Download Fungi: Eumycota

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The Fungi
(Eumycota)
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True Fungi: Eumycota
• Eukaryotic, spore-bearing
• Chemoorganoheterotrophs with absorptive
metabolism
• Saprophytes
– absorb nutrients from dead organic material by
releasing degradative enzymes
– osmotrophy - absorb soluble products
• Reproduce sexually and asexually
• Super Group Opisthokonta
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Terminology
• Mycology – study of fungi
• Mycologists – scientists who study fungi
• Mycoses – diseases caused by fungi
• Mycotoxicology – study of fungal toxins and
their effects
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Taxonomy of Fungi
• 90,000 fungal species have been described, possible
1.5 million
• six major fungal groups
Chytridiomycota
Zygomycota
Glomeromycota
Ascomycota
Basidiomycota
Microsporidia
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Fungal Distribution and
Importance
• Primarily terrestrial, few aquatic
– global from polar to tropical
• Primarily terrestrial
– few aquatic species
• Many are pathogenic in plants or animals
• Some form associations
– mycorrhizae – associations with plant roots
– lichens
• associations with algae or cyanobacteria
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Fungal Distribution and
Importance…
• Decomposers
– degrade complex organic material in the
environment to simple organic compounds
and inorganic molecules
– carbon, nitrogen, phosphorus, and other
critical constituents are recycled for other
living organisms
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Fungal Distribution and
Importance…
• Industrial importance
– fermentation – yeast used in making bread,
wine, beer, cheese, soy sauce
– organic acids – citric and gallic acid
– certain drugs – ergometrine, cortisone
– antibiotics – penicillin, griseofulvin
– immunosuppressive agents - cyclosporin
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Fungal Distribution and
Importance…
• Research use
– geneticists, cytologists, biochemists,
biophysicists, and microbiologists
– Saccharomyces cerevisiaea (Bakers/Brewers
Yeast
• yeast model system for cell biology, genetics,
and cancer
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Pathogenic Fungi
• Fungi are eukaryotic saprophytes
– ~50 produce mycoses in humans
– five groups depending on route of infection
• superficial, cutaneous, subcutaneous are all
direct contact
• systemic infections have disseminated to
visceral tissues (most are dimorphic, acquired
from inhalation of spores)
• opportunistic mycoses
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Opportunistic Diseases
• Opportunistic microorganism – harmless in its normal
environment but pathogenic in a compromised host
• Compromised host – seriously debilitated and has lowered
resistance to infection
– causes include (but not limited to):
• malnutrition/alcoholism
• cancer
• diabetes
• another infectious disease
• trauma from surgery or injury
• immunosuppression by drugs/hormones
• genetic deficiencies
• advanced age
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Fungal Structure
• Cell walls composed of chitin polysaccharide
• Single-celled microscopic fungi = yeasts
• Body/vegetative structure of a fungus = thallus (pl.
thalli) (undifferentiated structure)
– multicellular fungi are called molds
– thallus consists of long, branched hyphae filaments
tangled into a mycelium mass
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Fungal Reproduction
• Asexual reproduction
– Parent cell undergoes mitosis to form daughter cells
– May proceed through a spore form
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Fungal Reproduction
• Sexual reproduction
– Involves fusion of compatible nuclei
• Homothallic: Sexually-compatible gametes are formed
on the same mycelium (self-fertilizing)
• Heterothallic: Require outcrossing between different,
yet compatible mycelia (+ and – mating strains)
– A dikaryotic stage can exist temporarily prior to fusion of
two haploid nuclei
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Zygomycota
• Zygomycetes
• Most are saprophytes
– a few are plant and animal parasites
• Form coenocytic hyphae containing
numerous haploid nuclei
• Some of industrial importance
– foods, antibiotics and other drugs, meat
tenderizer, and food coloring
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Zygomycota
• Usually reproduce asexually by spores that
develop at the tips of aerial hyphae
• Sexual reproduction occurs when
environmental conditions are not favorable
– requires compatible opposite mating types
– hormone production causes hyphae to
produce gametes
– gametes fuse, forming a zygote
– zygote becomes zygospore
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Genus Rhizopus
• R. stolonifer
– grows on surface
of moist
carbohydrate rich
