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Klebsiella

Klebsiella are encapsulated gram-negative, lactose-fermenting bacilli. They form pink colonies on MacConkey agar due to lactose fermentation. The main virulence factor is a polysaccharide capsule. Klebsiella pneumoniae (the most important pathogenic species) is commonly associated with lobar aspiration pneumonia in patients with alcohol-use disorder. It also causes nosocomial infections, such as hospital-acquired pneumonia and urinary tract infections, as well as tissue-destructing abscesses (liver, lung, spleen). Treatment is with cephalosporins for sensitive strains. However, many Klebsiella species have plasmids that confer multidrug resistance.

Last update:

February 3, 2021
7:24 am

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Classification

Gram negative bacteria classification flowchart — Gram-negative bacteria:
Most bacteria can be classified according to a lab procedure called Gram staining.
Bacteria with cell walls that have a thin layer of peptidoglycan do not retain the crystal violet stain utilized in Gram staining. These bacteria do, however, retain the safranin counterstain and thus appear as pinkish-red on the stain, making them gram negative. These bacteria can be further classified according to morphology (diplococci, curved rods, bacilli, and coccobacilli) and their ability to grow in the presence of oxygen (aerobic versus anaerobic). The bacteria can be more narrowly identified by growing them on specific media (triple sugar iron (TSI) agar) where their enzymes can be identified (urease, oxidase) and their ability to ferment lactose can be tested.
* Stains poorly on Gram stain
** Pleomorphic rod/coccobacillus
*** Require special transport media
Image by Lecturio.

General Characteristics

General characteristics

Gram-negative bacilli
Facultative anaerobes
Non-motile
Encapsulated (polysaccharide capsule)
Single, in pairs, or short chains
Form large, mucoid colonies
Major pathogenic species: Klebsiella pneumoniae

Biochemistry

Lactose fermenters:
- Ferment lactose to lactic acid
- Pink colonies on MacConkey agar
Urease positive: hydrolysis of urea into ammonia and carbon dioxide
Oxidase negative
Can use citrate and glucose as sole carbon sources
Can use ammonia as a sole nitrogen source

Habitats/reservoirs

Water/soil
Plants, animals, and insects
Normal flora of human nose, mouth, and gastrointestinal tract

Virulence factors

Polysaccharide capsule:
- Evades phagocytosis
- 77 different capsule serotypes
- K1 and K2 types are the most virulent.
Hypermucoviscosity phenotype:
- Production of mucoviscous exopolysaccharide web
- Associated with liver abscesses and other destructive tissue abscesses
- String test: > 5-mm viscous string when the colony on agar plate is stretched using a bacteriologic loop
Lipopolysaccharide:
- Lipopolysaccharide type O side chain
- Protects bacteria from complement-mediated membrane damage
Siderophores:
- Iron chelators
- Enhance iron uptake, which is vital for Klebsiella growth
Pili (fimbriae):
- Mediate adherence to epithelial and mucosal surfaces
- Formation of treatment-resistant biofilms

Klebsiella pneumoniae — Klebsiella pneumoniae: Scanning electron micrograph of Carbapenem-resistant K. pneumoniae interacting with a human neutrophil
Image: “Klebsiella pneumoniae bacterium” by NIAID. License: CC BY 2.0

Klebsiella mucoid colonies — Klebsiella pneumoniae: Scanning electron micrograph of Carbapenem-resistant K. pneumoniae interacting with a human neutrophil
Image: “Klebsiella pneumoniae bacterium” by NIAID. License: CC BY 2.0

Clinical Relevance

Epidemiology and transmission

Carrier rates:
- 5%–38% intestinal colonization
- 1%–6% nasopharyngeal
- Higher carrier rates:
  - Individuals with alcohol-use disorder (nasopharyngeal)
  - Chinese ethnicity (intestinal)
  - Hospitalized patients
Transmission:
- Nosocomial infection most common
- Community-acquired less frequent
- Person-to-person
- Associated with aspiration (pneumonia)
- Contamination from the environment (rare)
Risk factors:
- Alcohol-use disorder (community-acquired pneumonia)
- Impaired host defenses:
  - Hospitalization, especially if catheterized or intubated
  - Diabetes
  - Severe chronic obstructive pulmonary disease

Infectious manifestations

Pneumonia:

7.6% of hospital-acquired pneumonias (intubated and non-intubated patients)
In community-acquired cases, predilection for posterior segments of right upper lobe
“Currant-jelly” sputum
Fever, cough, dyspnea, pleuritic chest pain
Complications:
- Lung abscess (may mimic tuberculosis on chest X-ray)
- Empyema

Urinary tract infections (UTIs):

3rd leading cause of UTIs
Can cause lower (cystitis) and upper (pyelonephritis) UTIs
May be associated with ammonium magnesium phosphate (struvite) renal stones
In hospitalized patients with urinary catheters

Catheter-related bacteremia:

Associated with central venous catheters
Relatively infrequent cause (approximately 5%)

Less frequent infections:

Intra-abdominal:
- Liver abscess
- Spleen abscess
- Spontaneous bacterial peritonitis
Meningitis: usually associated with neurosurgical procedures
Endocarditis
Endophthalmitis
Skin and soft-tissue infections

Radiological (A) and pathological (B) representation of Klebsiella pneumonia — Radiological (A) and pathological (B) representation of Klebsiella pneumoniae: prominent voluminous hyperdense, symmetric bilateral lung consolidation, and the massive infiltration of neutrophils in the interstitium and intra-alveolar spaces
Image: “Fulminant Klebsiella pneumoniae pneumonia in an immunocompetent patient without alcohol-use disorder” by Benyashvili Z, Djirbe A, Assy N. License: CC BY 3.0

Mnemonic

To help remember the clinical manifestations of Klebsiella, remember “the 5 As of KlebsiellA:”

Aspiration pneumonia
Alcohol-use disorder
Abscesses in lungs and liver
Di-A-betes
“Curr-A-nt jelly” sputum

Antibiotic resistance

Some strains produce extended-spectrum beta-lactamases (ESBL).
Resistance to most beta-lactam antibiotics: cephalosporins, penicillins, monobactams, carbapenems
Some strains are also cross-resistant to other antibiotics (multidrug resistance).
Major risk factor: prior antibiotic exposure
Mediated by plasmids that encode beta-lactamases and other modifying enzymes
Plasmids exchanged via pili

Plasmid exchange in Klebsiella — Plasmid exchange in Klebsiella
A pilus allows for the exchange of replicated plasmid between 2 cells. As soon as the pilus is formed, the plasmid is replicated and then transferred through the pilus from the donor into the recipient cell.
Image by Lecturio.

Identification

Gram stain:
- Sputum: sensitivity about 50%
Cultures:
- Blood
- Urine
- Body fluids
- Abscess aspirates

Related videos

Klebsiella pneumoniae

References:

Wen-Liang Y., Yin-Ching C. (2019). Clinical features, diagnosis, and treatment of Klebsiella pneumoniae infection. Retrieved 1 January 2021, from https://www.uptodate.com/contents/clinical-features-diagnosis-and-treatment-of-klebsiella-pneumoniae-infection
Wen-Liang Y., Yin-Ching C. (2019). Microbiology and pathogenesis of Klebsiella pneumoniae infection. Retrieved 1 January 2021, from https://www.uptodate.com/contents/microbiology-and-pathogenesis-of-klebsiella-pneumoniae-infection

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