Unit 9 Flashcards
Describe the kingdom of Fungi
Includes; mushrooms, yeast, and moulds
Can be unicellular or multicellular
Eukaryotic (has a nucleus and membrane bound organelles)
Has a cell wall
Heterotrophic -saprotrophs (feed on dead/decaying organic material)
Non motile
Describe the fungal eukaryotic cell
Complex cell wall contains Chitin (a carbohydrate found in insect exoskeletons)
Distinct nucleus and membrane bound organelles
Some have plasmid-like structures
Requires 400x-1000x magnification to see individual cells (larger than bacteria)
Yeast are fungi that grow as
Unicellular organisms
How do yeast replicate
Budding
Give examples of yeasts
Malasezzia (skin/ear infections)
candida
saccharomyces (bread/beer)
Describe moulds
Multicellular fungi (most fungi)
Complex; have multiple structures, multiple life stages, and more than one type of reproduction
What are the two life stages of moulds
Vegetative state
Reproductive state
Describe the vegetative state of moulds
Vegetative fungal cells are arranged end to end to form long strands (can branch) called Hyphae
Hyphae spread at the tips by mitosis
The end of each cell is an “end wall” and two end walls form a septum, the septum contains holes that allow for exchange of cytoplasmic materials between adjacent cells (not all hyphae are septate)
As hyphae continue to divide/branch, a mycelium forms (mass of hyphae that form the vegetative part of a fungus)
Can form on surfaces, underground or in water
Have a fuzzy surface
True or false
Hyphae are the individual vegetative cells and mycelium are the whole vegetative part of the fungus made of hyphae
True
When a yeast or mycelium is large enough to see on a surface it is called a
Colony
How do you describe macroscopic mycelia
Color (can have different colors throughout)
Texture
Depends on age of culture and type of media (always indicate these)
Size does NOT matter
How are fungi heterotrophs
All fungi require nutrition provided to them in the form of complex organic molecules
How are fungi saprophytes
Almost all fungi acquire nutrients from dead or decaying matter
How are fungi parasitic
Some fungi can infect plants or animal cells to obtain nutrition
Describe a fungi’s exoenzymes
Cells in hyphae release exoenzymes
These digestive enzymes are released into the environment to digest organic matter around them, the nutrients released are absorbed into the cell
True or false
Fungi have both asexual and sexual reproduction methods
True
What are the 3 asexual methods of reproduction in fungi
Budding (yeast)
Mycelium fragmentation
Producing spores
Asexual reproduction is achieved by ___ and results in progeny cells ___ to parents cells
Mitosis
Identical to parent cells
Describe budding
Asexual reproduction in yeast
Bulge forms on the side of the cell, cell contents replicate and fills the new bud, chromosomes undergo mitosis, a new copy of the genome moves into the bud
A single bud or chain of buds is formed depending on the species
Describe mycelium fragmentation
Pieces of hyphae break off and a new section will continue to grow from the tips via mitosis until a new mycelium forms
Describe asexual reproductive via producing spores
Spore: a reproductive particle, usually a single cell, released by a fungus, that may germinate into another hyphae and eventually a new mycelium (must be done in good conditions)
The spore is identical to the parent cell
Spores are released when the fungus is disturbed -these are carried to other locations to allow spread
True or false
Producing spores is the most common method of asexual reproduction in fungi
True
Different types of spores can be used to help
Identify different fungi
What are endospores
(AKA sporangiospores)
Spores are unicellular
Contained in a capsule (sporangium) which will release the endospores when disturbed
What are conidiospores
Unicellular or multicellular spores that are released directly from the tip or side of the hyphae
Only seen with a microscope
What are the two forms of conidiospores used to identify the fungus
Microconidia
Macroconidia
What are microconidia
Spore made up of a single cell
What are macroconidia
Multicellular spore, the entire unit breaks off to form a new fungus
Describe sexual reproduction of fungi
Done through meiosis -allows genetic variation
Triggered by change in environmental conditions
Requires 2 spores -can be from the same mycelium or different ones
Describe what happens If the two spores are from the same mycelium or different ones
Same: no genetic variation
Different: genetic variation
What are the 3 stages in sexual reproduction
1) Plasmogamy: two haploid cells fuse and mix their cytoplasm and organelles (results in one large cell with 2 nuclei)
2) karyogamy: the 2 haploid nuclei fuse to form a diploid nucleus
3) meiosis: the chromosomes randomly sort into two different spores (haploid)
Describe fungal spores
Easily spread in the wind/air due to very small size
Very difficult to destroy (resistant to all detergents, most chemical disinfectants, drying, heat and extreme cold)
Standards of sterilization are designed to be able to destroy fungal spores and bacterial endospores
Define mycoses
Fungal diseases
Define mycology
Study of fungal diseases
Fungal diseases can be due to (2)
1) infection by the fungus
2) exposure to fungal toxins (toxin from fungus)
Describe fungi
Ubiquitous in the environment
Most are saprophytic and non pathogenic
Many are transmitted via fomites (inhaled spores or hyphae when digging in soil)
Can be part of normal flora in; skin, ears, oral cavity, GIT, urogenital tract
What are the 4 types of mycoses
Superficial mycoses (dermatophytoses -ringworm)
Opportunistic mycoses
Systemic mycoses
Mycotoxicosis
All have zoonotic potential and cause similar diseases in humans
Describe Antifungals
Drugs used to treat fungal infections
Have more side effects because fungi are eukaryotic (like animal cells)
Antifungals only work on replicating cells -cannot treat spores
Describe superficial mycoses
Commonly seen, infections of epidermis, hairs, nails
Rarely spread to underlying tissue
Secrete extracellular enzymes that breakdown keratin to use for nutrients
Seen in cattle/horses/cats/dogs/people
What are common fungal agents
Microsporum
Trichophyton
What are diagnostic tests for dermatophytes
Wood’s lamp test
Tape sample of skin/hair
fungal culture: dermatophyte test medium and routine fungal cultures
What is the wood’s lamp test?
