A bacterial wound culture is primarily ordered to help determine whether a wound is infected, to identify the bacteria causing the infection, and to prepare a sample for susceptibility testing where required.

If a wound culture reveals the need for a susceptibility test, it is often performed automatically and without an additional test having to be ordered by the doctor. This can save time so that antimicrobial therapy can begin as soon as possible.

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.

This test is primarily ordered when a doctor suspects that a wound is infected. It may also occasionally be ordered when a person has been treated for a wound infection to evaluate the treatment’s effectiveness and may be ordered when indicated to help guide the treatment of a chronic wound infection. Some signs and symptoms of an infected wound may include:

• a wound that is slow to heal;
• heat, redness and swelling at the site;
• tenderness at the site;
• drainage of fluid or pus;
• fever.

If pathogenic bacteria are identified in the culture, then it is likely that they are the source of the infection. Often wounds have two or more pathogens (aerobes and/or anaerobes) that may be contributing to the infection. If more than three organisms are present, they may not be identified as individual bacterial species, and the report may refer to them as “mixed bacterial flora.” This may indicate a mixture of normal flora and pathogens from a contaminated sample or from a dirty wound. If there is only normal flora present, then the infection may be due to bacteria normally found on the skin, or the pathogen may have been missed in the sample due to low numbers present, or the infection may be due to another cause.

Very little growth may still be significant, especially when the wound infection is in an area of the body considered to be essentially sterile – such as the eye.

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.

With burn wounds, quantitative culture results may be requested – the number of bacteria that grow are correlated to the number of bacteria in the infected wound. When burn tissue specimens have a specific bacterial count above a certain number, then removal of dead tissue (debridement) may be indicated.

Wound culture results may be less typical when the patient has already been treated with antimicrobial drugs and when a patient has a chronic infection.

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.