Mycology

Aerial hyphae

Spores are formed by _____

Sabouraud Dextrose Agar (SDA)

A special nutrient-rich, non selective medium used to grow fungi

• pH 5.6 to prevent bacterial growth

• Sporing structures and pigmentation

Dermatophytes

A group of fungi that cause skin, hair, and nail infections in humans and animals

• contact with contaminated soil or infected animals/human

Mycotic keratitis

Fungal infection of the cornea

Candida

A genus of yeast-like fungi that commonly cause infections in the skin, mouth, vagina, and bloodstream

Non-candida fungal infections

These are fungal infections caused by filamentous fungi (molds) or other yeasts that are not part of the Candida genus

• Cryptococcus / Trichosporon

Mycosel Agar

A selective culture medium used to grow dermatophytes and other pathogenic fungi

• SDA w/ Chloramphenicol (antibacterial) and Cycloheximide

14 days

General incubation period

7 days

How many days to detect presence of yeast in mouth, throat, or vagina?

21 days

How many days — tissues and sterile body fluids other than blood

28 days

How many days — respiratory, bone marrow, blood, specimens w/ dimorphic fungus

Molds

Grow best at 25-30ºC

Yeast

Grow best at 35-37ºC

Pathogenic fungi

Grow best at 30-32ºC

karyogamy (nuclear fission) and meiosis

Sexual reproduction is alternation between _____

Plasmogamy

Haploid nucleus of donor cell penetrates cytoplasm of recipient cell

Karyogami

The fusion of the two nuclei to form a single diploid nucleus

Yeasts

Usually multiply asexually by budding

Hyphae/mycelium

Reproduction: like roots — septate if w/ crosswalls

Spores

Reproduction: like seeds — fungal spores can be asexual or sexual

• Conidia

• Sporangiospores

2 major types of asexual spores

Intercalary

Spores form in the middle of a hypha

Sessile

Spores form directly on the hypha without a stalk

Terminal

Spores form at the tip (end) of a hypha

Dematiaceous

Refers to fungi that have dark-colored hyphae or spores due to the presence of melanin

Lobomycosis

Chronic fungal skin infection caused by Lacazia loboi

• found in humans and bottle-nosed dolphins

• endemic in South & Central Americs

Phaeohyphomycosis

Caused by Wangiella dermatitidis

• dematiaceous (dark-pigmented) fungi that form dark-colored hyphae in tissue

• Exophiala, Cladophialophora, Fonsecaea, Alternaria, Bipolaris

Zygomycosis

• Most acute and fulminate fungal infection known

• Any infection due to a member of the Zygomycetes

• primitive, fast growing, terrestrial, largely saprophytic fungi

• involves rhino-facial-cranial area, lungs, GI tract, skin

Thermal dimorphism

Only dematiaceous fungus affecting humans (characteristic of fungi that can survive in diff. temperatures)

molds

At lower temperatures, thermal dimorphic fungi exist as _____, typically forming filamentous structures like hyphae and conidia

yeast

At body temperature, thermal dimorphic fungi convert into a _____ form, which is unicellular and adapted for infection within the host

Sporothrix schenckii

• “Rose gardener’s disease”

• contracted by inhalation

• no teleomorph

• dimorphic

Lymphocutaneous sporotrichosis

• Sporotrichosis that affects skin & lymphatic system

• Skin lesions

Pulmonary sporotrichosis

• From inhalation of conidia

• Haematogenous disseminations

• non-specific symptoms

Exophiala jeanselmei

• Dematiaceous fungus can cause phaeohyphomycosis and mycetoma

• Reservoirs: soil, trees, rotting wood, decaying vegetation

Pseudallescheria boydii

• “Madura foot” / “watering can foot”

• In the lungs, may form fungoma similar to aspergilloma

• Reservoir: temperate & subtropical zones in soil, manure, water from polluted streams & sewage

Mycetoma

Chronic subcutaneous infection induced by traumatic inoculation with any of several saprophytic species of fungi (eumycetoma) or actinomyces & nocardia (actinomycetoma) that are normally found in soil

White grain mycetoma

Mycetoma caused by

• Pseudoallesheria boydii

• Acremonium

Bacterial mycetoma

Mycetoma caused by

• Actinomyces

• Nocardia

• Streptomyces

• Actinomadura

Black grain mycetoma

Mycetoma caused by

• Exophiala jeasmsemi

• Madurella mycetomatis

Gastrointestinal zygomycosis

• Associated with severe malnutrition

• GI diseases - disrupt integrity of mucosa

• Primary infections:

  • ingestion of fungal elements

  • present as necrotic ulcers

Chromoblastomycosis

• Chronic fungal infection that affects the skin and subcutaneous tissues

• Develops slowly over time and remains localized to the area of initial infection