foods such as
bread
– hyphae quickly
cover surface as
rhizoids, absorb
nutrients
– stolon hyphae
become form
new rhizoids
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Importance of Genus Rhizopus
• Rhizopus-Burkholderia symbiosis
– seedling blight in rice bacterium Burkholderia
growing within Rhizopus produces toxin
• Used to produce tempeh from soybeans
• Used with soybeans to make sufu curd
• Commercially
– used to produce anesthetics, birth control,
alcohols, meat tenderizers, yellow coloring in
margarine
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Ascomycota
• Ascomycetes or sac fungi
– found in freshwater, marine, and terrestrial habitats
– red, brown, and blue-green molds cause food spoilage
– some are human and plant pathogens
– some yeasts and truffles are edible
– some used as research tools
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Ascomycota
Yeast Life Cycle
• Alternates between haploid and diploid
– in nutrient rich, mitosis and budding occurs at
non-scarred regions
– nutrient poor, meiosis and haploid ascus
containing ascospores formed
• haploid cells of opposite mating types fuse
• tightly regulated by pheromones
• Many are dimorphic (yeast form and mold form
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Ascomycota
Filamentous Form Life Cycle
• Asexual reproduction - conidia
• Sexual reproduction
– ascus formation with
ascospores
– opposite mating types form
zygote
– ascospores forcefully
released from ascocarp,
germinate
• Sclerotia masses of hyphae
survive the winter then
germinate
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Genus Aspergillus
• A. fumigatus
– ubiquitous environmental
– allergies and significant pathogen (ABPA and
Farmer's Lung)
• A. oryzae
– production of fermented foods
– important in biotechnology
• A. flavus
– Aflatoxin B
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Aspergillosis
• Usually caused by Aspergillus
fumigatus; also caused by A. flavus
• Invasive disease results in
pulmonary infection
– with fever, chest pain and cough that
disseminates to brain, kidney
– in severely compromised individuals,
lungs may fill with mycelia
• Diagnosis by examination of
pathological specimens or by
isolation and characterization of
fungus
• Treatment with antifungal drugs;
treat underlying disease
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More about Ascomycota
• Claviceps purpura
– parasite on higher plants
– ergotism
• toxic condition from eating infected
grain
• due to lysergic acid diethylamide
(LSD)
• Candida, Blastomyces, Histoplasma
– human pathogens
• Stachybotrys – “sick building
syndrome”
• Aspergillus – aflatoxins and cancer
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Candidiasis
• Caused by Candida albicans or C. glabrata,
dimorphic fungi
– members of normal microbiota
but numbers kept in check by
other microbes
• disease in healthy individuals occurs as result of
disruption of normal microbiota
– can also be spread by sexual contact
– wide spectrum of disease but most infections
involve the skin or mucous membranes
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Nosocomial Candidiasis
• Important nosocomial pathogens
• May represent up to 10% of nosocomial
bloodstream infections
• Mortality ~50% when in bloodstream and
disseminates to visceral organs
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Candidiasis
• Oropharyngeal candidiasis (thrush)
– common disease of newborns,
denture wearers, and those on
steroid therapies
• Paronychia and onychomycosis
– associated with Candida infections of
the subcutaneous tissues of digits
and nails, respectively
• usually result from continued immersion of hands
• Intertriginous candidiasis
– involves axillae, groin, and skin folds
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Candidiasis
• Napkin (diaper) candidiasis
– found in infants whose diapers are not
changed frequently
• Candidal vaginitis
– occurs when lactobacilli are depleted
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Candidiasis
• Diagnosis of candidiasis is difficult
• Treatment, control, and prevention
– no satisfactory treatment
– antifungals used for cutaneous lesions and
systemic candidiasis
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Airborne Diseases
• Blastomycosis
– systemic mycosis caused
by Blastomyces dermatitidis
(dimorphic fungus)
– three clinical forms: cutaneous, pulmonary, and
disseminated
– after lung inhalation spreads rapidly to skin causing
cutaneous ulcers and abscesses
– serologic tests for diagnosis
– amphotericin B/other anti-fungal drugs for treatment
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Airborne Diseases
• Coccidioidomycosis
– endemic areas
• Valley fever, San Joaquin fever,
or Desert Rheumatism
– dimorphic
• inhale the arthroconidia,
converts to large spherule in
body
• Diagnosis
– demonstration of spherule
• Prevention involves avoiding
