CH 27: opportunistic molds

Opportunistic fungi

• rarely cause disease in healthy individuals

  • medical conditions in pts who are immunocompromised

• found in high numbers in environment

  • inhalation

• respiratory infx

  • pneumonia, sinusitis, bronchitis, eye infx, ear infx, and allergies

Aspergillus spp.

• rapidly growing environmental mold

• usually blue to green to black color macroscopically

• identifiable by swollen vesicle at end of conidiophores

Aspergillus fumigatus

• conidia in single rows that only cover 2/3 top of vesicle

Aspergillus flavus

• circumferential conidia

Aspergillus niger

• black macroscopic mold

• 2 rows of circumferential, dark conidia

Penicillum spp.

• branching conidiophores w/ elongated phialides and chains of microconidia

• ‘brush-like’

Fusarium spp.

• canoe-shaped, multi-cellular, macroconidia

Paecilomyces spp.

• branching conidiophores w/ elongated, flask-shaped phialides

• long chains of oval conidia

Zygomycetes

• group of opportunistic molds

  • very serious and fatal infx

• hyphae are usually broad, no septation, and little to no branching

• principal agents

  • Rhizppus spp.

  • mucor spp.

Rhizopus

• large sporangia that arises directly from rhizoids

Mucor spp.

• large spherical sporangia

• NO rhizoids

Cutaneous mycoses

• fungal diseases of keratinized tissues

• collectively called ‘dermatophytes’

  • cause infx of hair, skin, and nails

    • Trichophyton

    • Microsporum

    • Epidermophyton

Cutaneous Mycoses infections

• tinea pedis - athlete’s foot

• tinea corporis - ringworm

• tinea unguium - onychomycosis

• tinea capitis - scalp infx

• tinea barbae - barber’s itch

• tinea cruris - jock itch

Trichophyton mentagrophytes

• macroconidia: thin-walled, smooth, and cigar-shaped

• microconidia: numerous , grape-like clusters

Trichophyton rubrum

• macroconidia: thin-walled, smooth, and cylindrical to club-shaped

• microconidia: sparse, club-shaped, and in singles

Epidermophyton floccosum

• macroconidia: thin-walled, smooth, and club-shaped; ‘beaver tail’ clusters

• microconidia: none

Microsporum canis

• macroconidia: thick-walled, spindle-shaped, tapered ends

• microconidia: unremarkable

Microsporum gypseum

• macroconidia: moderately thick walls, fusiform shape w/ rounded ends

• microconidia: numerous, but unremarkable

Subcutaneous mycoses

• fungal infx of subcutaneous tissues

• lesions are often dark in color, hard, or crusted

• organisms are collectively called ‘dematiaceous molds’

  • ‘dematiaceous’ refers to dark color

Mycetoma

• subcutaneous infx that cause granulomatous, pus-filled lesions, and draining tracts

  • can be bacterial (actinomyces) or fungal

  • conidia/spores introduced to subcutaneous tissue by skin trauma

• most common on feet/ankles

  • infx most common in Africa

• most common causes

  • Pseudallescheria boydii

  • Exophiala

  • Acremonium

  • Madurella

Pseudallescheria boydii

• asexual phase: rounded microconidia w/ truncated base

• sexual phase: large cleistochecia filled w/ spores

Exophiala

• short conidiophore w/ clusters of elongated conidia w/ rounded ends

Chromoblastomycosis

• chronic infx characterized by hard, scaly, or tumor-like lesions

  • introduced via skin trauma

• most common on feet/legs

  • tropical areas

• principal agents:

  • Fonsecaea pedrosoi

  • Phialophora verrucosa

  • Cladophialophora carrionii

Fonsecaea pedrosoi

• clusters of short chains of oval conidia from a single conidiophore

Phialophora verrucosa

• vase-like conidiophore w/ cup shaped top

Cladophialophora carrionii

• long, branching chains of oval conidia

Phaeohyphomycosis

• subcutaneous infx that can become systemic

  • brain abscesses, endocarditis, etc

• principal agents:

  • Alternaria

  • Bipolaris

  • Curvularia

  • Exophiala

  • Phialophora

Bipolaris

• oval, clustered, septate macroconidia from genticulate (bent) conidiophore

• each conidia has 3-5 septations

Alternaria

• chains of club-shaped conidia w/ transverse and longitudinal septations

• golden brown color

Curvularia

• rounded, septate conidia w/ 4 cells

• distinct swelling in cells when mature