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When a single stain is used to color a bacterial organism it is referred to as simple staining. The most common dyes for this method are methylene blue, basic fuchsin, and crystal violet. All of these dyes work well on bacteria because of their color-bearing ions or chromophores that are positively charged (cationic). Bacteria have a slight negative charge which produces a strong attraction between them and the cationic chromophore. These dyes are classified as basic dyes. Dyes that have anionic chromophores such as eosin are called acidic dyes. The staining time for most stains is 30 seconds to 2 minutes depending on its affinity. After the smear has been stained it is washed, blotted dry, and examined directly under oil immersion. Slides such as this are useful in determining basic morphology and the presence or absence of certain kinds of granules. Simple staining is quick basic technique that provides valuable information about the specimen.

When attempting to identify an unknown bacterium it is often necessary to determine whether or not the microorganism is motile. There are several ways in which you can do this. The easiest way to determine motility is to prepare a wet mount. This is done by placing several loopfuls of the microorganism on a clean slide and cover it with a cover glass. The best way to examine the slide is with a phase contrast microscope with a high dry objective. If the organisms are motile one will see them moving rapidly throughout the preparation. It is important to distinguish between true motility and Brownian movement. Brownian movement is when the bacteria move due to vibrations or other forces in the preparation. If a brightfield microscope is used it is necessary to reduce the lighting in order to provide more contrast. The oil immersion lens can then be moved into place. The other method is called the hanging drop method. In this method a drop containing the organisms is placed on a coverslip. The coverslip is then placed upside down on a depression slide. Great care must be used when examining the slide so that the cover slipe does not break. A brightfield microscope can be used with a high dry objective or an oil immersion objective.

Thanks to the Danish bacteriologist Christian Gram, microbiologists worldwide perform a technique called gram staining. This method of staining determines whether a bacterium is gram-negative or gram-positive. Knowing the difference between gram positive and gram negative bacteria is crucial for prescribing the proper medication. The first step involves staining the bacteria with crystal violet which turns both types of bacteria purple. Gram's iodine is then applied to the bacteria and their color does not change. Gram's iodine combines with crystal violet to form an insoluble compound in gram positive bacteria but not in gram negative bacteria. A decolorizing agent, 95% ethanol, is then added. The gram negative bacteria turn colorless and the gram positive bacteria remain purple. The final step involves adding a counterstain, safranin, which turns the gram negative bacteria pink and doesn't affect the color of the gram positive bacteria. EMD Chemicals Inc, Azer Scientific, and BD all supply products used in various microbiological staining procedures.