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Klebsiella, Enterobacter, and Serratia Infections


Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Feb 2020| Content last modified Mar 2021
Topic Resources

Klebsiella, Enterobacter, and Serratia are closely related gram-negative bacteria Overview of Gram-Negative Bacteria Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining is used on them. Gram-negative bacteria stain red when this process is used. Other... read more that occasionally infect the urinary tract or respiratory tract of people in hospitals or in long-term care facilities.

  • These bacteria may infect the urinary or respiratory tract, intravenous catheters used to give drugs or fluids, burns, wounds made during surgery, or the bloodstream.

  • Identifying the bacteria in a sample taken from blood or from infected tissue confirms the diagnosis.

  • If the infection is acquired in the community, antibiotics can cure it, but if it is acquired in a health care facility, it is difficult to treat because bacteria tend to be resistant to antibiotics.

Klebsiella, Enterobacter, and Serratia bacteria reside in the intestine of many healthy people and rarely cause infection in them. Infections with these bacteria are often acquired in hospitals and long-term care facilities. They usually occur in people whose resistance to infection is weakened and/or who have a medical device (such as catheters, drains, and airway tubes) in their body.

These bacteria may infect different places in the body:

Rarely, Klebsiella bacteria cause pneumonia in people who live outside a health care facility (in the community), usually in alcoholics, older people, people with diabetes, or people with a weakened immune system. Typically, this severe infection causes cough, bringing up a sticky, dark brown or dark red sputum, and collections of pus (abscesses Abscess in the Lungs A lung abscess is a pus-filled cavity in the lung surrounded by inflamed tissue and caused by an infection. A lung abscess is usually caused by bacteria that normally live in the mouth and are... read more ) in the lungs or in the membrane between the lungs and chest wall (empyema).

One species of Klebsiella produces a toxin that can cause inflammation of the colon and bleeding (hemorrhagic colitis) after antibiotics are taken. This disorder is called antibiotic-associated colitis. The antibiotics kill bacteria that normally reside in the intestine. Then Klebsiella bacteria are able to multiply and produce the toxin. However, antibiotic-associated colitis usually results from toxins produced by Clostridium difficile Clostridioides (formerly Clostridium) difficile-Induced Colitis Clostridioides difficile (C. difficile)–induced colitis is an inflammation of the large intestine (colon) that results in diarrhea. The inflammation is caused by toxin produced by C. difficile... read more .


  • Examination and culture of a sample of infected tissue

Doctors suspect one of these infections in people at high risk of getting one, such as people who live in a long-term care facility or in a place when there was an outbreak.

To confirm the diagnosis, doctors take a sample of sputum, lung secretions (obtained through a bronchoscope), blood, urine, or infected tissue. The sample is stained with Gram stain, cultured, and examined under a microscope. These bacteria can be readily identified.

Other tests depend on the type of infection. They may include imaging tests, such as ultrasonography, x-rays, and computed tomography (CT).


  • Antibiotics given intravenously

If an infection with any of these three bacteria is acquired in a health care facility, the infection is difficult to treat because bacteria acquired in such facilities are usually resistant to many antibiotics.

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