LB agar plate , 1.5 %
Pour 1.5 % w / v ( 7.5g / 500mL ) bacteriological grade agar into an autoclave safe container capable of holding at least 500mL q . s . to 500mL using LB media Stir vigorously at room temperature until particulates are no longer visible .
Loosely cap bottle and then autoclave for a minimum of 30 minutes ( increase to 45 minutes if making 1L ) using slow exhaust ( liquid ) cycle .
Remove from autoclave and let cool for 20 - 40 minutes or until sufficiently cool to permit handling with simple nitrile / latex gloves or bare handed ( about 40 - 60C ) .
[ Optional ] : Cool in 55C water bath to avoid having the agar cool too much prior to pouring .
Add antibiotic selection after agar has cooled down and mix well .
Carefully pour about 20 - 25mL of LB agar into 10cm Petri dishes ( about 20 - 25 plates ) .
Let agar cool before placing lid on top and inverting plate .
Alternatively , place lid open slightly to the side to allow for evaporation as the agar cools .
Wrap plates in plastic wrap or store sealed in plastic bag to prevent plates from drying out .
Wrap in aluminum foil to prevent degradation of light - sensitive antibiotics , e . g . ampicillin .
Store plates at 4C , inverted .
