09-10-2021-1830 - Rickettsia nonmotile pleomorphicbacteria pleo cleopatra cleos cleo Rickettsiales 1930 tick arthropod chigger flea lice mite crustacean thyphus typhus rickettsialpox Rickettsia species are the pathogens responsible for typhus, rickettsialpox, boutonneuse fever, African tick-bite fever, Rocky Mountain spotted fever, Flinders Island spotted fever, and Queensland tick typhus (Australian tick typhus).[11]]

Rickettsia is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphicbacteria that may occur in the forms of cocci (0.1 μm in diameter), bacilli (1–4 μm long), or threads (up to about 10 μm long). The term "rickettsia" has nothing to do with rickets(which is a deficiency disease resulting from lack of vitamin D); the bacterial genus Rickettsia instead was named after Howard Taylor Ricketts, in honor of his pioneering work on tick-borne spotted fever.

Properly, Rickettsia is the name of a single genus, but the informal term "rickettsia", plural "rickettsias", usually not capitalised, commonly applies to any members of the order Rickettsiales. Being obligate intracellular parasites, rickettsias depend on entry, growth, and replication within the cytoplasm of living eukaryotic host cells (typically endothelialcells).^[9] Accordingly, Rickettsia species cannot grow in artificial nutrient culture; they must be grown either in tissue or embryo cultures; typically, chicken embryos are used, following a method developed by Ernest William Goodpasture and his colleagues at Vanderbilt University in the early 1930s.

Rickettsia species are transmitted by numerous types of arthropod, including chigger, ticks, fleas, and lice, and are associated with both human and plant diseases.^[10] Most notably, Rickettsia species are the pathogens responsible for typhus, rickettsialpox, boutonneuse fever, African tick-bite fever, Rocky Mountain spotted fever, Flinders Island spotted fever, and Queensland tick typhus (Australian tick typhus).^[11] The majority of Rickettsia bacteria are susceptible to antibiotics of the tetracycline group.

Rickettsia
Red-stained Rickettsia rickettsii visible in cells of an Ixodid vector tick
Scientific classification
Domain:	Bacteria
Phylum:	Proteobacteria
Class:	Alphaproteobacteria
Order:	Rickettsiales
Family:	Rickettsiaceae
Tribe:	Rickettsieae
Genus:	Rickettsia da Rocha-Lima, 1916
Species groups and Species[8]
belli group Candidatus Rickettsia angustus Candidatus Rickettsia kingi Candidatus Rickettsia mendelii Candidatus Rickettsia tarasevichiae Rickettsia bellii Rickettsia canadensis [1][2] Rickettsia monteiroi spotted fever group Candidatus Rickettsia andeanae Candidatus Rickettsia antechini Candidatus Rickettsia barbariae Candidatus Rickettsia goldwasserii Candidatus Rickettsia hungarica Candidatus Rickettsia jingxinensis Candidatus Rickettsia kellyi Candidatus Rickettsia kotlanii Candidatus Rickettsia kulagini Candidatus Rickettsia leptotrombidium Candidatus Rickettsia longicornii Candidatus Rickettsia nicoyana Candidatus Rickettsia principis Candidatus Rickettsia rara Candidatus Rickettsia rioja Candidatus Rickettsia senegalensis Candidatus Rickettsia siciliensis Candidatus Rickettsia tasmanensis Candidatus Rickettsia uralica Candidatus Rickettsia wissemanii Rickettsia aeschlimannii [3] Rickettsia africae [4] Rickettsia akari [1] Rickettsia amblyommatis Rickettsia argasii Rickettsia asembonensis Rickettsia asiatica [5] Rickettsia australis [1] Rickettsia buchneri Rickettsia conorii R. conorii subsp. caspia R. conorii subsp. conorii R. conorii subsp. indica R. conorii subsp. israelensis Rickettsia cooleyi [6] Rickettsia felis [7] Rickettsia fournieri Rickettsia gravesii Rickettsia heilongjiangensis Rickettsia helvetica Rickettsia honei R. honei subsp. marmionii Rickettsia hoogstraalii Rickettsia hulinensis Rickettsia hulinii Rickettsia japonica Rickettsia lusitaniae Rickettsia marmionii Rickettsia martinet Rickettsia massiliae Rickettsia monacensis Rickettsia montanensis Rickettsia moreli Rickettsia parkeri [1] Rickettsia peacockii Rickettsia philipii Rickettsia raoultii Rickettsia rhipicephali Rickettsia rickettsii [1] Rickettsia sibirica subgroup Rickettsia sibirica [1] Rickettsia slovaca Rickettsia tamurae Rickettsia vini typhus group Rickettsia prowazekii [1] Rickettsia typhi [1] Rickettsia incertae sedis Rickettsia limoniae Candidatus Rickettsia colombianensi Candidatus Rickettsia laoensis Candidatus Rickettsia liberiensis Candidatus Rickettsia mahosotii

Schematic ribosomal RNA phylogeny of Alphaproteobacteria

Magnetococcidae     Magnetococcus marinus       Caulobacteridae       Rhodospirillales, Sphingomonadales,    Rhodobacteraceae, Hyphomicrobiales, etc.       Holosporales       Rickettsidae     Pelagibacterales     Pelagibacteraceae       Pelagibacter         Subgroups Ib, II, IIIa, IIIb, IV and V       Rickettsiales       Proto-mitochondria       Anaplasmataceae           Ehrlichia       Anaplasma         Wolbachia         Neorickettsia         Midichloriaceae       Midichloria       Rickettsiaceae       Rickettsia       Orientia

The cladogram of Rickettsidae has been inferred by Ferla et al. [15] from the comparison of 16S + 23S ribosomal RNA sequences.

https://en.wikipedia.org/wiki/Rickettsia