| Abstract |
Cowdria ruminantium is an intracellular organism parasitising the vascular
endothelial cells of ruminants. Recently, the organism has been
successfully cultured in endothelial cells of bovine umbilical cord or
other bovine vascular origin. In an ongoing study to identify more
suitable cell lines for the cultivation of the organism, an ovine cerebral
vascular endothelial cell (SBE189) was isolated and tested for its ability
to support the growth of infective C. ruminantium organisms in vitro. A
study of the developmental cycle of the organism was done on the SBE189
and E5 (a bovine umbilical cord cell line). Twenty-four hour samples were
taken post-infection (p.i.) of cultures. Electron microscopical studies of
the 24 h sample showed cells with 2 or 3 membrane-bound organisms. One of
the organisms was usually large, pleomorphic and reticulate, whereas the
smaller ones had a markedly denser matrix. In the 48 h sample, cells
contained larger colonies with a condensed matrix. In the 72 h sample,
colonies had almost doubled in size and had retained the same density as
the 48 h sample with a few of the organisms within the colonies containing
a lesser dense matrix. The 96 h sample showed a mixed population of
organisms, from pleomorphic reticulated forms to round reticulated forms
containing dark blotches of condensed matrix. The few organisms found in
the vacuole of the 120 h sample, were either dense pleomorphic forms or
what appeared to be degenerative pleomorphic forms with a dense outer
matrix surrounding a vacuole. The C. ruminantium in the SBE189 cells was
allowed to infect almost 100% of the cells by placing the flask on a slow
horizontal rocker. Eight days p.i. the culture material was injected
intravenously into mice, resulting in a 100% mortality within 10 d. The
lung smears of mice, killed in extremis, proved to contain single
organisms or colonies of C. ruminantium. The cell line was found to be
highly suitable for the growth of C. ruminantium and has been added to the
stock of endothelial cells currently in use for the maintenance of
C.ruminantium in vitro.
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