fungi 2

• Yeast


  • Microscopic (0.075 mm or 0.003 inch) in size
  • Reproduce through budding
  • Do not produce hyphae but can produce filamentous strings called pseudohyphae
  • Dimorphic fungi – ability to switch between two morphology (hyphae and yeast form)
• Types of fungal infections in humans

  • Superficial mycosis
  • Subcutaneous mycosis
  • Systemic mycosis
  • Opportunistic mycosis

  
• Superficial mycosis


  Fungal infection where fungi live exclusively on the dead layers of the skin and its appendages, with no contact with living tissue and no eliciting inflammatory response

  
• Superficial mycosis


  • Tinea (Pityriasis versicolor), Tinea nigra and piedra
• Cutaneous infection


  Fungal infection generally confined to the cornified layer of the skin and appendages, inducing various inflammatory and allergic responses in the host

  
• Cutaneous infection


  • Dermatophytosis caused by Dermatophytes
• Pityriasis versicolor (Tinea versicolor)


  Chronic, usually asymptomatic involvement of the stratum corneum
• Pityriasis versicolor has worldwide distribution, is more prevalent in tropics, and occurs mainly in young adults
• Causative agent of Pityriasis versicolor

  Malassezia furfur - Lipophilic, yeast-like fungus
• Pityriasis versicolor


  • Characteristic discrete or confluent macular areas of discolouration or depigmentation occur on the skin
  • The fungus may be demonstrated on normal skin and the disease may be considered an opportunistic infection

  
• Diagnosis of Pityriasis versicolor

  • Examination of skin scrapings shows an abundance of yeast-like cells and short, branched filaments
  • The fungus can be grown on Sabouraud dextrose agar covered with a layer of olive oil
• Tinea nigra


  Localized infection of stratum corneum, particularly of the palms, producing black or brownish macular lesions
• Causative agents of Tinea nigra

  • Exophiala werneckii
  • Exophiala castellanii
• Diagnosis of Tinea nigra

  • Skin scraping shows brownish, branched, septate hyphae and budding cells
  • Colonies on Sabouraud dextrose agar are grey or black in color
• Piedra


  Fungal infection of hair, characterized by the presence of firm, irregular nodules along the hair shaft, composed of fungal elements cemented together
• Varieties of Piedra


  • Black piedra- Piedraia hortae
  • White piedra – Trichospora beigelii
• Dermatophytoses (Tinea or Ringworm)


  Infection of keratinized structures (Hair, Nail and Skin) caused by a group of Keratinophilic fungi called Dermatophytes

  
• Dermatophytes


  • Hyaline filamentous fungi that digest keratin by enzymatic but unable to invade living tissue
  • Variety of pathological changes occur in the infected host because of fungi and their metabolic products
  • Resistant to chlorhexidine

  
• Genera of Dermatophytes


  • Microsporum (16 species)
  • Trichophyton (24 species)
  • Epidermatophyton (1 species)
• About 40 species of Dermatophytes are known to cause infections in humans and animals

  
• Dermatophytosis


  More common in males than females
• Clinical classification of Dermatophytosis

  • Tinea barbae (barber's itch)
  • Tinea corporis (Tinea glabrosa)
  • Tinea imbricata
  • Tinea capitis
  • Tinea cruris (jock itch)
  • Tinea pedis (athlete's foot)
  • Tinea manuum
  • Tinea unguium
• Causative agents of Dermatophytosis

  • Tinea capitis - Microsporum species, Trichophyton species
  • Favus - Microsporum gypseum, Trichophyton schoenleinii, Trichophyton violaceum
  • Tinea barbae - Trichophyton rubrum, Trichophyton mentagrophytes, Trichophyton verrucosum
  • Tinea imbricata - Trichophyton concentricum
  • Tinea corporis - Trichophyton rubrum and other Dermatophytes
  • Tinea cruris - Epidermatophyton floccosum, Trichophyton rubrum
  • Tinea pedis - Epidermatophyton floccosum, Trichophyton rubrum

