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Mycology--Chapter 5 (pp. 135-144) and Chapter 22 General Characteristics of Fungi
Eucaryotic Saprobes - most are harmless saprobes, feeding off dead and organic matter Heterotrophic Cell walls: chitin and cellulose Septum = Cell wall Morphological forms Yeasts: single-celled, facultative anaerobes, 37°C and above Grow a lot like bacteria o Soft uniform texture and appearance 8 to 10 times the size of bacteria Molds: consist of hyphae (mycelium), aerobes, at temperatures below 25°C o Long chains of cells o Long broad filaments o Mycelium - mat of intertwining organisms Cottony, hairy, or velvety texture Asexual reproduction Sporangiums, spore case
Monophasic vs. Biphasic
Some fungi are monophasic yeasts (Candida albicans, Saccharomyces sp.) Candida albicans - yeast infection Some fungi are monophasic molds (the dermatomycetes and Rhizopus sp.) Dermatomycetes - skin mold, ring worm Some fungal pathogens are biphasic or dimorphic (Coccidioides immitis, Histoplasma capsulatum) Dimorphic - existing in either form
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Fungi - Reproduction patterns
P. 141, Fig. 5.19 Asexual reproduction Produce many identical offspring through mitosis or budding Examples: o Sporangiospores o Conidiospores (phialospores) o Blastospores o Chlamydospores o Arthrospores
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Fungi - Sexual reproduction
Permits genetic exchange between different mating types Meiosis and mitosis Examples: Zygospores (bread molds) o Zygote - fertilized egg o Rhizopus - everything is haploid except where they merge then it is diploid o Inside of zygospore is only place for meiosis Basidiospores (mushrooms) o Coprinus Ascospores
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Fungi - General Disease Pattern
Route of entry Inhalation of spores Penetration through wounds - subcutaneous Infectious units usually: arthrospores, conidiospores or blastospores
Germination: initiates infection Degree of disease depends on the host immune system: cell-mediated response most effective Mycoses - fungal infections Virulence factors
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Fungi - Individuals at Risk
Laboratory workers - work with fungi - inhale spores Certain occupations at higher risks (florists, forestry workers, farmers) Florists - sphagnum moss harbors fungi Farmers - harvesting grain - need to dry grain or get lots of molds Immune compromised patients Individuals on antimicrobial therapy - because of superinfections Treatment - use antifungal drugs
Levels of Disease
Systemic Dermatomycoses (p. 669) - fungal skin infection Superficial o Extremely shallow epidermal colonizations Cutaneous o Involving the stratum corneum and occasionally the upper dermis Subcutaneous o Occurring after a puncture wound has introduced the fungus deeper into the subcutaneous tissues
Dermatophlosis - ?
Systemic mycoses
Most likely to produce life-threatening disease Most people do not develop life-threatening disease Frequently limited in geographical distribution 5 - 10% see more disseminated disease ?? Examples: Coccidioidomycosis
o o o Respiratory disease found in dry arid areas Respiratory disease with Tb-like symptoms Common in Missouri - Respiratory disease common to the Ohio and Mississippi River Valleys and the Rio Grand Valley
Blastomycosis Histoplasmosis
Details below.
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Coccidioidomycosis
Etiologic agent: Coccidioides immitis Spores in environment in western half of country “Kicking up” the spores Seasonal cycling Mycelial phase in winter (mold phase) o Outside in vegetation "Alternating" arthrospores produced in summer
Disease Primary respiratory disease - Secondary dissemination invading skin, internal organs, meninges
Geographic Distribution: SW U.S. (also known as San Joaquin Valley Fever or California Disease) Camping, hiking, geological surveys Diagnosis: Spherules with endospores in tissue biopsies Serological tests and delayed hypersensitivity reaction to coccidioidin o Once you have responded positive, difficult to get rid of it
Treatment: Amphotericin B or azole drugs
Blastomycosis
Etiologic agent: Blastomyces dermatitidis Acquired by spores Biphasic: Yeast phase of growth - inside of body Hyphae produce monospores "Figure-8" budding yeasts in host
Disease: (pets as well as human) Primary respiratory (Tb-like symptoms) Secondary disseminated disease o Cutaneous (wart-like skin disease) o Visceral (often mistaken for cancer) Internal viscera (kidney, spleen. . .)
Geographic Distribution: North Central, East Central U.S. Epidemiology: linked to bird droppings (creatine and uric acid encourage mold growth) Diagnosis: culture, serology, and delayed hypersensitivity to blastomycin Treatment with Amphotericin B
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Histoplasmosis
Most common in Missouri Etiologic agent: Histoplasma capsulatum Biphasic: Hyphae produces macroconidia and microconidia Yeast phase in host
Disease: Primary: respiratory, often subclinical Secondary: disseminated leading to meningitis, endocarditis, retinitis, etc.
