introduction to mycology ii

• Fungus can grow on


  • Bread
  • Meat
  • Fruits
  • Vegetables
  • Plant tissues
  • Fish skin
  • Walls and ceilings
  • Books
  • Different parts of the body (inside and outside)
• Mycosis


  Any fungal disease
• Chronic


  Fungi grow slowly
• Classification of fungal diseases based on pathological site


  • Superficial
  • Cutaneous
  • Subcutaneous
  • Systemic (deep)
  • Opportunistic
• Sources of fungal infection


  • Animals
  • Environment
• Domestic animals


  • Important sources of dermatophytes
• Animal sources


  • Pigeons and other bird droppings - carry Cryptococcus neoformans
  • Droppings at habitat of starling, chickens, and bats - source of Histoplasma capsulatum
  • Dog bite - Blastomyces
  • Bamboo rat in Thailand - Penicillium marneffei has been isolated
• Environment


  • Most pathogenic fungi are found in soil and associated vegetation
  • All opportunistic fungi are present in the rural, domestic, and hospital environment in the dust and air
• Pathogenic fungi in soil and air at endemic areas

  • Missouri-Mississippi river valley - Histoplasma capsulatum
  • Arizona, New Mexico - Coccidioides immitis
  • Ohio river valley - Blastomyces dermatitidis
  • Eucalyptus tree - Cryptococcus neoformans
• Routes of fungal transmission

  • Airborne - inhalation of fungal spores
  • Contact transmission - dissemination of spores / yeasts through skin-skin / skin-contaminated surface
  • Implantation / penetration through skin - (traumatic) implantation of fungal elements through skin
  • Use of intravenous devices
  • Vehicle-borne transmission
• Airborne transmission


  • Important transmission route for filamentous fungi (e.g. Aspergillus spp.)
  • Most common route of transmission in immunocompromised patients
• Contact transmission


  • Dermatophytosis
  • Outbreak of C. albicans - carried on the hands of healthcare workers
• Implantation / penetration through skin


  • Most important route of transmission for subcutaneous mycoses such as mycetoma, sporotrichosis, phaeohyphomycosis, and chromomycosis
  • Can cause mycotic keratitis
• Vehicle-borne transmission


  • Transmission of Candida and M. furfur through parenteral feed
  • Contaminated injectable anaesthetic agents
• Superficial mycoses


  • Confined to the non-living layer (top keratin-containing layer of the skin - stratum corneum) of the skin and extra-follicular part of the hair
  • Elicit no inflammation
  • No lesion, no pain, no itchiness or non-debilitating symptoms
  • Immune system does not respond to the presence of the fungus
• Different superficial mycoses

  • Malassezioses
  • Tinea nigra
  • Black piedra
  • White piedra
• Malassezioses


  Clinical forms of disease:

  Pityriasis (tinea) versicolor

  • hypo or hyperpigmented patches with scales on trunk, neck and upper arms

  Malassezia folliculitis

  • pruritic, follicular papules and pustules on the upper back, chest, shoulders, and less commonly the face and neck

  Seborrheic dermatitis

  • pruritic red patches with greasy scales on the scalp, eyebrows, nasolabial folds, ears, presternal area, axilla, and groin
  • cradle cap
• Malassezia


  Genus comprised of the Malassezia furfur-complex, a group of related lipophilic yeasts, and M. pachydermatis
• Malassezia identification


  • Skin scrapings examined with KOH-calcofluor white
  • Short, septatem occasionally branching filaments (2.5-4 µm)
  • Clusters of small, unicellular oval, or round budding yeast cells (4-8 µm)
  • Referred to as "spaghetti and meatballs"
  • Need oil to grow
• Tinea Nigra


  Asymptomatic, non-scaly, coin-sized, brown to gray patches on the palms and soles of young adults
• Tinea Nigra


  • Causative agent: Hortaea (Exophiala) werneckii
  • Confirmatory diagnosis: presence of pigmented hyphae on a potassium hydroxide (KOH) preparation
• Black Piedra


  Superficial infection of hair shafts by Piedraia hortae results in asymptomatic, stone-like concretions on scalp and facial hair
• Black Piedra


  • Alopecia does not occur, but hairs may break at the site of infection
  • Hairs with visible nodules should be plucked, treated with KOH and examined under the microscope
• White Piedra


  Discrete-to-coalesced nodules that typically are white, cream, or brown; found on facial, axillary, and pubic hair
• White Piedra


  • Causative agent: Trichosporon species including T. ovoides
  • Infection of perianal hair occurs with increased frequency in HIV-infected patients
  • Confirmatory diagnosis: hyaline arthroconidia, 2-4 septate hyphae, and differentiated blastoconidia that arise from loosely packed hyphae
• Tinea Nigra Treatment


  1. Topical therapy with an azole: miconazole, clotrimazole, econazole, or ketoconazole

  2. Other effective topical agents: naftifine, terbinafine, and Whitfield's ointment

  3. Oral therapy is rarely needed and griseofulvin is ineffective
• Piedra Treatment


  Black and white piedras may be treated with 2% ketoconazole shampoo
• Dermatophytoses


  Cutaneous mycoses caused by the agents of the genera: Epidermophyton, Microsporum, Trichophyton
• Dermatomycoses


  Cutaneous infections due to other fungi, the most common of which are Candida spp.
• Dermatomycoses

  • Affect deeper epidermal layer, producing more tissue destruction and symptoms
  • The fungus may secrete keratinase (enzyme that degrades keratin)
  • Infection is transmitted by direct contact or contact with infected hair (hair salon) or cells (nail files, shower floors e.g. in gyms)
• Primary Cutaneous Mycoses

  • Dermatophytoses
  • Dermatomycoses
• Dermatomycoses

  • Ringworm (Tinea capitis and T. corporis)
  • Athlete's foot (Tinea pedis)
  • Jock itch (Tinea cruris)
• Dermatophytes according to source of infection

  • Anthropophilic organisms
  • Geophilic organisms
  • Zoophilic organisms
• Anthropophilic organisms


  Acquired from other humans, infections are usually relatively noninflammatory
• Geophilic organisms


  Acquired from the soil
• Zoophilic organisms


  Acquired from animals, infections tend to be inflammatory
• Specimen collection

  Hair, skin, or nail scrapings collected for direct microscopic examination and culture
• Microscopy


  Material placed on glass slide, 20% KOH added
• There is a limitation in reporting if only KOH is used, so culture is also used to establish a more definitive diagnosis
• Culture


  A necessary adjunct to microscopic examination of specimens, important for therapeutic and epidemiological purposes