Rickettsiaceae
Rickettsia rickettsii
- Rickettsia da Rocha -Lima 1916
- Orientia Tamura et al. 1995
The Rickettsiaceae form a family within the Alphaproteobacteria and consist of the two genera Rickettsia and Orientia. All species are gram- negative and require oxygen ( aerobic). The cells of the various species are very small ( between 0.3 to 0.5 × 0.8 to 2 microns ) and rod- shaped or coccoid also. They have a typical bacterial cell wall and carry no flagella.
Way of life
All species are obligate intracellular parasites, they can only survive within the host cells. They are both a cause of many diseases in humans and animals. As vectors ( carriers ) are mainly arthropods (eg, different ticks, fleas, mites, lice). A free cultivation on agar has not been successful, they are within biological tissue, ie grown in eukaryotic cells.
Systematics and clinical classification
The family Rickettsiaceae are currently ( January 2013) associated with two genera Rickettsia and Orientia.
From a medical perspective, the Rickettsiaceae be divided into three groups:
- The tick bite fever group ( English: Spotted Fever Group): Rickettsia rickettsii and Others ( Rocky Mountain spotted fever ) Rickettsia conorii and ( Boutonneuse fever)
- The spotted fever group ( typhus group): Rickettsia typhi and Others ( murine typhus )
- The tsutsugamushi fever group ( Scrub Typhus Group): This group consists of only a single species, Orientia tsutsugamushi the causative agent of tsutsugamushi fever (English: Scrub typhus ).
Changes to the scheme
It should be noted that the classification of bacteria constantly in flux. So there are several variants of the systematics of this family. The original of this family asked genus Wolbachia ( sh below) can be found in the family Anaplasmataceae or else in the tribe Wolbachieae, which will continue to be made to the family Rickettsiaceae.
The Rickettsia tsutsugamushi originally named species was separated from the genus Rickettsia and placed in its own genus Orientia. The often lethal tsutsugamushi fever (English: Scrub typhus ) occurs frequently in Asia and Australia. As carriers serve mites of the genus Neotrombicula ( Syn: Trombicula ).
Previously Rickettsiaceae was divided into three tribes:
- Tribus Rickettsieae with the genera Rickettsia, Rochalimaea, and Coxiella
- Tribus Ehrlicheae with the genera: Ehrlichia, Cowdria and Neorickettsia
- Tribus Wolbachieae with the genera Wolbachia, Symbiotes and Rickettsiella
The genera of Ehrlicheae and the genus Wolbachia were counted to the family Anaplasmataceae. Coxiella and Rickettsiella were completely rearranged and made to the family Coxiellaceae within the Gammaproteobacteria class. The types of Rochalimaea are now assigned to the genus Bartonella ( Bartonellaceae ).
In the past, all intracellular living bacteria were assigned to the Rickettsiaceae ( Rickettsia ). Based on 16S rRNA analysis, however, this systematic classification was untenable.
Endosymbiontentheorie
Rickettsia prowazekii the type is of particular interest in relation to the endosymbiotic the mitochondria. The genome of Rickettsia prowazekii was completely sequenced and has strong similarities with the mitochondrial DNA on. Whether the original endosymbiont is actually derived from the rickettsia, however, unclear. The genome of Rickettsia prowazekii as well as the to be found in the mitochondria genome is very small. Both are probably shrunk in the billions of years of evolution, which is also a strong similarity of gene structure does not allow for a clear statement.