Why is aseptic bacteriologic technique so important in the isolation of pure cultures?

Aseptic technique is the name given to the procedures used by microbiologists to prevent microbial contamination of themselves, which may result in infection, contamination of the environment they are working in (e.g. fomites), and contamination of the specimen they are working on, which is especially important when a pure culture is desired. It is used whenever specimens are to be transferred between media, for example, when subculturing. Such a procedure, using a flame sterilization method, might occur as follows:





Test tubesA person would assemble the closed tube or flask from which鈥攁nd the closed tube or flask to which鈥攖he specimen is to be transferred, an inoculating loop, and a fire source, all on a clean, preferably microbe-free surface with some overhead protection from airborne microbes.


The person would start the fire, and move the end of the inoculating loop, in a slow back-and-forth motion, through the top of the blue part of the flame. The person would not allow the loop to touch anything except the specimen itself, until the entire procedure is finished.


Preparing to execute the specimen transfer, the person would hold both of the tubes or flasks in one hand, probably the opposite of the writing hand. The person would then open the tube or flask containing the specimen source and briefly hold the top of it in the flame, to kill unwanted microbes.


Quickly, so as to minimize the possible time for contamination of the specimen in the source tube or flask, the person would use the inoculating loop with their writing hand to retrieve the specimen, and then sterilize the top of the tube or flask again before immediately closing it.


Keeping in mind that the specimen on the inoculating loop could be contaminated during every unit of time it is exposed, the person would repeat the previous step identically with the tube or flask in which the specimen is to be deposited; however, the person would be depositing the sample into the tube or flask.


Students of microbiology are taught the principles of aseptic technique by means of hands-on laboratory experience. Practice is essential in learning how to handle the laboratory tools without contaminating them.