Studies in microbiology require the study of morphology of particular organisms. In some cases, organisms that are present in a mixed culture need to be separated before they can be studied. In such cases, it is important to isolate these microbial colonies. Bacterial cultures contain a large number of cells even in a single drop. Streaking on an agar plate dilutes this so that a single bacterial cell gets deposited in a specific area of the agar plate. Several such single cells are separated a few millimeters apart on the plate. Each of these single cells divides to form thousands of new cells, giving rise to isolated colonies.
The agar plate provides a nutrient-rich medium that encourages the growth and multiplication of microorganisms. Streaking uses the Quadrant Streaking method in which this entire plate is divided into four quadrants. As you move from one quadrant to another, there is a step-wise dilution of the original culture across the entire available surface. The quadrant with which you begin shows dense, undistinguished microbial growth that appears like a lawn of organisms, whereas the last quadrant shows the presence of isolated microbial colonies.
Streaking on an agar plate requires nutrient agar plates, a loop for inoculation, bacterial stock culture, a disinfectant solution such as 10-percent Lysol and a Bunsen burner. You will also need safety wear such as an apron, gloves and chemical splash goggles. The inoculum for streaking is taken from the bacterial stock culture using the loop and streaked across the nutrient agar plates. The Bunsen burner is for flaming the loop during the streaking. Use the disinfectant solution to clean the surface prior to starting the experiment.
Use a small quantity of the inoculum to streak the first quarter of the plate with a back-and-forth motion. Flame the loop and cool it by touching it to a part of the agar plate that has not been inoculated. Place it at one edge of the area you just streaked and draw streaks from there into the second quarter of the plate. Again flame and cool the loop and extend streaks from the second area into the third quadrant. Flame the loop and cool it and draw streaks from the edge of the third quadrant into the fourth quarter of the plate.