Coagulase-negative staphylococci (CoNS) are a type of staph bacteria that commonly live on a person’s skin. Doctors typically consider CoNS bacteria harmless when it remains outside the body. However, the bacteria can cause infections when present in large amounts, or when present in the bloodstream.

Doctors often divide staph bacteria into coagulase-positive and coagulase-negative types. Coagulase is an enzyme needed to make blood clot. This enzyme is present in Staphylococcus aureus (S. aureus) bacteria. Doctors typically associate this type with causing more serious infections.

Several different types of CoNS bacteria fall within this category. Often, each bacteria type may cause a different infection. Examples of these types include the following:

S. epidermidis

This CoNS bacteria type commonly live on the skin and don’t usually cause infections. A person who has a condition that compromises the immune system, such as lupus, is more likely to experience this infection type. Higher risk is also seen in people who have a foreign body implant, such as:

This bacterium causes skin infections and fever. The skin may be red, swollen, and inflamed. Sometimes the skin may leak pus.

S. saprophyticus

This CoNS bacteria type can collect in the urinary tract and cause urinary tract infections (UTIs). Symptoms associated with UTIs include:

  • pain when urinating
  • fever
  • flank pain, or pain in the lower back that radiates to the stomach
  • blood-tinged urine

S. lugdunensis

This bacteria species can cause infectious endocarditis. This is a serious infection on the heart valves, which can affect heart function and vessels away from the heart. The infection itself closely resembles endocarditis caused by S. aureus.

Symptoms of endocarditis may include:

  • fever
  • chills
  • aching joints
  • shortness of breath
  • chest pain when breathing
  • a new-onset heart murmur

These aren’t the only CoNS bacteria types. Others include:

  • S. simulans
  • S. hominis
  • S. haemolyticus
  • S. warnerii

The CoNS bacteria tend to thrive in warm, moist environments. These include the:

  • armpits
  • feet
  • groin
  • behind the knees
  • in the crook of the elbow
  • in the folds of the stomach

According to a 2007 review, most CoNS infections are nosocomial. This means a person is exposed to the bacteria in a hospital. A person may have had surgery or an illness that required a stay in the hospital where CoNS bacteria outside the body got into the body.

For this reason, it’s important that healthcare providers practice excellent hand hygiene. It’s also vital they practice sterile techniques when inserting catheters, starting IVs, and performing surgery.

Those who are at greatest risk for CoNS infections include:

  • People with a compromised immune system. This includes people with cancer, older adults, the very young, or those who have an autoimmune disorder.
  • People with an indwelling urinary catheter.
  • People with a central IV line. An example is a peripherally inserted central catheter (PICC) line.
  • People who’ve undergone certain procedures. This includes people who’ve had joint replacement surgery, a cerebrospinal fluid shunt, or a pacemaker, ocular, or cosmetic implant.

The presence of these risk factors is why many orthopedic surgeons won’t perform a joint replacement surgery on someone who has a skin infection. They will wait until the infection has healed.

Treating CoNS infections are traditionally difficult because many bacterial strains have become resistant to antibiotics. The medications doctors normally prescribe to kill the bacteria aren’t effective.

If a person has a CoNS infection, a doctor may perform what’s called a culture. They’ll take a sample of blood, tissue, body fluid, or all of these and send it to a laboratory.

Laboratory staff will then identify the infecting organism. They can do this in two different ways, using either the Kirby-Bauer antibiotic testing method or an automated system.

For the Kirby-Bauer method, a laboratory technician puts the bacteria into a special dish that has different types of antibiotics. For the automated method, a sample of bacteria is placed in a device that automatically exposes the bacteria to changing concentrations of antibiotic. For both methods, if the bacteria stops growing, a doctor can tell which antibiotic will kill the infection.

Smaller hospitals prefer the first method. Most academic centers prefer an automated system.

Doctors have been doing this for years. It’s given them a strong idea of the types of mediations that will kill different types of staph bacteria. This means doctors can start treating people as quickly as possible.

Doctors often initially prescribe a very strong antibiotic called vancomycin to treat CoNS infections. They usually give this medication through an IV. Then, based on the antibiotic data, they can choose a better antibiotic.

If a person has a severe CoNS infection, they may experience a condition known as sepsis. This occurs when the immune system triggers an inflammatory response due to the side effects of fighting the infection.

Sepsis can result in low blood pressure, which affects the body’s ability to send blood to vital organs. A person can experience organ failure due to sepsis. This makes it a life-threatening illness.

Symptoms associated with severe infection and sepsis include:

  • fast heart rate
  • fever, which may occur with shivering
  • mental confusion
  • pain or discomfort at a surgical site or IV access site
  • problems breathing and shortness of breath
  • sweaty or clammy skin

Seek immediate emergency medical attention if you suspect you or a loved one has sepsis.

When looking at all staph bacteria, CoNS bacteria tend to be less virulent. This means they cause fewer and less severe infections than other bacteria types. However, some people may experience severe infections related to these bacteria. This is especially the case for people with a compromised immune system.

Because CoNS infections are traditionally hard to treat, it’s important that a person see a doctor as early as possible. Early treatment will prevent the bacteria from continuing to multiply.