Bacterial Culture Protocol

Culturing bacteria involves three important factors. These are to multiply the bacteria to a visually readable level, to prevent unwanted contaminating bacteria from growing too fast and taking over the growth media and finally to isolate pure colonies of the particular bacterial group you want to study.

Enrichment

As bacteria generally exist at low levels in a sample, they must be allowed to multiply in a medium that provides a rich source of nutrients. The initial enrichment depends on the type of bacteria you want to culture. Allow the initial enrichment to incubate for a time. Commonly this is 24 hours.

Temperature

Incubate the culture at a temperature that the bacteria is likely to thrive at. A common temperature is 30 to 35 degrees Celsius, but different bacteria require different growth temperatures.

Subculturing

The bacteria are then subcultured onto a growth medium, an agar plate for example, that is specific to the type to be isolated. For example, Baird Parker Agar is used for isolating Staphylococcus strains. The most common methods to transfer bacteria onto an agar plate are spreading a drop of culture over the plate or streaking a drop across a plate using a loop of culture.

Final Incubation

Incubate the plates under a specific temperature range as in the first step. The time for the isolated colonies to grow will depend on the bacteria, but commonly this step takes 24 to 72 hours.

References

• Protocol Online: Bacteria Growth and Replication
• Ohio State University; Growth and Culturing of Bacteria