Microbiological culture

Culturing is the practice of growing microorganisms, such as yeast or bacteria, in the lab. The nutrients the microbes need are provided by the culture medium. Microorganisms can be grown in liquid culture or on media made solid by the addition of agar, which gives culture media a gel-like consistency. When culturing microorganisms, good aseptic technique is required to keep the culture free from external contaminations. Correct aseptic technique also keeps those working in the lab safe, which is particularly important when working with pathogenic organisms.

Setting up liquid and solid cultures

To create a liquid culture, a colony from an agar plate is added to liquid medium using a culture loop, or a small volume of liquid culture is added using a pipette. To create a solid culture, a colony is streaked across a petri dish containing solid medium (known as an agar plate) using a culture loop or a small volume of liquid culture is added to the plate and spread across the surface using a spreader. All equipment must be sterilized before and after each use.

Controls

To ensure good aseptic technique is used, the best negative control is uncultured medium. Since the medium and equipment should be sterile, microbial growth in this control indicates a contamination. Everything else should be treated the same across the sample and control.