87. Pathogenic importance of fungi. Dermatophytons.

Question 1

Dermatophytes?

Answer 1

DERMATOPHYTES
Key points:
- Members of Ascomycota
- Affinity to keratinized structures,
- colonize and invade skin, hair and nails
- Slow growing: Sabouraud + yeast extract is needed
- Obligate aerobic
- Tolerate cycloheximide in media
- Mycelium often pigmented
- Macroconidia formed in culture
- Arthrospores, shed from infected animals, remain infective for many
months
- Zoophilic group (M. canis, M. gallinae, T. equinum,
T. mentagrophytes, T. verrucosum) comprises obligate pathogens
- Cause characteristic circular skin lesions termed „RINGWORM”

Question 2

Trichophyton?

Answer 2

TRICHOPHYTON
skin, hair, feather ĺ ringworm
detection in skin scrapings
culture: Sabouraud medium + yeast extract + cycloheximide, pH 7, 1-4 weeks, 25°C
T. verrucosum: cattle, human
(culture, 25°C, 35 days; chlamydospores in chains)
T. equinum: horse, human
T. mentagrophytes: dog, cat, human, rabbit

Question 3

Microsporum?

Answer 3

MICROSPORUM ( similar to Trichophyton)
M. gypseum: dog, horse, human
M. canis: dog, cat, horse, human
M. nanum: swine
M. gallinae: chicken, turkey

Question 4

General features of fungi associated with disease in animals

Answer 4

General features of fungi associated with disease in animals
Eukaryotic
Non-photosynthetic
Widely distributed
Cell walls contain chitin and other polysaccharides
Heterotrophs, produce exoenzymes and obtain nutrients by absorption
Branching hyphae and unicellular yeasts are the two major forms
Reproduce both sexually and asexually with the production of spores
Grow aerobically at 25°C
Resistant to antimicrobial drugs which are effective against bacteria

Question 5

General features of fungi associated with disease in animals 2?

Answer 5

Majority are saprophytes, some cause opportunistic infections
Dermatophytes are pathogens that cause ringworm.
saprophytes: environmental fungi
commensal fungi
fungi of the skin and gut (sometimes facultative pathogens)

facultative pathogens:
Mycosis: (tissue invasion)
superficial: dermatomycosis (Candida sp., Malassezia pachydermatis)
dermatophytosis (Microsporum sp., Trichophyton sp.) (invasion and destruction of keratinized structures)
subcutaneous mycosis: (following penetration by foreign body)
systemic mycosis: prolonged AB therapy, immunosuppression
Mycotoxicosis: ingestion of fungal toxins which have been preformed in stored food or standing crops
Induction of hypersensitivity: (allergy) – rare – associated with Chronic Pulmonary Disease in cattle or horses