When bacteria are cultured on agar in a Petri dish, unwanted microorganisms from the air, hands or equipment must be kept out. If they get in, the culture is contaminated and the results cannot be trusted. Aseptic technique is the set of steps used to prevent this.
Before use, glassware and growth media are sterilised in an autoclave, which uses high-pressure steam to kill all microorganisms. The bench is wiped with alcohol to kill microorganisms on its surface. An inoculating loop is passed through a flame to kill any microorganisms on it, and is then left to cool so that the heat does not kill the bacteria being transferred.
The work is done close to a lit Bunsen burner. The hot air rising from the flame carries microorganisms away from the open dish, so fewer contaminants fall onto the growth medium. The lid of the dish is lifted only slightly and for as short a time as possible, and it is put back straight away.
