Mycology

Question 1

Fungi characterisitcs

Answer 1

Fungi are eukaryotes - they have a nucleus
Free-living microorganisms
Heterotrophs - obtain carbon by consuming other organsms
Reproduce asexually by fragmentation, budding, and through spores (sexual production in some fungi)

Question 2

Fungi cell characteristics

Answer 2

Cell membrane contains sterols (ergosterol)
Plant-like cell wall
-contains glucan, mannan, and chitin, not cellulose

Unicellular forms = yeast
Multicellular forms = mold
-mold has hyphae and fruiting bodies which contain spores
-Mycelium is a group of tangled hyphae

Question 3

Fungal structures

Answer 3

Hyphae - main element (tubular structure) of the vegetative or growing form
Septa - cross-walls that divide the hyphae
Mycelium - filamentous mass of hyphae
Dark pigmented hyphae = Dematiaceous fungus
Non-pigmented hyphae = Hyaline fungus

Question 4

Fungal infection characteristics

Answer 4

Fungus invades the tissues and induces its pathogenic effect
Infects mainly immunocompromised hosts
Characteristically induce chronic, granulomatous infection
Infections are uncommon, but often spectacular, serious infections
Antimicrobial agents to treat are limited
-humans and fungus are both eukaryotes
-anything used to fight/damage fungus, can also have the potential of hurting the host

Question 5

Mycotoxicoses

Answer 5

Fungal disease

Fungal contamination or growth on food material leads to accumulation of toxins and when consumed induce severe disease

Question 6

Allergies

Answer 6

Fungal disease

Inhaled fungal spores induce hypersensitivity and allergy

Question 7

Fungal infection locations

Answer 7

Superficial - infections limited to the outermost layers of the skin and hair
Cutaneous - infections that extend deeper into the epidermis, as well as invasive hair and nail diseases
Subcutaneous - infections involving the dermis, subcutaneous tissue, muscle, and fascia
Systemic - infections that originate primarily in the lung but spread to many other organs

Question 8

Fungal culture and media for diagnosis

Answer 8

Requires special media and growth conditions
Grows best at ambient environmental temperatures under aerobic conditions

Fungal media:
Sabouraud Dextrose Agar (classic fungal medium)
-low pH and dextose in the media inhibit bacterial growth to a limited extent
Sabouraud Dextrose Agar with Cycloheximide
-cycloheimide inhibits growth of saprophytic molds allowing selection for pathogenic fungi

Question 9

Antifungal drugs

Answer 9

Polyenes - Amphoterocin B, natamycin, nystatin
= inhibit ergosterol
Flucytosine = inhibit nucleic acid synthesis
Azoles - imidazoles and Trizoles
= inhibit ergosterol
Allylamines - Terbinafine
= inhibit ergosterol
Griseofulvin
= binds to mitotic spindles, inhibits mitosis, accumulates in keratin; only used for dermatophyes
= drug reaches the superficial keratinzed epithelium and inhibits fungal DNA synthesis

Question 10

Immunity to fungal infections

Answer 10

Immunity is mainly cell-mediated
Antibodies are produced, but not protective
Most lesions are granulomatous

Question 11

Phaeohyphomycosis

Answer 11

A mycotic infection of humans and lower animals caused by a number of dematiaceous (brown-pigmented) fungus

Question 12

Chromoblastomycosis

Answer 12

A mycotic infection of the cutaneous and subcutaneous tissues characterized by the development in tissue of dematiaceous (brown-pigmented), round sclerotic bodies
Infections are caused by traumatic implantation of fungal elements into the skin and are chronic, slowly progressive, and localized

Question 13

Zygomycosis

Answer 13

Any infection due to a member of the Zygomycetes

Primitive, fast growing, terrestrial, largely saprophytic fungi

Question 14

Mycetoma

Answer 14

A mycotic infection of humans and animals caused by a number of different fungi and actinomycetes
Characterized by draining sinuses, granules, and tumefactions
The disease results from the traumatic implantation of the etiologic agent and usually involves cutaneous and subcutaneous tissue, fascia, and bone of the foot or hand

Question 15

Dermatophytes

Answer 15

Superficial Mycosis (Ringworm or tinea)
Fungal parasites of keratinized epithelium of skin and nails
Highly contagious (arthrospores)
Zoonotic

Question 16

Three types of Dermatophyte reservoirs

Answer 16

Anthrophilic - human reservoir
Zoophilic - animal reservoir
Geophilic - soil or environmental reservoir

Question 17

Common Dermatophyts and their hosts

Answer 17

Microsporum canis, M. audouinii, M. gypsium = dogs, cats, humans
Trichohyton mentagrophytes = broad host range
Trichophyton verrucosum = cattle
Trichophyton equinum = horses
Microsporum (Nannizia) nanum = pigs

Question 18

Classic Ringworm lesions

Answer 18

Slowly expanding, circular area of alopecia and desquamated epithelium
Central hair regrowth, inflamed edge
Center is normal, periphery is not (collect material from periphery for diagnosis)
Often multiple differently sized lesions

Question 19

Kerion

Answer 19

Nodular (kerion) lesions caused by Dermatophytes, localized or generalized folliculitis, and often with furunculosis

Question 20

Diagnosis of Ringworm

Answer 20

Woods lamp detection of fluorescence

-used for detecting Microsporum canis infection

Question 21

Dermatophyte sample collection

Answer 21

Sample should be collected form the periphery of the lesion
Collect in small containers with loose caps - closed tubes are not recommended for specimens since they retain moisture, which may result in an overgrowth of bacterial as well as fungal contaminants
See large numbers of spores (arthroconidia) on broken hairs
Their location, whether ectothrix (outside the hair follicle) or endothrix (inside the hair follicle), can be used for species identification
Phenol red indicator and color change for presumptive identification (beware of false positives)

Question 22

Microsporum gallinae

Answer 22

Avian ringworm or favus

Spontaneous recovery; treatment to minimize discomfort, progression, and spread