At a Glance
Why Get Tested?
When to Get Tested?
Test Preparation Needed?
The Test Sample
What is being tested?
A bacterial wound culture is a test that is used to detect and identify pathogenic bacteria in a potentially infected wound. Wounds may be superficial breaks in the skin such as scrapes, cuts and scratches or may involve deeper tissues such as incisions, bites, punctures or burns. Any wound may become infected with a variety of bacteria. A culture helps to determine when a wound has become infected with specific types of bacteria, and which antibiotic would best treat the infection to aid wound healing.
A culture is performed by collecting a sample of fluid, cells or tissue from the wound and placing it on or in appropriate nutrient media. The media encourages the growth of bacteria that may be present, allowing for further testing and identification. Often in a sample from a wound infection there will be either a pure culture of a pathogenic microorganism (only one kind will be found) or one type will predominate within a mixture of organisms. In some cases, such as with a human or animal bite, there may be several pathogens present.
Wounds may harbor different types of organisms that have different requirements for growth. These organisms may be somewhat predictable from the site of infection so specific growth requirements from different specimen types are catered for within the laboratory. Some bacteria infecting a wound may require air for growth (aerobic) while some require a no-oxygen or reduced-oxygen environment (anaerobic or microaerophilic). Care must be taken when handling the samples so that their growth is encouraged and the probability of their detection and identification are optimized.
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 sample before it is cultured or on the bacteria found growing in the culture. One such test is the Gram stain. It involves placing sample or smearing individual colony types onto a glass slide and treating the slide 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 bacilli (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. This may require additional time in the laboratory to separate and identify each bacterial species.
The wound culture, Gram stain, and susceptibility testing all contribute to inform the doctor which pathogen(s) is present and what antibiotic therapy is likely to inhibit its growth.
How is the sample collected for testing?
A sterile swab may be used to collect cells or pus from a superficial wound site. From deeper wounds, aspirations of fluid into a syringe and/or a tissue biopsy are the optimal specimens to allow for the recovery of aerobic and anaerobic bacteria.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.