Skin Culture

Skin Culture

 

Definition

A skin culture is a test that is done to identify the microorganism (bacteria, fungus, or virus) causing a skin infection and to determine the antibiotic or other treatment that will effectively treat the infection.

Purpose

Microorganisms can infect healthy skin, but more often they infect skin already damaged by an injury or abrasion. Skin infections are contagious and, if left untreated, can lead to serious complications. A culture enables a physician to diagnose and treat a skin infection.

Description

Several groups of microorganisms cause skin infections: bacteria, fungi (molds and yeast), and viruses. Based on the appearance of the infection, the physician determines what group of microorganisms is likely causing the infection, then he or she collects a specimen for one or more types of cultures. A sample of material-such as skin cells, pus, or fluid-is taken from the infection site, placed in a sterile container, and sent to the laboratory. In the laboratory, each type of culture is handled differently.
Bacterial infections are the most common. Bacteria cause lesions, ulcers, cellulitis, and boils. Pyoderma are pus-containing skin infections, such as impetigo, caused by Staphylococcus or group A Streptococcus bacteria. To culture bacteria, a portion of material from the infection site is spread over the surface of a culture plate and placed in an incubator at body temperature for one to two days. Bacteria in the skin sample multiply and appear on the plates as visible colonies. They are identified by noting the appearance of their colonies, and by performing biochemical tests and a Gram's stain.
The Gram's stain is done by smearing part of a colony onto a microscope slide. After it dries, the slide is colored with purple and red stains, then examined under a microscope. The color of stain picked up and retained by the bacteria (purple or red), their shape (such as round or rectangle), and their size provide valuable clues as to their identity.
A sensitivity test, also called antibiotic susceptibility test, is also done. The bacteria are tested against different antibiotics to determine which will effectively treat the infection by killing the bacteria.
Fungal cultures are done less frequently. A group of fungi called dermatophytes cause a skin infection called ringworm. Yeast causes an infection called thrush. These infections are usually diagnosed using a method other than culture, such as the KOH test. A culture is done only when specific identification of the mold or yeast is necessary. The specimen is spread on a culture plate designed to grow fungi, then incubated. Several different biochemical tests and stains are used to identify molds and yeasts.
Viruses, such as herpes, can also cause skin infections. Specimens for viral cultures are mixed with commercially-prepared animal cells in a test tube. Characteristic changes to the cells caused by the growing virus help identify the virus.
Results for bacterial cultures are usually available in one to three days. Cultures for fungi and viruses may take longer-up to three weeks. Cultures are covered by insurance.

Preparation

After cleaning the infected area with sterile saline and alcohol, the physician collects skin cells, pus, or fluid using a needle or swab. If necessary, the physician will open a lesion to collect the specimen. To collect a specimen for a fungal culture, the physician uses a scalpel to scrape skin cells into a sterile container.

Normal results

Many types of microorganisms are normally found on a person's skin. Presence of these microorganisms is noted on a skin culture report as "normal flora."

Abnormal results

A microorganism is considered to be a cause of the infection if it is either the only or predominant microorganism that grew, if it grew in large numbers, or if it is known to produce infection.

Resources

Periodicals

Carroll, John A. "Common Bacterial Pyodermas." Postgraduate Medicine September 1996: 311-322.

Key terms

Pyoderma — A pus-containing skin infection, such as impetigo, caused by Staphylococcus or group A Streptococcus bacteria.
Sensitivity test — A test that determines which antibiotics will treat an infection by killing the bacteria.
References in periodicals archive ?
A skin culture was not performed in this case, although histopathologic results of the integument suggested a bacterial infection.
Paul Levick, who began his career as a consultant plastic, burns and trauma surgeon at the site, pioneered specialist techniques in reconstructive surgery - and set up Europe's first skin culture laboratory to grow new skin for burns victims.
Skin culture systems for research may be broadly categorised into those that attempt to replicate natural human skin in the in vivo situation ('mimic') and those that have limited structural and functional similarity to natural skin and consequently are only predictive for a limited range of parameters ('model').
The hospital patient's skin culture provided three lessons:
Has the presence or absence of Borrelia burgdorferi sensu lato as detected by skin culture any influence on the course of erythema migrans.
The cells were harvested by Dr Debra Balderson, a skin culture specialist, who runs a laboratory based at the burns unit.
Skin cultures were taken before and after incision.
Puigdemont's team verified the composition of their skin cultures microscopically, and their findings showed the tissue-engineered skin to be fully compatible with the original skin biopsies.
And among the dozens of other tests performed, such as stool ova and parasite analysis and skin cultures, none showed any evidence of infestation.
The concept was validated on living human skin cultures (phototype III) in which the UVAB induced 2-fold increase in the number of melanocytes was totally inhibited in the presence of Wonderlight.
EXHIBITION: Skinterfaces launches the Human Futures programme with an exhibition examining the limits between art and science including a coat made of skin cultures and a model brain with growing moss.
In-vitro studies of human skin cultures also found that N-acetyl glucosamine and niacinamide stimulated the production of hyaluronic acid and increased healthy collagen expression.