Methods of purification culture and strain preservation of microorganisms

Principle: Dilute or disperse the bacteria into single cells on the culture medium to make it grow into a single colony. This colony is a purified bacterial colony.

Method: scribing on plate, dilution and coating on plate.

Scribing on plate:

2. Cool the inoculation loop by the flame, then open the cotton plug.

3. Pass the mouth of the test tube through the flame.

4. Extend the cooled inoculation loop into the bacterial solution in the test tube and dip a loop of bacterial solution.

5. Pass the mouth of the test tube through the flame, and then plug the mouth of the test tube with a cotton plug.

6. Open a gap in the lid of the dish with the left hand, and quickly extend the inoculation loop stained with the bacterial solution into the plate with the right hand, draw three to five parallel lines, and then close the lid. Be careful not to scratch the medium.

7. Burn the inoculation loop, and after it cools, start scoring from the end of the scoring in the first region to the second region. Repeat the above operations to draw lines in the third, fourth, and fifth areas. Be careful not to connect the dashed line in the last area to the first area.

8. Invert the plate and place it in the culture medium.

Schematic diagram of several marking methods

Dilution and coating on plate.

The dilution and coating on plate method is to carry out a series of gradient dilutions of the bacterial solution, and then apply the bacterial solution of different dilutions to the surface of the agar solid medium for cultivation. 

In a bacterial solution with a sufficiently high dilution, the aggregated microorganisms will be dispersed into single cells, which can form a single colony on the surface of the medium.

Dilution operation

Coating on plate operation

2. Take a small amount of bacterial liquid (not more than 0.1ml) and add it dropwise to the surface of the culture medium.

3. Ignite the applicator with a small amount of alcohol on the flame, and let it cool for 8-10 seconds after the alcohol burns out.

4. Spread the bacterial liquid evenly on the surface of the culture medium with a spreader. When coating, the petri dish can be rotated to make the coating uniform.