Ames Test (external lab)

Test organism

Mutants of the bacterium Salmonella typhimurium, which themselves are not capable of producing the amino acid histidine (his-deficient mutants), cannot grow on histidine-free culture media under controlled conditions.
Upon contact with a mutagenic substance, the bacteria can mutate back and thus regain the histidine-producing capability.
Such bacteria can now reproduce on the histidine-free culture medium
The higher the number of mutated colonies of bacteria exposed to environmental pollutants, the higher the mutagenic activity of these pollutants.

Indicates Relatively quickly a potential mutagenic effect of substances or mixtures of substances (short waiting time for the occurrence of mutations due to fast bacterial reproduction)
Easy detectability of a small number of mutated cells besides numerous undamaged cells.

However:

In-vitro assay system: the behaviour of substances in the body cannot be exactly simulated (partial simulation by adding S9 mixture (liver homogenate with enzymes of the xenobiotic metabolism) is possible)
Mutagen for bacteria ≠ mutagen for mammals
Different complexitiy of bacterial and mammalian cells (mammalian cells activate a cytostatic or apoptotic mechanism when DNA defects are detected; the bacterium is a unicellular organism)

Deutsches Institut für Normung (1999). Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung - Suborganismische Testverfahren (Gruppe T) - Teil 4: Bestimmung des erbgutverändernden Potentials mit dem Salmonella-Mikrosomen-Test (Ames Test) (T 4). DIN 38415-4.
International Organization for Standardization (2005). Water quality -- Determination of the genotoxicity of water and waste water -- Salmonella/microsome test (Ames test). ISO 16240, 20 p.