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

DEMONSTRATION OF DERMATOPHYTES

• Dermartophytes can be demonstrated microscopically from the infected skin, hair or nails.
• Hair should be pulled out from the center and the edges of the lesions with forceps and treated in a drop of 10 to 40% KOH or lactophenol on a slide under a coverslip.
• The material is gently heated and seen under the microscope.
• The spores of Trichophyton are characterized by a linear parallel arrangement inside (endothrix) or outside (ectothrix) the hair.
• The spores of Microsporum surround the hair’s shaft in mosaic pattern.
• Culturally they can be grown on a number of common laboratory media, Sabouraud’s glucose agar being quite satisfactory.
• The specimens for cultural examination can be treated with 70% alcohol to prevent bacterial contamination.
• The incorporation of penicillin (10 units/ml) and streptomycin (40 units/ml) into medium are also suitable for the same purpose.
• Actidione (0.1 to 0.5 mg/ml) prevents overgrowth of saprophytic moulds.
• The incubation should be carried out at room temperature for about 2 weeks and examined early when growth is visible.
• The colonies may be smooth and waxy or with a chalky surface, producing a range of colours of the aerial mycelia in different species.
• For cultural examination a portion of the aerial growth is removed on the slide with the help of a sterile wire and treated in a drop of lactophenol cotton blue.
• The mycelium should be teased with a needle and gently heated after covering with a cover glass, before examination.