Rickettsia

Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1–4 μm long) or thread-like (10 μm long). Being obligate intracellular parasites, the Rickettsia survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells (typically endothelial cells).

Because of this, Rickettsia cannot live in artificial nutrient environments and are grown either in tissue or embryo cultures (typically, chicken embryos are used). In the past they were positioned somewhere between viruses and true bacteria. However unlike Chlamydia, Mycoplasma, and Ureaplasma, Rickettsial organisms possess true cell walls similar to other gram-negative bacteria. The majority of Rickettsia bacteria are susceptible to antibiotics of the tetracycline group.

Despite the similar name, Rickettsia bacteria do not cause rickets, which is a result of vitamin D deficiency.

Rickettsia species are carried by many ticks, fleas, and lice, and cause diseases in humans such as typhus, rickettsialpox, Boutonneuse fever, African tick bite fever, Rocky Mountain spotted fever, Flinders Island spotted fever and Queensland tick typhus (Australian Tick Typhus). They have also been associated with a range of plant diseases. The name rickettsia is often used for any member of the Rickettsiales. They are one of closest living relatives to bacteria that were the origin of the mitochondria organelle that exists inside most eukaryotic cells.

The method of growing Rickettsia in chicken embryos was invented by Ernest William Goodpasture and his colleagues at Vanderbilt University in the early 1930s.