Aseptic Technique 

In nature, microorganisms usually exist as mixed populations of different species of bacteria, fungi, and even viruses. If we are to study, characterize, and identify microorganisms, we must have the organisms in the form of a pure culture, that is of only one species of microorganism. A pure culture is one in which all organisms are descendants of the same organism.  In working with microorganisms we must also have a sterile nutrient-containing-medium in which to grow the organisms. Anything in or on which we grow a microorganism is termed a medium. A sterile medium is one which is free of all life forms. It is usually sterilized by heating it to a temperature at which all contaminating microorganisms are destroyed. Finally, in working with microorganisms, we must have a method of transferring growing organisms (called the inoculum) from a pure culture to a sterile medium without introducing any unwanted outside contaminants. This method of preventing unwanted microorganisms from gaining access is termed aseptic technique. (1)

Inoculation is the purposeful introduction of bacteria into a sterile growth medium. A material is sterile when it has no living organisms present; contamination is the presence of unwanted microorganisms. Aseptic techniques are practices that prevent the contamination of growth media.

When working in a microbiology laboratory, you must always remember that bacteria are present on all surfaces in the lab, as well as on your own hands and clothing. Aseptic techniques are designed to prevent the transfer of bacteria from the surrounding environment into a culture medium. These techniques require care and concentration. Pay attention to what you are doing at all times!

Aseptic techniques include the following practices:

1. Minimize the time that cultures and growth media are open to the environment.

2. Disinfect the work area before and after use.

3. Do not touch or breathe into the sterile culture media or the stock cultures.

4. Loops, needles, pipets, etc. should be sterilized before they are used.

5. When working with tubes, the tube caps should not be placed on the table top; they should be held in your hand while inoculating.

6. When removing the caps from test tubes, heat/flame the lip of the test tube after the cap is removed. This heats the air inside the tube, so the air moves out of the tube, preventing contaminants from entering the tube.