Bacteria in liquid culture can be streaked on a plate to obtain individual colonies. It is important for a molecular biologist to work with bacteria that are genetically identical. By streaking for single colonies, one isolated colony will form from a single bacterial cell and thus the colony is genetically identical.
One method is to streak bacteria around the petri
plate, working in a circle and diluting the bacterial population as you
go. The microbiological loop is either flamed, or a new loop is used, at
four steps. These are represented by different colors in the figures below.
|#1 = a loopful of bacteria is obtained from a resuspended
liquid culture, and a dime to penny sized circle is made on the plate (BLACK).
#2 - a second loop is used to make four lines moving out from the circle (RED).
#3 - a third loop is used to make four more lines which overlap the first four (BLUE).
#4 - a fourth loop is used to make four more lines which overlap the second four (GREEN).
NOTE that the same loop is used to make the final four lines (GREEN).
|On this plate, many isolated colonies are seen on the third set of streaks.|
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