Fungal Physiology

Outline the structure of fungi

• eukaryotic micro-organisms

• cytoplasm enclosed in cell wall

• chitin cell wall

What is the cell wall of fungi made of?

chitin

How do fungi get nutrition?

absorption of organic molecules from immediate surroundings

How do fungi reproduce?

sexual and asexual spores

What are the 2 main morphological forms of fungi?

moulds and yeasts

What does this image show?

mould

What are the white fluffy areas?

hypha

What are the blue/green areas?

spores being produced by fungus

What are hyphae?

basic cell unit of the moulds

What is the typical structure of hyphae?

• apically elongating cylinder capable of branching

• cross walls

What is the role of the cross walls/septa in hyphae?

• strengthen tubular wall

• have a central pore where the cytoplasm can stream through

What does this image show?

hyphae

What are the blue arrows pointing to?

cross walls

What are mycelium?

network of hyphae forming the body of the mould

What can mycelium consist of?

• submerged vegetative mycelium

• aerial mycelium

• bearing asexual spores

What does this image show?

mycelia

What are yeasts?

alternative growth form to the hypha

What cells do yeasts consist of?

discrete, often ovoid cells

How do yeasts reproduce?

budding

What are dimorphic fungi?

produce both yeasts and hyphae depending on environmental conditions

What are fungi that produce both yeasts and hyphae depending on environmental conditions?

dimorphic

What are pseudo-mycelium?

intermediate form of growth between hyphae and yeasts in which elongated budding cells form pseudohyphae

What is a ‘colony’?

in culture, a mycelium/mass of yeast cells, usually grown from a single hyphal fragment/yeast cell

What does this image show?

pseudo-mycelium

What do these images show?

colony

Name the 4 phyla of fungi

• zygomycota

• ascomycota

• basidiomycota

• deuteromycota (fungi imperfecti)

Are the fungi that are “yeasts” a taxonomic group?

NO (they represent unicellular fungi which may be members of any of the other phyla)

What are deuteromycota (fungi imperfecti)?

artificial assemblage of fungi which only produce conidia, there being no sexual reproductive state

What phyla do most pathogenic fungi species fit in?

deuteromycota (fungi imperfecti)

What have many dueteromycota evolved from?

ascomycota or basidiomycota

What does this image show?

aspergillus fumigatus

Where are aspergillus fumigatus common?

decaying vegetation

What do aspergillus fumigatus produce?

spores (so cause respiratory diseases)

What are arthrospores?

conidia formed by simple fragmentation of hyphae in dermatophytes

What spreads arthrospores?

itching

In what ways can fungi act as pathogens?

• mycosis (infection)

• allergy (inhaled spores)

• toxicosis (ingesting)

What are the 2 ways toxicosis can occur?

• mycotoxicosis (spoiled feed)

• mycetism (ingesting poisonous fungi)

What is the main way fungi can be pathogens?

mycosis (fungus grown in/on the individual)

What are the 2 types of sources of fungal infection?

• endogenous

• exogenous

Endogenous sources of fungal infection

commensal flora (e.g. candida in GI tract)

Exogenous sources of fungal infection

• free living saprophytes (e.g. aspergillus in hay)

• parasitic on another animal host (e.g. microsporum causing ringworm)

What are the different types of infections (mycoses)?

• superficial

• subcutaneous

• deep

What are superficial mycoses?

epidermis, nail/hair/claws/spines/feathers

What are subcutaneous mycoses?

traumatic inoculation through skin

What are deep mycoses?

inhaled, deep wound or endogenous

What are the most common type of fungal infection?

superficial mycoses

Why are we seeing more deep mycoses?

due to increased animal age so more immunosuppressed

What does this image illustrate?

1. spore/fragments land on skin

2. hyphae bud/germinate into skin

3. skin reacts by multiplying faster → inflammation

4. can get deep into body

What does this image show?

microsporum canis

How can you identify microsporum canis infection?

UV

What does this image show?

trichophyton verrucosum (cattle ringworm)

What does this image show?

trichophyton verrucosum

What should you avoid doing to the bubbly pustules of trichophyton verrucosum?

DON’T SCRATCH

What are the disadvantages of cattle ringworm?

• loss in growth rate

• lower milk yield

• scarring affects hide value and stock sales

• contamination persists for years

In what ways can you treat ringworm?

• topical

• systemic

• environmental decontamination

What can you use to treat ringworm TOPICALLY?

• miconazole

• enilconazole

What systemic treatments can you treat ringworm with?

• griseofulvin

• terbinafine and itraconazole (not licenced)

How can you do environmental decontamination?

• restrict movements of animals

• burn bedding, collars, grooming tools

• fog spray/wash other surfaces (e.g. eniconazole (bleach) persulphate)

What temperature do deep mycoses grow well at?

blood temperature

What are general characteristics of deep mycoses?

• not contagious

• opportunistic (attack when host has a predisposition)

What causes predisposition to fungal infection?

• immune suppression

• age (young and old)

• trauma

• exposure to heavy spore loads

What are examples of deep mycoses that are mould infections?

• aspergillosis

• mucoromycosis

• mycotic abortion

What are examples of deep mycoses that are yeast infections?

candidosis

cryptococcosis

What is the main source of aspergillosis?

hay, straw

How big are aspergillosis spores?

2-3um

What do aspergillosis spores impact on?

alveolar wall

What does aspergillosis do in tissues?

septate hyphae in tissues

What are the 2 types of aspergillosis?

• avian

• mammalian

What are the 2 types of avian aspergillosis?

• young chicks (acute)

• mature birds (chronic)

What are the 2 types of mammalian aspergillosis?

• neonatal (acute)

• mature (chronic)

What does this image show?

acute aspergillosis in a young chick lung

What does this image show?

acute aspergillosis in a piglet lung

Why is there necrosis due to acute aspergillosis?

acid and alcohol produced that break down tissues

What does this image show?

chronic aspergillosis in avian air sac

What does this image show?

chronic aspergillosis - nasal lesion of dog

Can you do topical treatments for chronic aspergillosis (nasal lesion of dog)

Not really

What does this image show?

candidosis

What does this image show?

cryptococcosis

What are general facts about candidosis?

• yeasts of normal gut flora

• opportunistic infections

What does candidosis cause?

• mucosal lesions

• thrush

• gut ulcers

• mastitis

• deep systemic

What is cryptococcosis found in?

saprophytic in bird guano

What does cryptococcosis cause?

• nasal granuloma

• skin ulcers

• deep localised

• brain

• mastitis

Is cryptococcosis opportunistic?

yes - goes dormant in brain then infection emerges when stressed/immunosuppressed

What does this image show?

cryptococcosis

In this image, what does cryptococcosis manifest as?

skin lesions

How can you diagnose fungal infections?

• direct microscopy

• culture & ID

• PCR

• ELISA

What characteristic look do cryptococcosis infections have?

creamy goo