exposure to dust
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Airborne Diseases
• Cryptococcosis
– systemic mycosis caused by yeast Cryptococcus
neoformans
– source is dried pigeon droppings
– inhalation
• serious disease including
meningitis in immunocompromised (e.g., AIDS); mild
or pneumonia-like in others
• Detecting encapsulated yeast
in clinical specimen is
diagnostic
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Airborne Diseases
• Histoplasmosis – common lung disease
– caused by Histoplasma capsulatum var. capsulatum
(dimorphic)
– inhalation of airborne microconidia in bird droppings
• converts to yeast phase in body; flu-like illness
• only rarely becomes disseminated
– Prevented/controlled by wearing protective clothing in
endemic areas and by soil decontamination
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Direct Contact Diseases
• Superficial mycoses
– piedras
• infections of hair shaft
– tineas
• infections involving outer layers of skin, nails,
and hair
• Trycophyton
– most occur in tropics
– treatment, prevention, and control
• removal of skin scales and infected hairs
• good personal hygiene
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Direct Contact Diseases
• Cutaneous mycoses
– dermatomycoses, ringworms, or tineas
• different diseases distinguished according to
causative agent and area of body affected
– most common fungal diseases, occurring
worldwide
– diagnosis
• microscopic examination of skin biopsies and
culture on Sabouraud’s glucose agar
– treatment, prevention, and control
• topical ointments and antifungal agents
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Direct Contact Diseases
• Examples of cutaneous mycoses
– Tinea capitis – infection of scalp hair
– Tinea pedis – athlete’s foot
– Tinea unguium – infection of the
nailbed
– Tinea cruris – jock itch
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Subcutaneous Mycoses
• Caused by saprophytic inhabitants of soil
• Introduced in soil-contaminated puncture wounds
• Clinical manifestations
– develops slowly over a period of years
– nodules form and ulcerate
– organisms spread along lymphatic channels,
producing more nodules
• Diagnosis
– culture and examination of fungus from infected
tissue
• Treatment, prevention, and control
– antifungal agents and surgical excision
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Subcutaneous Mycoses
• Chromoblastomycosis
– dark brown pigmented nodules
• Maduromycosis
– destroys subcutaneous tissue and
produces serious deformities
– often called a eumycotic mycetoma
• Sporotrichosis
– when spread throughout body, referred
to as extracutaneous sporotrichosis
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Basidiomycota
• Basidiomycetes (club fungi)
– examples include rusts, shelf fungi, puffballs,
toadstools, mushrooms
– sexual reproduction form basidium
• basidiospores are released at maturity
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Human Impact Basidiomycota
• Decomposers
• Edible and non-edible mushrooms
– toxins are poisons and hallucinogenic
• Pathogens of humans, other animals, and plants
– e.g., Cryptococcus neoformans – cryptococcosis
• systemic infection, primarily of lungs and central
nervous system
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Microsporidia
• Obligate intracellular fungal parasites that infect
insects, fish, and humans
– Aquatic birds are common hosts and contribute to
large numbers of spores in environment
• Transitional form is a spore structure capable of
surviving outside the host
• Structurally similar to ‘classic’ fungi
– contain chitin, trehalose, and mitosomes
– however, lack mitochondria, peroxisomes and
centrioles
– unique morphology is polar tube essential for host
invasion
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Microsporidia
• Obligate intracellular fungi that belong to phylum
Microspora
– an emerging infectious disease, found mostly in HIV
patients
• Domestic and feral animals are reservoirs for
species that infect humans
• Produce highly resistant spore
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Microsporidia
• Infection of host cell occurs when microsporidia
extrudes polar tubule from within the spore
• Symptoms
– wide variety including hepatitis, pneumonia, skin
lesions, diarrhea, weight loss, and wasting syndrome
• Diagnosis
– based on clinical symptoms and identification of
microsporidia in gram or giema-stained specimens
– identification can also be made using electron
microscopy or PCR
• Treatment, control, and prevention
– some treatment success with antifungal drugs
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Microsporidia Pathogenesis
• Human infections
– Enterocystozoon
bieneusi
• diarrhea
• pneumonia
– Encephalitozoon
cuniculi
• encephalitis
• nephritis
– severe in
HIV/AIDS
patients
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