• sclerotic (hard cells) aka Medlar bodies

• globe-shaped, cigar-colored, thick-walled structures

F. pedrosoi

• Causes chromoblastomycosis

• Common in humid climates

C. carrionii

• Causes chromoblastomycosis

• Found in dry areas

Farming

Most common occupation in patients with chromoblastomycosis

Fonsecaea monophora

Predominant etiologic agent of chromoblastomycosis in Southern China

• Phialophora verrucosa

• Fonsecaea pedrosoi

• Fonsecaea compacta

• Cladophialophora carrionii

Causative agents of chromoblastomycosis

BHI (Brain Heart Infusion Agar)

rich, non-selective culture medium used for growing fastidious fungi

IMA (Inhibitory Mold Agar)

a selective culture medium primarily used for the isolation and cultivation of pathogenic fungi

PDA (Potato Dextrose Agar)

Culture medium — mold sporulation and pigment production in dermatophytes

Geophilic

• Fungi live in soil or decaying organic matter

• They can infect humans when someone comes in contact with contaminated soil

• cause acute, inflammatory lesions

Zoophilic

• Fungi primarily live on animals

• These fungi can spread to humans through direct contact with infected animals

• cause acute, inflammatory lesions

Anthropophilic

• Fungi live on humans and spread easily from person to person.

• These fungi cause infections in humans, often spreading through close contact

Superficial mycoses

• Limited to stratum corneum; no inflammation

• Skin:

  • Malassezia furfur

  • Exophiala werneckii

• Hair:

  • Trichosporon beigelii

  • Piedraia hortae

Tinea

• Ringworm

• Infections of the hair, nails, deeper layers of epidermis

Tinea nigra (tinea nigra palmaris)

• Fungal infection caused by the Hortaea werneckii

• prevalent in warm coastal regions and among young women

• Dematiaceous

Piedra

A fungal infection that affects hair, causing the formation of hard nodules (on the hair shafts)

• endemic in tropical countries

Black piedra

Nodular infection of the hair shaft caused by Piedraia hortae

• hard nodules

White piedra

Nodular infection of the hair shaft caused by Trichosporon spp.

• larger, softer, yellowish nodules

Malassezia furfur

Causes:

• Pityriasis / tinea versicolor

• Pityriasis / tinea folliculitis

• Seborrhoeic dermatitis (dandruff)

• Systemic infection (blood of neonates & adults)

Ectothrix/Exothrix

Pattern of hair shaft invasion

• infects the hair surface (forms a sheath around shaft)

• “gray-patch” tinea capitis

• will fluoresce in UV Wood’s lamp

• resolves at puberty

Endothrix

Pattern of hair shaft invasion

• Dermatophyte invades hair shaft (produce spores within the shaft)

• will not fluoresce in UV Wood’s lamp

• “black dot” tinea capitis

Favus

Inflammation of hair follicle caused by Trichophyton schoenleinii → scutula (crusts)

M. canis ringworm

Zoophilic dermatophyte (fungus associated with animals), primarily transmitted from cats and dogs to humans

Microsporum audouinii

• Anthropophilic fungus

• Non-inflammatory infection of scalp

• Gray patch tinea capitis

Microsporum ferrugineum

• Epidemic juvenile tinea capitis in humans

Wood’s lamp

Light that uses long wave UV light

• fungus may glow if infected with tinea

blue green

Color of M. audonii under Wood’s lamp

yellow green

Color of M. canis under Wood’s lamp

yellow green

Color of M. ferrugineum under Wood’s lamp

Microsporum gypseum

• Most common geophilic species causing human infections

• Sources: skin scrapings or stubs of hair

• hyaline, septate, branched

• macroconidia are ellipsoid/cucumber-shaped

Epidermophyton floccosum

• Dermatophyte fungus that causes tinea infections (ringworm) in humans, primarily affecting the skin and nails, but not the hair

• It is one of the main causes of tinea cruris (jock itch) and tinea pedis (athlete's foot)

• beaver tail shape

T. concentricium

Dermatophyte fungus that causes tinea corporis (ringworm) with a unique pattern of concentric rings

T. mentagrophytes var. interdigitale

Variety of the dermatophyte fungus Trichophyton mentagrophytes, which is commonly associated with tinea pedis (athlete's foot), especially in the spaces between the toes

• flat, white to cream colonies; suede-like

T. rubrum

• Anthropophilic

• Most widely distributed dermatophyte of humans

• Chronic inflammation of skin, nails, and rarely scalp

Clavate microconidia

Club-shaped or cylindrical fungal spores that are typically produced by certain dermatophyte fungi

T. schoenleinii

Anthropophilic fungus causing favus (fungal infection of skin and scalp)

T. tonsurans

Anthropophilic fungus primarily associated with tinea capitis (scalp ringworm) in humans

T. verrucosum

• Zoophilic fungus causing ringworm in cattle

• In humans: from direct contact with cattle or infected fomites

• young button-shaped colonies

T. violaceum

• Black dot tinea capitis

• anthropophilic fungus

Kerion

Severe combined inflammatory and hypersensitivity reaction from zoophilic species

Chromoblastomycosis

• Verrucoid crusted lesions/nodules on skin

• If not treated → resemble cauliflower

T. tonsurans

Chief cause of “black dot” tinea capitis

Pityriasis vesicolor

Chornic superficial infection of stratum corneum by species of Malassezia

Malassezia furfur

• “spaghetti and meatballs”

• part of the normal skin microbiota

• warm, humid climates

• immunosuppression