Ames Test for Mutagenicity

What is (+) and (-) controls and their purpose?

(-) = water, provides a frame of references for spontaneous mutations (+) = Sodium azide, to compare with CFUs from (-) to confirm legitimacy of the test and reference of toxicity

How is toxicity determined?

> Complete media = sufficient [His] to ensure dense growth everywhere > The presence of "zones of clearing"

How is mutagenicity determined?

> Minimal Media plates: low [His] ensure growth only if mutation occurs > If the # of CFUs in substance > 2x CFUs in (-) control

Auxotrophic v. Prototrophic

Auxotrophic: cells require environmental source of AA Prototrophic: cells can synthesize their own AA

Why are mammalian liver enzymes often added to the media?

Substances can often initially be non-mutagenic but become mutagens once metabolism by the liver

What is the purpose of the Ames test?

To determine whether substance is mutagenic or toxic

What is a carcinogen?

a cancer-causing substance as a result of induced mutations or from extensive damage due to repeated exposure

What is a mutagen?

a substance that can alter the genetic information. Not always a carcinogen.

What are the advantages to this method for testing mutagencity?

fast, easy, cheap and does not require the time consuming and unethical process of inoculating animal models

Why is the importance of using a specifically mutated strain of Salmonella typhimurium?

his-: cannot synthesize histidine uvrB-: prevents mutation fixing rfa-: increases porosity of CM to ensure substance has access to DNA