Certain genera of gram-positive rods have the property of forming highly resistant endospores under certain growth conditions. These spores are not reproductive bodies but permit survival of an individual bacterial cell under severe conditions (e.g., heat, dryness). These endospores are difficult to stain and can often be seen as refractile, clear bodies within bacterial cells stained by methods such as simple stains or the Gram stain.
One popular spore-staining technique involves heating to introduce a primary stain, such as malachite green, into the endospores, which, once stained, are difficult to decolorize with a water rinse. Vegetative cells are readily stained and readily decolorized with water. They are then stained with a counterstain, such as safranin.
The major spore-forming genera are Bacillus and Clostridium. The size and location of the endospore within the vegetative cell (exosporium) often are useful in identification of species within these genera.
This "animated" (with sound) PowerPoint presentation can be utilized in the classroom to provide:
1. An introduction (brief history and structural basis) to the spore stain.
2. Stepwise instructions for the staining techniques.
3. "Cartoons" of how the cells appear at each step.
4. Views of typical spore-stained microorganisms.
Please note: the tutorial above is optimized for Microsoft Internet Explorer and will not work in Netscape Navigator. In Internet Explorer, upon clicking on the link to the tutorial above, you will see frames containing the outline and the slide show. You may use the outline on the left-hand side to scroll through the slide show. In the lower right-hand corner of your screen there is a "Full slide show" icon. If you click on this, you will be able to view the full slide show with sound effects. Use the space bar to advance the slides and use the ESC key to exit the slide show at any time.