Ticks harbor several different genera of endosymbiotic bacteria. These obligate intracellular bacteria, most of which appear to be nonpathogenic for the tick, persist in nature by being transmitted transovarially from generation to generation. Those in the genus Rickettsiabelong to the spotted fever group (SFG) of rickettsia which includes both mammalian pathogenic and nonpathogenic species. The species that cause spotted fevers in humans, e.g. Rickettsia rickettsii, are well characterized but those not known to cause disease remain poorly understood. Transmission electron microscopy on SFG rickettsia cultured in tick cell cultures offers a powerful way to examine dynamic host parasite interactions in these apparently nonpathogenic SFG species.

We have successfully isolated two unknown, nonpathogenic rickettsia strains in tick cell lines. T2 was isolated from an Ixodes ricinus tick collected in the English Garden in Munich, Germany and is propagated in an Ixodes scapularis cell line, ISE6.