Grease or oil free slides are essential for the preparation of microbial smears. Grease or oil from the fingers on the slides is removed by washing the slides with soap and water. Wipe the slides with spirit or alcohol. After cleaning, dry the slides and place them on laboratory towels until ready for use.

Why is it important to form bacterial smears by mixing cells with a small amount of liquid and spreading them over a slide surface? Morphological features are most readily visible if cells present are separated rather than in a dense mass. Smears dilute the cellular material.

Water is applied to the slide before emulsifying cells from a solid medium. Why is it important that the cells are not distorted during the smear preparation and staining process? A.) Microscopic examination can show their true shape and arrangement if done correctly.

The preparation of a smear is required for many laboratory procedures, including the Gram-stain. The purpose of making a smear is to fix the bacteria onto the slide and to prevent the sample from being lost during a staining procedure. A smear can be prepared from a solid or broth medium.

A bacterial smear is simply that—a small amount of culture spread in a very thin film on the surface of the slide. To prevent the bacteria from washing away during the staining steps, the smear may be chemically or physically “fixed” to the surface of the slide.

The primary dye (crystal violet) and the mordant (Grams’ iodine) react similarly in both cell types. The decolorizer, ethyl alcohol, is the most crtitical step. Ethyl alcohol is a nonpolar solvent, and thus penetrates the cell walls of Gram negative cells more readily and removes the crystal violet-iodine complex.

Do NOT decolorize for a full minute! The decolorizer should stay on the slide for no more than 15 seconds! If the decolorizer is left on too long, even gram positive cells will lose the crystal violet and will stain red.

It is possible to leave the decolorizer on too long and strip the blue stain out of all the bacteria, even the Gram positive ones. If the decolorizer is not left on long enough, the blue color will remain in the Gram negatives and they will appear Gram positive (purple) Page 4 c.

Ethanol, also known as ethyl alcohol, C2H5OH, is a colorless flammable slightly toxic compound that is made in fermentation and is used as a solvent and as an antifreeze. Ethanol also known as ethyl alcohol because it is commonly known as the alcohol found in alcoholic beverages.

Sanitizer Alcohol Percentage The World Health Organization suggests that 70% ethyl alcohol is superior to isopropyl alcohol against the influenza virus, however, both provide adequate germicidal properties. Ethanol is recommended at higher % concentration, usually 80%.

30 ml bottle of 95% ethyl alcohol, also known as denatured ethanol or grain alcohol….Ethyl Alcohol, 95%, 30 ml.