lecture 9 fungi and fungal diseases

kingdom fungi

• mushrooms, yeast, mould

• unicellular or multicellular

• eukaryotic

• cell wall

• heterotrophic

• non-motile

Fungal eukaryotic cell

• Complex cell wall contains chitin

• distinct nucleus and membrane-bound organelles

• plasmid-like structured

• requires 400x-100x magnification to see

yeast

• fungi that grow as unicellular organisms

  replicate by “budding”

• ex malasezzia, candida

moulds (multicellular fungi)

• Most fungi are multicellular organisms aka mould

• more complex

2 life stages of moulds

vegetative state

reproductive state

vegetative state : hyphae and mycelium

• arranged end-to-end to form long, slender stands called hyphae

• Hyphae can spread

• The end of each cell is made of an “end wall to form a septum

• This allows the exchange of cytoplasmic material

• As hypohae continue to divide and branch mycelium forms

mycelium

The mass of hyphae that form the vegetative part of a fungus

can form on surfaces, underground, in liquids

describing microscopic mycelia

• When yeast or mycelium is large enough to see on a surface, is it a colony

  • color

  • texture

  • Size does not matter

  • age of culture and type of media

heterotrophs

all fungi require nutrition provided to them in form of complex organic molecules

saprophytes

almost all fungi acquire nutrients from dead or decaying organic matter

exoenzymes

• Cells in hyphae release exoenzymes

• digestive enzymes released into environment- digest organic matter- absorb digested materials into cell

Fungal reproduction

• both sexual and asexual

asexual fungal reproduction

• budding

• mycelium fragmentation

• producing spores

through mitosis

the potency cell are identical to the parent cell

budding

• asexual reproduction of yeast

• bulge forms on cell, cell contents replicate and fill new bud, chromosomes undergo mitosis, new genetic material also moves to bus

• single bud or chains

mycelium fragmentation

• pieces of hyphae break off

• asexual

• new section will continue to grow from tips via mitosis until new mycelium forms

spore

• reproductive particle, usually a single cell, released by a fungus, that may germinate into another

• identical to the parent cell

• When fungus is disturbed, spores are released - allowing spread

• can help identify fungus

endospores

• aka sporangiospores

• unicellular

• contained in a capsule (sporangium) which will release endospore when disturbed

conidiospores

• unicellular or multicellular spores released directly from the tip or side of the hyphae

• only seen with microscope

microconidia

small, unicellular conidia formed from hyphae of certain fungi.

macroconidia

multicellular spore

the entire unit breaks off to form a new fungus

sexual reproduction of fungi

• meiosis

• allows genetic variation

• triggered by environmental changes

• requires “spore 1” and “spore 2”

• can be from same or different mycelium

3 stages of sexual reproduction

1. Plasmogamy- two haploid cells fuse and mix their cytoplasm and organelles results in a large cell with 2 nuclei

2. karyogamy - the 2 haploid nuclei fuse to form diploid (2n) nucleus

3. meiosis - teh chromosomes randomly sort into 2 different spores

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fungal spores

• spreads easily in wind due to small size

• very difficult to destroy

• resistant to all detergents, most disinfectants, drying, heat, cold

• standards of sterilization are designed to be able to destroy fungal spored and bacterial endospores

mycoses

fungal disease

mycology

study of fungal disease

fungal disease can be due to

1. exposure by the fungus

2. exposure to fungal toxins

fungi

• unbiquitious in the environment

• most are saprophytic, non-pathogenic

• transmitted via fomites

• part of normal flora

4 types of mycoses

• superficial “ringworm”

