Gram stain: negative Cell shape: rod-shaped or coccobacilli; highly pleomorphic Arrangement: Oxygen requirements: Other: Very small organisms -- 0.8 - 2.0 micrometers; these organisms are obligate intracellular parasites (they can only reproduce within a host cell). These organisms are transmitted to humans by insects and ticks. In humans they damage the permeability of capillaries; severe infections can cause the cardiovascular system to collapse. Patients exhibit a characteristic rash: progresses from small pink spots called macules to pink red pimple-like spots called papules which fuse together to form a maculopapular rash. Usually cultivated in lab only within living cultures such as fertilized eggs or animals.
Habitat:
Pathogenicity: causative agent of Rocky Mountain Spotted Fever: high fever lasting for many days, persistent headache, rash. Currently not a problem in the West; usually found in S.E. and Atlantic coastal states.
Transmission: several genera of ticks
Treatment: tetracycline and chloramphenicol.
* This genus is named after its discoverer in 1909, Howard Taylor Ricketts. Ricketts died from endemic typhus during his studies of this organism!
Rickettsia rickettsii
