sentence: The genus Rickettsiae belongs to the family Rickettsiaceae and is divided into four major groups : the spotted fever group ( SFG ) , which contains the vast majority of known rickettsiae ( e.g ., Rickettsia rickettsii and Rickettsia conorii ) , the typhus group ( TG ) ( R. typhi and Rickettsia prowazekii ) , the transitional group ( Rickettsia felis , Rickettsia akari , and Rickettsia australis ) , and the ancestral group ( Rickettsia bellii and Rickettsia canadensis ) ( 1 – 3 ) .