Higher order taxa
Description and significance
The Lautropia mirabilis is a motile Gram-negative, facultatively anaerobic bacterium. It was first referenced by J. Ørskov in 1930 before being identified by Gerner-Smidt et al. as a distinct species belonging to the beta subgroup of Proteobacteria in 1994 . It is an aggregate-forming, coccoid bacterium that has been found in oral and pulmonary sites including the oral cavities of children infected with human immunodeficiency virus (HIV)  and the sputa of a patient with cystic fibrosis .
The annotated linear genome of Lautropia mirabilis ATCC 51599 was completed in April of 2017. Composed of 3151925 nucleotides, it has a high G-C content (65.5%). Of the 2595 genes present, 2498 code for proteins, 51 as pseudo genes and 41 tRNAs (4). Plasmids are not associated with this species .
Cell structure and metabolism
As a gram-negative bacterium L. mirabilis stains pink under the Gram test. Lautropia mirabilis can be cultured on most enriched media and observed using phase contrast microscopes in wet mounts . Strain-specific cellular fatty acid (CFA) composition of the bacteria in conjunction with its coccoid morphology and capacity to ferment D-glucose can be used for identification  in addition to 16S rRNA gene sequencing . The colonies are highly pleomorphic with cell diameters ranging from 1 to >10µm  and three distinct colony morphologies based upon age  suggesting distinct developmental stages when in communities. The colonies vary from non-pigmented to purple, rough and pitted surface to raised and round . The mucoid colonies contain capsulated cocci, motile cocci with flagellar tufts containing nine flagella and a single fimbria and large, sphaeroblast-like cells. Unusually, while containing the two triple-layer membranes with a thin peptidoglycan layer common to gram-negative bacteria, Lautropia mirabilis have membranous structures parallel to the plasma membrane and small, electron-dense granules localised in the nuclear regions . Lautropia mirabilis has a KEGG TCA cycle VI classifying it as an obligate autotroph  and ferments glucose, fructose, sucrose and mannitol . It cannot ferment lactose, trehalose, raffinose, inulin, salicin, adonitol, dulcitol, sorbitol, inositol, xylose, rhamnose or arabinose or hydrolyse starch. Strains of Lautropia mirabilis are oxidase, catalase and urease positive. This species reduces nitrate and nitrites .
A facultative anaerobe, L. mirabilis is capable of producing ATP via aerobic respiration in the presence of oxygen and fermentation in the absence of oxygen. Both conditions are possible in the oral cavity and upper respiratory tract in which the organism is found  although this species grows best under aerobic conditions with no requirement for CO2 .
While the pathogenicity of L.mirabilis is unknown and it has been found in both ill and healthy persons , there has been a significant correlation with its presence in immunodeficiency virus-infected children . Gerner-Smidt et al. identified the bacterium’s polysaccharide production from sucrose as a possible contributing factor to dental plaque. A patient study in which tests showed unusually large quantities of the bacterium in sputum of a patient with cystic fibrosis may also imply correlation between the bacterium and quality of health. The presence of L.mirabilis in samples taken from normally sterile sites such as blood and peritoneal fluid suggest that L.mirabilis may have the potential to cause invasive disease . L.mirabilis is sensitive to antibiotics such as penicillin and ampicillin .
Broader studies considering L.mirabilis and other microorganisms as potential biomarkers to differentiate malignant disorders of the oral cavity are currently under consideration. The correlation of L.mirabilis to poor health suggest that identification of L.mirabilis in patients may be used as an indicator of concern for oral recovery after treatment such as periodontitis  or oral disorders such as oral lichen planus  or cancer .
 Gerner-Smidt, P., Keiser-Nielsen, H., Dorsch, M., Stackebrandt, E., Ursing, J., Blom, J., Christensen, A.C., Christensen, J.J., Frederiksen, W., Hoffmann, S., Holten-Andersen, W., and Ying, Y.T. (1994) Lautropia mirabilis gen. nov., sp. nov., a Gramnegative motile coccus with unusual morphology isolated from the human mouth. Microbiology 140: 1787-1797.
 Rossmann, S.N., Wilson, P.H., Hicks, J. Carter, B., Cron, S.G., Simon, C., Flaitz, C.M., Demmler, G.J., Shearer, W.T., and Kline, M.W. (1998) Isolation of Lautropia mirabilis from Oral Cavities of Human Immunodeficiency Virus-Infected Children. J Clin Microbiol 36(6):1756-1760.
 Colombo, A.P., Bennet, S., Cotton, S.L., Goodson, J.M., Kent, R., Haffajee, A.D., Socransky, S.S., Hasturk, H., Van Dyke, T.E., Dewhirst, F.E., and Paster, B.J. (2012) Impact of periodontal therapy on the subgingival microbiota of severe periodontitis: comparison between good responders and individuals with refractory periodontitis using the human oral microbe identification microarray. J Periodontol 83(10): 1279-1287.
 Mok, S.F., Karuthan, C., Cheah, Y.K., Ngeow, W.C., Rosnah, Z., Yap, S.F., and Ong, H.K.A. (2017) The oral microbiome community variations associated with normal, potentially malignant disorders and malignant lesions of the oral cavity. Malays J Pathol 39(1): 1-15.
This page is written by <Kimberley Strachan> for the MICR3004 course, Semester 2, 2017