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:

  • Staphylococcusepidermidis (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 addicts etc), 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, but also in anaerobic conditions (without air). It forms white colonies on blood agar.

The hosts for the Staphylococcus epidermidis are humans and other warm-blooded animals (3).

How Is S. epidermidis Spread?

Staphylococcus epidermidis is spread by skin-to-skin contact. In hospitals it can spread by medical instruments, stethoscopes, oxygen masks, bed lining, and so on.

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 hard to diagnose and treat and may be life threatening.

Staph Endocarditis

A person with congenital heart defect may get endocarditis after bacteremia from tooth extraction, skin infection or infection of internal prosthetic devices (1).

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?

At most risk are individuals with (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), they secrete teichoic acid, which 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).

S. Epidermidis Antibiotic Resistance

Because of their massive use, Staphylococcus epidermidis has recently developed significant resistance to several antibiotics, and became (beside S.aureus) one of the leading cause of hospital-acquired infections (1).

Staph Epidermidis Treatment

Antibiotics should be used on the basis of antibiotic susceptibility test of a sample taken from an infected lesion. In general, most potent antibiotics are vancomycin, linezolid, daptomycin, gentamicin and rifampin (3).

Infected prosthetic valves, articles and cerebro-vascular shunts usually have to be removed and replaced (3).

Related Articles:

References:

  1. Staph epidermidis  (ispub.com)
  2. Biofilm and staph epidermidis antiibiotic resistance  (bioinfo.pl)
  3. hTreatment of S. epidermidis  (hopkins-abxguide.org)

Article reviewed by Dr. Greg. Last updated on August 3, 2013