Streaking
A colony, originating from a streaking, generally form a clone because most probably it originates from a single bacterial cell. There are, however, exceptions because some bacteria grow in the form of aggregates rather than as single cells. For bacteria that tend to swarm, plates which reduces the risk (for example, CLED agar for soma bacteria) should be used. Updated: 2013-03-05. |
Streaking is a technique used in bacteriology for isolating individual bacterial species or strains from a sample containing a mixed bacterial flora. A sterile inoculation loop (plastic or platinum), which has been dipped into the sample, is used to streak on 1/3 (alt. 1/4) of an agar plate. Then you take a new loop and streak from the first third to the next third of the plate. This is then repeated once (or twice). In this way you get a significant decrease of bacteria between each third (or fourth) of the plate and the chance is good that somewhere on the plate, you can find individual colonies of the bacterium or bacteria you want to isolate. The panel to the right shows a streaking of Staphylococcus aureus subsp. aureus in three steps on a bovine blood agar plate. The two images (A and B) show the same plate photographed with lighting from above and in backlight, respectively. Note that on plate B it is possible to see the traces of the streaks even when bacterial colonies cannot be observed.