Leptospira
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Leptospira
Leptospira
(from
the
Greek
leptos,
meaning
fine or
thin,
and the
Latin
spira,
meaning
coil) is
a genus
of
spirochaete
bacteria,
including
a small
number
of
pathogenic
and
saprophytic
species.
Leptospira
was
first
observed
in 1907
in
kidney
tissue
slices
of a
leptospirosis
victim
who was
described
as
having
died of
"yellow
fever." Morphology Although over 200 serovars of Leptospira have been described, all members of the genus have similar morphology. Leptospira are spiral-shaped bacteria that are 6-20 μm long and 0.1 μm in diameter with a wavelength of about 0.5 μm.[8] One or both ends of the spirochete are usually hooked. Because they are so thin, live Leptospira are best observed by darkfield microscopy. The bacteria have a number of freedom degrees; when ready to proliferate via binary fission, the bacterium noticeably bends in the place of the future split. [edit] Cellular structure Leptospira have a Gram-negative-like cell envelope consisting of a cytoplasmic and outer membrane. However, the peptidoglycan layer is associated with the cytoplasmic rather than the outer membrane, an arrangement that is unique to spirochetes. The two flagella of Leptospira extend from the cytoplasmic membrane at the ends of the bacteria into the periplasmic space and are necessary for the motility of Leptospira. The outer membrane contains a variety of lipoproteins and transmembrane outer membrane proteins. As expected, the protein composition of the outer membrane differs when comparing Leptospira growing in artificial medium with Leptospira present in an infected animal. Several leptospiral outer membrane proteins have been shown to attach to the host extracellular matrix and to factor H. These proteins may be important for adhesion of Leptospira to host tissues and in resisting complement, respectively.
The
outer
membrane
of
Leptospira,
like
those of
most
other
Gram-negative
bacteria,
contains
lipopolysaccharide
(LPS).
Differences
in the
highly
immunogenic
LPS
structure
account
for the
numerous
serovars
of
Leptospira..
Consequently,
immunity
is
serovar
specific;
current
leptospiral
vaccines,
which
consist
of one
or
several
serovars
of
Leptospira
endemic
in the
population
to be
immunized,
protect
only
against
the
serovars
contained
in the
vaccine
preparation.
Leptospiral
LPS has
low
endotoxin
activity..
An
unusual
feature
of
leptospiral
LPS is
that it
that it
activates
host
cells
via TLR2
rather
than
TLR4.
The
unique
structure
of the
lipid A
portion
of the
LPS
molecule
may
acccount
for this
observation.
Finally,
the LPS
O
antigen
content
of L.
interrogans
differs
in an
acutely
infected
versus a
chronically
infected
animal.
The role
of O
antigen
changes
in the
establishment
or
maintenance
of acute
or
chronic
infection,
if any,
is
unknown.
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