Blood agar plate
| Uses |
Microbiological culture Art |
|---|---|
| Related items |
Petri dish Growth medium |
An agar plate is a Petri dish that contains a growth medium (typically agar plus nutrients) used to culture microorganisms or small plants like the moss Physcomitrella patens. Sometimes selective compounds will be added to influence growth, such as antibiotics.
Individual microorganisms placed on the plate will grow into individual colonies, each a clone genetically identical to the individual ancestor organism (except for the low, unavoidable rate of mutation). Thus, the plate can be used either to estimate the concentration of organisms in a liquid culture or a suitable dilution of that culture using a colony counter, or to generate genetically pure cultures from a mixed culture of genetically different organisms.
Several methods are available to plate out cells. One technique is known as "streaking". In this technique, a drop of the culture on the end of a thin, sterile loop of wire, sometimes known as an inoculator, is streaked across the surface of the agar leaving organisms behind, a higher number at the beginning of the streak and a lower number at the end. At some point during a successful "streak", the number of organisms deposited will be such that distinct individual colonies will grow in that area which may be removed for further culturing, using another sterile loop.
Another type plating out organisms, next to streaking, on agar plates is the spot analysis. This type of analysis is often used to check the viability of cells and performed with pinners (often also called froggers). A third used technique is the use of sterile, glass, beads to plate out cells. In this technique cells are grown in a liquid culture of which a small volume is pipetted on the agar plate and then spread out with the sterile, glass beads. Replicate plating is another technique in order to plate out cells on agar plates. These four techniques are the most used ones, but others are also possible. It is crucial to work in a sterile manner in order to prevent contamination on the agar plates. Plating is thus often done in a laminar flow cabinet or on the working bench next to a bunsen burner.
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