Skin cultures include samples taken from the skin, nail, and hair. Although many microorganisms exist in low numbers on the skin of a healthy person, skin cultures are used to identify organisms that cause integumentary infections such as cellulitis, pyoderma, impetigo, folliculitis, furuncles, and carbuncles. Fungal diseases such as athlete's foot, ringworm, rashes with well-defined borders, and tinea cruris (jock itch) are often evaluated via skin culture. Specimen collection methods are dependent on the sample site, but generally include a scraping, swabbing, or actual "clipping" of the specimen and its lesions; placement of the specimen in a growth medium, on a slide, or in an appropriate transport container; and laboratory incubation and examination of the specimen.
Hair culture specimens, such as hair stubs, shaft, and root, as well as scrapings from suspicious areas of the scalp, are clipped or plucked from the affected area and sent to the laboratory in a petri dish. A sterile scalpel or scissors are used to collect nail scrapings or clippings. Skin specimens include scrapings from the skin or several sites from the edge of a lesion, if present; fluid or pus obtained with needle aspiration; and material collected from moist, warm, skin folds that exhibit a rash with well-defined borders.
Normal Findings. Low numbers of microorganisms usually found on the skin; absence of large quantities of pathogenic microorganisms.
Variations from Normal. Boils and furuncles are caused by Staphylococcus aureus. Acne and pimples usually contain Staphyloccus epidermis or Propionibacterium acnes. Impetigo, a contagious skin infection, is caused by S. pyogenes or S. aureus.
The fungi Microsporum, Trichophyton, and Epidermophyton are associated with ringworm, athlete's foot, and tinea cruris and are cultured from the skin, hair, or nails. Trichophyton is a fungal pathogenic microorganism identified by skin, hair, and nail culture. Candida is found in skin and hair cultures, and Epidermophyton is usually cultured from hair and nails.
Interfering Circumstances. Improper collection techniques, contamination or alteration of the specimen, and a delay in transport to the laboratory interfere with culture results.
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