''Klebsiella'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

, oxidase-negative, rod-shaped

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

with a prominent polysaccharide-based capsule. ''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 and other animals including humans. ''Klebsiella'' is named after German-Swiss microbiologist Edwin Klebs (1834–1913). Carl Friedlander described ''Klebsiella'' bacillus which is why it was termed Friedlander bacillus for many years. The members of the genus ''Klebsiella'' are a part of the human and animal's normal flora in the nose, mouth and intestines. The species of ''Klebsiella'' are all gram-negative and usually non-motile. They tend to be shorter and thicker when compared to others in the family Enterobacteriaceae. The cells are rods in shape and generally measures 0.3 to 1.5 µm wide by 0.5 to 5.0 µm long. They can be found singly, in pairs, in chains or linked end to end. ''Klebsiella'' can grow on ordinary lab medium and do not have special growth requirements, like the other members of Enterobacteriaceae. The species are

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...

but

facultatively anaerobic A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

. Their ideal growth temperature is 35° to 37 °C, while their ideal pH level is about 7.2.

List of species

* ''K. aerogenes'', previously known as ''Enterobacter aerogenes'' and ''Bacterium aerogenes'' * ''K. granulomatis'' * ''K. oxytoca'' * ''K. michiganensis'' * ''K. pneumoniae'' (type-species) ** ''K. p.'' subsp. ''ozaenae'' ** ''K. p.'' subsp. ''pneumoniae'' ** ''K. p.'' subsp. ''rhinoscleromatis'' * ''K. quasipneumoniae'' ** ''K. q.'' subsp. ''quasipneumoniae'' ** ''K. q.'' subsp. ''similipneumoniae'' * ''K. grimontii'' * ''K. variicola''

Features

''Klebsiella'' bacteria tend to be rounder and thicker than other members of the family Enterobacteriaceae. They typically occur as straight rods with rounded or slightly pointed ends. They can be found singly, in pairs, or in short chains. Diplobacillary forms are commonly found ''in vivo''. 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 A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

, and most strains can survive with

citrate Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the ...

and

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

as their sole

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...

sources and

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

as their sole

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

source. Members of the genus produce a prominent capsule, or slime layer, which can be used for

serologic Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mic ...

identification, but molecular serotyping may replace this method. Members of the genus ''Klebsiella'' typically express two types of

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...

s on their cell surfaces. The first, O antigen, is a component of the

lipopolysaccharide Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer ...

(LPS), of which 9 varieties exist. The second is K antigen, a capsular polysaccharide with more than 80 varieties. Both contribute to pathogenicity and form the basis for serogrouping. Based on those two major antigenic determinants several vaccines have been designed.

In humans

''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 Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...

, urinary tract infections,

sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...

, meningitis,

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...

, peritonitis and soft tissue infections. ''Klebsiella'' species have also been implicated in the pathogenesis of

ankylosing spondylitis Ankylosing spondylitis (AS) is a type of arthritis characterized by long-term inflammation of the joints of the spine typically where the spine joins the pelvis. Occasionally areas affected may include other joints such as the shoulders or hi ...

and other

spondyloarthropathies Spondyloarthropathy or spondyloarthrosis refers to any joint disease of the vertebral column. As such, it is a class or category of diseases rather than a single, specific entity. It differs from spondylopathy, which is a disease of the vertebra ...

. 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. During the last 40 years, many trials for constructing effective '' K. pneumoniae'' vaccines have been tried, and new techniques were followed to construct vaccines against ''Klebsiella''. However, currently, no ''Klebsiella'' vaccine has been licensed for use in the US. ''K. pneumoniae'' is the most common cause of nosocomial respiratory tract and premature intensive care infections, and the second-most frequent cause of Gram-negative bacteraemia and urinary tract infections . Drug-resistant isolates remain an important hospital-acquired bacterial pathogen, add significantly to hospital stays, and are especially problematic in high-impact medical areas such as intensive care units. This

antimicrobial resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. P ...

is thought to be attributable mainly to multidrug efflux pumps. The ability of ''K. pneumoniae'' to colonize the hospital environment, including carpeting, sinks, flowers, and various surfaces, as well as the skin of patients and hospital staff, has been identified as a major factor in the spread of

hospital-acquired infection A hospital-acquired infection, also known as a nosocomial infection (from the Greek , meaning "hospital"), is an infection that is acquired in a hospital or other health care facility. To emphasize both hospital and nonhospital settings, it is so ...

In animals

In addition to certain ''Klebsiella'' spp. being discovered as human pathogens, others such as ''K. variicola'' have been identified as emerging pathogens in humans and animals alike. For instance, ''K. variicola'' has been identified as one of the causes of bovine mastitis.

In plants

In plant systems, ''Klebsiella'' can be found in a variety of plant hosts. ''K. pneumoniae'' and ''K. oxytoca'' are able to fix atmospheric nitrogen into a form that can be used by plants, thus are called associative nitrogen fixers or diazotrophs. The bacteria attach strongly to

root hair Root hair, or absorbent hairs, are outgrowths of epidermal cells, specialized cells at the tip of a plant root. They are lateral extensions of a single cell and are only rarely branched. They are found in the region of maturation, of the root. Root ...

s and less strongly to the surface of the zone of elongation and the root cap

mucilage Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...

. They are bacteria of interest in an agricultural context, due to their ability to increase crop yields under agricultural conditions. Their high numbers in plants are thought to be at least partly attributable to their lack of a

flagellum A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

, as flagella are known to induce plant defenses. Additionally, ''K. variicola'' is known to associate with a number of different plants including banana trees, sugarcane and has been isolated from the fungal gardens of leaf-cutter ants.

References

External links

''Klebsiella'' article
from eMedicine.com {{Taxonbar, from=Q131854 Enterobacteriaceae Healthcare-associated infections Bacteria genera