ISSN 2398-2969      

Fungal culture


Synonym(s): Dermatophyte test medium (DTM)


  • Dermatophyte test medium (DTM) is a selective medium for dermatophytes and is suitable to diagnose dermatophytosis in rabbits.
  • It contains Sabouraud dextrose agar with added gentamycin, chlortetracycline and cyclohexamide which inhibit non-dermatophyte growth. Phenol red is included as a pH indicator.
  • Dermatophytes utilize protein in the medium and create an alkaline pH which changes the medium from yellow to red.
  • The medium will change color soon as dermatophyte mycelium growth is noted.
  • Saprophytic fungi utilize carbohydrates first, so no color change occurs initially. Once carbohydrates are depleted and protein is utilized the medium will then change color after several days.
  • It is important to observe the DTM daily as a color change either before colonies are seen or during early visible growth is positive for dermatophytes.
  • DTM inhibits conidia formation and makes colony morphology less distinctive. Species identification requires additional culture on plain Sabouraud’s dextrose agar (SDA).


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login



  • Culture can be performed at room temperature, but 30°​C/86°​F is considered optimal; a small water dish should be added to the incubator to prevent insufficient humidity.
  • Avoid direct light as UV light inhibits fungal growth. Placing samples and cultures in a dark area is advised.
  • Positive results can be obtained after 5 days but culture must be continued for 14 days before a sample can be considered negative.
  • Species identification requires additional culture on plain Sabouraud’s dextrose agar:
    • Gross colony morphology is less distinctive on DTM.
    • Microscopic examination of conidia is required for definitive species identification and DTM inhibits growth.
  • On SDA species morphology is very distinctive:
    • Trichophyton mentagrophytes Trichophyton spp colonies are flat with a powdery to granular surface and may have a raised central tuft or folding. Color varies from white to buff with a yellow-brown underside.
    • Microsporum canis Microsporum canis colonies appear white and resemble cotton wool. They often have an orange-yellow undersurface.
  • Once colonies are observed, forceps can be used to gently touch the colony surface with a small section of acetate tape, eg Scotch pressure sensitive tape® (3M). Place samples on a slide with lactophenol cotton blue and examine under x100.
  • T. mentagrophytes conidia are long and cigar-shaped whereas M. canis are spindle-shaped, thick-walled and have a terminal knob .


  • Fungal culture can be performed in-house as long as samples are examined daily.
  • Commercial point-of-care test kits are available, eg Dermaphyt® (Kruuse).
  • Many commercial laboratories will offer the test, but samples should be submitted in paper to avoid false-negative results.



  •  Careful selection of sample material has a significant impact on successful culture.


  • Colonies are more easily identified on plain SDA.
  • Microscopic analysis of hyphae and macroconidia structure is required to identify species in addition to colony morphology.
  • False results can occur if interpretation relies on assessing only medium color change.  

Technique (intrinsic) limitations

  • Fastidious cultural requirements.
  • Plain SDA plates are prone to overgrowth by bacteria and saprophytes.
  • DTM limits ability to identify species morphology.

Technician (extrinsic) limitations

  • Interpretation is dependent on experience.

Result Data

This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Coyner K S (2010) How to perform and interpret dermatophyte cultures: Use this guide – put together by a veterinary dermatologist – to maximize your success with this indispensable in-house test. Vet Med 105 (7), 304-307.
  • Borman A M, Szekely A, Campbell C K & Johnson E M (2006) Evaluation of the viability of pathogenic filamentous fungi after prolonged storage in sterile water and review of recent published studies on storage methods. Mycopathologia 161 (6), 361-368 PubMed.
  • Canny C J & Gamble C S (2003) Fungal diseases of rabbits. Vet Clin North Am Exotic Anim Pract 6 (2), 429-433 PubMed.
  • Sinski J T, Wallis B M & Kelley L M (1979) Effect of storage temperature on viability of Trichophyton mentagrophytes in infected guinea pig skin scales. J Clin Microbiol 10 (6), 841-843 PubMed.

Other sources of information

  • Miller W H, Griffin C E & Campbell L (2013) Diagnostic Methods. In: Muller & Kirk’s Small Animal Dermatology. 7th edn. Elsevier Inc, USA. pp 86-91.


Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field