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Imogen McDougall Bench B 31/08/2016 ^[1]

Classification

Higher order taxa

Bacteria - Proteobacteria - Neisseriales - Neiseeriaceae - Kingella

Species

Species: Kingella oralis ^[2]

Type strain: UB-38 ^[1]

Description and significance

Kingella oralis was first discovered in a 1989 study conducted by Chen et al. The study focussed on Eikenella corrodens found in human oral samples ^[3] . It was noticed that during culturing and biochemical studies that there was a larger than expected level of variation for one species ^[3] . In 1990 Chen et al investigated these variants further and identified three Eikenella like species; UB-38, UB-204 and UB-294 ^[4] . Further studies on UB-38, Kingella oralis (originally Kingella orale) was conducted by Dewhirst et al. in 1993.

K.oralis has been found in a range of sites in the human oral cavity. It has been found in saliva, on mucosal surfaces and in dental plaque of both sub and supra-gingival origin ^[5] . In peridontally healthy individuals K. oralis is more prominent in subgingival plaques however in both adult and juvenile periodontitis cases, k. oralis is more common in the supraginigval plaques ^[5] .

This gram negative bacilli bacteria has been successfully cultured using a trypticase soy agar plate with 5% sheep blood and incubated in conditions designed to replicate the human oral cavity (37^oC, aerobic, 5% CO2) ^[3].

Due to K. oralis presence in subgingival and supragingival plaque and its potential association to periodontitis as described by Chen in 1996, this microorganism is important to study. A better understanding of K.oralis interactions with its host and other microorganisms as well as its biochemical pathways and lifestyle could lead to a better understanding of its association with periodontitis. This in turn could lead to advancements in diagnosis and treatments of this condition.

Genome structure

Strain: ATCC51147

Size: 2.4 Mb

GC content: 54%

Genes: 2435

Pseudogenes: 64

rRNA: 6 ^[6]

Cell structure and metabolism

K. oralis is a gram negative bacteria and has been found in dental plaque, both sub and supraginigval. It therefore can take part in biofilms, however it is unknown at what stage in biofilm formation K.oralis is involved. K.oralis cells are not motile on their own, they do not have flagella, instead they form spreading colonies ^[2]. This spreading ability may indicate a potential for twitching motility which has been observed in other Kingella, Eikenella and Neisseria species^[2]. K. oralis is a chemoorganotroph, it uses energy and carbon acquired by breaking chemical bonds in organic compounds. It is oxidase positive and catalase negative and can produce acid weakly from glucose but not other sugars^[2].

Ecology

K.oralis is an aerobe or faculative anaerobe and is found in dental plaque both supra and subgingival. It is believed that human dental plaque is the natural habitat for K.oralis, however it can be found in other areas of the oral cavity such as saliva and mucosal surfaces ^[2]. No evidence has yet been found of K.oralis in other environments. As the specific growth requirements are still unknown, this can not be said with extreme confidence ^[2].

Currently interactions between K.oralis and its human host are still unknown^[2].

Pathology

Currently the ability of K.oralis to produce disease in humans is unknown ^[2]. It has been found in both healthy and diseased individuals.

In Chen's 1996 study on the distribution of Kingella oralis in the human oral cavity, it was noted that K.oralis shared many phenotypic features and its distribution with Eikenella corrodens which has been associated to periodontitis ^[5]. Due to its poorly understood function in the human oral microbiome it is still possible that K.oralis may be involved in periodontitis.

Several research groups have looked into K.oralis involvement in other oral diseases such as root caries. These studies refer to K.oralis as a health associated bacteria, and have made a tentative link between its abundance and the health of the patients teeth ^[8] ^[9]

No evidence of disease outside the oral cavity by K.oralis has been observed. However its closest relative, Kingella kingae is an opportunistic and invasive pathogen. It can cause a range of diseases from bacteraemia to endocarditis ^[7].

While unsupported, it is possible that K.oralis could act as a plasmid reservoir, as supposed by Chen. K.oralis is related to K.kingae and Eikenella species, both of which have been known to exchange antibiotic resistance plasmids with other species. Chen suggested that, although not necessarily pathogenic itself, K.oralis could give plasmids to other pathogenic species possibly leading to more severe or harder to treat diseases^[2].

Application to biotechnology

There are currently no biotechology applications of K.oralis.

Current research

Due to the uncertain nature of this bacteria as pathogenic, there has been little research conducted specifically on K.oralis. In 2009 K.oralis whole genome was published as a reference genome for the Human Microbiome Project ^[6].

Originally K.oralis was thought to be associated with periodontitis ^[2] ^[3] ^[4], however more recently it is viewed as a health associated bacteria^[8] ^[9]. In several studies focusing on various oral diseases, it has been found that there is an association between a healthy subject and high levels of K.oralis. Presence of K.oralis has been seen to reduce root caries in the elderly^[8] and decrease dental caries in both permanent and deciduous teeth in children^[9].