Module Three 13.7 How can we be sure we are using microorganisms safely?

Microorganisms can be grown in a culture medium containing:

• carbohydrates as an energy source,
• mineral ions, and in some cases supplementary protein and vitamins. 

These nutrients are often contained in an agar medium which can be poured into a petri dish.

In order to prepare useful products, uncontaminated cultures of microorganisms are required. For this:

• petri dishes and culture media must be sterilised before use to kill unwanted microorganisms;
• inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame;
• the lid of the petri dish should be sealed with adhesive tape to prevent microorganisms from the air contaminating the culture.

In school and college laboratories, cultures should be incubated at a maximum temperature of 25°C to prevent the growth of pathogens that might be harmful to humans. In industrial conditions higher temperatures can produce more rapid growth.