topic 13 Flashcards
compare and contrast fungi from other eukaryotes
Similar to other Eukaryotes:
Membrane bound nucleus
80S ribosome
Mitochondria
Differ from other Eukaryotes:
Non-motile
Heterotrophs: can’t fix carbon, must obtain from organic material
Cell wall containing chitin, glucan and mannan
Membranes contain ergosterol rather than cholesterol
Fungi are not plants!
Because they lack chlorophyll they can:
Grow in dark places
Grow in any orientation
What are some ways in which fungi obtain nutrients?
Saprophytes: scavenge organic material from dead host
Parasites: live host (protist/plant/animal/etc) is harmed
Symbionts: beneficial association with live host such as plant roots (Mycorrhizae) or algae (Lichens)
How are fungi classically divided? Are they mutually exclusive?
yeasts and moulds. They are not mutually exclusive. Some fungi can interchange.
What are some characteristics of yeasts?
Fungi with single-celled vegetative form that reproduces by budding
Elongated chains of budding yeast with a constriction between cells are called pseudohyphae
Moist mucoid colonies
What are some characteristics of moulds?
Moulds:
Fungi with cylindrical, filamentous vegetative form called hyphae
Hyphae may be septate (cross walls) or aseptate
A mass of hyphae is called a mycelium
Hyphae grow by elongation at tip
May produce metabolically inactive spores or conidia
May form fuzzy/wooly/velvety colonies
What are thermally dimorphic fungi? dematiacious fungi? hyaline fungi? conidia fungi?
Thermally Dimorphic Fungi: appear as a yeast at body temperature and a mould at room temperature.
Dematiacious: brown or black pigmented hyphae due to melanin production (phaeo-)
Hyaline: clear, no melanin production
Conidia: asexual spores that form from hyphae
What is fungal reproduction like?
Many reproduce both sexually (meiosis) and asexually (mitosis)
Sexual state called telomorph
Asexual state called anamorph
Genus/species names differ for telomorph and anamorph, as most not initially recognized to be same mould
Proper nomenclature is that of the sexual state (when known)
Homothallic: self-fertile, do not require a mate for sexual reproduction
Heterothallic: require a mate for sexual reproduction
What are 3 ways in which fungi can reproduce sexually and how do they work?
Zygotic Meiosis Haploid vegetative body Haploid ametes produced by mitosis Gametes fuse to form diploid zygote Zygote divides by meiosis to form new haploid generation
2. Gametangial Meiosis Diploid vegetative body Haploid gametes produced by meiosis Gametes fuse to form diploid zygote Zygote divides by mitosis to form new diploid generation
- Sporic Meiosis
Haploid vegetative body
Haploid gametes produced by mitosis
Gametes fuse to form diploid zygote
Zygote divides by mitosis to form new diploid generation
Some cells undergo meiosis to become haploid spores
Haploid spores divide by mitosis to become a new haploid generation
ITS COMPLICATED
How does the micro lab identify fungi?
Direct patient samples:
KOH prep: dissolves host cells, allows fungi to be visualized
Calcofluor: fluorochrome that binds to cellulose and chitin in fungal cell wall
Growth on plates:
Sab-Dex plate: appearance of colony on fungal media. Examine color and texture of forward and reverse
Tape prep: lactophenol cotton blue staining from colony growth to identify structures
How many fungi cause disease to humans? How are they classified?
A few hundred
Skin/Tissue Infection
Superficial
Cutaneous
Subcutaneous
Systemic Infections
Dimorphic
Opportunistic
What is a superficial fungal infection like? An example?
Superficial: tissue not invaded, no pathological changes
Tinea versicolor
Malassezia furfur
What are some examples of cutaneous fungal infections?
Cutaneous:
Dermathphytosis: Infections of skin, hair or nails (live off keratin) (jock itch, etc.)
caused by: Microsporum, Trichophyton, Epidermophyton
Dermatomycosis : Similar infections caused by other fungi
What are some examples of subcutaneous fungal infections?
c. Subcutaneous: Chronic, localized, follow traumatic implantation with soil fungi
Sporotrichosis: “rose-handlers disease”
Sporothrix schenckii
Chromoblastomycosis: warty nodules and crusty abscesses along lymphatics following implantation of dematiacious fungi. Medlar bodies in tissue. skin or subcutaneous tissue. (Multiple etiologic agents)
Mycetoma: abscesses with draining sinus tracts and granules following traumatic implantation, usually to feet. cutaneous, subcutaneous, fascia, bone. (Multiple etiologic agents)
What are 4 examples of dimorphic systemic fungal infections? What are their common features (transmission, etc.)
