| Slides are not sterile and are coated with bacteria (other than the ones you are interested in), grease (which will prevent bacteria sticking to the slide) and dust (which will stain). Slides need to be cleaned by passing them through a bunsen flame once or twice. | With liquid cultures, one or two wire loopfuls will form a thin film of cells, depending on the density of the culture. If the bacteria have been grown on agar, place a small drop of sterile water on the slide. Scoop up a LITTLE of one of the colonies with a flamed and cooled wire loop and mix thoroughly to form a thin film: |
As you will see, your slides should not have too thick a film of bacteria or you will not be able to see any detail when they are stained. On the other hand, there should be enough cells to be easily visible under the microscope! They should look something like this:
Don't forget to label your slides so you know which is which! You cannot use a marker pen to do this since the ink will wash off during staining - scratch a label with a diamond pen.
