Staphylococcus epidermidis is a bacteria that, as the name implies, is found mostly on the skin of humans ("epidermis" is the medical term for skin).  The bacteria is a frequent "contaminant" of blood cultures drawn from children.  Routinely, when blood is drawn from children with a needle, the skin area is cleaned first with an alcohol swab.  If bacteria in the area are not destroyed by the alcohol, they can stick to the needle to be deposited into the drawn blood sample.  This makes the blood culture appear to be "positive." Once Staphylococcus epidermidis or a similar bacteria are identified after a few days of culturing, the bacteria can be declared a contaminant.  Staphylococcus epidermidis does cause infections in some cases.  Children with immunodeficiencies or with any medical device protruding throught the skin (i.e., a central venous line) can have a true Staphylococcus epidermidis bloodstream infection.

Diseases

Infections of foreign devices within the body

• Intravenous catheters
• Hemodialysis shunts and grafts
• Cerebrospinal fluid shunts (VP shunts)
• Peritoneal dialysis catheters
• Pacemaker wires and electrodes
• Prosthetic joints
• Vascular grafts
• Prosthetic cardiac valves

Infections in immunocompromised children

Infections of heart valves

Appearance (under a microscope)

Gram-positive cocci in clusters (like a cluster of purple grapes!)

Habitat and Transmission

• Staphylococcus epidermidis is found on th skin and mucous membranes of healthy children without symptoms.  This bacteria can spread to the bloodstream when a child is immunocompromised or when a medical device is left within the body (i.e., a central venous catheter)
• All children have varying degrees of Staphylococcus epidermidis and similar bacteria on the skin, therefore contagiousness is not important.

Weapons and defenses

• Contain the "plans" (plasmid DNA) for resistance to multiple antibiotics.  In some cases, these plans can be transmitted to other bacteria types (like Staphylococcus aureus).
• Forms "biofilms." Can attach to medical devices and form a layer of bacterial cells that is difficult to defeat with antibiotics.
• Cell wall components protect the bacteria like a shield and prevent destruction by antibiotics and white blood cells
• Has developed ways to resist the effects of many antibiotics.

Weaknesses

• Staphylococcus epidermidis is typically a weak pathogen (disease-causing thing).
• It typically requires a weak immune system or a implanted medical device to cause infection.
• Despite increasing bacterial resistance, antibiotics are available that treat Staphylococcus epidermidis  infections.

Photo - This colorized version of PHIL 259, depicts a scanning electron micrograph (SEM) of two Staphylococcus epidermidis bacteria. CDC/ Segrid McAllister. Janice Carr. Used with permission.