Abstract:
Three isolates of Ehrlichia ruminantium (Kümm 2, Omatjenne and Riverside), the causative
agent of heartwater in domestic ruminants, were isolated in Ixodes scapularis (IDE8) tick cell
cultures using the leukocyte fraction of infected sheep blood. All stocks were successfully
propagated in IDE8 cells, whereas initiation attempts using endothelial cell cultures were
unsuccessful. Therefore, the new technique should be included in any attempt to isolate field
strains of E. ruminantium to enhance the probability of getting E. ruminantium isolates which
might not be initiated in endothelial cells. Draft genome sequences of all three isolates were
generated and compared with published genomes. The data confirmed previous phylogenetic
studies that these three isolates are genetically very close to each other, but distinct
from previously characterised E. ruminantium isolates. Genome comparisons indicated that
the gene content and genomic synteny were highly conserved, with the exception of the
membrane protein families. These findings expand our understanding of the genetic diversity
of E. ruminantium and confirm the distinct phenotypic and genetic characteristics shared by
these three isolates.
