Biology of spotted fever group rickettsiae in tick cell cultures (Rickettsia peacockii, Dermacentor andersoni, Ixodes ricinus)

Spotted fever group (SFG) rickettsiae are obligately intracellular bacteria, some of which are pathogens of arthropods and mammals. Acarines serve as vectors for pathogenic SFG rickettsiae as well as maintenance hosts for rickettsiae that pass to the next generation of ticks through the female germinal tissues. However, many rickettsiae remain poorly characterized due to an inability to be propagated in vertebrate culture systems. Tick cell culture offers a viable approach for the isolation and propagation of SFG rickettsiae refractory to vertebrate culture. In addition, tick cell culture provides an in vitro system for the elucidation of the interactions between SFG rickettsiae and ticks.; Here, I have described the use of tick cell culture for the isolation and the antigenic, phenotypic, and genotypic characterizations of SFG rickettsiae harbored within ticks. One of these, Rickettsia peacockii DaE100R, was isolated from an embryonic cell line of the Rocky Mountain wood tick, Dermacentor andersoni, The other, IrR/Munich, was isolated from a castor bean tick, Ixodes ricinus.; R. peacockii, which is nonpathogenic for both ticks and mammals is reported to interfere with the maintenance of pathogenic rickettsiae in ticks. This rickettsia could be maintained, without deleterious affects, in tick cell lines. In addition, R. peacockii lacked a full length rickettsial outer membrane protein A which was hypothesized to correlate with its inability to disrupt host cell actin structures for mobility and to infect mammalian cells.; IrR/Munich, of undetermined pathogenicity, is an isolate of a novel SFG genotype. In contrast to R. peacockii, IrR/Munich lysed tick and mammalian cells. This rickettsia was able to disrupt host cell actin structures for mobility within and between cells. Hamsters seroconverted to injection with IrR/Munich, suggesting this organism was infection for the animals.; The techniques of the in vitro isolation of SFG rickettsiae could readily be applied to other tick associated organisms. Tick cell culture provides an environment analogous to the vector phase of tick transmitted organisms. Understanding the mechanisms by which tick vectored organisms interact with their host will aid in the manipulation of those interactions for the control of ticks and tick borne diseases.