Rickettsia felis from Cat Fleas: Isolation and Culture in a Tick-Derived Cell Line

Abstract

Rickettsia felis , the etiologic agent of spotted fever, is maintained in cat fleas by vertical transmission and resembles other tick-borne spotted fever group rickettsiae. In the present study, we utilized an Ixodes scapularis -derived tick cell line, ISE6, to achieve isolation and propagation of R. felis . A cytopathic effect of increased vacuolization was commonly observed in R. felis -infected cells, while lysis of host cells was not evident despite large numbers of rickettsiae. Electron microscopy identified rickettsia-like organisms in ISE6 cells, and sequence analyses of portions of the citrate synthase ( gltA ), 16S rRNA, Rickettsia genus-specific 17-kDa antigen, and spotted fever group-specific outer membrane protein A ( ompA ) genes and, notably, R. felis conjugative plasmids indicate that this cultivatable strain (LSU) was R. felis . Establishment of R. felis (LSU) in a tick-derived cell line provides an alternative and promising system for the expansion of studies investigating the interactions between R. felis and arthropod hosts.