Gram Staining Bacteria

grain staining bacteriaBacteria can be differentiated based on how they react to a a procedure of dying cells called Gram stain. Bacteria are divided into a group that turns purple (gram positive) and a group that turns red (gram negative). Bacteria that are gram (+) include Staphylococcs, Streptococcus, Bacillus and Micrococcus. Gram (-) bacteria include E.coli and Salmonella. The Gram staining procedure is as follows:

Gram Staining Bacteria Procedure

1.Place a drop of distilled water on a slide and, using a swab or inoculating loop, mix the bacteria with the water an smear the mixture on the slide. The mixture will appear cloudy. Using a flame, heat fix the bacteria to the slide (pass the slide through the flame a few times to “dry” the bacteria and affix it to the slide).

2. Using a dropper, add crystal violet to the slide. Let stand for 1 minute.

3. Add iodine to the slide. Let stand for 3 minutes.

4. Decolorize the sample with alcohol. Let stand for 30 seconds.

5. Counter stain the sample with safranin. Let stand 1-2 minutes. Using a dropper, rinse with distilled water.

Gram Staining Results

Gram positive bacteria will appear purple under the microscope. They have a single, thick cell wall. The crystal violet and iodine combine to attach to this wall. The decolorizer (alcohol) dehydrates the cell wall, causing the pores to close, trapping the stain inside. the safranin added in the final step, does not penetrate the wall.

Gram negative bacteria will appear red. The have a cell wall and additional thin layers of fatty sugars. The decolorizer easily penetrates these thin sugar layers, washing away the crystal violet – iodine chemical (purple color). The safranin in the last step attaches to these layers and appears red.

Warblettes Lab Activity Book

In a previous post on warblettes, we conducted a small experiment demonstrating the absorption characteristics of warblettes. There is a small summary below that you can use as a refresher, or you can view the actual warblette experiment.


Warblettes Lab Activity

As mentioned in the previous post, warblettes are co-polymers that absorb up to 200 times their volume in water. Warblettes are perfect for science fair experiments, in the classroom, or just as a fun activity for your family. Warblettes, which are sometimes referred to as water marbles, are non-toxic and come in clear, red, blue, green, and yellow colors.

The basic absorption experiment we posted on warblette absorption is a simple experiment that uses household objects. Warblettes can be used for much deeper science and educational learning. Heath Scientific has created a lab manual for this purpose.

Warblette Activity Book

The warblette lab activity book has activities for every age student. There are 13 activities ranging from math and graphing to cellular biology. You can use warblettes to demonstrate potential and kinetic energy, change over time (graphing), man-made and natural polymers, and light refraction. The labs include explanations and procedures. If needed, modify the activities to fit your students abilities or needs.

The Labs Cover:

1.) Calculating Volume – Math
2.) Observation Skills
3.) Polymers and Water Absorbtion
4.) Absorption of Household Liquids
5.) Water Absorption and Time
6.) Water Absorption and Temperature
7.) Advanced Measurement – Volume, Calipers, Averaging, and Reading Charts
8.) Graphing – Line Graph
9.) Potential Energy – Comparing Diameter to Rolling Distance
10.) Varying the Height of an Inclined Plane
11.) The Effects of Acidity on Water Absorbtion
12.) Light Refraction
13.) Density

Both the warblettes and the lab activity book are available at Heath Scientific, which has been providing educational supplies for over 20 years.