Overview Chlamydia and Rickettsia are 2 groups of Gram-negative bacteria Both bacteria are obligate intracellular parasites they must steal host ATP to live login to view 2 more bullets they cannot be cultured on non-living artificial media login to view 1 more bullet about the size of large viruses (i.e. quite small) however, they are not viruses because they login to view 4 more bullets Important differences between the 2 groups include Differences between Chlamydia and Rickettsia Chlamydia Rickettsia Transmission Person-to-person Arthropod vector Site of replication Endosomes Cytoplasm Type of cell attacked Columnar epithelium Endothelium