From Wikipedia,
the free encyclopedia
The Ames test is a
biological assay used in
genetics, generally
genetic toxicology, to test
for
mutagenic properties of a
chemical compound. A compound is
said to be
mutagenic if it causes a
change in the
DNA (deoxyriboneucleic acid)
of a living cell or organism. The
test is named after its inventor,
Bruce Ames.
General procedure
This assay is carried out using
strains of
bacteria, generally
Escherichia coli or
Salmonella typhimurium that
already have a single mutation,
for example, a
strain that cannot produce
histidine, an
amino acid that is essential
for the bacterium to grow if not
provided externally with essential
nutrients. Cultures of the
bacteria are grown in an
agar containing dish so that a
"lawn" of bacteria is present.
The experimental cultures are
exposed to the agent to be tested
while the positive control
cultures are exposed to a known
mutagen to confirm that there has
been no contamination of the
strain. Strains of bacteria are
available which have been
genetically modified such that
only a certain type of mutation
(i.e. a base pair mutation or a
frameshift mutation) will cause
the strand to revert to a normal
state, not requiring nutrients to
grow. If the mutation screened for
has in fact occurred, dense spots
in the colonies will form. A
certain number of spots may form
due to random mutation not caused
by the agent; therefore, data
analysis using control dishes is
necessary. Occasionally a tested
agent will be toxic enough to
simply kill the bacterial culture
in which case a "thin lawn" is
observed.
S-9
In some Ames assays an S-9 mix
is added. The S-9 mix contains
liver
enzymes, generally from a
rat. These enzymes can
metabolize the agent being tested
in order to predict the mutagenic
properties within a living system,
specifically the source of the S-9
enzymes.
Mutagenic and carcinogenic
correlation
Studies have shown that the
majority of substances shown to be
mutagenic by an Ames assay will be
carcinogenic in humans.
