Skin Biopsy

by Jim Hutchinson

A variety of organisms may be associated with skin lesions and thus any growth of organisms other than normal skin flora should be considered significant.

Setup Prepare 3 touch preparation slides from fresh cut surfaces of representative material: one for Gram stain, one for KOH Calcofluor white stain (if requested) and one unstained (stored in the “extra smear” slide box).

Macerate the entire (or remaining) specimen with a small volume of sterile saline from the original container using a grinder.

Direct Examination

Gram stain

If fungus is requested, add: KOH Calcofluor stain

Culture

Media Incubation
Blood Agar (BA) CO2, 35°C x 48 hours
Chocolate Agar (CHOC) CO2, 35°C x 48 hours
MacConkey Agar (MAC) O2, 35°C x 48 hours

If fungus requested, add:

Sabouraud’s Heart Infusion Agar (SABHI) O2, 30°C x 4 weeks
SABHI with Chloramphenicol (SABHI-C) O2, 30°C x 4 weeks

Interpretation Examine the culture plates after 24 and 48 hours incubation. Any growth of organisms other than Normal Skin flora should be considered significant.
Reporting

Gram stain

Report with quantitation the presence of pus cells and organisms.

Culture

Negative Report
“No growth” or “Normal skin flora”

Positive Report
Quantitate all significant isolates with appropriate susceptibilities. If other organisms are also present, report as “Normal skin flora” with quantitation.

References H.D. Isenberg. 2004. Specimen Collection, Transport and Acceptability p. 2.1.1 – 2.1.28. In Clinical Microbiology Procedures handbook, 2nd Edition, Vol 1 ASM Press, Washington, D.C

H.D. Isenberg, 2004. Wound Cultures – Wound and Soft Tissue Cultures, p. 3.13.1.1 – 3.13.1.16. In Clinical Microbiology Procedures Handbook, 2nd Edition, Vol 1 ASM Press, Washington, D.C.

Cumitech 23 Infections of the Skin and Subcutaneous Tissues June 1988