Microbiology Exam 3: Fungi

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Mycology

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study of fungi
Over 100,000 identifiable different species. Probably many more yet to be identified

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Fungi General Characteristics

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• large eukaryotic cells, unicellular and multicellular forms
• chemoheterotrophs - most are saprobes - a type of chemoheterotroph that produce extracellular enzymes to digest molecules in their surroundings then absorb nutrients. Most saprobes are decomposers.
• cell membranes contain ergosterol in place of cholesterol found in animal cells
• cell walls contain chitin
• most are aerobes (yeast - facultative anaerobes)
• most have complex life cycles, most reproduce asexually and sexually
• many form spores as a form of reproduction

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Fungi General Characteristics

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some are opportunistic pathogens to animals (opportunistic pathogen - normally not pathogenic, usually normal body flora, but a change in body chemistry, antibiotic treatment, or being immunocompromised can allow this organism to become pathogenic.)
• most known plant diseases are fungal - molds, rusts or smuts
• most prefer moderate temperatures
• can tolerate high salt or sugar concentrations, used to create selective growth media
• prefer a mildly acidic pH, also used to create growth media
• Some have very diverse metabolism, can actually degrade hydrocarbons or cellulose.
• Immunocompromised and diabetic patients are most susceptible to fungal infections.

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mycosis (Fungi General Characteristics)

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any fungal infection
Mycoses are more common than before because of more widespread use of antibacterial agents, immunosuppressive drugs and diabetes.

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Growth Characteristics

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Fungi are essentially single-celled organisms
In some fungal species the cells may show various degrees of specialization

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Yeast (Growth Characteristics)

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The simplest morphologic form of fungi: single-celled
Reproduce by "budding"

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Budding (Growth Characteristics)

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a new cell forms at the surface of the original cell, enlarges, then breaks free to assume an independent existence

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Growth Characteristics

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As complexity increases, elongation of the cell without separation of newly formed cells results in thread-like hyphae

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hyphae (Growth Characteristics)

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One of the threadlike elements of the mycelium

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mycelium (Growth Characteristics)

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An intertwined mass of hyphae

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mold (Growth Characteristics)

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refers to filamentous hyphae or a mass of mycelium

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Microscopic spores (Growth Characteristics)

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produced from structures (conidia) formed from the hyphae

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Conidial structures (Growth Characteristics)

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are used for identification and classification

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Spores (Growth Characteristics)

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Transported by air currents
Allergies common
Very common laboratory contaminants

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Growth Characteristics

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In some higher forms, hyphae are cemented together to form large, structurally complex, fruiting bodies, such as mushrooms

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Mushrooms (Growth Characteristics)

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actually the spore-producing structure. Spores are produced in the underneath gills of the cap.

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Dimorphic fungi (Growth Characteristics)

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fungi that alternate body forms. May exhibit the filamentous forms at cooler incubation temperature and the unicellular form at body temperature.

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Rhizopus stolonifer

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common laboratory contaminant, found on produce and breads. Used in the industrial production of steroids, meat tenderizers, chemicals and certain coloring agents.

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Penicillium notatum

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common lab contaminant, source of antibiotic - penicillin.

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Aspergillus flavus

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aspergillosis, opportunistic pathogen. Produces highly toxic aflatoxin, causes tumor formation in animals. Common lab contaminant.

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Histoplasma capsulatum

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histoplasmosis, resembles TB, may be transported by macrophages, may be self-limiting or progressive and fatal, may develop immunity, may be detected by a skin test, associated with bird and bat droppings, primarily a disease of rural areas in Midwestern U.S.

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Blastomyces dermatitidis

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blastomycosis, assoc. with dusty soil and bird droppings, spores enter through skin abrasions or inhaled. Can be self-healing or fatal.

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Coccidioides immitis

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coccidiomycosis (San Joaquin Valley Fever), influenza-like symptoms, can be self-limiting or become disseminated throughout the body and affect many organs, spores found in soil of desert regions

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Cryptococcus neoformans

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cryptococcus, most dangerous of all fungal diseases, associated with bird droppings and the soil, occurs world-wide. AIDS patients are extremely susceptible

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Pneumocystis jiroveci (formerly carinii)

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the most common cause of non-bacterial pneumonia in HIV patients, originally thought to be a protozoan, complex life cycle.

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Claviceps purpurea

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ergotism, rye grain contaminant, widespread in the Middle Ages, causes bizarre behavior.

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Sporothrix schenkii

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sporotrichosis, transmitted by punctures, associated with horticultural activities.

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Saccharomyces ssp

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baker's yeast

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Candida albicans

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normal oral and genital flora, opportunistic pathogen, causes thrush and vaginitis, dimorphic - in deep infections, the yeast form predominates, whereas in superficial infections of keratinized skin layers, the mycelial form is more common.

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Stachybotrys chartarum

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slimy greenish black mold, grows in damp conditions, produces trichothecene mycotoxin that inhibits DNA replication, transcription and translation. Inhalation of spores can be fatal.

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Trichophyton, Epidermophyton, Microsporum

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dermatophytes

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tinea pedis

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athletes foot

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tinea cruris

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jock itch

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tinea capitis

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ringworm of the head

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tinea corporis

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ringworm of the body

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tinea unguium

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ringworm of the nails

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Note:

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Fungi do not respond to antibiotics. Antifungal agents are necessary.

Why? - Fungi are eukaryotes and antibiotics only affect prokaryote structures or prokaryotic metabolism. Long term use of antifungal agents may have adverse effects on human eukaryotic cells.