Using a laboratory weighing scale, measure out bacto-tryptone (10g), yeast extract (5g), sodium chloride (5g) and laboratory- or research-grade agar. Using graduated measuring cylinders or a pipette, measure out 1ml of 1N sodium hydroxide. Sterile handling is not required, so these steps can be carried out on a normal laboratory bench. This recipe is a standard and basic Luria broth, routinely used to make agar plates, and does not contain any supplements. Other variations of this broth exist but the correct one which supports the growth of the specific microorganism must be used.
Add the powdered reagents into a 1l (or larger) flat-bottomed autoclavable flask, then add the sodium hydroxide. Top up with sterile distilled water to make a liter of mixture. To 500ml of this medium, add 7.5g of agar and autoclave. Cool down in a water bath set to 50 degrees C. From here on, every step must be performed under sterile conditions, so work in a containment hood or under a flame. If supplements such as antibiotics or growth agents need to be added, filter-sterilize these and then add to the media. Do not add to media that has not been cooled yet, as the heat will destroy the supplements.
While the media is cooling, set up the plates by taking them out of their packaging (sleeve), removing their lids and labeling the bottom of the plates with the type of broth (media) as well as the supplement it contains. In addition, it is essential to write the date the plate was made, and the name of the person doing this.
While the agar is fluid (best between 45 and 50 degrees C), use thermal protective gloves and pour about 15 ml of the agar broth into the center of the plate and allow this to reach no more than a few centimeters from the top of the plate. Allow the agar to spread by itself but do not agitate the plates or media too much, as any bubbles in the fluid medium will solidify in the agar plate. Continue pouring the rest of the plates. Once poured, leave the lids off the plates to allow them to solidify, then replace the lid, turn the plates upside down onto their lids, and stack them back into their packaging.