Klebsiella pneumoniae
A Gram-negative bacterium causing pneumonia and nosocomial infections.
Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It is the most significant member of the genus Klebsiella within the Enterobacteriaceae in clinical settings, capable of causing destructive lung infections and other nosocomial diseases.
- field
- Microbiology, Infectious Disease
- known_for
- Cause of Friedländer's pneumonia; nitrogen-fixing diazotroph; multidrug-resistant strains including NDM-1
- gram_stain
- Negative
- morphology
- Rod-shaped, encapsulated
- metabolism
- Facultative anaerobic
- natural_habitat
- Soil, normal flora of mouth, skin, and intestines
Lore & Background
The genus Klebsiella was named after German microbiologist Edwin Klebs. The bacterium is also known as Friedlander's bacillum in honor of Carl Friedländer, who proposed it as the etiological factor for pneumonia in immunocompromised individuals, such as those with chronic diseases or alcoholics. Community-acquired pneumonia caused by this bacterium may occasionally be called Friedländer's pneumonia. Klebsiella pneumoniae naturally occurs in soil, and about 30% of strains can fix nitrogen in anaerobic conditions. As a free-living diazotroph, its nitrogen-fixation system has been much-studied and is of agricultural interest, as it has been demonstrated to increase crop yields. It is closely related to K. oxytoca, from which it is distinguished by being indole-negative and by its ability to grow on melezitose but not 3-hydroxybutyrate. In recent years, Klebsiella species have become important pathogens in nosocomial infections. A hypervirulent variant (hvKp) has emerged, significantly more virulent than classical K. pneumoniae, causing disease in healthy individuals and infecting virtually every site of the body. hvKp originated from Asia and has a high mortality rate; it often spreads to the central nervous system and eye, causing endophthalmitis, nonhepatic abscesses, pneumonia, necrotizing fasciitis, and meningitis.
Reader's Guide
Klebsiella pneumoniae is a significant pathogen in both community and hospital settings. It is the most common cause of bacterial pneumonia outside the hospital among Klebsiella species, typically presenting as bronchopneumonia or bronchitis, with patients prone to lung abscesses, cavitation, empyema, and pleural adhesions. The bacterium possesses beta-lactamase, giving it resistance to ampicillin, and many strains have acquired extended-spectrum beta-lactamases conferring resistance to carbenicillin, amoxicillin, and ceftazidime. The emergence of New Delhi metallo-beta-lactamase (NDM-1) in strains from India and Pakistan has led to resistance against carbapenems. Hypervirulent K. pneumoniae (hvKp) is clinically concerning because it affects healthy individuals and can colonize the gastrointestinal tract, facilitating community spread. Environmental sources such as ready-to-eat vegetables, pork, public water, and fresh oysters have been found to harbor hvKp strains, underscoring the importance of surveillance. The bacterium's ability to fix nitrogen also gives it agricultural relevance, as it has been shown to increase crop yields.
Did You Know?
- Klebsiella pneumoniae is named after German microbiologist Edwin Klebs and is also known as Friedlander's bacillum.
- About 30% of strains can fix nitrogen in anaerobic conditions, and the bacterium has been demonstrated to increase crop yields.
- Hypervirulent K. pneumoniae (hvKp) can cause disease in healthy individuals and has been isolated from ready-to-eat vegetables, pork, public water, and fresh oysters.
- Strains with the New Delhi metallo-beta-lactamase (NDM-1) gene, discovered in India and Pakistan, are resistant to the intravenous antibiotic carbapenem.
Frequently Asked Questions
What is Klebsiella pneumoniae?
It is a rod-shaped, Gram-negative, encapsulated bacterium in the Enterobacteriaceae family and the most clinically significant species of the Klebsiella genus. It ferments lactose and can grow with or without oxygen, making it a versatile facultative anaerobe.
What diseases is Klebsiella pneumoniae known for causing?
It is the classic agent of Friedländer's pneumonia, a severe and destructive lung infection. It also frequently appears as a hospital-acquired (nosocomial) pathogen, particularly in immunocompromised or intubated patients.
Why are Klebsiella pneumoniae strains such a major concern in modern medicine?
Multidrug-resistant variants, especially those harbouring the NDM-1 carbapenemase gene, have become a serious threat in clinical settings. These strains resist nearly all available antibiotics and can spread rapidly among vulnerable, hospitalized patients.
Where does Klebsiella pneumoniae normally live?
It is a routine member of the normal flora in the human mouth, on the skin, and throughout the intestinal tract. It also colonises soil, so it is encountered in both environmental and human-associated niches.
What makes Klebsiella pneumoniae metabolically unusual for a gut bacterium?
It is a nitrogen-fixing diazotroph, meaning it can convert atmospheric nitrogen into biologically usable forms. This trait is rare among Enterobacteriaceae and gives it an extra metabolic edge in nutrient-poor environments.
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