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Objectives of Streak Plate Method:
*To obtain a pure culture of bacteria from a mixed culture
*To obtain well-isolated colonies
*To propagate bacteria

What is Streak Plate Method?
The streak plate method is a microbiological laboratory technique of isolating pure cultures, and/or getting well-isolated colonies of bacteria from a mixed population.

Quadrant Streaking:
It is the most commonly used and the most preferred method where four equal-sized sections of the agar plate are streaked. It is also referred to as the “four-quadrant streak” or “four sectors” or “four-way streak” method.

In this method, each plate is divided into four equal sectors and each adjacent sector is streaked sequentially. The sector which is streaked first is called the first sector or the first quadrant, and it has the highest concentration of inoculum. Gradually the second, third, and fourth quadrants will have diluted inoculum. By the time the fourth quadrant is streaked, the inoculum is highly diluted giving rise to isolated colonies following the incubation.

Mostly, a discontinuous fashion of streaking is followed where the loop is sterilized at the end of each quadrant prior to streaking over the next quadrant. However, if the bacterial load is too small (or highly diluted), continuous fashion can also be used. In the latter, the loop needs not be sterilized at the end of every quadrant.

Although being the most popular method, it limits us to use only one specimen per plate. If we try two or more specimens in a single 10 cm plate, this method is not suitable.