Rickettsiales

noun plural

Rick·​ett·​si·​a·​les ri-ˌket-sē-ˈā-(ˌ)lēz 

: 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 Ehrlichiaceae and Rickettsiaceae