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Microscopy of Spotted Fever Rickettsia Movement through Tick Cells

Published online by Cambridge University Press:  28 July 2005

Ulrike G. Munderloh
Affiliation:
Department of Entomology, University of Minnesota, 1980 Folwell Avenue, St. Paul, MN 55108
Stanley F. Hayes
Affiliation:
Microscopy Branch, Rocky Mountain Laboratories, National Institutes of Health, Hamilton, MT 59840
Joel Cummings
Affiliation:
Department of Entomology, University of Minnesota, 1980 Folwell Avenue, St. Paul, MN 55108
Timothy J. Kurtti
Affiliation:
Department of Entomology, University of Minnesota, 1980 Folwell Avenue, St. Paul, MN 55108
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Abstract

Spotted fever group (SFG) rickettsiae are obligate intracellular prokaryotes that include tick-borne pathogens of vertebrates as well as nonpathogenic organisms living in symbiotic association with their tick hosts. We investigated the ability of SFG rickettsiae to move between and within host cells using tick cell culture and a SFG rickettsial isolate from a lone star tick (Amblyomma americanum) collected in Missouri. The isolate (MOAa), which is closely related to Rickettsia montana, grew in cell lines from the ticks Ixodes scapularis and Rhipicephalus appendiculatus. Transmission electron microscopy demonstrated that immediately following entry into tick cells, rickettsiae escaped from the host cell membrane, and intracellular rickettsiae came to lie in direct contact with host-cell cytoplasm. There was evidence of damage to the endoplasmic reticulum membrane which was broken down into vesicular structures. When rickettsiae exited host cells, host membrane stretched around them but was lost before re-entry. Use of a fluorescein-tagged monoclonal antibody to rickettsial outer membrane protein B and rhodamine-labeled phalloidin demonstrated association of actin tails with rickettsiae and suggested that SFG rickettsiae utilized host cytoskeletal components for movement. During early stages of infection, when cells harbored only one or a few organisms, “comet tails” of F-actin formed on one end of rickettsial cells, presumably pushing them ahead. Actin tails were not seen during later stages of infection when tick cells became completely filled with rickettsiae.

Type
Research Article
Copyright
© 2005 Microscopy Society of America

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