MODEL RELEASED. Bacterial contamination tests. Laboratory workers processing petri dishes being used to culture human tissue samples. Any bacteria or other micro-organisms found growing in the petri dishes will need to be identified. The worker in the foreground is transferring a sample from one petri dish (on table) to another (in her hand) for further culturing and identification, a process known as subculturing. The petri dishes contain nutrient media on which micro-organisms will grow if placed in the right conditions. The tissues being tested range from blood to bone.