Question

1. Evaluate the virtues of flaming the cotton plug of test tubes and putting out the burning cotton with the hand before transferring cultures, a procedure advocated by some.
2. Evaluate the virtues of the method of transfer of cultures in which both tubes are opened at once, with the plugs held between the fingers, against the procedure in which only one tube is opened at a time.
3. What bacteriologic risks are encountered when both tubes are opened and two loopfuls are transferred from a pure culture to a tube of medium without flaming the loop between transfer?
4. When might errors result if the loop, in different procedures, was flamed but inadequately cooled?
5. In a view of experimental evidence, at what points is there risk of air contamination in plating or transferring cultures?

Answer 1

1. This is to avoid contamination of the culture or medium inside the test tube. The cotton plug that go inner side of the test tube must be sterile while keeping it back to avoid contamination.

2. This is to reduce the time of exposure of the tube to the outside environment that might increase the chance of catching the contaminants.

3. Inoculation loops are subjected to heat sterilize to prevent the the chances of cross contamination of the culture being inoculated.

4. The loop must be cooled to prevent the killing of bacteria. If the loop I too hot it will kill the bacteria and sizzle and melt the media that further promotes contamination.

5. While plating the glass rod should be sterile. Wash the glass rod with 70% ethanol and heat sterilize it.

You shouldn't place the lid of the agar plate facing the inner surface up which increases the chance of contamination. Keep the lid on a disinfected surface within the filed of the bunser burner fcaing the inner surface down.

When the lid is facing up, there is a higher chance of contamination from the moving object or hands creating air currents that cause microorganisms and dust particles to descend to the inside surface of the lid.