Microbiology Techniques

Bacteria, yeast and molds are tiny organism that are found everywhere. To study them scientists grow them in the laboratory using special techniques of microbiology and bacteriology. Under the right conditions bacteria can grow rapidly. The population can divide every 20 minutes. A single cell can grow to millions of cells in 24 hours.

Growing Cultures

Microorganisms can be grown on a petri dish that is filled with nutrient agar. Agar is a jelly that is made from seaweed. It provides a moist, rich place that bacteria easily grow.

Since it is difficult to work with a single bacterial cell we usually attempt to isolate a colony of millions of cells that have come from single starting cell. One technique is to apply a solution that might contain bacterial cells to one side of an agar plate with a loop. Then sterilize the loop in a flame and pass it through the first smear to spread out the cells and dilute them again. In the picture to the right the first smear on the lower right resulted in a solid growth. The second and third spreads are done at angles resulting in individual cell colonies in the upper right corner. This is useful way to isolate and identify individual bacteria species from a mixed sample.

Once you have a separate colony that has likely grown from a single cell you can transfer this to another growth medium. Allow the bacteria to multiply and repeat the process of plating until you have a pure culture of one strain of bacteria.


One word of warning. It is possible to collect and grow some very dangerous bacteria using these techniques. Your teacher should supervise any work you do with bacteria. You should wear a lab coat, and never touch bacterial cultures. Wash you hands frequently and don't touch your face or mouth. Tape dishes closed and sterilize the culture before disposing of it safely. These are the techniques that bacteriologists used to work with bacteria safely.

Safety Guidelines