VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

CULTURAL CHARACTERISTICS

• The most common media for propagating dermatophytes are dermatophyte test medium (DTM) or Sabouraud's dextrose agar, a 2% agar containing 1% peptone and 4% glucose.
• Its acidity (pH 5.6) renders it mildly bacteriostatic and selec­tive.
• The selectivity is enhanced by addition of cycloheximide (500µg/ml), which inhibits other fungi, and gentamicin and tetracycline (100 µg/ml of each), or chloramphenicol (50 µg/ml).
• Dermatophytes are aerobes-and nonfermenters. Some attack proteins and deaminate amino acids.
• They grow optimally at 25°C to 30°C and require several days to weeks of incubation.
• Some dermatophytes in skin and hair (but not in culture) produce a green fluorescence due to a tryptophan metabolite that is visible under a Wood's light. Of animal dermatophytes, only Microsporum canis produces this reaction.