topic 13

Question 1

compare and contrast fungi from other eukaryotes

Answer 1

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

Question 2

What are some ways in which fungi obtain nutrients?

Answer 2

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)

Question 3

How are fungi classically divided? Are they mutually exclusive?

Answer 3

yeasts and moulds. They are not mutually exclusive. Some fungi can interchange.

Question 4

What are some characteristics of yeasts?

Answer 4

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

Question 5

What are some characteristics of moulds?

Answer 5

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

Question 6

What are thermally dimorphic fungi? dematiacious fungi? hyaline fungi? conidia fungi?

Answer 6

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

Question 7

What is fungal reproduction like?

Answer 7

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

Question 8

What are 3 ways in which fungi can reproduce sexually and how do they work?

Answer 8

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

3. 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

Question 9

How does the micro lab identify fungi?

Answer 9

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

Question 10

How many fungi cause disease to humans? How are they classified?

Answer 10

A few hundred

Skin/Tissue Infection
Superficial
Cutaneous
Subcutaneous

Systemic Infections
Dimorphic
Opportunistic

Question 11

What is a superficial fungal infection like? An example?

Answer 11

Superficial: tissue not invaded, no pathological changes
Tinea versicolor
Malassezia furfur

Question 12

What are some examples of cutaneous fungal infections?

Answer 12

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

Question 13

What are some examples of subcutaneous fungal infections?

Answer 13

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)

Question 14

What are 4 examples of dimorphic systemic fungal infections? What are their common features (transmission, etc.)

Answer 14

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

Question 15

What are some characteristics of histoplasma capsalatum?

Answer 15

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.

Question 16

What are some characteristics of blastomyces dermatidis?

Answer 16

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.

Question 17

What are some characteristics of Coccidiomycoses?

Answer 17

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

Question 18

What are some characteristics of paracoccidiomycoses?

Answer 18

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.

Question 19

What are some examples of opportunistic fungal infections? What are some characteristics?

Answer 19

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

Question 20

What are some characteristics of candidiasis

Answer 20

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”

Question 21

What are some clinical manifestations of candidiasis?

Answer 21

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

Question 22

What are some characteristics of cryptococcosis and how is it diagnosed?

Answer 22

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

Question 23

What are some characteristics of aspergillosis?

Answer 23

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.

Question 24

What are some characteristics of mucormycosis?

Answer 24

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.

Question 25

What are some characteristics of pneumocystic jirovecii

Answer 25

Causes pneumonia in immunosuppressed individuals particularly in HIV
Organism ubiquitous in nature
Disease formerly thought to be reactivation of latent infection
Now believed to be airborne transmission*
Infection/disease higher in immunosuppressed
Hypoxemia a hallmark of PCP pneumonia