Geographical distribution: Ohio and Mississippi River Valleys and Rio Grand Valley Epidemiology: Associated with poultry farms, bird roosts Speleonosis (cave sickness) Not spread from human to human
Diagnosis: culture, serological tests or delayed hypersensitivity to histoplasmin (skin testing with antigen) Treatment: Amphotericin B or azole drugs (such as ketoconazole)
Sporotrichosis
Sporothrix schenckii A subcutaneous mycosis (usually) Biphasic Pathogenesis Wound contaminant: "purple necrosis" Inhalation of spores: respiratory infection, may disseminate
Epidemiology Prevalent in Mississippi and Missouri River Valleys and NE U.S. Common in wood, soil, and with forestry workers and florists
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Dermatomycoses
Etiologic agents belong to three genera: Microsporum, Trichophyton, and Epidermophyton All are monophasic hyphal organisms Clinically designation: "Tinea" (ringworm) Enzymes permit invasion: keratinase, elastase, collagenase Tinea ("ringworm") diseases include: Tinea pedis (athlete's foot) Tinea capitis (scalp) Tinea corporis (body) Tinea barbae (barber's itch) Tinea unguium (nails) Tinea cruris ("jock itch")
Epidemiology: human to human; also from pets Diagnosis: skin scrapings show septate hyphae with arthrospores Treatment Alter pH or moisture of environment Undecylinic acid (Desenex) Griseofulvin (oral drug, fragments hyphae)
Cryptococcosis
Cryptococcus neoformans Figure 22.24, p. 684 Monophasic yeast o Exists only in yeast form, not in mold phase Capsule enhances virulence
Disease T-cells help in immune response Primary: pulmonary, often subclinical Secondary: disseminates meningitis
Epidemiology: grows in bird droppings (creatine and uric acid), humans acquire through aerosols
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Candidiasis
pp. 682-683 Candida albicans Some people have this as part of their normal flora in their mouths. Monophasic yeast Forms of disease Oral thrush (infants [before T-cells mature], AIDS pts.) o Before T-cells mature o AIDS patients (in other than infants) Vaginal candidiasis (associated with diabetes, pregnancy, the "pill", antibiotics)
o o o Diabetes - slightly acidic pH levels in body Birth control pills - alteration of pH levels Antibiotics - eliminates normal flora
Systemic candidiasis (disseminated) Chronic mucocutaneous candidiasis Complication of T cell deficiency
Treatment Cutaneous: nystatin, gentian violet, azole drugs (miconazole) o Gentian violet - crystal violet; athlete’s foot Systemic: amphotericin B, flucytosine, fluconazole o Amphotericin B - potent, but might be used for a systemic infection (kidney and liver damage)
Pneumocystis carinii (aka jiroveci)
Transmitted by aerosols Not usually a serious pathogen Many people carry this as part of their normal flora Causes pneumonia (PCP) in AIDS patients (most common cause of death in AIDS patients) One of the opportunist infections people with AIDS die of (primary one)
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Aspergillosis
Figure 22.28, p. 686 Aspergillus fumigatus Pervasive in the environment Monophasic hyphal organism Only known to exist in hyphal phase of growth Disease forms Allergic aspergillosis (asthma-like disease) Colonizing aspergillosis ("fungus balls" in lungs) Invasive aspergillosis (disseminated)
Diagnosis: identify conidia in specimens or cultures
Mucormycosis (Zygomycosis)
Caused by various fungi: Rhizopus, Mucor, etc. Disease Spores inhaled Hyphal phase disseminate throughout body Most common in: o Diabetics (result of ketoacidosis) burn patients o Leukemia patients
Mycotoxins
Aspergillus.flavus: aflatoxin (toxic to animals, carcinogenic) Fusarium: T2 toxin and vomitotoxin ("yellow rain"--chemical warfare) Amanita: "death angel" mushroom results in mycetismus (mushroom poisoning) Claviceps purpurea: results in "ergotism" (hallucinogenic symptoms) Ergotism - rust that grows on grains Stachybotrys chartarum: black mold linked to “sick building syndrome” Table 22.1, p. 662 summarizes fungal pathogens
Chapter 5, page 157: questions 7, 8, 9, 10, 12 Chapter 22, pages 691-692: questions 1, 3, 6, 7, 8, 10, 11, 14, 15, 16, 18