1. Rickettsias. This subgroup multiplies by binary fission not by a complex developmental cycle most live in an obligate intracellular association parasitic or mutualistic, with eukaryotic hosts ( vertebrates or arthropods)
a few can be grown on moderately complex bacteriological media containing blood
.
The cell walls contain muramic acid Glutamate is oxidized with generation of ATP. Rickettsias are mainly rod-shaped, coccoid, and often pleomorphic bacteria that stain Gram negative and lack flagella; exceptions may occur for each of these features, as follows: