Question

You join a food chemistry lab where the researchers have found two new additives that are quite good at preventing food from spoiling. Before putting these chemicals out on the market, they decide that they should probably make sure there are no harmful effects to humans. They do an Ames test and observe the following results. Needless to say, they decide not to use the additives on food.

Bacterial Strain his mutation # of colony forming units on plates lacking histidine Untreated Treated Treated with | Treated Treated with with Additive A with Additive B Additive A and liver Additive B and liver extract extract 1.6 + 0.5 1.7 +0. 1 3 .0 + 1.0 2.2 + 0. 4 1 239 + 28 9.3 + 3.0 10+ 4. 0 12 + 3.2 11 + 2.8 12 + 2.2 TAF TAT Frameshift T:A changed to A:T A:T changed to C:G TAG 0.7 +0.3 621 +24 654 + 31 1.0 + 0.5 1.2 + 0.6

Explain why the numbers of colonies on the plates of the TAF bacteria treated with additive B are different with and without liver extract whereas the numbers of colonies on the plates of the TAG bacteria treated with additive A with and without liver extract are not different.

Answer 1

● Perform plating procedures without contaminating media. ● Isolate single bacterial colonies by the streak-plating method. ● Use pour-plating and spread-plating methods to determine the concentration of bacteria. ● Perform soft agar overlays when working with phage. ● Transfer bacterial cells from one plate to another using the replica-plating procedure. ● Given an experimental task, select the appropriate plating method.