TAXONOMY: cellular organisms -> Bacteria -> Proteobacteria -> Gammaproteobacteria -> Enterobacteriales -> Enterobacteriaceae -> Klebsiella
Klebsiella is a genus of nonmotile, Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule. It is named after the German microbiologist Edwin Klebs (1834–1913). Klebsiella species are found everywhere in nature. This is thought to be due to distinct sublineages developing specific niche adaptations, with associated biochemical adaptations which make them better suited to a particular environment. They can be found in water, soil, plants, insects, animals, and humans. They have no specific growth requirements and grow well on standard laboratory media, but grow best between 35 and 37 °C and at pH 7.2. The species are facultative anaerobes, and most strains can survive with citrate and glucose as their sole carbon sources and ammonia as their sole nitrogen source. Klebsiella species are routinely found in the human nose, mouth, and gastrointestinal tract as normal flora; however, they can also behave as opportunistic human pathogens. Klebsiella species are known to also infect a variety of other animals, both as normal flora and opportunistic pathogens. Klebsiella organisms can lead to a wide range of disease states, notably pneumonia, urinary tract infections, septicemia, meningitis, diarrhea, and soft tissue infections. Klebsiella species have also been implicated in the pathogenesis of ankylosing spondylitis and other spondyloarthropathies. The majority of human Klebsiella infections are caused by K. pneumoniae, followed by K. oxytoca. Infections are more common in the very young, very old, and those with other underlying diseases, such as cancer, and most infections involve contamination of an invasive medical device.
The Voges–Proskauer test is usually positive. Lactic, acetic, and formic acids are formed in smaller amounts and ethanol in larger amounts than in a mixed acid fermentation. All strains utilize l-arabinose, d-arabitol, d-cellobiose, citrate, d-fructose, d-galactose, d-glucose, 2-ketogluconate, maltose, d-mannitol, d-melibiose, d-raffinose, d-trehalose, and d-xylose as sole carbon sources. With the exception of some K. pneumoniae subsp. ozaenae strains, all Klebsiella strains utilize myo-inositol, l-rhamnose, and sucrose as sole carbon sources. With the exception of some K. pneumoniae subsp. ozaenae and K. pneumoniae subsp. rhinoscleromatis strains, all strains utilize lactose and d-sorbitol as sole carbon sources. No strain utilizes betaine, caprate, caprylate, glutarate, itaconate, 3-phenylpropionate, and propionate. H2S is not produced, β-glucuronides are not hydrolyzed, and l-tryptophan and l-histidine are not deaminated. Ornithine is not decarboxylated by klebsiellae strains except K. mobilis, K. ornithinolytica, and rare strains of K. pneumoniae. Most strains hydrolyze urea and β-galactosides. Some strains fix nitrogen. Occur in intestinal contents, clinical specimens from humans and animals (e.g., horses, swine, monkeys), soil, water, or on plants.
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]