Dimorphic
Histoplasmosis Histoplasma capsalatum Blastomycosis Blastomyces dermatitidis Coccidioidomycosis Coccidioides immitis Paracoccidioidomycosis Paracoccidioides brasiliensis
Entry into host by inhalation of airborne spores
Spores germinate in lung
Asymptomatic primary pulmonary infection is common
Acute pulmonary disease less common
Chronic pulmonary or disseminated infection is rare
What are some characteristics of histoplasma capsalatum?
Found in soil contaminated with bird droppings or guano
Endemic in Ohio and Mississippi river basins
Histoplasmosis can be acute and benign pulmonary disease to chronic (otherwise healthy), progressive and fatal (immunocompromised and elderly).
Localized or disseminated.
Contracted by inhaling conidia. Lives in RES (reticuloendothelial) cells.
What are some characteristics of blastomyces dermatidis?
Lives in soil and decaying wood
Highest incidence in Mississippi, Ohio and Missouri valleys
Blastomycosis: cutaneous and systemic infections. Acquired by inhalation or direct inoculation. Can disseminate to most organs, particularly in immunocompromised.
Characteristic broad based budding with thick wall that appears double contoured.
What are some characteristics of Coccidiomycoses?
Caused by Coccidiodes immitis
Most cases occur in the arid areas of SW USA, central and SA
In soil, fungus produces arthrospores by septation of fungal filaments; inhaled
Can disseminate to bones and CNS
What are some characteristics of paracoccidiomycoses?
Paracoccidiodes brasilensis
South American blastomycosis
Major endemic dimorphic fungus in Latin America
Clinical presentation similar to histo and blasto EXCEPT most common 2o site of infection is the mucosa of the mouth and nose where destructive lesions may develop
90% of symptomatic disease occurs in males; female hormones may be inhibitory
Mariner’s wheel.
What are some examples of opportunistic fungal infections? What are some characteristics?
Candidiasis Candida albicans, other spp. Cryptococcosis Cryptococcus neoformans Aspergillosis Aspergillus fumigatus, other spp. Mucormycosis Rhizopus, other genus. Pneumocystis jiroveci
Rarely manifest disease in healthy individuals
Immunosuppressed, chemotherapy, diabetes
What are some characteristics of candidiasis
Candida albicans most common species
Yeast and hyphal forms
Reproduces by budding
Normal flora of skin, mucous membranes, GI tract, GU tract
Almost all infections are endogenous
Lab identification by culture
C. albicans: germ tube positive, yeast with “feet”
What are some clinical manifestations of candidiasis?
Mucutaneous: thrush, vulvovaginitis, esophagitis, diaper rash
Systemic candidiasis occurs in immunosuppressed, cancer patients, patients on antibiotic therapy
Can involve GI tract, kidneys, liver, spleen, bloodstream, urinary tract, respiratory tract, heart, eye
What are some characteristics of cryptococcosis and how is it diagnosed?
Cryptococcosis: Cryptococcus neoformans
Sites of infection: lung, meninges, CSF, blood, skin, mucous membranes, systemic
Usually 2-4 µm, narrow based budding, capsules stain with mucicarmine
Cryptococcus neoformans diagnosis:
India ink: demonstrates capsule
Cryptococcal antigen: Test for capsular polycaccharide, performed on CSF or blood.
Culture
What are some characteristics of aspergillosis?
Caused by several species of the filamentous fungus, Aspergillus.
Most common species is A. fumigatus
Found in soil, dust, decomposing organic matter
Clinical manifestations depend on what kind of immunosuppression a person has?
Hyaline septate hyphae
dichotomously branched (branches approximately the width of the parent hyphae)
branching at 45 degree angles
Tend to appear in radial fashion with hyphae nearly parallel to one another
In cavitary lesions, conidial heads may be observed.
What are some characteristics of mucormycosis?
Infection with zygomycete, Rhizopus most common
Rhinocerebral mucormycosis: infection begins in the nasal mucosa or sinuses progresses to the orbits, palate and brain
Very aggressive
Rapidly fatal
Surgical debridement must be performed
Pulmonary mucormycosis: severe tissue-destructive pneumonia-1oly in neutropenic
Cutaneous mucormycosis-trauma assoc.
