Streak-Plate Method: Click Here to View Images
In order to identify bacteria, it is necessary to obtain a pure culture. This is
done by using the streak-plate method. Bacterial cells are spread over the
surface of an agar plate in a continuous dilution, so that the cells will be
separated from each other. When the plate is incubated, those individual
cells will grow into colonies that originated from a single cell.
Tips for Success:
Obtaining well isolated colonies takes practice. There are a variety of
techniques used, and each microbiologist obtains his or her own style by
experience. Keep the plate covered as much as possible to avoid
contamination. While streaking a section of the plate, try to keep the
inoculating loop in contact with the surface of the agar at all times.
Procedure:
In order to identify bacteria, it is necessary to obtain a pure culture. This is
done by using the streak-plate method. Bacterial cells are spread over the
surface of an agar plate in a continuous dilution, so that the cells will be
separated from each other. When the plate is incubated, those individual
cells will grow into colonies that originated from a single cell.
Tips for Success:
Obtaining well isolated colonies takes practice. There are a variety of
techniques used, and each microbiologist obtains his or her own style by
experience. Keep the plate covered as much as possible to avoid
contamination. While streaking a section of the plate, try to keep the
inoculating loop in contact with the surface of the agar at all times.
Procedure:
- Heat sterilize an inoculating loop.
- For a liquid culture, dip the loop into the broth, or for solid media,
lightly touch a colony with the loop. - Using the loop, spread the culture over the surface of one quadrant
of the plate as shown in the figure below. - Sterilize the inoculating loop again.
- Continue the streak into the next quadrant.
- Repeat steps 3-5 until the pattern is complete.
- Incubate the plate.
- Observe for the presence of well isolated colonies.
| Isolation of Bacteria for Identification |
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