Annie made a batch of broth media (Batch 1) and sterilized it before creating and autoclaving another batch of the same number and type of media (Batch 2). A few days later, she noticed that Batch 1 had growth in all tubes and Batch 2 had growth in one tube only. When was contamination likely introduced into each batch?
Batch 1: likely during media preparation and before a (failed) autoclave run.
Batch 2: likely after the (successful) autoclave run.
Batch 1: likely after the (failed) autoclave run.
Batch 2: likely during media preparation and before a (failed) autoclave run.