Although skin is home to many different microbial species, it is not the most hospitable place for most microorganisms, due to its dryness and relative saltiness. A skin swab is a way to sample the microbes living on the skin. As doctors typically are only interested in the bacteria, viruses or fungi that cause infection, a patient does not usually have healthy skin swabbed, just the infected areas. In certain situations, such as when the management of a health-care facility wishes to identify the presence of dangerous pathogens, healthy skin may be swabbed. This form of analysis is also important to researchers of microbial ecology and disease transmission.
Swabs for use in microbiology are typically bits of material that are completely sterile. The material of the swabs may be on the end of a long handle for the medical professional to hold. Different types of swabs exist, but they all perform the same function, which is to be rubbed over a surface in order to remove biological substances of interest. Swabs for skin are typically for picking up microbes, whereas some other types of swabs, such as cervical swabs, are designed to collect cells from the patient.
When a patient has an infection on the skin, the swabs that a medical professional may use to sample the infection can fall under the definition of a skin swab. Typically, the doctor takes the sample from the infected area, such as the abscess, and not from the unaffected surrounding skin. Sampling pus or liquid from an infected area is generally, however, more useful than a swab. Research is ongoing into the potential to use a skin swab to diagnose certain types of infectious disease, such as chlamydia, instead of more invasive swab tests.
Certain dangerous pathogens can travel harmlessly on some people's skin, but pose a risk to others if passed on. An example is Methicillin-Resistant Staphylococcus Aureus (MRSA) that is closely related to normal skin flora, but has evolved to be very resistant to antibiotics. This makes infection with the bacterium very risky, especially for people who are already sick, or who have open wounds.
MRSA can travel into hospitals on the skin of healthy, or sick, people, and become established in the hospital. When the staff of a health-care facility suspects that MRSA may be present, they may perform a skin swab test on the patients, to find out who, if anybody, carries the bacterium. Favorite places on the body for the bacterium includes the sides of the nose, the areas under the arm and skin overall.
Scientists who study the natural habitats of microbes are also interested in the results of skin swabs. These represent the population of microbes that can live naturally on the skin. Differences in population profile over time can also tell the scientists which microbes live there longterm and which use the skin as a transient home before moving on.