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The
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• 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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• 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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• 90,000 fungal species have been described, possible
1.5 million
• six major fungal groups
Chytridiomycota
Glomeromycota
Basidiomycota
Zygomycota
Ascomycota
Microsporidia
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• 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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• 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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• 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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• 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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• 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 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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• 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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• Asexual reproduction
– Parent cell undergoes mitosis to form daughter cells
– May proceed through a spore form
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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Napkin (diaper) candidiasis
– found in infants whose diapers are not changed frequently
• Candidal vaginitis
– occurs when lactobacilli are depleted
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• Diagnosis of candidiasis is difficult
• Treatment, control, and prevention
– no satisfactory treatment
– antifungals used for cutaneous lesions and systemic candidiasis
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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Basidiomycetes (club fungi)
– examples include rusts, shelf fungi, puffballs, toadstools, mushrooms
– sexual reproduction form basidium
• basidiospores are released at maturity
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• 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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• 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 45

• 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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• 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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• Human infections
– Enterocystozoon bieneusi
• diarrhea
• pneumonia
– Encephalitozoon cuniculi
• encephalitis
• nephritis
– severe in
HIV/AIDS patients
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