1.7 Growing and Investigating Bacteria

Culturing microorganisms

The action of antibiotics and disinfectants can be investigated using cultures of microorganisms (populations of microorganisms that have been grown for a purpose). It is important that the cultures are uncontaminated by other microorganisms, so sterile conditions are needed:

• the Petri dishes, nutrient agar jelly and other culture media must be sterilised
• the inoculating loops used to transfer microorganisms must be sterilised (usually by passing the metal loop through a Bunsen burner flame)
• the lid of the Petri dish is sealed with sticky tape to stop microorganisms from the air getting in and contaminating the culture.

Growing Cultures

To grow cultures in a lab you must need;

• Liquid/gel containing nutrients - a culture medium. Contains carbs as energy source and other minerals. (Common medium used is called agar jelly)

• Warmth and Oxygen.

• Kept incubated at 25 degrees in school labs and at 35 degree in industry.(for safety - in school pathogens able to grow at 25 degree can't harm humans)

Pure Cultures

• Kill all bacteria on equipment. Metal loops through flame, boiling solutions + agar.
• Prevent microorganisms from air getting into the equipment.