''Kingella kingae'' is a species of

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 ...

facultative anaerobic β-hemolytic coccobacilli. First isolated in 1960 by Elizabeth O. King, it was not recognized as a significant cause of infection in young children until the 1990s, when culture techniques had improved enough for it to be recognized. It is best known as a cause of

septic arthritis Acute septic arthritis, infectious arthritis, suppurative arthritis, osteomyelitis, or joint infection is the invasion of a joint by an infectious agent resulting in joint inflammation. Generally speaking, symptoms typically include redness, h ...

osteomyelitis Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children e.g. the femur and humerus, while the ...

spondylodiscitis Spondylodiscitis is a combination of discitis (inflammation of one or more intervertebral disc spaces) and spondylitis (inflammation of one or more vertebrae), the latter generally involving the areas adjacent to the intervertebral disc space. C ...

bacteraemia Bloodstream infections (BSIs), which include bacteremias when the infections are bacterial and fungemias when the infections are fungal, are infections present in the blood. Blood is normally a sterile environment, so the detection of micro ...

, and

endocarditis Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or the ...

, and less frequently lower respiratory tract infections and meningitis. There are four species of ''Kingella'': ''K. kingae'', the most common, is part of the bacterial flora of the

throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebrae. It contains the pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the trachea (windpip ...

in young children and is transmitted from child to child. When it causes disease, the clinical presentation is often subtle and preceded by a recent history of

stomatitis Stomatitis is inflammation of the mouth and lips. It refers to any inflammatory process affecting the mucous membranes of the mouth and lips, with or without oral ulceration. In its widest meaning, stomatitis can have a multitude of different cau ...

or upper respiratory infection. Other species are ''K. indologenes'', ''K. denitrificans'' (both causing

) and '' K. oralis'' found in dental plaque. One notable exception is in cases of endocarditis (heart valve infection), which can be more refractory to treatment. ''K. kingae'' is the fifth member of the HACEK group of fastidious Gram-negative bacteria that cause endocarditis. Routine laboratory tests may be normal because the organism is difficult to culture. Inoculating the fluid from infected joints directly into blood culture vials can enhance the chances of an accurate culture, but extended culture times are not helpful. The organism has also been known as ''Moraxella kingae''. ''K. kingae'' is oxidase-positive, catalase-negative, and beta-hemolytic.

Mechanism of infection

''Kingella kingae'' is thought to begin infection by colonizing the pharynx, crossing the epithelium by using an

RTX toxin The RTX toxin superfamily is a group of cytolysins and cytotoxins produced by bacteria. There are over 1000 known members with a variety of functions. The RTX family is defined by two common features: characteristic repeats in the toxin protein se ...

, and entering the circulation and reaching deeper tissues, such as bones and joints. ''K. kingae'' expresses

type IV pili A pilus (Latin for 'hair'; plural: ''pili'') is a hair-like appendage found on the surface of many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some r ...

, which allow for enhanced adhesion to respiratory epithelial and synovial cells and thus increased likelihood of colonization. These pili have also been shown to be reduced in number as pathogenesis progresses. σ54 regulates the transcription of pilA1, a major pilus subunit. PilS and PilR, regulatory transcription factors best known from the ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aerug ...

'' pilus system, also may regulate pilA expression. High levels of type IV pili on ''K. kingae'' are associated with spreading/corroding colony types, while low levels of type IV pili are associated with nonspreading/noncorroding colony types of ''K. kingae''. The three different types of populations are: spreading/corroding (with high-density piliation), nonspreading/noncorroding colonies (low density piliation), and domed colonies (no piliation, and thus no adherence to epithelium). Generally, respiratory and nonendocarditis infections tend to be highly piliated, while joint fluid, bone, and endocarditis blood isolates are less piliated, if at all.

Spondylodiscitis

Children under three years of age may become infected with ''K. kingae'' and develop spondylodiscitis. Typical symptoms include back pain, abdominal pain, and damage to the bones and joints. It generally targets the lumbar region of the spinal cord, and the only true way of diagnosing it is through biopsy or needle aspiration, as blood plate growth gives many false negatives.

Osteomyelitis

Osteomyelitis occurs in previously healthy children. The infection rate is poorly documented, thus the illness tends to go underdiagnosed. ''K. kingae'' can be transmitted person to person in rare cases. Diagnostic tools include low-grade fever, elevated inflammatory markers (ESR and CRP), but white blood cell counts are generally unreliable since they vary among infected patients. ''K. kingae'' infections are generally comcomitant with upper respiratory diseases or stomatitis, since disrupted respiratory or buccal mucosa is likely to facilitate bacterial invasion and hematogenous dissemination. The cause of osteoarticular infections is frequently not identified. Less than 15% of ''K. kingae''-positive clinical specimens reveal organisms on Gram stain. Infections due to ''K. kingae'' are treatable with a wide variety of

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...

, such as beta-lactams,

tetracyclines Tetracyclines are a group of broad-spectrum antibiotic compounds that have a common basic structure and are either isolated directly from several species of ''Streptomyces'' bacteria or produced semi-synthetically from those isolated compounds. T ...

, erythromycin, and

fluoroquinolones A quinolone antibiotic is a member of a large group of broad-spectrum bacteriocidals that share a bicyclic core structure related to the substance 4-quinolone. They are used in human and veterinary medicine to treat bacterial infections, as we ...

. Minimum inhibitory concentrations of

penicillins Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from ''Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum using ...

, rifampicin, and

azithromycin Azithromycin, sold under the brand names Zithromax (in oral form) and Azasite (as an eye drop), is an antibiotic medication used for the treatment of a number of bacterial infections. This includes middle ear infections, strep throat, pneumo ...

are easily achieved. Multiple studies have shown that inoculating synovial fluid or bone samples directly into blood culture bottles substantially increases the detection of ''K. kingae'' compared with direct plating of specimens on solid media. As an oropharyngeal colonizer, ''K. kingae'' is transmitted by respiratory secretions, saliva, and potentially oral contact with contaminated objects. Recent studies suggest ''K. kingae'' strains may demonstrate varying degrees of pathogenicity, which could support the person-to-person transfer of pathogenic ''K. kingae''. Infection has been shown to have high prevalence in the autumn and winter months.

Infections in adults

''K.kingae'' infections are rare in adults, but they occur in immunocompromised patients. Poor oral hygiene, pharyngitis, and mucosal ulceration are also predisposing factors for infection. The infection can occur in the respiratory or urinary tracts, as it is a part of the normal flora in those two areas, and will develop into

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 ...

. Most ''K. kingae'' are sensitive to beta-lactam antibiotics, but reports describe strains producing beta-lactamases. Options include aminoglycosides, macrolides and fluoroquinolones. ''K. kingae'' can also cause infectious endocarditis, in children as well as in adults.Debora Pierce, Bethany C. Calkins, Kirsten Thornton, Infectious Endocarditis: Diagnosis and Treatment, Am Fam Physician, 2012, 15;85(10):981-986

References

External links

''Kingella kingae'' at NCBI Taxonomy Browser (id=504)Type strain of ''Kingella kingae'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q1950143 Neisseriales Gram-negative bacteria