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Rickettsia is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria 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 genus was named after Howard Taylor Ricketts in honor of his pioneering work on tick-borne spotted fever.
Rickettsia rickettsii is a Gram-negative, intracellular, cocco-bacillus bacterium that was first discovered in 1902. [1] Having a reduced genome, the bacterium harvests nutrients from its host cell to carry out respiration, making it an organo-heterotroph.
The genus Rickettsia is the most prominent genus within the family. The bacteria that eventually formed the mitochondrion (an organelle in eukaryotic cells) is believed to have originated from this family. Most human pathogens in this family are in genus Rickettsia.
They are obligate intracellular parasites, and some are notable pathogens, including Rickettsia, which causes a variety of diseases in humans, and Ehrlichia, which causes diseases in livestock. Another genus of well-known Rickettsiales is the Wolbachia, which infect about two-thirds of all arthropods and nearly all filarial nematodes. [2]
Rickettsial diseases are a group of infectious diseases caused by various species of bacteria belonging to the genus Rickettsia.These bacteria are typically transmitted to humans through the bites of infected arthropods, such as ticks, fleas, and lice.
Rickettsia typhi is a small, aerobic, obligate intracellular, rod shaped gram negative bacterium. [1] It belongs to the typhus group of the Rickettsia genus, along with R. prowazekii . [ 2 ] R. typhi has an uncertain history, as it may have long gone shadowed by epidemic typhus ( R. prowazekii ). [ 3 ]
The genus Ehrlichia is named after German microbiologist Paul Ehrlich. The first ehrlichial disease was recognized in South Africa during the 19th century. Its tick-borne nature was determined in 1900. The organism itself was demonstrated in 1925 when it was recognized to be a Rickettsia.
Rickettsia parkeri (abbreviated R. parkeri) is a gram-negative intracellular bacterium. The organism is found in the Western Hemisphere and is transmitted via the bite of hard ticks of the genus Amblyomma .