Bacterial Wound Culture (Aerobic wound culture; Anaerobic wound culture)
At a Glance
Why Get Tested?
When to Get Tested?
Test Preparation Needed?
The Test Sample
What is being tested?
The next step in the process is to identify the different types of microorganisms present. Identification is a step-by-step process that may involve many tests and evaluations performed on the bacteria found growing in the culture. One such test, the gram stain, involves smearing individual colony types onto glass slides and treating them with a special stain. Under the microscope, the bacteria can be classified into gram-positive and gram-negative organisms and by shape into cocci (spheres) or rods. With this information and additional biochemical tests, the types of bacteria present can be identified.
For many of the pathogens identified in the wound culture, antimicrobial susceptibility testing is required to guide treatment and to determine whether the strain of bacteria present is likely to respond to specific antibiotics. In order to do this, a pure culture (isolate) of the identified bacteria must be available, which may require additional time in the laboratory to separate and identify each bacterial species.
The wound culture, gram stain test, and susceptibility testing all contribute to inform the doctor which pathogen(s) are present and what antibiotic therapy is likely to inhibit their growth.
How is the sample collected for testing?
Is any test preparation needed to ensure the quality of the sample?
How is it used?
Gram stains are routinely performed on the original sample that is collected for the wound culture. This is done to give the doctor an initial evaluation of the wound – to look for any bacteria that might be present in the original sample. A gram stain that does not show the presence of bacteria does not rule out a wound infection.
A wound culture may also sometimes be ordered on a patient who has undergone treatment for a wound infection, to determine whether the treatment was effective. It may also be ordered at intervals on a person who has a chronic infection, to help guide further treatment.
If a fungal infection is suspected, then a fungal culture of the wound specimen may be ordered along with the bacterial wound culture. Yeast and some fungi may grow on the same media as bacteria, but many fungi are slow-growing. The media used to recover fungi inhibits bacterial growth and supports fungal growth for several weeks.
When is it ordered?
- a wound that is slow to heal;
- heat, redness and swelling at the site;
- tenderness at the site;
- drainage of fluid or pus;
What does the test result mean?
If there are no bacteria recovered in the wound specimen, then there may not be a bacterial infection, or the pathogen was not successfully recovered with the sample and test.
Is there anything else I should know?
Typically if an infection has spread from a wound into the blood and/or organs such as the kidneys, then the same microorganism(s) will be detected in blood and/or urine cultures.