STUDENT INSTRUCTIONS
Take a sterile cotton-tipped applicator and a sterile agar dish to any area of the campus you wish to sample. If sampling a dry surface, moisten the cotton with sterile water. Streak the surface of the agar with your sample. NOTE: Heat-sterilization of the applicator between streaks is neither necessary or desirable, as it will catch fire! Properly label the dish, invert, and incubate.
If contact plates are available, choose a surface to sample where numbers and distribution of bacteria are of interest. Open the dish and place the surface of the agar directly on the environmental surface to be sampled, pressing very lightly. Lift the plate without shifting the agar along the surface, and replace the lid. Label and incubate. Colony distribution on the agar surface after incubation will match bacterial distribution on the environmental surface where sampled. The raised agar surface aids in such a sampling procedure, and the grid in the dish facilitates bacterial counting procedures.
After 48 hours, retrieve and observe.