Staining Bacteria: Preparing a Bacterial Smear and a Simple Stain

Returning to lab on Thursday, we found that we were able to obtain a pure culture sample (pictured below) from our original sample from the Ohio river.

Next we have to prepare a bacteria smear from the pure culture sample. This is done by spreading the bacteria into a thin film on a clean microscope slide. 

First we put a loopful of distilled water in the center of the slide.

Then we sterilized the loop via Bunsen burner and transferred a small amount of the pure culture sample and placed it into the water drop. We once again sterilized the loop via Bunsen burner and set it down on the table.

Afterwards we spread the mixture into a thin film and allowed the smear to air dry. 

In order to fix the dried smear we passed the slide, containing the culture sample, quickly through the flame of the Bunsen burner three times making sure the smear side was up. Now it is considered heat-fixed. 

Now, in order to see our bacteria more clearly under a microscope we need to stain the bacteria. This is down with a staining rack which we put over a sink and methylene blue stain. 

After we put our fixed smear onto the staining rack we covered the bacteria with several drops of the methylene blue stain and left it on for about 1 minute as indicated in our lab book. 

Then, we rinsed the slide with water over the sink to remove the excess stain.

Finally, we blot water from the slide with pieces of bibulous paper. 

We are now ready to see the bacteria we obtained from the Ohio river and look at what we saw through the microscope!