- (non-motile, Gram-negative, non-sporeforming bacteria).
- Highly pleomorphic: can present as cocci (0.1 µm in diameter), rods (1-4 µm long) or thread-like (10 µm long).
- Obligate intracellular parasite. Survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells.
- –Unlike Chlamydia, Mycoplasma, and Ureaplasma, Rickettsial organisms possess true cell walls similar to other Gram-negative bacteria.
- Frequently carried by chiggers, ticks, fleas, and lice.
- Causative organism in typhus, rickettsial pox, Boutonneuse fever, African tick bite fever, Rocky Mountain spotted fever, Flinders Island spotted fever and Queensland tick typhus.