Week 4: Acid-Fast Staining

Welcome back!

This week in lab, we worked on determining if our mysterious soil microbe was acid-fast or not. Acid-fast staining is a technique used to test for waxy cell walls in bacteria - it is similar to gram-staining because it involves using dyes to stain the cells, but the dyes are different and have different affects on the cells. If a bacteria in acid-fast staining stains a pink-ish color, the bacteria is said to be acid-fast, meaning it has a very waxy cell wall, and these are considered to be the micobacteria. If a bacteria in acid-fast staining stains a purple or blue color, the bacteria is said to be non-acid-fast, meaning it does not have a waxy cell wall.

We tested our soil microbe against some controls, which were all non-acid-fast. For our non-acid-fast control, Katie and I used B. megaterium, which is also a Gram-positive control that we used in last week's Gram-staining procedure. We expected our control to be a blue/purple color, and we compared the result of our control to our soil microbe and determined which type of acid-fast bacteria we assumed we had. An image of our soil microbe under the oil-immersion lens of the microscope is shown below:

As you can tell from this image, our microbe is clearly very non-acid-fast. The purple/dark blue color indicates to us that it is very non-acid-fast and thus has a thin waxy cell wall.

Using a dichotomous key, we can start to classify our microbe. I used a key provided by the professor, and since our microbe was Gram-negative, the next step on the dichotomous key is to determine if it is an anaerobic or aerobic, or facultatively anaerobic microbe. Since we have not done an experiment to determine this yet, we will have to wait to continue to classify our organism. Stay tuned until next week to see how we classify our microbe further!

Patricia