Staphylococcus Epidermidis – Coagolase Negative Staphylococci

There are numerous species of bacteria that naturally live on the skin surface. These bacteria are referred to as the normal skin flora, just as naturally occurring bowel bacteria are known as the normal intestinal flora. Some of these bacteria are relatively harmless but can undergo changes where it may become pathogenic. It will result in an infection if the conditions are suitable, like when there is an open wound and the immune system is weakened.

What Are Coagulase Negative Staphylococci (CNS)?

Staph bacteria are noted as coagulase negative, if they do not coagulate during coagulase enzyme test. All staphylococci causing disease in human, (except Staphylococcus aureus), are coagulase negative and include:

  • Staphylococcus epidermidis (by far the most common CNS)
  • S.saprophyticus
  • S.lungudensis
  • S.haemolyticus
  • S.hominis
  • S.cohnii
  • S.warneri

What Is Staphylococcus Epidermidis?

Staphylococcus epidermidis (staph epidermidis, S.epidermidis / epidermis) is a part of a normal skin flora, and it is often attached to the upper layer of the skin (epidermis) or mucosa, without causing any symptoms (staph epidermidis carrier state). When the skin is injured (wounds, burns, intravenous drug usage and so on), Staphylococcus epidermidis may enter into deeper layers of the skin or even the blood and cause an infection.

Staphylococcus epidermidis is a gram positive, coagulase negative hemolytic. It grows in aerobic conditions (where air is present), but also in anaerobic conditions (without air). It forms white colonies on blood agar. Depending on the severity of the wound, the host’s immune system and any medical intervention, Staphylococcus epidermidis can cause mild to serious skin infections which may spread to deeper tissue.

The hosts for the Staphylococcus epidermidis are humans and other warm-blooded animals (3). It tends to live on the surface of host mammals as part of the normal surface floa.

How Is S. epidermidis Spread?

Staphylococcus epidermidis is spread by skin-to-skin contact. However, infection is not spread unless a person has an open wound and the bacteria gain entry into this wound. In hospitals it can spread by medical instruments, stethoscopes, oxygen masks, bed lining and so on. With the rise in multi-drug resistance, hospital acquired infections tend to be of greater concern.

How Is S. epidermidis Diagnosed?

Swabs from skin or mucosal lesions or blood samples have to be taken and sent to microbiological laboratory. Staphylococcus epidermidis is coagulase negative and non-hemolytic on blood agar, while Staphylococcus aureus is coagulase positive (some strains may still be coagulase negative), and hemolytic. For additional explanation see lab tests for staph.

Symptoms of S. Epidermidis Infection

Symptoms of a Staphylococcus epidermidis infection do not differ much from symptoms of S. aureus infection; both may be mild or life threatening.

Staph Skin Infections

Staphylococcus epidermidis and rarely Staphylococcus saprophyiticus may sometimes cause staph skin infections.

Staph Eye Infections

Staphylococcus epidermidis may cause infection of conjunctiva (conjunctivitis), cornea (keratitis) or hair follicles on the edge of the eyelid (folliculitis, stye) (1).

Urinary Infections

S.epidermidis and S. saprophyticus often cause hospital acquired urinary infections, mostly in old, catheterized patients with urinary tract complications.

Staph Sepsis

Sepsis (blood infection) with high fever, rapid heart beat and breathing, weakness, dizziness and affected consciousness often arise from skin vascular catheters, infected intestine in heavily ill patients or those receiving long term antibiotic treatment (1). Sepsis is one of the more serious complications of an infection as it can lead to death if left untreated. At times the symptoms may be vague and sepsis may not be immediately spotted.

Staph Endocarditis

A person with congenital heart defect may develop endocarditis after bacteremia from tooth extraction, skin infection or infection of internal prosthetic devices (1). Endocarditis is inflammation of the inner lining of the heart, including the heart valves. If left untreated or if severe, it may require replacement of the damaged valves. Endocarditis can be deadly.

Infection of Internal Prosthetic Devices

Persons with artificial heart valves, hips, cerebro-vascular shunts (meningitis), patients on peritoneal dialysis (peritonitis), operations of bones (osteomyelitis), eye operations (endophtalmitis) are all at greater risk to get Staphylococcus epidermidis infection.

Who Is at Risk to Get S. Epidermidis Infection?

Any person can develop a Staphylococcus epidermidis infection. However, this is rare in people with a healthy immune system and where there is good wound care. People who are at the greatest risk include the following (1):

  • Lowered immunity due to cancer, chemotherapy, AIDS, heavy disease (especially in old people), low birth weight (newborns)
  • Congenital heart or vascular disease
  • Internal prosthetic devices: artificial heart valves, artificial hip, cerebrovascular shunts, and so on
  • Vascular or urinary catheters, peritoneal dialysis
  • Skin diseases, injuries, burns
  • Injured gastrointestinal mucosa and those receiving oral antibiotics that kill normal gut bacteria and thus provide place for antibiotic resistant Staphylococcus epidermidis strains

Biofilm and S. Epidermidis Resistance to Macrophages

When Staphylococcus epidermidis bacteria settle on internal prosthetic devices (especially if these are made from polystyrene), it secretes a compound known as teichoic acid. This acid then forms a thin layer, called biofilm, into which bacteria are embedded and thus protected from the immune cells (macrophages) (1), and partly from antibiotics (2). It is one of the reasons why these infections can be difficult to treat and may tend to recur.

S. Epidermidis Antibiotic Resistance

Due to the overuse and incorrect use of antibiotics and antimicrobial topical applicants like ointments, Staphylococcus epidermidis has recently developed significant resistance to several antibiotics. In fact it as become one of the leading cause of hospital-acquired infections (1) second only to Staphylococcus aureus infections, particularly drug-resistant S. aureus.

Staph Epidermidis Treatment

Antibiotics should be used on the basis of an antibiotic susceptibility test of a sample taken from an infected lesion. In general, the more potent antibiotics are vancomycin, linezolid, daptomycin, gentamicin and rifampin (3). However, these antibiotics are also associated with various side effects and are only prescribed once laboratory tests indicate drug resistance. Infected prosthetic valves, articles and cerebro-vascular shunts usually have to be removed and replaced (3).

Related Articles:


  1. Staph epidermidis  (
  2. Biofilm and staph epidermidis antiibiotic resistance  (
  3. hTreatment of S. epidermidis  (
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