  
• Clinical features of Dermatophytosis

  • Lesions in the skin tend to be circular, dry, erythymatous, scaly and itchy
  • Lesions of the hair include Kerion, scarring and alopecia
  • Favus: Dense crusts (Scutula) develop in the hair follicles, leading to alopecia and scarring
  • Kerion: Severe boggy lesions with marked inflammatory reaction that sometimes develops in scalp
  • Nails infected by Dermatophytes are deformed, friable and discolored with accumulation of debris under the nails
  • In lesions Dermatophytes appear as hyphae and arthrospores
• Pathogenicity of Dermatophytes


  • Dermatophytes grow only on the keratinized layer of the skin and its appendages, do not ordinarily penetrate living tissue
  • Fungal products may be responsible for inciting local inflammation
  • Hypersensitivity of fungal infection may play a vital role and may be responsible for sterile vesicular lesions
  • The reaction may follow oral antifungal therapy and confused with an allergic drug reaction (dermatophytids or id reactions)
  • Hypersensitivity can be demonstrated by skin testing with fungus antigen trichophytin

  
• Laboratory diagnosis of Dermatophytosis


  • Specimens: Scraping of skin and nail, Short length of plucked hair from scalp
  • Direct Microscopy examination: 10-20% KOH wet mount preparation, Wood's lamp examination for Tinea capitis
  • Culture: Sabouraud glucose neopeptone agar, Sabouraud dextrose agar, Dermatophytes Test Medium (DTM)
  • Cycloheximide –Inhibits the saprophyte molds, Gentamicin- and Chlortetracycline- Inhibit the bacteria, Phenol Red- indicator changes yellow to red within 14 days when the medium is alkaline as a result of dermatophytes
  • Incubation Temp: 25-30 ºC upto 21 days
• Colony characteristics of Dermatophytes

  • Trichophyton: Colonies may be powdery, velvety or waxy with pigmentation, Macroconidia - usually rare, elongated and blunt ends, smooth, thin walls & Variable in shape, Microconidia - abundant, arranged in clusters along the hyphae on conidiophores, Special hyphae - Spiral hyphae, Racquet hyphae, Favic chandeliers
  • Microsporum: Colonies are velvety, cottony or powdery with white to brown pigmentation, Macroconidia - Numerous, typically thick walled and rough, varying in shape (fusiform to obovate), No. of septa: 3-15 and size: 5-100 X 3-8 µm, Microconidia - Scarce, pyriform or clavate, usually arranged in singly along the sides of the hyphae
  • Epidermatophyton: Colonies are powdery and greenish yellow, Microconidia - Absent, Macroconidia - club shaped, 2-6 septa, Size: 20-40 X 6-8 µm in size, Thin and slightly thick walled and are singly or clusters
• Colony characteristics of some Dermatophyte species

  • Trichophyton mentagrophytes - White to tan, cottony or powdery pigment variable
  • Trichophyton rubrum - Velvety, red pigment on reverse
  • Trichophyton violaceum - Very slow growing, waxy, violet or purple pigment
  • Microsporum canis - Cottony, orange pigment on reverse
  • Microsporum audouinii - Velvety, brownish slow growing
  • Microsporum gypseum - Powdery buff colored
  • Epidermatophyton floccosum - Yellowish green, powdery
• Trichophyton mentagrophytes


  • Clusters of microconidia, cigar shaped macroconidia with terminal rat-tail filaments
• Trichophyton rubrum


  • Few, long, pencil shaped macroconidia
• Fungal spores


  • Roughened
  • Varying in shape (fusiform to obovate)
  • 3-15 septa
  • 5-100 X 3-8 µm in size
• Microconidia


  • Scarce, pyriform or clavate, usually arranged singly along the sides of the hyphae
• Epidermatophyton colonies


  • Powdery and greenish yellow
• Epidermatophyton microconidia


  • Absent
• Epidermatophyton macroconidia


  • Club shaped, 2-6 septa, 20-40 X 6-8 µm in size, thin and slightly thick walled, singly or in clusters

  
• Trichophyton mentagrophytes


  • White to tan, cottony or powdery, pigment variable
• Trichophyton rubrum


  • Velvety, red pigment on reverse
• Trichophyton violaceum


  • Very slow growing, waxy, violet or purple pigment
• Microsporum canis


  • Cottony, orange pigment on reverse
• Microsporum audouinii


  • Velvety, brownish slow growing