Medical Definition of Rickettsiales
: 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
Seen and Heard
What made you want to look up Rickettsiales? Please tell us where you read or heard it (including the quote, if possible).