Structure
of
Rickettsiae
- The
rickettsiae
(sing.
rickettsia)
measure
about
0.3
-
0.5
µm
in
diameter
and
0.3
-0.4
µm
in
length
and
usually
appear
as
rods
with
rounded
edges,
a
form
known
as
the
Coccobacillus.
They
also
exist
in
alternate
shapes
and
hence
pleomorphic.They
are
hardly
visible
under
the
light
microscope.
They
have
no
flagella,
pili,
Capsules,
or
spores.
The
cell
wall
is
chemically
similar
to
that
of
Gram
negative
bacteria
and
the
cytoplasm
contains
both
DNA
and
RNA
as
well
as
many
of
the
enzymes.
Reproduction
is
by
binary
fission.
Except
for
the
organism
of
trench
fever,
they
do
not
grow
on
artificial
laboratory
media.
Living
tissues
as
vertebrate
cell
cultures,
fertilised
chicken
eggs
or
live
animals
are
used
for
their
growth.
They
are,
therefore,
obligate
intracellular
parasites.
