Ch. 17 - Fungi

Question 1

Structural properties of fungi

Answer 1

Plasmalemma - cell membrane

• ergosterol = sterol unique to fungi, target for antifungal therapy
• no cholesterol

Cell wall - chitin (polymer of NAG)
-glucagon and mannan

Capsule - some fungi have one

• antigenic: evade immune response
• anti phagocytic: evade phagocytosis

Microtubules - make up cytoskeleton of cell; hold shape of cell intact

Microvesicles - synthesize chitin; fuse with apical plasmalemma

Question 2

Growth properties of fungi

Answer 2

Aerobic
Humid conditions
Mildly acidic (ph 5-6)

Easy to grow in lab - not fastidious, can grow on almost anything

Dimorphic:

• at ambient temps (25C), grow as filamentous molds
• at body temp (37C), converted to unicellular, pathogenic yeast-like forms

Question 3

Yeast form

Answer 3

Large variety of unicellular fungi

Spheres

~ 4 micrometers

Divid by budding (blastopore daughter cells)

• asexual reproduction
• cell swollen at one edge –> new cell (blastopore) buds from parent cell–> spore breaks free to live independently

Question 4

Mold form

Answer 4

Multicellular, branching

Form filaments = HYPHAE (intertwined tubular filaments, can be highly branched; morphological unit of filamentous fungus)

Hyphae form MYCELIUM = thick mass of hyphae, visible to naked eye

1. Aerial mycelium= mycelium growing above nutrient media; give rise to spores (Eg moldy fruit, bread)
2. Vegetative mycelium = penetrates substrate, gets nutrients; anchors and absorbs nutrients

Question 5

Pathogenic fungi

Answer 5

Grow in yeast form in tissues of host, when causing infection (37C)

Grow in mold form when free-living, outside of host (25C)

Question 6

Fungal Reproduction - Asexual

Answer 6

Asexual reproduction by production of spores

Fruiting bodies = part of fungus in which spores are formed, and from which they are released

Drier cells easily disseminated
Hardy

Mitosis - thousands of spores produced, all genetically identical

Question 7

Conidia

Answer 7

Asexual spores

Named according to how they develop:

1. Chlamydospores - thick, swollen, round cells
2. Blastopore so - form via budding (eg yeast)
3. Arthrospores - thick, rectangular cells

Question 8

Fungal Reproduction - Sexual

Answer 8

Produce spores by sexual reproduction –> mating types come together and fuse

Mating of cells:
Haploid nucleus from two gametes fuse –> diploid nucleus –> meiosis: chromosome halved, return to haploid

Question 9

Fungi imperfecti

Answer 9

Only asexual reproduction has been observed

These fungi do not produce sexual spores

Question 10

Amphotericin B

Nystatin

Answer 10

Class - polyenes

Mechanism - bind ergosterol

Question 11

Micronazole

Tolnafatate

Answer 11

Class - Azores fluconazole

Mechanism: inhibit ergosterol synthesis

Question 12

5FC (flucytosine)

Answer 12

Class - pyrimidines

Mechanism: inhibit DNA/RNA synthesis

Question 13

Griseofulvin

Answer 13

Class - grisan

Mechanism - inhibit microtubule assembly

Question 14

Mycotoxicoses

Answer 14

Toxic diseases

Produce mycotoxins

Eg. Mushrooms - product neurotoxin

Question 15

Mycoses

Answer 15

Fungal infections

Affect many body regions (esp. Skin or body surfaces)

Classified according to tissue level they infect

Question 16

Mycoses 1

Answer 16

Superficial - limited to outermost layers of skin and hair

Cutaneous - infection goes deeper into epidermis, also hair and nails
Ex: tine as, ringworm, athlete’s foot

Question 17

Mycoses 2

Answer 17

Systemic/deep:

• systemic infections
• spores inhaled
• got to lung –> damage lung, disseminate into bloodstream, can be fatal

Opportunistic - common in HIV or immunocompromised
–> weakened immune system contribute to occurrence of infection
Ex: Cryptococcus neoformans, Candida albicans

Question 18

Cryptococcus neoformans

Answer 18

Most dangerous fungal disease = Cryptococcus meningitis (mycotic meningitis)

Lung infection mild to severe; fatal
Healthy: pneumonia
Immunocompromised: meningitis

C. Neoformans thrives in CSF –> meningitis

Transmission: inhalation of yeast from soil or pigeon droppings (grown actively in pigeon droppings)

no mold stage of reproduction (unique!)

Diagnosis: encapsulated, budding yeast in CSF; resist phagocytosis

Treatment: amphotericin B (binds to ergosterol) and flucytosine ( inhibit RNA/DNA synthesis)

Question 19

Candida albicans

Answer 19

Yeast infection = candidiasis

Normal flora in oral cavity, vagina, and GI tract –> change in normal microbiota population - candid can flourish –> candidiasis

VULVOVAGINITIS = yeast infection in vagina

THRUSH = oral candidiasis
-small, white flecks on mucus membranes of oral cavity; newborns most common

Usual morphological features - easy/rapid to diagnose
-germ tubes: add little blood/serum to grown medium –> form germ tubes

If recurrent - sign of underlying condition (can be early sign of AIDS–> related to suppressed immune system)

Treatment: nystatin (bind to ergosterol)

Antibiotics may increase yeast infection –> grow more rapidly w/o competition

Question 20

Fungi - general

Answer 20

Eukaryotes - multicellular, diploid, one or more nuclei

Extracellular digestion –> acquire nutrients through absorption –> secrete enzymes into surrounding environment to hydrolyze complex organic compounds into simpler ones

Major groups:

1. Molds - grown as long, tangled filaments (hyphae) that give rise to visible colonies (mycelium)
2. Yeast - unicellular organisms, whose colonies on agar resemble bacteria