Klebsiella pneumoniae is a Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

, non-motile, encapsulated, lactose

Lactose

Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...

 fermenting

Fermentation (biochemistry)

Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

, facultative anaerobic, rod shaped bacterium found in the normal flora of the mouth, skin, and intestines.

It is clinically the most important member of the Klebsiella

Klebsiella

Klebsiella is a genus of non-motile, Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule. It is named after the German microbiologist Edwin Klebs...

genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of Enterobacteriaceae

Enterobacteriaceae

The Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...

.

Seven species of the Klebsiella genus, with demonstrated similarities in DNA homology are known. These are (1) Klebsiella pneumoniae, (2) Klebsiella ozaenae, (3) Klebsiella terrigena

Klebsiella terrigena

Klebsiella terrigena is a Gram-negative bacterial species of the genus Klebsiella. It has primarily been isolated from soil and water samples but rarely from humans. As such, it has shown no connection with disease in humans despite expressing many of the virulence factors expressed by other...

, (4) Klebsiella rhinoscleromatis, (5) Klebsiella oxytoca

Klebsiella oxytoca

Klebsiella oxytoca is a Gram-negative, rod-shaped bacterium that is closely related to K. pneumoniae, from which it is distinguished by being indole-positive; it also has slightly different growth characteristics in that it is able to grow on melezitose, but not 3-hydroxybutyrate.- Industrial uses...

, (6) Klebsiella planticola, and (7) Klebsiella ornithinolytica.