Ehrlichia muris subsp. eauclairensis is recognized as the etiological agent of human ehrlichiosis in Minnesota and Wisconsin. We describe the culture isolation of this organism from a field-collected tick and detail its relationship to other species of Ehrlichia. The isolate could be grown in a variety of cultured cell lines and was effectively transmitted between Ixodes scapularis ticks and rodents, with PCR and microscopy demonstrating a broad pattern of dissemination in arthropod and mammalian tissues. Conversely, Amblyomma americanum ticks were not susceptible to infection by the Ehrlichia. Histologic sections further revealed that the wild-type isolate was highly virulent for mice and hamsters, causing severe systemic disease that was frequently lethal. A Himar1 transposase system was used to create mCherry- and mKate-expressing EmCRT mutants, which retained the ability to infect rodents and ticks. IMPORTANCE Ehrlichioses are zoonotic diseases caused by intracellular bacteria that are transmitted by ixodid ticks. Here we report the culture isolation of bacteria which are closely related to, or the same as the Ehrlichia muris subsp. eauclairensis, a recently recognized human pathogen. EmCRT, obtained from a tick removed from deer at Camp Ripley, MN, is the second isolate of this subspecies described and is distinctive in that it was cultured directly from a field-collected tick. The isolate's cellular tropism, pathogenic changes caused in rodent tissues, and tick transmission to and from rodents are detailed in this study. We also describe the genetic mutants created from the EmCRT isolate, which are valuable tools for the further study of this intracellular pathogen.
Bibliographical noteFunding Information:
The study was funded under grant R01AI042792 provided by the National Institutes of Health (USA) and awarded to U.G.M. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
ACKNOWLEDGMENTS We thank Lisa Price for contributing PCR sequences for Camp Ripley ticks, the University of Minnesota Imaging Centers for sectioning and staining samples for TEM and assistance with microscope operation, and Mike Herron for contributing GFP-expressing LifeAct RF/6A cells. The study was funded under grant R01AI042792 provided by the National Institutes of Health (USA) and awarded to U.G.M. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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Copyright 2020 Elsevier B.V., All rights reserved.
- Amblyomma americanum
- Ehrlichia muris
- Ixodes scapularis
- cell culture