Approx 50% of microsporum canis will fluoresce under UV light
Never a definitive test
Lots of false negatives: 50% do not fluoresce (trichophyton never fluoresce
Lots of false positives: purulent discharge, certain dyes and conditioners fluoresce
How do you take a tape sample
Using scotch or packing tape, press over lesion (take skin and hair)
Perform an in clinic microscopic examination with simple stain for spores
How do you prep for collecting clinical samples for culture (hair/skin scrapings)
Wear gloves
Wipe affected area with 70% alcohol to remove bacterial contamination and medications
Always take samples from OUTER margins of the lesion where the fungus is actively growing
How do you collect hair samples for cultures
Hairs should be pulled/plucked out (NOT cut)
If wood’s lamp test is positive, take fluorescent hairs
If there are broken hairs, take the broken hairs
describe skin scrapes and crusts for culturing
Always Collect any crusts
Can perform superficial skin scraping of the affected area (from the edge of the lesion on the red border, use the blunted scalpel blade and no mineral oil)
Describe toothbrushing for spores
Use a new toothbrush (medium to hard)
Brush all over hairs to collect spores
Submit the whole toothbrush for testing
How do you transport cultures
Place in dry sterile container such as a sealed envelope (tape shut do not lick) or sterile container
No plastic bags -moisture can cause bacterial overgrowth
Keep at room temperature (fungi need to be room temp, bacteria need to be cold)
What are the 2 methods of culturing dermatophytes
Routine culture on supportive media -cultures all types of fungi
Dermatophyte test media (DTM) (supportive/differential): specific to grow trichophyton and microsporum. Produces easy to recognize colonies and contains dyes that turn red/pink in the presence of exoenzymes secreted by dermatophytes
How do you inoculate DTM
Place hair and skin scraping onto media (push toothbrush into media)
Seal the container to prevent media from drying out (depending on how long it will be stored and type of container, some fungi need oxygen to survive)
Leave at room temp and in the dark
Takes up to 3 weeks
Describe a positive DTM test
How long do you have to wait to see a positive result? A negative one?
Media turns RED and colonies are white and fluffy
Minimum 9 days for a positive culture on regular DTM
minimum 2 days for a positive culture on rapid DTM (lots of false positives)
Negative cultures must wait 3 weeks to confirm
How do you prevent the spread of ring worm
Zoonotic
Wear gloves
wipe exam tables with damp cloth to prevent dispersal of spores
Clean equipment (disinfecting agent with fungicide claims)
Vaccum repeatedly (do not sweep)
Mop with a Disinfectant
Describe opportunistic mycoses
Give examples of 3
Require either:
1) very large inoculum (lots of spores)
2) immunosuppressed host
Ex. Aspergillosis, candidiasis, malassezia
Describe aspergillosis (genus) fungi
Common in the environment, not in normal flora
Opportunistic -not very pathogenic
All species are susceptible to it
Most commonly affect the respiratory tract; lungs (mycotic pneumonia), nasal cavities (nasal aspergillosis), guttural pouch (guttural pouch mycoses, also leads to cranial nerve and carotid artery infections)
Can also cause abortions and mastitis
Describe Candida (genus) fungi
Yeast
Normal flora of URT, GIT, genital mucosa
Opportunistic infection occurs with immunocompromised patients or if antibiotics remove competing bacteria
Common infections sites in dogs; oral cavity, MM in the UGT
Soft white growth over the surface
Can cause severe systemic infections or oral thrush
Describe malassezia (genus)
Yeast
Normal flora of skin and ears
Opportunistic infection
Overgrowth occurs if moist and hot or if antibiotic therapy removes competing bacteria
Common infection in ears, skin and feet
Diff quick swab analysis shows characteristic bowling pin shapes of budding
Describe systemic mycoses
Infections of the internal tissues/organs
Transmission is usually by inhalation of spores
Severe, difficult to treat, life threatening
Most common in southern Saskatchewan: blastomycosis
What is blastomycosis
Infection caused by blastomyces dermatitidis
This is endemic in North America, Great Lakes and Regina
Found in yeast and mycelium forms
Mycelium and spores are located in the ground in decaying vegetation (dogs inhale when digging)
Always found in yeast form in clinical samples
Primary pathogen
Zoonotic
Most commonly causes pulmonary infections (can spread to skin and eyes)
What is mycotoxicosis
AKA fungal toxicosis
Fungi can produce toxins which can remain in the cell or be secreted into the environment (contamination of feed with mould or mushroom/compost ingestion)
Most are resistant to heat and chemicals
Severe disease: GI effects, neurotoxins, cardiotoxins, hallucinogens, carcinogens, anaphylactic reactions
What is mouldy sweet clover
Certain legumes (sweet clover) produce a chemical called coumarin
Coumarin is converted by mould into dicoumarin
If dicoumarin is ingested by cattle it binds to vitamin K, which prevents clotting processes and increases fatal risk of bleeding
What is Ergot
Disease caused by claviceps prupurea
Mould infects rye, barley, wheat, oats, grasses
Mould produces toxins that cause disease when ingested. See;
- vasoconstriction (most common) which decreases blood flow to tissues and causes necrosis
- neurological disease
- abortion
