Agar powder combined with water creates a solution that passes through an incubator to sterilize and kill any microorganisms, ensuring that only the required bacteria will grow. The heating process also makes the solution of agar and water solidify in the petri dish, becoming a gel in which to culture the bacteria. Petri dishes usually remain covered to avoid contamination.
Scientists isolate the needed bacteria before using a sterilized loop to add it to the gel in a zigzag manner known as streaking. After finishing the first round, the researcher turns the petri dish 60 degrees before gently performing more streaking to avoid destroying the gel. After the streaking process, the researcher covers the petri dish with its lid.
The petri dish goes into an incubator set to 37 degrees Celsius, or 98.6 degrees Fahrenheit, as most bacteria can survive under such temperatures. Petri dishes can sit at room temperature without an incubator, but the bacteria colonies take longer to grow.
The petri dish comes out of the incubator after 24 to 48 hours. The researcher checks the growth of the bacteria colonies from the top of the petri dish while it remains covered, because bacteria in the atmosphere can spread to the petri dish, leading to growth of undesired bacteria colonies.
Harmless bacteria may accidentally become contaminated with harmful pathogens, presenting a health risk for the person handling the bacteria culture. Wearing gloves, however, reduces the risk of contamination. An April 2010 study conducted in Vienna, Austria, to investigate the effect of glove usage on hand contamination found that technologists working without gloves had a significantly increased risk of contamination from bacteria called methicillin-resistant Staphylococcus aureus, or MRSA. Wearing protective clothing, such as a laboratory coat, serves as an additional safety measure.