Finding the right tests…
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Emergency services available 24 x 7
Finding the right tests…
Microbiology
When a wound, boil, or abscess is draining pus, your doctor often needs to know exactly which bacteria are inside it before deciding what antibiotic will actually work. A sample of the pus is collected, either by swab or by drawing fluid out with a syringe, and sent to the lab to grow. This matters most for wounds that keep draining, aren't healing on the antibiotic already prescribed, or affect someone with diabetes or a weak immune system, since guessing wrong on the antibiotic can let the infection spread deeper into the tissue underneath the skin.
This test identifies which bacteria are growing in pus from an infected wound, boil, or abscess, and then checks which antibiotics work against that specific organism. A methicillin-resistant staph infection, for instance, needs a different drug than an ordinary skin infection, and the two look identical to the eye. The result also tells your doctor whether more than one type of bacteria is present, which is common in deeper or longer-standing wounds, and whether the infection is likely to respond to a standard antibiotic or needs a more targeted one.
Redness, warmth, and pus-like drainage can come from several different bacteria, and some of the most concerning ones, including drug-resistant staph, look no different from ordinary skin infections until they're grown in the lab. A culture replaces that guesswork with an actual identification.
A clinician either swabs the draining wound directly or, for a closed abscess, draws fluid out with a needle and syringe before it's opened. The sample is placed onto growth plates in the lab, where any bacteria present multiply into colonies large enough to identify. Each colony is then tested against a panel of antibiotics to see which ones stop it from growing.
Bacteria need to multiply many times over before there's enough of them to identify and test, which is why a culture takes noticeably longer than tests that just look at a sample under a microscope. Slower-growing organisms extend that further.
A negative culture means no organism grew, which points away from a bacterial cause or suggests antibiotics already started may have suppressed growth. A positive result names the organism and lists which antibiotics it's sensitive or resistant to, which is what actually guides the prescription change.
For an open, draining wound, a sterile swab is wiped across the drainage. For a closed abscess, a clinician draws the fluid out with a needle and syringe, usually right before or during drainage of the abscess.
A visible infection can be caused by several different bacteria that look identical on the skin, including drug-resistant ones. A culture identifies the actual organism so the antibiotic chosen is one it's known to respond to.
Mixed growth is common in deeper wounds, bite wounds, or infections that have been present a while, since more than one type of bacteria can colonize the same site. Your doctor uses the sensitivity results for each organism found to choose treatment.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes. Antibiotics started before the sample is taken can suppress bacterial growth and cause a falsely negative culture. Tell your doctor or the centre about any antibiotics you've already taken.
No. An MRSA screening swab checks specifically for that one resistant bacteria, usually from the nose, to see if you carry it without infection. A pus culture identifies whatever is actually causing an active, draining infection, which may or may not be MRSA.
It means no bacteria grew from the sample, which can happen if the cause isn't bacterial or if antibiotics taken beforehand suppressed growth. Your doctor weighs this alongside how the wound looks and responds to treatment.