Culturing Microorganisms

Culturing microorganisms, like bacteria and yeast, requires a sterile environment to avoid contamination by other microorganisms.
To sterilise equipment, it can be autoclaved. An autoclave uses pressurised steam to kill microorganisms and spores.
The use of aseptic technique also helps maintain sterility during the culturing process. This includes practices like flaming the necks of bottles before and after transfers of living cultures.

Microorganisms are grown on a suitable culture medium, which provides the necessary nutrients and conducive conditions for their growth.
One common culture medium is nutrient agar, which contains a mixture of substances such as beef extract and peptone.
The culture medium is heated to dissolve the nutrients and then cooled to around 50°C before pour into (or used to make) sterile petri dishes.

To start the culture, the microorganism is introduced into the culture medium in a process called inoculation. Often, a sterile wire loop or needle is used.
When culturing bacteria, the preparation is typically stroked over the surface of the agar in a zigzag motion to spread the bacteria as widely as possible across the surface of the agar.

The inoculated culture is then incubated at a suitable temperature to encourage growth. In school labs, this will usually be at temperatures no higher than 25°C to prevent the growth of harmful pathogens.
During incubation, the microorganisms multiply and form visible colonies.

After incubation, individual colonies can be counted to give an estimate of the size of the bacterial population.
Due to the fact that each colony develops from a single bacterium, colony counts can be used to estimate the number of bacteria originally present in a sample.

When culturing microorganisms, it’s important to be aware of potential hazards, such as the risk of producing harmful gases, or of contamination by the cultured organisms.
To reduce risks, always follow guidelines for safe working practices in a lab. Following aseptic techniques, wearing protective clothing, using the lowest practicable temperature for incubations are among precautions that should be taken.

Cultures of microorganisms are used in research, medicine, and industry. For example, they can be used in the testing of antibiotics in laboratories, in the production of yoghurts and cheeses in food industry, and used in the manufacture of medicines.

Pure cultures - cultures containing a single type of microorganism - are particularly important in laboratory and medical work. They allow the study of a single type of microorganism without the influence of others, providing more reliable and accurate results.