Klebsiella Pneumoniae: A Leading Cause of Hospital Infections

A microscopic image of Klebsiella bacteria (yellow).

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Medical students classically associate Klebsiella pneumoniae with pneumonia affecting homeless people dependent on alcohol. However, the bacteria Klebsiella pneumonia is most prevalent in hospital settings and a leading cause of nosocomial infection. ("Nosocomial" is medical jargon and refers to disease originating in the hospital.)

Klebsiella pneumoniae is a gram-negative rod encased in a thick polysaccharide capsule. On a related note, this thick capsule makes the bacteria hard to treat with antibiotics. 

Where It's Found

In 5% of the population, Klebsiella pneumoniae resides in the gut (feces) and respiratory tract. Unlike E. coli, another common gut (enteric) bacteria, Klebsiella is also found naturally growing in environmental reservoirs like soil and surface water, without a source of fecal contamination. It is spread by contact.

Klebsiella Infection

Klebsiella pneumoniae poisons the body by means of an endotoxin located within the bacteria and not by an (excreted) exotoxin.

As you can probably surmise from its name, Klebsiella pneumoniae can cause bacterial pneumonia. Pneumonia is an infection of the lungs which results in fever, chills, shortness of breath, fatigue and more. Typically, Klebsiella pneumonia is rare except among members of the community with alcohol dependence. 

Klebsiella pneumonia usually hits the right upper lung lobe and results in cavitation and pyogenic (aka pus-producing) tissue death (aka necrosis); this distinct pathophysiology is evident on chest X-ray.

In hospital settings, Klebsiella pneumoniae can ascend from the gut and cause a urinary tract infection or infect by means of a urinary catheter. Moreover, especially among children hospitalized in the pediatric ICU (PICU), Klebsiella pneumoniae can cause life-threatening blood infection (aka septicemia) and septic shock.

There are subspecies of Klebsiella pneumoniae which cause particularly terrible sickness: Klebsiella ozaenae and Klebsiella rhinoscleromatis. Infection with Klebsiella ozaenae can result in malodorous wasting away (atrophy) of the nasal mucous membranes. Somewhat similarly, Klebsiella rhinoscleromatis causes rhinoscleroma, a destructive nodular inflammation of the nose and throat. 

Diagnosis and Treatment

A diagnosis of Klebsiella pneumoniae is based on medical history, physical exam, diagnostic testing (think X-ray), and laboratory testing.

When possible, physicians prefer to treat Klebsiella pneumoniae with quinolones or third- or fourth-generation cephalosporins. However, certain strains of Klebsiella pneumoniae are resistant to conventional antibiotics, and bacterial resistance profiles must be checked when testing and treating the disease.

Beginning in the 1970s, strains of Klebsiella pneumoniae resistant to aminoglycosides began to take hold. These strains were soon followed by extended-spectrum beta-lactamase producing Klebsiella which were resistant to penicillins and cephalosporins. 

More recently, strains of carbapenem-resistant Klebsiella have emerged in hospitals. Carbapenems are powerful antibiotics used as last-line treatment. The fact that Klebsiella has microevolved to resist these drugs worries members of the medical community.


Because Klebsiella pneumoniae most often causes infection in hospitalized patients—especially those who have been in the hospital a long time and have weakened immune systems (think ICU)—it's imperative that inpatient health care personnel do their best to minimize the spread of the bacteria.

In addition to keeping medical instruments clean and minimizing the length of time that indwelling catheters are placed, hand washing is a prime defense against infection. Even as a loved one visiting a friend or family member in the hospital, it's an excellent idea to keep your hands washed and off the medical equipment.

On a final note, for more than 40 years, researchers have been searching for a vaccine to prevent infection with Klebsiella pneumoniae. Currently, there are several independent groups working on such a vaccine.

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