Editing Ames test (section)

==Limitations==
''Salmonella typhimurium'' is a prokaryote, therefore it is not a perfect model for humans.  Rat liver [[S9 fraction]] is used to mimic the mammalian metabolic conditions so that the mutagenic potential of metabolites formed by a parent molecule in the hepatic system can be assessed; however, there are differences in metabolism between humans and rats that can affect the mutagenicity of the chemicals being tested.<ref>{{cite journal | vauthors = Hakura A, Suzuki S, Satoh T | title = Advantage of the use of human liver S9 in the Ames test | journal = Mutation Research | volume = 438 | issue = 1 | pages = 29–36 | date = January 1999 | pmid = 9858674 | doi = 10.1016/s1383-5718(98)00159-4 | bibcode = 1999MRGTE.438...29H }}</ref>  The test may therefore be improved by the use of human liver S9 fraction; its use was previously limited by its availability, but it is now available commercially and therefore may be more feasible.<ref>{{cite book | title=Optimization in Drug Discovery: in vitro methods | series=Methods in Pharmacology and toxicology | editor1-first=Zhengyin | editor1-last=Yan | editor2-first=Gary | editor2-last=Caldwell | name-list-style = vanc | publisher=Humana Press | year=2004 | isbn=978-1-58829-332-9 | first1 = Atsushi | last1 = Hakura | first2 = Satoshi | last2 = Suzuki | first3 = Tetsuo | last3 = Satoh | chapter=Improvement of the Ames test using human liver S9 preparation }}</ref>  An adapted ''in vitro'' model has been made for eukaryotic cells, for example yeast.

Mutagens identified in the Ames test need not necessarily be carcinogenic, and further tests are required for any potential carcinogen identified in the test.  Drugs that contain the nitrate moiety sometimes come back positive for Ames when they are indeed safe.  The nitrate compounds may generate [[nitric oxide]], an important signal molecule that can give a false positive.  [[Nitroglycerin]] is an example that gives a positive Ames yet is still used in treatment today.  Nitrates in food however may be reduced by bacterial action to nitrites which are known to generate carcinogens by reacting with amines and amides.  Long toxicology and outcome studies are needed with such compounds to disprove a positive Ames test.