Dermatophilus congolensis

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  • Filamentous, branching actinomycete
  • Aerobic
  • Produces motile zoospores
  • No growth on Sabouraud dextrose agar
  • Dermatophilosis most prevalent in tropical and subtropical regions
  • Organisms found in scabs and in foci in skin of carrier animals
  • Dormant zoospores become activated when moisture and temperature levels are favourable
  • Zoospores may survive 3 years in scabs
  • Pathogenicity:
    • Does not usually invade healthy skin
    • Entrance after trauma or persistent wetting
    • Activated zoospores produce germ tubes which develop into filaments which invade the epidermis
    • Invasion causes an accute inflammatory response with many neutrophils
    • Microabscesses are formed in the skin
    • Raised crusts develop in the affected regions
  • Pathology
  • Diagnosis:
    • Giemsa-stained smears from scabs reveal branching filaments containing zoospores
    • Immunofluorescence
    • Scab material can be cultured on blood agar at 37 degrees centigrade, 2.5-10% carbon dioxide for 5 days
    • Zoospores can be cultured
    • After incubation, colonies are yellow and haemolytic (after 48 hours); they later become rough and yellow, and gain a mucoid appearance
    • No growth on Sabouraud dectrose agar
  • Clinical infections: