Some Aspects of Variation in Rickettsial Virulence

Weiss, Emilio

doi:10.1111/j.1749-6632.1960.tb20120.x

Rickettsia

Yu

¹

,

Walker

²

2015

Bergey's Manual of Systematics of Archaea and Bacteria

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Rick.ett' si.a . M.L. fem. n. Rickettsia named after Howard Taylor Ricketts, who first associated organisms of this description with spotted fever and typhus and who died of typhus contracted in the course of his studies. Proteobacteria / Alphaproteobacteria / Rickettsiales / Rickettsiaceae / Rickettsia Short , often paired rods , 0 . 3–0 . 5 × 0 . 8–2 . 0 μ m . The rickettsial envelope has a typical Gram‐negative structure with a bilayer inner membrane, a peptidoglycan layer, and a bilayer outer membrane. The cells are often surrounded by a protein microcapsular layer and slime layer. Rickettsiae retain basic fuchsin when stained by the method of Giménez (1964). The organisms are obligately intracellular and reside free in the cytoplasm of the eucaryotic host cell , where they divide by binary fission . Rickettsiae of the spotted fever group (SFG) may also reside in the nucleus of the eucaryotic host cells. Rickettsiae are closely associated with arthropods (ticks, mites, fleas, lice, and other insects) for their maintenance in nature . Their natural cycle usually involves both a vertebrate and an invertebrate host. For some, the arthropod host is both a reservoir and a vector. Transovarian transmission of the agent from the infected female to the next generation is the essential mechanism for the maintenance of many species (Burgdorfer, 1988). Rickettsial cells are usually unstable when separated from host components, except for highly stable forms found in the feces of arthropod hosts; stability can be enhanced by certain proteins, sucrose, and reagents that tend to maintain the integrity of outer membranes, osmolarity, and ATP level. Rickettsiae are best preserved by rapid freezing and storage below −50°C. The cells are rapidly inactivated at 56°C. Rickettsiae derive energy from the metabolism of glutamate via the citric acid cycle, but do not utilize glucose. They transport and metabolize phosphorylated compounds but do not synthesize or degrade nucleoside monophosphates. Rickettsiae are etiological agents of typhus and spotted fevers in humans . There are 21 recognized species. The mol % G + C of the DNA is : 29–33. Type species : Rickettsia prowazekii da Rocha‐Lima 1916, 567 (Nom. Cons. Opin. 19, Jud. Comm. 1958, 158.)

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Rickettsia

Fournier¹,

Raoult²

2019

Bergey's Manual of Systematics of Archaea and Bacteria

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Rick.ett'si.a. N.L. fem. n. Rickettsia, named after Howard Taylor Ricketts, who first associated these microorganisms with spotted fever and typhus and who died of typhus contracted in the course of his studies. Proteobacteria / Alphaproteobacteria / Rickettsiales / Rickettsiaceae / Rickettsia Short , often paired rods , 0 . 3–0 . 5 μ m × 0 . 8–2 . 0 μ m . The rickettsial envelope has a typical Gram‐negative structure with a bilayer inner membrane, a peptidoglycan layer, and a bilayer outer membrane. The cells are often surrounded by a protein microcapsular layer and slime layer. Rickettsiae retain basic fuchsin when stained by Giménez method. The organisms are obligately intracellular and reside free in the cytoplasm of eukaryotic host cells , where they divide by binary fission . Rickettsiae of the spotted fever group (SFG) may also reside in the nucleus of eukaryotic host cells. Rickettsiae are closely associated with arthropods (ticks, mites, fleas, lice, and other insects) for their maintenance in nature . Their natural cycle usually involves both a vertebrate and an invertebrate host. For some, the arthropod host is both a reservoir and a vector. Transovarian transmission of the agent from the infected female to the next generation is the essential mechanism for the maintenance of many species. Rickettsial cells are usually unstable when separated from host components, except for highly stable forms found in the feces of arthropod hosts; stability can be enhanced by certain proteins, sucrose, and reagents that tend to maintain the integrity of outer membranes, osmolarity, and ATP level. Rickettsiae are best preserved by rapid freezing and storage below −50°C. The cells are rapidly inactivated at 56°C. Rickettsiae derive energy from the metabolism of glutamate via the citric acid cycle, but do not utilize glucose. They transport and metabolize phosphorylated compounds but do not synthesize or degrade nucleoside monophosphates. Rickettsial species have genomes ranging from 1.1 to 2.3 Mb. They may also have up to four plasmids. Rickettsiae are etiological agents of typhus and spotted fevers in humans . There are 31 recognized species. DNA G + C content (mol%) : 29–33. Type species : Rickettsia prowazekii da Rocha‐Lima 1916, 567. (Nom. Cons. Opin. 19, Jud. Comm. 1958, 158.)

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