Bacterial Streak Plate
Growth and Check of Bacterial Strains
Bacteria can be propagated on liquid or solid media. The use of liquid allows large quantities of bacteria to be harvested but does not permit easy selection or determination of phenotype of single cells. The technique of "streaking" cells onto a solid media provides simple isolation of colonies arising from single cells. Colonies selected for the desired phenotype are then used to inoculate liquid broth. A single colony inoculum is preferred because bacteria can undergo many types of mutations naturally. The instability of some of the mutations, especially transposons and phages, can allow some cells to lose characteristics important to the selection scheme and may complicate the analysis. It is always wise to check the parent strain for proper phenotype that reflects the genotype and then use "picks" from single colonies to start liquid cultures.
Aseptic removal of toothpicksObtain toothpicks from the sterile container using aseptic technique. Remove the cap and hold the tube horizontally. Tap lightly on the top of the tube to cause a toothpick to come part of the way out of the tube. Remove a single toothpick being very careful not to touch the opening of the tube or any part of other toothpicks that may be at the opening. Do not allow any toothpick that was touched to return to the tube. Replace the cap.
PROTOCOL (dispose of toothpicks in biohazard bag, not in regular trash)
NOTE: plates have been prepared for you;
the information about the media is included
here so you will know the contents.
*adjust pH to 7.0 with NaOH and bring to 1 L; sterilize
by autoclaving for 20 minutes at 121°C at 15 psi
Antibiotic for selection:
Obtain a plate. The first thing you should do is label your plate with the plasmid ID, the bacterial strain, today's date, and "who" streaked the plate--put your "Team #" on each plate in your group. Label the bottom, since lids can readily be separated and mixed up.
Single colonies can be produced in the following manner.
Examine your “streak” plates and record your observations in your notebook. Did you get single, well-isolated colonies? If not, how might you modify your technique next time to obtain single colonies?
We would like to thank New England Biolabs for their generous support of our laboratory program
Copyright and Intended Use
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Created by David R. Caprette (firstname.lastname@example.org), Rice University 14 Jul 08
Author: Beth Beason Abmayr, Ph.D., Rice University
Updated 7 January 2015