MSD Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Klebsiella, Enterobacter, and Serratia Infections


Larry M. Bush

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

Reviewed/Revised Apr 2022 | Modified Sep 2023
Topic Resources

Klebsiella, Enterobacter, and Serratia are closely related gram-negative bacteria Overview of Gram-Negative Bacteria Bacteria are classified by how they appear under the microscope and by other features. Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining... 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.

  • Infections caused by all three bacteria are treated with antibiotics given by vein (intravenously).

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 people with an alcohol use disorder, 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 Clostridioides 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... 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 by vein (intravenously)

Infections caused by any of these three bacteria are treated with antibiotics given intravenously. Antibiotics include cephalosporins, cefepime, carbapenems, fluoroquinolones, piperacillin/tazobactam, or aminoglycosides. However, sometimes these bacteria are resistant to many antibiotics, so doctors do susceptibility testing. If an infection with any of these three bacteria is acquired in a health care facility, the infection can be difficult to treat because bacteria acquired in such facilities are usually resistant to many antibiotics.

quiz link

Test your knowledge

Take a Quiz!