Acid
Fast
Techniques
Bacteria
of
the
genus
Mycobacterium
possess
waxy
materials
in
their
cell
walls.
They
are
difficult
to
stain
by
ordinary
methods,
and
heat
must
be
applied
to
force
the
dye
molecules
through
to
the
cytoplasm.
Once
stained,
however,
the
cells
are
not
easily
decolorized,
even
with
alcohol
solution
containing
5%
acid.
The
organisms
are
said
to
be
acid
resistant
or
acid-fast.
Air
dried
heat
fixed
smears
are
heated
while
being
stained
with
ZiehlNeelsen's
Carbolfuchsin.
The
cells
become
bright
red.
The
smear
is
then
rinsed
with
acid
alcohol
decolorizer.
During
this
time
the
acid
fast
bacteria
remain
red
while
other
bacteria
lose
their
color
.
