in hay or parasitic on another animal host, such as microsporum causing ringworm
What are 3 types of fungal infections?
Superficial mycoses – epidermis, nail/hair/claws, spines/feathers. Most fungi are better adapted to outer part of the body where temperatures are cooler.
Sub-cutaneous mycoses – traumatic inoculation through skin. Few fungi survive this temperature.
Deep mycoses – inhaled, deep wound or endogenous. Being increasingly seen as they are hard to detect/diagnose and animals are living longer and there is sudden splitting open of encasement within the body.
Why is only topical treatment not enough for fungal infections?
Superficial fungi burrow down. Topical treatments will get rid of surface but not target roots. Response is to have increased epidermal growth so bump forms around. Then hyphae move out from original site of infection to find new areas to grow, which is where the most inflammation comes from and why ringworm has its appearance.
Which fungus glows under UV light and why?
Microsporum canis
Due to chitin
Name 2 superficial fungal infections.
Microsporum canis
Trichophyton verrucosum
What are the effects of cattle ringworm?
- Loss in growth rate
- Lower milk yield
- Scarring affects hide value and stock salves
- Contamination persists for years – often does not work with just topical treatments. Systemic needed as well to kill infection.
Why are fungi less resistant than bacteria?
The ones we are interested in only reproduce via budding. If mutation, it will only pass it to other fungi it divides to, cannot pass horizontally.
What are some topical antimycotic drugs?
Miconazole shampoo or enilconazole wash or spray
What are some systemic antimycotic drugs?
Griseofulvin and terbinafine itraconazole (not licensed)
Why is environmental decontamination needed and how is it done?
Dermatology cases often come back in continuously, as the animal can become re-affected from the environment, so:
- Restrict movement of animals
- Burn/get rid of bedding, collars and grooming tools
- Fog spray or wash other surfaces using enilconazole, bleach (less good) or persulphate
What are the properties of deep mycoses?
Grow well at blood temperature
- Saprophytes of decaying/self-heating vegetation, such as hay, straw and compost. Aspergillus, mucors
- Gut commensals, such as candida
Not contagious
Opportunistic (predisposition)
