Mycology
Services for routine mycological culture for isolation and identification of fungi are available.
Dermatophytes(Ringworm)
Choice of Sample Site
Use of a UV light can be a helpful adjunct in the selection of infected hairs for culture. Choose fluorescing hairs and skin fragments. The periphery of active lesions is the best area to obtain the samples. Hairs that are fluorescent, distorted, or fractured should be cultured. Culture of the basal portion of infected hair is recommended. Place at least 10-12 hairs in a sterile screw-cap container.
Preparation of Collection Site
To prevent bacterial interference with laboratory evaluation for fungi, the collection site should be cleaned if grossly contaminated. Soap and water may be used -- gently, to avoid mechanical removal of infected material. A gauze sponge soaked in 70% alcohol may be laid over the sample site for 30 seconds or wiped gently over the site. Let the site dry before collecting the sample. Avoid iodine or other fungicidal preps, as they may effect sterilization of the sample.
Cutaneous Specimens
- With a skin lesion, the area of infection should be washed off with a mild disinfectant or soapy warm water, (if the hair is very long- trim off the excess down to a length of about a 1/4"). The sample should be taken from the active border of the lesion by plucking the hair and scraping the area deeply to insure that (1) the root hairs just beneath the skin surface are obtained and (2) there is sufficient sample for a microscopic examination and 2 cultures. This sample should then be placed in a sterile cont.
- Skin scrapings are taken from an area previously cleansed with 70% alcohol on gauze sponges (use sterile water or broth if alcohol is not available). Scrape the entire periphery of the lesion(s) with a sterile scalpel or the edge of a glass slide. Place scrapings in a sterile screw-cap container or between clean glass slides in a slide holder, or inoculate fungal medium). Note: Lesions should be untreated with topical antifungal agents for at least 1 week before culturing.
- A skin biopsy specimen or punch biopsy specimen should be placed between two gauze squares moistened with sterile water or saline. Place these in a sterile screw-cap container.
- Do not use oil to collect the sample, DO NOT use a swab as these are absolutely useless for mycotic culturing and if submitting the sample with a scalpel blade place in a rigid container. The use of culture swabs for sample collection and transport is recommended only for environmental and cage evaluation.
- Recommended specimen container should have a wide mouth and be sterile, eg, sterile urine container or sterile pill bottle. Specimen should always be within the container - no hairs sticking out so as to eliminate the chance of contaminating any one/thing it may be in contact with during transit to the lab.
- For hair, a sterile toothbrush can be used to scrape active border areas showing scaling or hair loss. The back side of a scalpel blade may be used to scrape skin scales and crusts. Suspicious hairs (intact, broken, or stubs) can be plucked with clean hemostats or tweezers.
- To evaluate the incidence of lesionless, asymptomatic carrier rats, using a sterile surgical scrub brush (a variation of MacKenzie's hair brush technique), hold the animal over a sterile paper towel, drape, or glove wrap, and brush the animal so that hair, flakes, and cellular debris fall onto the sterile paper. Carefully fold the paper and submit to RRDA for culture.
- Biopsy and histopathology of affected skin is supportive in attributing lesion development to the dermatophyte if invasion of epidermal structures can be demonstrated. Histopathology services are available from RRDA.
- Systemic Mycoses - The deep seated mycoses (e.g.histoplasmosis) are handled in a special manner. They are yeasts in tissue and grow as molds at room temperature. With these diseases submit infected tissue for culture and histology as you would for a bacterial infection.
- Room temperature storage of these specimens is sufficient if there is to be any delay in transport.
- Do not refrigerate samples suspected of Histoplasma, Blastomyces, or Cryptococcus. Swabs should not be used, as the cotton fibers may be confused with hyphae on direct microscopic examination.
- Delayed processing of specimens for fungal culture is not as detrimental as with virolgic, parasitologic, or certain bacteriologic specimens.
- In general, if specimen processing is delayed, storage at room temperature is considered optimum. Storage at 4°C is usually acceptable; however, an occasional dermatophyte may not tolerate refrigeration.
- Only T. mentagrophytes is associated with ringworm in rodents and is more common in laboratory mice and guinea pigs than in rats. The asymptomatic carrier state may be common
- In rats, lesions are most common on the neck, back and base of tail, being scurfy or papular-pustular in appearance with irregular patchy hair loss instead of the classical circular areas of alopecia
- In guinea pigs, facial lesions are usually seen. With good husbandry and sanitation, the disease is usually self limiting
- In dogs and cats in the US, only three fungi cause 99% of all clinical cases of ringworm: Microsporum canis, M. gypseum, and Trichophyton mentagrophytes.
- Most dermatophytes require a minimum of 7-10 days for proper identification and are generally are held for 30 days
- Ringworm is contagious to man