CH 27: Medically Significant Fungi

Into to fungi

• EURKARYOTES

  • chitinous cell walls

  • true nucleus and mitochondria

• chemoheterotrophs

  • obtain E and nutrients from environment

• prefer moist environment w/ neutral pH

  • obligate aerobes

  • spores and conidia can survive for extended lengths time

    • great for distribution

Mycology terms

• yeasts: UNIcellular fungi

• molds: MULTIcellular fungi

• dimorphic fungi: both yeast and mold stage

• mycosis: fungal infx

Mold structure

• hyphae

  • long, branching structures that make up body

  • aerial or subsurface (vegetative)

• reproduce asexually or sexually

  • asex = conidia

  • sex = spores

• conidia, conidiophores, and other reproductive structures are important in identification

  • conidiophore (stalk) produces conidia (spore)

Mold culture

• grow best around room temp (25-30 C)

  • below body temp → disadvantage

• media

  • Sabouraud-brain heart infusion (SABHI) agar

    • supportive media for ALL fungi

    • selective by adding antibiotics

  • Dermatophyte test medium (DTM)

    • used to isolate dermatophytes

• few days to wks to grow

  • human immune system kick out

• spread easily during reproduction

Yeast structure

• SINGE CELLED

  • no aerial structures

• ASEXUAL reproduction

  • budding

    • direct contact for infx

• pseudohyphae or true hyphae

Yeast culture

• 22-35 C growth

• media

  • SABHI

  • Cornmeal agar w/ Tween 80

    • differentiate Candida species

  • grow on most standard bacteria media

• usually grow more quickly than molds

  • 24-48 hrs

Direct examination

• wet preparations

  • UNSTAINED samples under 40x w/ NO oil

  • detecting presence of fungi, not ID

  • urine or vaginal specimens

• KOH preparations

  • addition of KOH to wet preps

  • removes cellular debris and makes fungus more visible

  • nail scraping, skin flakes, hair, or thin slices of tissue

Direct examination w/ stains

• calcofluor white

  • fluorescent stain that binds chitin

• lactophenol cotton blue (LPCB)

  • blue stain and mountin fluid for wet preps

  • 100x w/ oil

Candida spp.

• most common yeast genus isolated from humans

• candidiasis

  • thrush - oral cavity

    • most common babies

  • vulvovaginitis - vaginal yeast infx

  • onychomycosis - nail infx

• opportunistic

  • pneumonia, ear infx, sinus infx, UTIs, wound infx, septicemia

  • predispositions include antimicrobial therapy, diabetes mellituss, and anything that alters immune system/microbiome

    • pregnancy, illness, burns

Candida albicans

• MOST COMMON isolated Candida organisms from humans

  • normal flora of mucous membranes

• characteristics

  • only species that forms TRUE hyphae

    • (+) germ tube test

  • colonies on solid media produce star-like projections or ‘feet’

Cyrptococcus neoformans

• pulmonary infx, meningitis, and septicemia in severely immunocompromised

  • HIV/AIDS

• environmental pathogen

• characteristics

  • encapsulated

    • mucoid colonies

    • view capsule using india ink

  • NO structures like pseudohyphae

  • brown colonies on bird seed agar

Malassezia furfur

• causes tinea versicolor and possibly dandruff

• characteristics

  • skin scrapings show ‘spaghetti and meatball's’ morphology

  • require lipids for growth and media must be supplemented

Pneumocystis jiroveci

• major pulmonary pathogen in immnuoDEFICIENT hosts

  • especially pts w/ AIDS

• characteristics

  • cannot be easily cultured

  • irregularly shaped singular yeast cells w/ central dot

Thermally dimorphic fungi

• change from yeast to mold and BACK depending on temp

  • yeast = 37 C

  • mold = 25-30 C

• important fungal pathogen

  • fungi that are capable of causing systemic infx

  • form change allows highly infective AND highly pathogenic

Histoplasma capsulatum

• histoplasmosis - potentially fatal lung condition that can spread to spleen, liver, and kidneys

• distribution

  • common in Ohio and MS River valleys

  • inhalation of spores from barns, chicken houses, and bat caves

• identification

  • mold: small, tear-drop, microconidia; large, circular, spiny, macroconidia

  • yeast: unremarkable, single budding

Blastomyces dermatitidis

• blastomycosis - pulmonary infx that can spread to skin and bones

• distribution

  • moist environments

  • common in Ohio and MS River valleys

• identification

  • mold: single, smooth-walled, round conidia

  • yeast: broad-based buds w/ double walls

Coccidiodes immitis

• coccidiodomycosis - pulmonary infx that can spread to skin and bones

• distribution

  • southern CA, southwestern US, Mexico, and South America

• identification

  • tissue specimens show large spherules filled w/ spores

    • spherules are not yeasts

  • mold: septate hyphae w/ barrel-shaped conidia that alternate w/ empty cells

Paracoccidioides brasiliensis

• paracoccidioidomycosis - pulmonary infx that can spread to skin, mucosa, and reticuloendothelial system

• distribution

  • rainforests of central and south America

• identification

  • mold: mostly hyphae, unremarkable

  • yeast: large, round yeasts w/ circumferential budding; mariner’s wheel

Sporothrix schenckii

• sporotrichosis - cutaneous infx that can lead to lymph infx

  • ulcerative lesions

  • ‘Rose-gardener’s dx’

    • puncture wounds from contaminated plants

• identification

  • mold: delicate hyphae w/ conidiophores topped by clusters of microconidia

    • rosette morphology

  • yeast: oval or elongated, thin buds w/ narrow base