• opportunistic

• systemic

• mycotoxicosis

all have zoonotic potential

antifungals

• drugs used to treat fungal infections

• more side effects because fungi are eukaryotic cells

• only work on replicating cells

• cannot treat spores

superficial mycoses

• commonly seen on epidermis of hair, skin nails

• rarely spread to underlying tissue

• secret enzymes that break down keratin

• fungal agents

  • microsporum

  • trichophyton

diagnostic tests for dermatophytes

• woods lamp

• tape sample or skin and hair

• fungal culture

  • dermatophyte test medium

  • routine fungal culture

woods lamp test

• approx 50% of Micrococcus canis will fluoresce

• never a definitive test

• lots of false negatives

  • 50% of Microsporum does not fluoresce

  • trichophyton never flureses

• lots of faulse positoveis

  • purulent discharge dyes, conditioners

tape sample and exam dematophytes

• Scotch or packing tape

• Press over area to take skin and hair

• examine in clinic microscope

culturing dermatophytes

routine culture on supportive media

prep for dermatophyte sample collection

• ALWAYS WEAR GLOVES

• wipe affected area with 70% alcohol to remove surface bacteria

• Always take a sample from the outer margins of the lesion

Collecting hair for dermatophyte culture

• hair should be pulled/ plucked

• if woods lamp positive take those hairs

• if broke hairs, take the broken ones

skin scraped and crusts for dermatophyte culture

• Collect any crusts

• can preform superficial skin scraping

• from edge of lesion

toothbrush to collect dermatophyte spores

• use a new toothbrush

• brush all over hairs

• submit whole toothrush

Transporting dermatophyte samples

• place in a dry sterile container like envelope

• no plastic bags- moisture will cause bacterial damage

• room temp

Dermatophyte test media (DTM)

• specific media designed to grow Trichphyton and Microsporum

• produces easy to recognise colonies

• contains dye that turns red/pink if positive

how to inoculate DTM

• place hair onto surface

• press gently to adhere to surface of media

• seal container

• leave at room temp, dark

• takes up to 3 wks

Positive DTM test

• Media turns red and colonies are white and fluffy

• min 9 days for positive on regular DTM

• min 2 days for positive on rapid DTM

preventing the spread of ringworm

• Zoonotic

• Wear gloves and a lab coat

• Wipe table with a DAMP CLOTH to prevent the dispersal of spores

• use a disinfecting agent with fungicide

• vacuum

• mop with disinfectant

opportunistic mycoses

requires either

• very large inoculum

• immunosuppressed host

  ex aspergillus, candidasa, malassezia

aspergillus fungi

• not common in the environment

• not normal flora

• opportunistic pathogen

• all species susceptible

• most common affects respritory tract

candida ( yeast)

• normal flora of the upper respiratory tract, GI tract, and genital

• opportunistic infection if immunocompromised or if antibiotic remove bacteria competing for the same space

• common infection places in dogs- oral cavity, mucus membranes

• causes severe systemic infections

Malassezia (yeast )

• normal flora in skin and ears

• opportunistic infection

• overgrowth. If moist, hot or antibiotic therapy removes bacteria

systemic mycoses

• infections of internal organs/ tissues

• transmission usually by inhalation of spores

• severe, difficult to treat, life threatening

• Most common blastomycosis

Blastomycosis

• infection by Blastomyces dermatitidis

• Fdungus is endemic

• found in yeast an mycelial forms

• located on the ground in decaying vegetation

• Dogs inhale when digging, and spores spread systemically

• primary pathogen

• found in yeast forms in clinical samples

• zoonotic

mycotoxicosis

• aka fungal toxicosis

• Fungi can produce toxins which either remain in the cell or are secreted into the environment

  • feed with mould, mushroom/compost ingestion

• are resistant to heat and chemicals

• severe disease - Gi effects, neurotoxins, cardiotoxins, halucinogenes, carcinogens, anaphylactic reactions

moldy sweet clover

• Certain legumes produce a chemical called coumarin

• coumaCrin is converted by mould to dicoumarin which can cause a bleeding disorder in livestock due to its anticoagulant properties.

ergot

• disease caused by Claviceps purpurea

• mould infects rye, barley, wheat, oats, and grasses

• causes disease when ingested

• vasoconstriction most common

• decreases blood flow to tissues and tissue necrosis occurs

• neurological disease

• abortion