Rickettsiales

Rick·ett·si·a·les ri-.ket-sē-'ā-(.)lēz n pl an order of small pleomorphic gram-negative bacteria that are obligate parasites living in vertebrates or in arthropods which often serve as vectors of those parasitic in vertebrates and are placed in the families Anaplasmataceae, Bartonellaceae, and Rickettsiaceae

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Rick·ett·si·a·les (rĭ-ket″se-aґlēz) an order of bacteria of the class Alphaproteobacteria, phylum Proteobacteria, comprising small, gram-negative, nonflagellated, rod-shaped or coccoid, often pleomorphic microorganisms that multiply only inside the cells of the host. Bacteria are found as parasites in arthropods (which may serve as vectors), helminths, and vertebrates; some species are pathogenic. The order includes the families Anaplasmataceae and Rickettsiaceae.