Mycology. BioV 400. Clinical classification. Clinical classification. Fungi as Infectious Agents. Thermal dimorphism. Handout 6

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1 BioV 400 Mycology Handout 6 Fungi as Infectious Agents True or primary fungal pathogens invades and grows in a healthy, noncompromise d host Most striking adaptation to survival and growth in the human host is the ability to switch from hyphal cells to yeast cells Thermal dimorphism grow as molds at 30 C and as yeasts at 37 C Thermal dimorphism Clinical classification 3 The Superficial mycoses (or cutaneous mycoses) Confined to the outer layers of the skin, nail, or hair Rarely invading the deeper tissue or viscera The fungi involved are called dermatophytes The Subcutaneous mycoses Confined to the subcutaneous tissue Rarely spread systemically Form deep, ulcerated skin lesions or fungating masses Most commonly involving t he lower extremities The causative organisms are soil saprophytes introduced through trauma to the feet or legs Clinical classification Levels of invasion by fungal pathogens The Systemic mycoses May involve deep viscera and become widely disseminated Each fungus predilection for various organs The opportunistic mycoses Caused by ubiquitous saprophytes Occasional pathogens that inva de the tissues of those patients having Predisposing disease (diabetes, cancer, leukemia, etc.) Predisposing conditions (agammaglobulinemia, steroid or antibiotic therapy) 1

2 Dermatophytes The superficial (cutaneous) mycoses are usually confined to the outer layers of skin, hair, and nails Do not invade living tissues Keratinophilic fungi produce extracellular enzymes (keratinases) Superficial vs cutaneous Superficial mycoses Causative agents grow on the outer-most layers of the skin Do not evoke an immune reaction Cutaneous mycoses Confined to the keratinized layers Higher invasive properties Evoke a highly inflammatory reaction Superficial mycoses Limited to the keratinized tissues Skin (pityriasis versicolor and tinea nigra) Hair (black piedra and white piedra) Cosmetic problems (no physical discomfort) Easy to diagnose and treat Superficial mycoses Disease Pityriasis ve rsicolor Tinea nigra Black piedra White pie dra Fungus species Malassezia furfur Exophiala werneckii Piedraia hortae Trichosporon beigelii tissue Skin Hair Pityriasis versicolor Tinea ve rsicolor Discoloration or the skin (macular lesions) Chest, arm, and abdomen M. furfur (a lipophilic yeastlike organism) Diagnosis (KOH skin scrapings) Typical aspect of mycelia and spores Spaghetti and meatballs appearance Normal flora of the skin 2

3 Tinea nigra E. wernekii (dimorphic fungus) Brown to black lesions (macular) Produce melanin Diagnosis by direct visualization of KOH mounted skin scrapings Culture on Sabouraud s medium Tinea versicolor (Spaghetti and meatballs) Black piedra Hair infection (P. hortae) Teleomorphic state during infection Asci and ascospores Anamorphic state in culture Brown to black mycelia Hard nodules on infected hair Diagnosis by microscopic examination White piedra Hair infe ction (T. beigelii) Culture on Sabouraud s medium Septate hyphae arthoconidia blastoconidia (dimorphic fungus) Dire ct microscopic examination of the hair White (young culture) yellow (old culture) 3

4 Treatment Pytiriasis versicolor and tinea nigra Removal from the skin Micronazole nitrate Hair infection Shaving Prope r personal hygiene Dermatophytes Asexual stage Trichophyton (24) Microsporum (16) Epidermophyton floccosum Sexual stage Arthroderma ascomycota Not observed Disease Ringworm (Tinea) Natural habitat Keratinized tissues, soil, wild and domesticated animals Ecology Anthropophilic usually associated with humans only Zoophilic usually associated with animals transmission to man by close contact with animals Geophilic usually found in the soil transmitted to man by direct exposure Clinical manifestations Tinea corporis (small lesions everywhere) Tinea pedis (athlete s foot) Tinea unguium (nails) Tinea capitis (head) Tinea barbae (bearded areas) 4

5 Tinea corporis Tinea unguium T. rubrum Ringworm on the arm T. rubrum Members are found in the soil, humans or animals Leading causes of hair, skin and nail infections Tinea capitis Trichophyton Infect skin, hair and nails Take 2-3 weeks to grow in culture The conidia are large (macroconidia), smooth, thin-wall, septate (0-10 septa), and pencil-shape d Trichophyton rubrum is one of the most common cause of tinea Rarely can cause subcutaneous infections (in immuno-compromise d individuals) Microsporum May infect skin and hair, rarely nails One species (M. audouini) could easily be identified on the scalp because infected hairs fluoresce a bright green color when illuminated with UV The loose, cottony m ycelia produce macroconidia which are thick- walled and spindle-shaped Microsporumcanis is one of the most common dermatophyte species infecting humans Epidermophyton floccosum Infect skin and nails and rarely hair hyphae with multiple, smooth, club-shaped macroconidia of 2-4 cells 5

6 Onychom ycosis Epidermophyton or Trichophyton Destroying the toenails Ke toconazole (Oral) Therapy seems to be most effective for tinea versicolor and other dermatophytes Griseofulvin for infections involving the scalp and particularly the nails Itraconazole and terbinafine are the drugs of choice for onychomycoses 6