Wound Cultures and Biopsies

Unlike years ago, several methods are now available for obtaining and analyzing wound samples. A wound culture is a diagnostic test used to identify microorganisms such as bacteria, fungi, or viruses that may be growing inside a wound. A skin, tissue, or fluid sample is extracted from the affected area and placed in a special container with a nutrient-enriched substance (culture medium) that supports the growth of microorganisms. If nothing substantial grows, the results of the culture are negative. Conversely, any growth of infection-causing microorganisms (pathogens) yields a positive culture result. These pathogens may then be identified using a microscope, chemical test, or combination thereof.

Aerobic (with oxygen) cultures are always included in wound cultures. Direct-smear evaluation (gram stain) and anaerobic (without oxygen) cultures are only performed on wound samples when indicated or ordered by a physician. The purpose of a wound culture is to identify and isolate any infection-causing bacteria or fungi so that effective antibiotics against those microorganisms can also be identified. Cultures are typically analyzed by scientists and medical technologists specializing in clinical microbiology.

Most infected wounds contain multiple microorganisms (pathogens).
These are the most common pathogens isolated from wounds:

• Aeromonas
• Bacteroides
• Candida
• Clostridium
• Enterobacter
• Enterococci
• Escherichia Coli
• Fusobacterium
• Klebsiella
• Peptostreptococcus
• Proteus
• Pseudomonas
• Streptococcus
• Staphylococcus aureus

Not only does wound infection prevent healing, the microorganisms can spread to other parts of the body, including the bloodstream. Septicemia (infection in the blood) can be fatal. As a result, it is critical to identify and treat an infected wound as soon as possible with an appropriate regimen of antibiotics to promote healing and prevent further complications.

Because it is the least invasive, the swab culture technique is the most widely used. However, a swab culture can only access organisms on the wound’s surface while missing those within the tissue. For that reason, many clinicians find it to be an ineffective way to accurately measure infection in a wound.

Although it’s moderately invasive and not always feasible, clinicians typically prefer a biopsy sample. For this method, the patient is given a local anesthetic before the tissue is removed with a cutting sheath. Bleeding is controlled throughout the biopsy procedure by applying gentle pressure to the wound.

Needle aspiration is a less-invasive technique used in wounds with minimal skin loss, for instance, puncture wounds. For this method, a small, 22-gauge needle is inserted. To obtain a sample of the fluid to be analyzed, the clinician pulls back on the plunger and changes the needle’s angle two or three times while removing fluid from different wound areas.