Direct Stains

Background

The cell wall of most bacteria has an overall net negative charge and thus can be stained directly with a single basic (positively charged) stain or dye. This type of stain allows us to observe the shape, size and arrangement of bacteria.

Procedure

1. Use the smear prepared in the previous procedure. Staining is done at the sink.

2. Add several drops of Methylene blue, enough to cover the smear, and wait 1 min.

slide covered with stain

3. Rinse the slide with water from the squirt bottle

slide rinsed with water

4. Blot the slide with bibulous paper. Redraw the focus line on the top of the slide if necessary.

slide on blot paper slide blotted with paper

5. Focus on the line with the 10X objective. Once you have focused on the specimen using the 10X objective, move the 40X objective lens into position. Use the fine adjustment knob to bring the specimen into focus. Now use the oil immersion procedure to view the specimen using the 100X

6. Draw the organisms observed in the microscopic field. 

Oil Immersion Procedure

Results

Note: Saccharomyces cerevisiae is a species of yeast. It is a relatively large single-celled eucaryotic organism. Escherichia coli is a "tiny" rod shaped bacteria (prokaryotic).

Direct stain of yeast and bacteria at 1000x magnification