Preparation of Agar plates

Preparation of Agar plates    

Prepare media and add 1.5 % agar before autoclaving it (15g per liter). After autoclavation, cool the media in a 55 degree waterbath. Do not allow the solution to cool below this temperature as the agar gets solid at that temperature. At this step, one can leave the agar/media mixture for a long time. Before plating, add proper antibiotics and glucose if needed. Pour ca 25 ml per small agar plate (9 cm diameter) and ca 250 ml per big agar plate (20cm diameter) and let it cool. Keep at room temperatur over night and store at 4 degrees. Plates without antibiotica can be stored up to 6 months, with ampicillin, typically 4 weeks.

Hints: Many antibiotica are destroyed at high temperatures, it is important to let the media cool before adding antibiotica.

Agar melts at more than 100 degrees but gets solid at 55.

When pouring many plates, one might want to grab a pile of them, sequentially lifting the lowest lid and simply pour the agar media until it covers the bottom, then proceed with the next plate and so on. Pouring too little media may result in cracks in the surface and should be avoided.