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= Mycoplasma orale = M. orale is a fairly new, very small bacterium found in the class Mollicutes. M. orale's fairly recent discovery provokes questions that still remain unanswered about various aspects of this species' existence; however, since it belongs to the Mycoplasma genus, some similar traits are known. Similar to other Mycoplasma species, M. orale is commonly associated with infections in humans and is not readily treated with antibiotics due to its lack of a peptidoglycan cell wall. It has also been known to contaminate laboratory experiments.

Discovery
L.G. Tallgren et al. published the first documented evidence of Mycoplasma orale in 1974. The first encounter was from a sample of bone marrow in a three-year-old boy suffering from Eosinophilic leukaemia around 1974. The sample was obtained from a bone marrow biopsy and occurred at Aurora Hospital in Helsinki, Finland. Arthurs noted this organism had a typical Mycoplasma "fried egg" appearance when cultured on media.

Genomics
The Mycoplasma genus is known for its incredibly small genome size. The genome of M. orale specifically has not been sequenced, but the average Mycoplasma species genome size is roughly 0.6 Mb. M. orale's 16S rRNA gene is 1,510 bp. This is the smallest discovered self replicating genome of all known organisms. One hypothesized explanation for this significantly reduced genome size is the evolution of this taxon into obligate parasites, thus making most of their metabolic pathways non-essential. Due to their significantly limited biosynthetic capabilities, Mycoplasma species typically invade and adhere to host cells from which they obtain their nurtrients usually at the expense of the host. Because of their small genome size, they lack many non-essential biosynthetic pathways, including specifically those for cell wall synthesis and purine synthesis. Therefore, they are a model genus for the Minimal Genome Concept. M. orale and the Mycoplasma genus in general have a low G+C content compared to other bacteria.

Hosts and Reproduction
M. orale is an obligate parasite found in humans and according to the GIDEON Guide of medically relevant bacteria, primates as well. M. orale may divide by binary fission or form mycelial filaments in colonies. The division via binary fission was found deeper within colony growth on agar while mycelial growth was found to occur more toward the surface of the media. Mycelial growth is more associated with an aerobic environment (surface) while binary fission is more associated with a deeper, less oxygen available environment.

Pathology
M. orale is considered under most circumstances to be non-pathogenic especially in immunocompetent individuals; however, abscesses have been noted in patients who are immunocompromised. A particular study was conducted on samples obtained from a 33 year old immunocompromised man who presented to physicians with a fever, significant weight loss, and shoulder pain among other significant laboratory findings. The samples obtained from the patient were cultured on media and tested via 16S rRNA sequencing confirming M. orale.

Taxonomic and Phylogenetic Classification
Mycoplasma orale is a species of bacteria belonging to the genus Mycoplasma as determined by 16S rRNA sequencing. It is most closely related to Mycoplasma salivarius and most distantly related to Mycoplasma mycoides. Mycoplasma orale and Mycoplasma salivarius were found in the same habitat, the human oral cavity, thus giving more evidence to their close proximity in the Mycoplasma genus.

Of the over 100 documented species in the genus Mycoplasma, 14 are known to infect humans. This is expected as the Mollicutes are common commensals or pathogens of several different organisms. Many species in the Mycoplasma genus are commonly found associated with pelvic or genital region infections including Mycoplasma fermentans and Mycoplasma hominis. Other species in this genus are causative agents of respiratory related infections; these species include Mycoplasma pneumoniae. The family of Mycoplastaceae includes the genera Mycoplasma and Ureaplasma. Bacteria in the Ureaplasma genus are known commensals in humans and contain the enzyme Urease, which catalyzes the breakdown of urea to carbon dioxide and ammonia.

Preliminary characterization
Mycoplasma orale has been cultured from the oral cavities of humans. This organism was found to grow optimally at pH 6.0, and Mycoplasma orale had phosphatase activity at .2 Ual/Mg of protein. Another distinguishing feature of the Mycoplasma genus is that they lack of a cell wall, thus treatment of infections by these organisms with antibiotics is difficult. It is also well known for its small physical size; on average the size is approximately 0.1 micrometer in diameter. All members of the Mycoplasma genus are obligate parasites and inhabit a wide range of hosts. Mycoplasma orale has an incubation period of 1-3 days and is considered to be mesophilic as it grows best at a temperature of 37 ̊C. Mycoplasma orale has been known to grow on 1076b. SP4-Z MEDIUM, a specialized media that can be obtained from the company DSMZ.